Battery monitoring device for hybrid vehicle

This application is based on Japanese Patent Application No. 2006-024667, the contents of which are hereby incorporated by reference.

1. Field of the Invention

The present invention relates to a voltage-measuring device in particular, to a voltage-measuring device for measuring voltage of an in-vehicle high voltage battery that consists of a plurality of rechargeable batteries connected in series with each other.

2. Description of the Related Art

Recently, a hybrid car (hereafter referred to as HEV) that runs using an electric motor together with the engine has become widespread. This HEV includes a low voltage battery for starting engine, and a high voltage battery for driving the electric motor. The high voltage battery consists of a plurality of rechargeable batteries, such as a nickel-hydrogen battery or a lithium battery connected in series with each other.

After repeating charge and discharge, a state of charge (SOC) of each rechargeable battery of the high voltage battery varies. Regarding the charge and discharge of the battery, from a viewpoint of durability of each rechargeable battery and safety, when the rechargeable battery having the highest SOC reaches the upper limit SOC, the charge cycle stops, and when the rechargeable battery having the lowest SOC reaches the lower limit SOC, the discharge cycle stops. Regarding HEV, battery energy is added to a gasoline engine when going up a hill, and the energy is regenerated and stored in the battery. Therefore, the voltage of the high voltage battery often changes by the state of running. Thus, it is necessary to always observe the voltage of a high-voltage battery while the HEV is running.

Japanese published patent application No. Hei 11-176480 discloses a voltage-measuring device that measures voltage of each rechargeable battery that composes the high voltage battery. In this voltage-measuring device, a main battery (high voltage-battery) is divided into a plurality of modules, and after measuring a voltage of each module, the device measures a total voltage of the entire main battery. Then, the device judges whether the voltage of each module and the total voltage of the main battery are abnormal or not. If both of the voltages are normal, the device repeats the processing, and if both of the voltages are abnormal, the device informs of the battery abnormality, and stops the charge and discharge cycle.

The voltage measuring device described above measures the voltage of each module, then measures the total voltage of the main battery, and judges whether both of the voltages are abnormal or not. Therefore, there is a problem of taking time to the detection of abnormality. Further, when a big change of a voltage is measured at a certain module compared with other modules, the judgment whether it is caused by the change of the current value that the main battery supplies (for instance, change of the running state of the HEV) or by abnormality of the rechargeable battery is late.

Accordingly, an object of the present invention is to provide a voltage-measuring device to rapidly detect an abnormality of a high voltage battery consisting of rechargeable batteries connected in series with each other when judging the abnormality.

In order to attain the object, according to the present invention, there is provided a voltage measuring device for an in-vehicle high voltage battery consisting of a plurality of rechargeable batteries connected in series with each other, said device including: voltage measuring members respectively mounted on a plurality of blocks for measuring voltages of the blocks, each of which having at least one rechargeable battery; a control member for causing the voltage measuring members of two different blocks to alternately measure voltages three times or more, followed by judging abnormality of the in-vehicle high voltage battery on the basis of the measured voltages, then repeating the same measuring and judging for other combinations of two different blocks in turn.

Preferably, after the control member causes the two voltage measuring members to measure the voltages of the respective blocks, when a difference between the two measured voltages is equal to or more than a predetermined value, the control member judges that the in-vehicle high voltage battery is abnormal.

Preferably, when at least one of the measured voltage values is out of a region of predetermined voltage values, the control member judges that the in-vehicle high voltage battery is abnormal.

These and other objects, features, and advantages of the present invention will become more apparent upon reading of the following detailed description along with the accompanied drawings.

FIG. 1 is a circuit diagram showing an embodiment of a voltage-measuring device according to the present invention;

FIG. 2 is a flow chart showing a processing procedure where a low voltage system CPU 30 that composes the voltage-measuring device shown in FIG. 1 detects abnormality from the both voltages that two voltage measuring circuits measured;

FIGS. 3A and 3B are explanatory views showing a change of a block voltage; and

FIG. 4 is a flow chart showing a processing procedure in which a CPU 25 in a high voltage system forming the voltage-measuring device in FIG. 1 measures the block voltage.

A first embodiment of a voltage-measuring device according to the present invention will be described with reference to Figures. In FIG. 1 , a reference symbol BL indicates a low voltage battery. As shown in FIG. 1 , the low voltage battery BL consists of, for example, a rechargeable battery. The BL is used for operating a stator St that starts an engine. If necessary, an alternator utilized as a charger is connected to both ends of the BL.

A reference symbol BH indicates a high voltage battery. The high voltage battery is used for a power for an electric motor M of the HEV. If necessary, the motor M as a load or the alternator as a charger is connected to both ends of the BH.

The high voltage battery BH is divided into m blocks B 1 to Bm (where m is an optional integer). Each of blocks B 1 to Bm consists of n rechargeable batteries C 11 to Cmn (n is an optional integer). Each of the rechargeable batteries C 1 to Cmn supplies the same voltage and the same current, and is connected in series with the other. The rechargeable batteries C 1 n , C 2 n , . . . C(m-1)n that are disposed in boundaries with adjoining blocks are common rechargeable batteries to which both voltage measuring circuits 11 to 1 m can measure. Namely, the common rechargeable battery C 1 n is connected to both the voltage measuring circuits 11 and 12 , the common rechargeable battery C 2 n is connected to the voltage measuring circuit 11 and 13 , and the common rechargeable battery C(m-1)n is connected to the voltage measuring circuit 1 (m-1) and 1 m.

The voltage measuring device includes a voltage measuring circuits 11 to 1 m as voltage measuring means, a CPU 30 in a low voltage system as a control means, transmitting interfaces IFt 1 to IFtm, and receiving interfaces IFr 1 to IFrm.

The voltage measuring circuits 11 to 11 m correspond to blocks B 1 to Bm. The voltage measuring circuits 11 to 11 m are powered by the rechargeable batteries C 11 to Cmn composing the corresponding block B 1 to Bm. Namely, grounds of the voltage measuring circuits 11 to 1 m are respectively connected to cathode terminals of the corresponding blocks B 1 to Bm. Thus, a voltage of devices composing the voltage measuring circuits 11 to 1 m can be measured.

Each of the voltage measuring circuit 11 to 1 m includes: a differential amplifier OP for measuring the voltage of the corresponding block and the voltage of the rechargeable batteries C 11 to Cmn in the block; selective switches 24 for connecting the corresponding block B 1 to Bm or rechargeable batteries C 11 to Cmn composing the block to the differential amplifier OP; an A/D converter 22 for converting the voltage measured by the differential amplifier OP to digital values; a CPU 25 for a high voltage system for switching the selective switches 24 . The selective switches consist of normally close switches connected to both ends of the rechargeable batteries C 11 to Cmn. Here, the voltage between both ends of the block means the voltage between one end and the other end of the rechargeable batteries connected in series to each other in the block, for example, a voltage between a cathode of C 11 and an anode of C 1 n in block B 1 .

Further, each of the voltage measuring circuits 11 to 1 m includes: a high voltage power circuit 23 for outputting a constant voltage as an operating power of the differential amplifier OP, A/D converter 22 , and the high voltage CPU 25 inputted from the source batteries of blocks B 1 to Bm; and a breaker switch Sc 1 interposed between the high voltage power circuit 23 , and the operational amplifier OP and A/D converter 22 . The high voltage CPU 25 controls this breaker switch Sc 1 .

Each of the voltage measuring circuits 11 to 1 m is made of one chip. External resistors R 1 to Rm are connected to the voltage measuring circuits 11 to 1 m respectively. The external resistors R 1 to Rm correspond to addresses of the blocks B 1 to Bm, and have different values. The high voltage CPU 25 reads the resistance values of the external resistors R 1 to Rm corresponding to turning on of each high voltage power circuit 23 , and stores the values as addresses of each high voltage CPU 25 in a not-shown store device.

The low voltage CPU 30 includes a not-shown memory and operates under a power supply from a low voltage battery BL. The CPU 30 controls the voltage measuring circuits 11 to 1 m according to a program stored in the memory, a measuring route, and upper and lower voltages of the blocks.

A transmitting bus line BLt and a receiving bus line BLr are provided between the voltage measuring circuits 11 to 1 m and the low voltage CPU 30 . The transmitting bus line BLt and the receiving bus line BLr respectively branches from the low voltage CPU 30 to the voltage measuring circuits 11 to 1 m . Insulated transmitting interfaces IFt 1 to IFtm and insulated receiving interfaces IFr 1 to IFrm are respectively provided on the transmitting bus line BLt and the receiving bus line BLr after branched. Namely, branch points of the transmitting bus line BLt and the receiving bus line BLr are provided at the low voltage CPU 30 side and not at the insulated transmitting interfaces IFt 1 to IFtm and insulated receiving interfaces IFr 1 to IFrm sides.

The insulated transmitting interfaces IFt 1 to IFtm and insulated receiving interfaces IFr 1 to IFrm connect the voltage measuring circuits 11 to 1 m to the low voltage CPU 30 while they are electrically insulated to each other. Thus, the high voltage battery BH and the low voltage battery BL are insulated from each other. As the insulated transmitting interfaces IFt 1 to IFtm, for example, a photo coupler consisting of a light emitting device and a light receiving device or a magnetic coupler are already known.

FIGS. 2 to 4 show a procedure for measuring the voltages of blocks B 1 to Bm, and judging abnormality from the voltages in the above voltage measuring device. The low voltage CPU 30 and the high voltage CPU 25 carry out flow charts in FIGS. 2 and 4 when an ignition switch of the HEV is on. Namely, the low voltage CPU 30 executes the flow chart in FIG. 2 , to make the voltage measuring circuits 11 to 1 m measure the voltages of the blocks and judge the abnormality. The high voltage CPU 25 executes the flow chart shown in FIG. 4 to measure the voltages of the blocks.

First, in FIG. 2 , a procedure for measuring the voltages of the blocks by the voltage measuring circuits will be explained. In step S 101 , the voltage measuring circuits 11 to 1 m are turned on and then the procedure goes to step S 103 .

In step S 102 , variables k and l indicating both the voltage measuring circuit and the block number is set to 1 and the procedure goes to step S 103 .

Next, in step S 103 , the voltage measuring circuit 1 k measures the voltage and the voltage measuring circuit 1 l measures the voltage. Then, the procedure goes to step S 104 . For example, when the step is from step S 102 , the voltage measuring circuit 11 measures the voltage of the block B 1 , and the voltage measuring circuit 12 measures the voltage of the block B 2 .

Next, in step S 104 , the CPU 30 receives voltages V 1 k and V 1 l corresponding to the voltage measuring circuits 1 k and 1 l , and stores the voltage values in the memory in the CPU 30 . Then, the procedure goes to step S 105 .

In the step S 105 , the voltage measuring circuit 1 k again measures the voltage V 1 k ′ and the CPU 30 stores the voltage data in the memory. Then, the procedure goes to step S 107 . Namely, in step S 103 to S 106 , two voltage measuring circuits measure voltages of the blocks three times.

Next, in step S 107 , transmitted voltage values are corrected owing to a measuring error between the measuring circuits. Then, the procedure goes to step S 108 . The correction between the voltage measuring circuits is done as follows. Previously, while the ignition switch is off, voltages of each of common rechargeable batteries C 1 n , C 2 n . . . C(m-1)n are measured by two voltage measuring circuits having the common rechargeable batteries. A difference between the voltages of the two rechargeable batteries is a measuring error. The correction is done by adding the measuring error to the voltage of the block.

Next, in step 108 , whether the voltage V 1 k , V 1 l , V 1 k ′ corrected in step S 107 are between an upper limit voltage and a lower limit voltage on product standard of rechargeable battery in the block previously stored in the memory is judged. Namely, whether the measured voltage is within the predetermined voltage value or not is judged. Then, the CPU 30 compares the V 1 k , V 1 l , V 1 k ′ and goes to step S 108 . The voltages V 1 k , V 1 l , V 1 k ′ are compared as follows. When a difference between V 1 k and V 1 l is more than the predetermined value stored in The memory of the law voltage CPU, and a difference between V 1 l and V 1 k ′ is less than the predetermined value, the CPU 30 judges normal because the voltages of the blocks are changed owing to a change of the vehicle's running state. When the difference between V 1 k and V 1 l is more than the predetermined value, and the difference between V 1 l and V 1 k ′ is more than the predetermined value, the CPU judges that the block Bk or the block B 1 is abnormal because it is thought that the change is not owing to the change of the vehicle's running state. When The difference between V 1 k and V 1 l is less than the predetermined value and the difference between V 1 l and V 1 k ′ is more than the predetermined value, th CPU judges that the block Bk or the block B 1 is abnormal. Namely, when the difference between V 1 l and V 1 k ′ is more than the predetermined value, the CPU 30 judges that the high voltage battery BH is abnormal.

As an example, the blocks B 1 and B 2 (k=1, l=k+1) will be explained with reference to FIGS. 3A and 3B . First, in FIG. 3A , the voltage measuring circuit 11 measures the voltage of the block B 1 at a time t 1 and the measured voltage is V 1 . Then, the voltage measuring circuit 12 measures the voltage of the block B 2 at a time t 2 and the measured voltage is V 2 . The difference between V 1 and V 2 is more than the predetermined voltage. Then, the voltage measuring circuit 11 measures again the voltage of the block B 1 at a time t 3 and the measured voltage is around V 2 (namely within the predetermined value). In this case, the CPU 30 judges that such a voltage shift is caused by for example running on a slope at the time after t 1 . However, as shown in FIG. 3B , if the voltage of block B 1 measured at the time t 3 is around V 1 (namely more than the predetermined value), the CPU 30 judges that the block B 1 or B 2 is abnormal. Here, the difference more than the predetermined value is a detectable voltage shift caused by charge or discharge of the rechargeable battery.

Next, in step S 109 , when in step S 108 the measured voltages are over the block voltage of a product standard (more than the upper limit voltage or less than the lower limit voltage), or the voltage difference is judged abnormal, the procedure goes to step S 110 . When the measured voltages are within the block voltage of the product standard, and the voltage difference is judged normal, the procedure goes to step S 111 .

In step S 110 , the CPU 30 sends to a not-shown higher unit that the high voltage battery BH is abnormal, and then the procedure goes to step S 111 . According to the received data, the higher unit warns a HEV driver and prohibits the charge and discharge to the high voltage battery.

Next, in step S 111 , the CPU 30 adds the variable k to 1, and adds the variable l to 1. In step S 112 , if the result is less than m, the procedure goes back to step S 103 . If the result is more than m, the step goes back to S 102 . If the result is m, the procedure goes to step S 113 .

In step S 113 , the variable l is set to 1, and then the procedure goes back to step S 103 . Thus, the voltage measuring circuits 1 m and 11 measure.

Namely, according to this flow chart, voltages of two different blocks are measured three times, and the abnormality of the high voltage battery can be detected.

Next, a procedure to measure the voltage of the blocks by the high voltage CPU 25 of the voltage measuring circuits 11 to 1 m corresponding to the voltage measuring command which is sent from the low voltage CPU 30 to the voltage measuring circuits at steps S 103 and S 105 of the flowchart in FIG. 2 will be explained with reference to the flowchart of FIG. 4 .

First, in step S 201 , the CPU 25 judges that the power-on signal is received or not. The power-on signal is sent from the low voltage CPU 30 through the bus line BLt and interfaces IFt 1 to IFtm to the voltage measuring circuits 11 to 1 m . When the signal is received (yes), the procedure goes to step S 202 . When the signal is not received (no), step S 201 is repeated until the CPU 25 receives the signal.

Next, in step S 202 , breaker switches Sc 1 of the voltage measuring circuits 11 to 11 m are turned on. Thus, power is supplied from blocks B 1 to Bm to the differential amplifiers OP and A/D converters 22 , which constitute the measuring circuits 11 to 11 m.

Next, in step S 203 , the CPU 25 judges whether a measuring instruction is received or not. The measuring instruction is transmitted from the low voltage CPU 30 to voltage measuring circuits 11 to 1 m through the transmitting bus line BLt and the transmitting interfaces IFt 1 to IFtm. If the instruction is received (YES), the procedure goes to step S 204 . If the instruction is not received (NO), the procedure goes to step S 206 .

In step S 204 , the CPU 25 judges whether an address designated by the measuring instruction received in step S 203 is its own address or not. If it is its own address, the procedure goes to step S 205 . If it is not its own address, the procedure goes to step S 206 .

Next, in step S 205 , the CPU 25 measures the block voltage, and then the procedure goes to step S 206 . The high voltage CPU 25 connects both ends of the block to the differential amplifier OP. Thus, a digital value of the block voltage is supplied to the high voltage CPU 25 from the A/D converter 22 . In response to this, the high-voltage CPU 25 transmits the digital value of the voltage of the block, to which its own address is designated, to the receiving interfaces IFr 1 to IFrm. The digital value of the voltage of the block transmitted to the receiving interfaces IFr 1 to IFrm is transmitted to the low voltage CPU 30 through the receiving bus line BLr.

In step S 206 , the CPU 25 judges whether or not a power off signal, which is transmitted from the low voltage CPU 30 to each of the voltage measuring circuits 11 - 1 m through the transmitting bus line BLt and the transmitting interfaces IFt 1 to IFtm, is received. Then, if judged received (YES), the procedure goes to step S 207 . On the other hand, if judged not received (NO), the procedure returns to step S 203 .

In step S 207 , the breaker switches Sc 1 of the voltage measuring circuits 11 to 1 m are turned off. Thereby, electric power from the corresponding block B 1 to Bm to the differential amplifier OP and the A/D converter 22 , which constitute the corresponding voltage measuring circuit 11 to 1 m , is shut off.

According to the voltage measuring device, for example, the device measures the voltage of the block B 1 , then measures the voltage of block B 2 , and then measures again the voltage of the block B 1 . Namely, the device measures three times with two voltage measuring circuits. Thus, abnormality of the in-vehicle high voltage battery can be rapidly detected. Namely, because the in-vehicle high voltage battery BH is divided into a plurality of blocks B 1 to Bm, and the CPU 30 judges the abnormality of the voltages of two blocks, the device can detect the abnormality of the high voltage battery BH earlier than a system judging after all the voltages of the blocks B 1 to Bm are measured.

Further, according to the voltage measuring device, the device measures alternately the voltages of the blocks, for example, measuring the voltage measuring circuit 11 , measuring the voltage measuring circuit 12 , measuring the voltage measuring circuit 11 again, and when the difference between the voltage of the voltage measuring circuit 12 and the voltage measured by the measuring circuit 11 again is more than the predetermined value, the device can judge that the high voltage battery BH is abnormal. Namely, measuring alternately three times the voltages, and judging whether the difference is more than the predetermined value allows to judge whether the voltage change between the blocks B 1 and B 2 is owing to a change of running state or owing to the abnormality of the rechargeable battery in the block. Namely, it is possible to detect the abnormality of the high voltage battery BH even if not measuring the batteries of all the blocks 11 to 1 m . Therefore, the abnormality of the in-vehicle high voltage battery BH can be rapidly detected.

Further, when the voltage of the block measured by, for example, the voltage measuring circuits 11 , 12 is out of a predetermined range (over the upper limit or under the lower limit), the device can judge that the block is abnormal. Namely, it is possible to detect the abnormality of the high voltage battery BH even if not measuring the batteries of all the blocks 11 to 11 m . Therefore, the abnormality of the in-vehicle high voltage battery BH can be rapidly detected.

Incidentally, in the above embodiment, the two voltage measuring circuits adjacent to each other measure the voltage of the block to detect the abnormality of the in-vehicle high voltage battery. However, it is not necessary that the voltage measuring circuits are adjacent to each other.

Further, in the above embodiment, the voltages of the blocks are measured three times by two voltage measuring circuits. However, it is possible that the voltages are measured not less than three times.

Further, in the above embodiment, the high-voltage battery is composed of electric cells each consisting of a rechargeable battery. However, instead, the high-voltage battery may be composed of unit batteries or unit cells each consisting of a secondary battery.

Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise noted such changes and modifications departing from the scope of the present invention presently defined, should be construed as being included therein.