Abstract:
A cell which has become inactive is detected in a multi-cell battery ( 15 ) comprising plural cells (C n ). An inactivity detecting circuit comprising a signal generator (D n   1 ) and a diode (D n   2 ) connected in series, is connected in parallel with the cell (C n ) When the cell becomes inactive, the signal generator (D n   1 ) emits a signal to indicate the state of the cell. Hence, it is possible to economically detect loss of cell activity.

Description:
FIELD OF THE INVENTION 
     This invention relates to detection of a cell which has become inactive in a multi-cell battery. 
     BACKGROUND OF THE INVENTION 
     When the activity of a battery cell is lost due to minute short-circuits in a multi-cell battery, it is difficult to detect the inactive cell simply from the terminal voltage. 
     Tokkai Hei 9-84274 published by the Japanese Patent Office in 1997 provides a voltage detecting circuit for each cell, wherein charging/discharging is performed while monitoring the voltage of each cell. 
     SUMMARY OF THE INVENTION 
     When a voltage detecting circuit was provided for every cell, the cost of the battery is inevitably increased. 
     It is therefore an object of this invention to provide a detecting device for detecting a cell which has become inactive. 
     In order to achieve the above object, this invention provides an inactivity detecting device for detecting a cell which has become inactive in a multi-cell battery comprising plural cells. The device comprises an inactivity detecting circuit connected with a cell in parallel. The inactivity detecting circuit comprises a signal generator and a diode connected in series. 
     This invention also provides a device for detecting the inactivity of battery modules, each comprising plural cells connected in series, in a multi-cell battery. The device comprises an inactivity detecting circuit connected with a module in parallel. The inactivity detecting circuit comprises a signal generator and a diode connected in series. 
     This invention also provides a method for detecting an inactivity of a cell in a multi-cell battery comprising plural cells. The method comprises connecting an inactivity detecting circuit with the cell in parallel. The inactivity detecting circuit comprises a signal generator and a diode connected in series. The inactivity of the cell is then detected from a signal generated by the signal generator. 
     The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic dram of a hybrid vehicle according to this invention. 
     FIG. 2 is a schematic diagram of an inactivity detecting circuit according to this invention. 
     FIGS. 3A and 3B are timing charts showing the relation between cell voltage and discharge current during discharge. 
     FIG. 4 is a circuit diagram of an inactivity detecting circuit according to a second embodiment of this invention. 
     FIG. 5 is a circuit diagram of an inactivity detecting circuit according to a third embodiment of this invention. 
     FIG. 6 is a circuit diagram of an inactivity detecting circuit according to a fourth embodiment of this invention. 
     FIG. 7 is similar to FIG. 6, but showing a case where each of modular units comprises plural cells connected in parallel. 
     FIG. 8 is similar to FIG. 6, but showing a case where each of modular units comprises plural cells connected both in series and in parallel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 of the drawings, a hybrid vehicle to which this invention is applied drives drive wheels  8  using the power of an engine  2  and motor  4 . 
     The motor  4  is connected to an input shaft of a continuously variable transmission (CVT)  5 . 
     The output shaft of the engine  2  is joined to a rotating shaft of the motor  4  via a clutch  3 . 
     The output of the continuously variable transmission  5  is transmitted to the drive wheels  8  via a reduction gear  6  and a differential gear  7 . 
     When the clutch  3  is engaged, therefore, the drive wheels  8  rotate due to a rotation torque of the engine  2  and motor  4 , and when the clutch  3  is disengaged, the drive wheels  8  rotate due only to the rotation torque of the motor  4 . 
     The continuously variable transmission  5  varies a speed ratio according to an oil pressure supplied from an oil pump  9  driven by a motor  10 . 
     A motor/generator  1  is joined to the engine  2 . 
     Due to a supply current from a battery  15 , the motor/generator  1  functions as a starter motor for starting the engine  2 , and functions as a generator to charge the battery  15  when the engine  2  is running. 
     The motor/generator  1  and motor  4 ,  10  are AC devices such as a triphase synchronous motor or triphase induction motor. 
     If a motor/generator is applied to the motor  4 , electricity is generated by the rotation torque of the drive wheels  8  when the vehicle is slowing down, and a regenerative braking force based on the rotation resistance at this time may also be arranged to apply to the drive wheels  8 . 
     The clutch  3  is an electromagnetic powder clutch which can regulate the transmission torque, but a dry type sheet clutch or wet type multiple disc clutch can also be used. 
     The motor/generator  1  and motor  4 ,  10  are respectively controlled by inverters  11 ,  12  and  13 . 
     DC current motors may also be used for the motor/generator  1  and motor  4 , 10 . In this case, DC/DC converters may be used instead of the inverters  11 ,  12  and  13 . 
     The inverters  11 ,  12  and  13  are connected to the battery  15  via a common DC link  14 . 
     The inverters  11 ,  12  and  13  convert DC power stored in the battery  15  to AC power, and supply this to the motor/generator  1  and motor  4 , 10 . 
     The inverter  11  also converts AC power generated by the motor/generator  1  and charges the battery  15 . 
     If the motor  4  performs regenerative braking as described above, the power generated by the motor  4  during regenerative braking may be used directly as a drive force for the DC motor  10  or motor/generator  1  via the DC link  14 . The battery  15  may be a lithium ion battery, a nickel metal hydride battery or a lithium polymer battery. 
     The rotation speed of the engine  2 , transmission torque of the clutch  3 , rotation speed of the motor/generator  1  and motor  4 ,  10 , speed ratio of the continuously variable transmission  5  and charging/discharging of the battery  15  are respectively controlled by output signals from a controller  16 . 
     The controller  16  comprises a microcomputer comprising a central processing unit (CPU), read only memory (ROM), random access memory (RAM) and input/output (I/O) interface. 
     The controller  16  controls the rotational speed of the engine  2 , transmission torque of the clutch  3 , rotational speed of the motors  1 , 4 , 10 , speed ratio of the continuously variable transmission  5 , and charging/discharging of the battery  15 . 
     Next, the circuit of the battery  15  will be described referring to FIG.  2 . 
     The battery  15  is a multi-cell battery wherein n battery cells are connected in series. 
     An inactivity detecting circuit is connected between a positive and a negative electrode of the cells C n . The inactivity detecting circuit comprises light emitting diodes (LED) D n   1 , D n   2 , and resistors R n which are connected in series. The “n” attached to the signs of members specifies a positive integer. 
     The cathodes of the light emitting diodes D n   1 , D n   2  are connected to the anode side of the cell C n . The resistor R n  is a protection resistor for preventing D n   2  may be a non-light emitting diode, such as shown in FIG. 2 a current exceeding the maximum rated current from flowing through the light-emitting diodes D n   1 , D n   2 . 
     FIG. 3 shows the relation between a cell voltage Vc and discharge current while the cell C n  is discharging. 
     In a multi-cell battery comprising plural cells connected in series, if discharging is performed when any cell is inactive and its voltage Vc is 0, a polarity inversion occurs due to the internal resistance of the cell, and the diode D n   2  becomes conducting so that part of the discharge current flows through the inactivity detecting circuit. 
     When the voltage Vc which is directly proportional to the product of the internal resistance of the inactive cell and the discharge current, falls below Vcl, the light-emitting diode D n   1  lights so as to warn the user that the cell has become inactive. 
     Hence, an economical device can be provided wherein the inactive state of a cell can be displayed merely by connecting an inactivity detecting circuit having diodes D n   1 , D n   2  to each of the cells C n . 
     Next, a second embodiment of the invention will be described referring to FIG.  4 . 
     According to this embodiment, a Zener diode Z n  is used instead of the diode D n   2  of the inactivity detecting circuit shown in FIG.  2 . 
     The cathode of the Zener diode Z n  is connected to the anode side of the cell C n . When the cell C n  is discharging, an identical function to that of the diode D n   2  of the aforesaid first embodiment is provided by the characteristics of the arrangement of Zener diodes Z n . Also, when the cell charging cell voltage Vc exceeds a Zener voltage VZ of the Zener diode Z n , the charging current that should flow into the cell C n  flows into the inactivity detecting circuit. 
     Therefore, according to this embodiment, not only can an inactive cell be displayed, but overcharging of the cells can be prevented, and the voltage of each cell can be made uniform. 
     Next, a third embodiment of the invention will be described referring to FIG.  5 . 
     This embodiment uses a photocoupler D n   3  instead of the light emitting diode D n   1  of the aforesaid first embodiment. A control circuit  17  is connected to the output terminal of the photocoupler D n   3  of each of the cells C n . 
     If a cell becomes inactive and polarity inversion occurs during discharge, current flows into the inactivity detecting circuit, and the photocoupler D n   3  outputs a signal to a control circuit  17 . When the control circuit  17  receives this signal, a message is displayed showing the inactive cell together with an alarm. 
     According to this embodiment, not only is an inactive cell displayed, but an interlock signal so as to stop charging and discharging of the battery  15  is output from the control circuit  17  which is insulated from the battery  15 , when inactivation occurs. By using the photocoupler D n   3  therefore, it is not necessary to arrange a special insulation between the signal output circuit and the battery  15  as in the case where the inactivity signal is output via an electric wire. 
     Next, a fourth embodiment of the invention will be described referring to FIGS. 6-8. 
     In this embodiment, the battery  15  comprises plural modular unit M n each comprising plural cells C n . The cells C n may be connected in series as shown in FIG. 6, or in parallel as shown in FIG. 7, or in a complex configuration of both as shown in FIG.  8 . 
     This invention may be applied to detect an inactive modular unit M n in these batteries  15 . For this purpose, the inactivity detecting circuit IDC n  according to any of the aforesaid first-third embodiments is provided for each modular unit M n  instead of detecting the inactivity of each cell C n . 
     The contents of Tokugan Hei 10-132184, with a filing date of May 14, 1998 in Japan, are hereby incorporated by reference. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. 
     For example, this invention is applied to a hybrid vehicle in the above embodiments, but it can be applied to various batteries of various electric vehicles including hybrid vehicles. It is also applicable to batteries other than those installed in electric vehicles.