METHOD FOR CHARGING BATTERY AND APPARATUS THEREFOR

Abstract: A method and apparatus for charging quickly batteries such as a lead storage battery, in which an initial charging process (a) from time 0 to t₁, a quick charging process (b) from time T₁ to T₂, and a final charging process (c) from time t₂ to t₃ are executed by stepwise and continuously. In the initial charging process (a), charging current whose magnitude is increased gradually is made to flow. In the quick charging process (b), charging current of a greater quantity of charge than that in the initial charging process (a) is made to flow intermittently into a battery (6), while monitoring its voltage. In the final charging process (c), charging current being reduced gradually is made to flow into the battery (6) when the voltage reaches a charging end value. Thereby, charging in a very short time is possible, and more over the battery suffers no damage, and also, charging which permeates even the inside of electrode plates is possible.

Description: TECHNICAL FIELD The present invention relates to a battery charging method for charging a battery such as a lead acid storage battery quickly, and a battery charging apparatus used in carrying out said battery charging method: TECHNICAL BACKGROUND Conventionally, as a battery charging method, there are a constant-voltage charging method which applies a constant voltage to a battery for charging, and a constant-current charging method which applies a constant current continuously to the battery for charging. Though there are both merits and demerits in either of these methods, it is not easy to realize shortening of charging time considerably by any of existing methods. In recent years, from a view point of environment protection, practical use of a so-called electromobile vehicle which uses the batteries as a driving source is strongly desired. For wide use of the electromobile, while it is necessary to shorten the battery charging time a great deal, the battery charging method which complies with this request sufficiently is still not developed at present. Incidentally, a capacity of a battery is defined by an ampere-hour capacity (Ah) and an hour rate. For example, when the battery capacity of 10 Ah/10 hour rate is discharged at a current of LA, it can be used continuously for 10 hours. When this battery is discharged at a current of 4A, while the continuous usable time is 2.5 hours by calculation, it takes, as a matter of fact, approximately 1.5 hours to reach the charge-end voltage. In the same way, when discharged at a current of 10A, while the continuous usable time is 1 hour by calculation, a practical continuous usable time is approximately 35 minutes. Similarly, this applies to charging, too. For example, when a battery of 10 Ah/lO hour rate capacity is charged at a constant current of 1A for 10 hours, it reaches fully charged state. When it is charged at a constant current of 10A, the chemical reaction in the battery proceeds faster than the calculation, and as a matter of fact, it approaches to the fully charged state by a half of the calculated time of one hour. However, when the charging current is simply increased, it is liable to be overcharged and there is possibility of damaging electrodes of the battery. Moreover, there is a problem that only the surface of the electrodes is charged and the charging does not penetrate into the electrodes. EP-A-293 664 refers to a standard continuous three-rate charging process in accordance with the first part of Claim 1. US-A-4 670 703 also teaches a three-rate charging process, with a first low trickle charging step, a second rapid charging step, and a third low charging step. EP-A-479 249 and EP-A-390 079 disclose gradually increasing charging currents. The present invention has been devised in view of the above-mentioned problems. It is the object, therefore, to provide a battery charging method and its apparatus which is able to charge in a very short time and to penetrate the charging into the electrodes without damaging a battery. DISCLOSURE OF THE INVENTION The charging method according to the invention is characterized as shown in the characterizing portion of appended claim 1, and an apparatus for carrying out this method is claimed in appended claim 2. According to a battery charging method and a battery charging apparatus of the present invention, since a battery is charged by applying a charging current having a large volume of electricity intermittently after applying the initial stage charging current, charging can be finished in a short time and the charging has penetrated into electrodes without damaging the electrodes of the battery. Since a terminal voltage of the battery is watched during the quick charging and the quick charging process is moved to the final charging process when the battery terminal voltage has reached the charge-end voltage, overcharging is prevented and the battery is not damaged. Since the battery defect is judged by watching the charging current in the initial charging process, a quick charging can be carried out only on an appropriate battery. Due to the charging suspension period during which the supply of the charging current is suspended, charging penetrates more into the electrodes and spreads throughout the battery, thereby keeping the balance of charging between the electrodes. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory view showing the principle of battery charging method of the present invention, Fig. 2 is an electrical circuit diagram showing an example of circuit configuration of a battery charging apparatus according to the present invention, Fig. 3 is a block diagram showing a schematic configuration of a control unit, Fig. 4 is a block diagram showing a specific example of a drive control unit, Fig. 5 is an explanatory view showing the principle of generation of a control signal in a control signal generating unit, Fig. 6 is a flow chart showing control procedures by an operation control unit, and Fig. 7 is time charts showing the circuit operation of a drive control unit. PREFERRED FORM FOR THE EMBODIMENT OF THE INVENTION Fig. 1 shows the principle of battery charging method according to one embodiment of the present invention. In the figure, the lapse of time is plotted along the abscissa. In this battery charging method, an initial charging period "a" between times "0" to "t1", a quick charging period "b" between times "t1" to "t2" and a final charging period "c" between times "t2" to "t3" are carried out in step-wise and continuously. A battery terminal voltage and charging current are plotted along the ordinate. In the figure, a character Q (V) shows variations of the battery terminal voltage at charging, and a character Q (I) shows variations of mean value (hereinafter referred to as "mean current value") per unit time of the charging current at charging. The initial charging process a is the process, whereby the charging current whose volume of electricity is increased gradually is applied to start charging of the battery. In this embodiment, the charging current is applied in pulse form and soon after starting the charging, a pulse width t N of the pulse-shaped charging current is set to a sufficiently small value, and as the time elapses, the pulse width t N relative to a pulse interval t F is set larger in step-wise at every fixed time to increase the volume of electricity or the mean current value gradually. In the initial charging process a, a battery defect is judged by watching the charging current, thus when the mean current value at the time point, when a fixed time (say 30 seconds) has elapsed, has reached a predetermined reference value, it is judged that the battery is normal and the charging process moves to the quick charging process b, and when the reference value is not reached, it is judged that the battery is abnormal and extraordinary measures such as stopping the charging are taken. The following quick charging process b is the process, whereby the battery is charged by applying the charging current whose volume of electricity is larger than that of the initial charging process a intermittently while watching the battery terminal voltage. In this quick charging process b, the pulse widths t F are respectively set large, thereby the charging current is set to the larger volume of electricity (mean current value) than the initial charging process a. A value (pulse height) of the charging current is set to two to four times of the battery capacity, that is, in the case of battery having the capacity of 10 Ah/10 hour rate, it is set to two to four times of 10A. Furthermore, in this quick charging process b, a continuous charging period T1 (say approximately 10 seconds) during which the intermittent supply of the charging current is continued, and a charging suspension period T2 (say approximately 2 seconds) during which the intermittent supply of the charging current is suspended are set alternately till the battery terminal voltage reaches a charge-end voltage V E . The battery terminal voltage is measured during each of the charging suspension periods T2, preferably just before starting the continuous charging period T1. In the figure, a character P designates measuring time points of the battery terminal voltage. The final charging process c is the process, whereby charging of the battery is finished by applying the charging current whose volume of electricity is reduced gradually, when the battery terminal voltage reaches the charge-end voltage V E . In this embodiment, the volume of electricity (mean current value) is reduced gradually by applying the charging current in pulse form and setting the pulse width t N relative to the pulse interval t F of the charging current smaller in step-wise at every fixed time as the time elapses. Fig. 2 is an example of circuit configuration of a battery charging apparatus used in carrying out the above-mentioned battery charging method. In the battery charging apparatus shown in the figure, a charging circuit comprises a primary circuit 1 and a secondary circuit 2 connected by a transformer 3. Power input terminals 5, 5 connected to a single-phase A.C. power source 4 are provided in the primary circuit 1, and battery connecting terminals 7, 7 connected to a battery 6 are provided in the secondary circuit 2. In the primary circuit 1, a control switch 8 consisting of a semiconductor switch such as SSR is provided. The control switch 8 operates to turn on and off by a control signal given from a control unit 9, and the timing of on-off operation against the control signal input is selected automatically by a zero-cross point of the A.C. input. In the secondary circuit 2, a rectifier 10 which performs all-wave rectification of a secondary output of the transformer 3, a charging current detector 11 for detecting the charging current flowing through the secondary circuit 2 and a terminal voltage detector 12 for detecting the terminal voltage of the battery 6 are provided. Detected values by the charging current detector 11 and the terminal voltage detector 12 are taken into the control unit 9. In the figure, numeral 13 designates a power circuit for supplying a D.C. voltage necessary for the operation of the control unit 9, and including a transformer 14, a rectifier 15 and a voltage converter 16. Fig. 3 is a block diagram showing a schematic configuration of the control unit 9. In the control unit 9, an operation control unit 20, a clock generator 21, a drive control unit 22, a display control unit 23 and a timer 24 are included. The control switch 8 is connected to the drive control unit 22 and an LED group 26 is connected to the display control unit 23. The LED group 26 consists of a plurality of LEDs, which are let and indicate operating states of the battery charging apparatus under the control of display control unit 23. The operation control unit 20 is constituted by a microcomputer, and includes a CPU 27 which is the main body of control and operation, a ROM 28 storing programs and a RAM 29 which reads and writes data. To the CPU 27, the charging current detector 11 and the terminal voltage detector 12 are connected via a bus 25, besides the drive control unit 22, display control unit 23 and timer 24. Fig. 4 shows a specific circuit configuration of the drive control unit 22, consisting of a control signal generating unit 30, a period setting unit 31, a gate circuit unit 32 and a fall-edge detecting circuit 33. The control signal generating unit 30 is for generating a control signal which controls the on-off operation of the control switch 8, and includes a saw-tooth wave generating circuit 34, a comparator 35, a setter 36 and an inversion circuit 37. Fig. 5 shows the generating principle of the control signal in the control signal generating unit 30. Fig. 5 (1) is a saw-tooth wave [1] generated by the saw-tooth wave generating circuit 34. The comparator 35 compares the size of a voltage level of the saw-tooth wave [1] with a set point TH set in the setter 36. When the voltage level of the saw-tooth wave [1] is above the set point TH, as shown in Fig. 5(2), an output level of the comparator 35 becomes "1", and when below the set point TH, the output level becomes "0". Comparison output [2] of the comparator 35 is inverted by the inversion circuit 37, and as the inversion output, a control signal [3] shown in Fig. 5 (3) is obtained. When the set point TH is set to a high level, a pulse width of the control signal [3] becomes larger than a pulse interval. Thus, in the quick charging process b, the charging current having a large volume of electricity is obtained by setting such a high level set point TH to generate the control signal [3]. When the set point TH is set to a low level, the pulse width of the control signal [3] becomes smaller than the pulse interval. Thus, in the initial charging process a and the final charging process c, the charging current whose volume of electricity increases and decreases gradually is obtained by setting such a low level set point TH variably and in step-wise at every fixed time to generate the control signal [3]. Returning to Fig. 4, the period setting unit 31 is for setting a period during which the control signal [3] is given to the control switch 8, and includes a counter 39 to which a clock signal CK is given via an AND circuit 38, first and second comparators 40, 41 which compare the count value of the counter 39 with set points set in the setters 42, 43. The clock signal CK is given to the AND circuit 38 from the clock generator 21, and the AND circuit 38 outputs the clock signal CK to the counter 39 when a starting signal is given from the CPU 27. In the initial charging process a and the final charging process c, any values which are sufficiently large are set in the setters 42, 43, and in the quick charging process b, a value corresponding to the continuous charging time T1 is set in one setter 42, and a value corresponding to a sum of the continuous charging time T1 and the charging suspension time T2, or a one cycle length T3 is set in the other setter 43. The first and second comparators 40, 41 are that, when the count value of the counter 39 reaches the set points of respective setters 42, 43, the comparison values become "1", the comparison output of the second comparator 41 is given to the counter 39 as a reset signal via an OR circuit 44. The comparison output of the first comparator 40 is given to an AND circuit 46 together with the starting signal via the inversion circuit 45. By the output of the AND circuit 46, the gate circuit unit 32 is controlled to open and close, and the control signal [3] is given to the control switch 8 as the output signal when the gate circuit is in open-state. The fall-edge detecting circuit 33 detects the fall output of the AND circuit 45 and outputs an edge detecting signal to the CPU 27. When the CPU 27 receives the edge detecting signal, takes in the detected value of the terminal voltage detector 12 at an adequate timing. Fig. 6 shows control procedures of the operation control unit 20, and Fig. 7 shows time charts of the drive control unit 22. In Fig. 6, Step 1 (shown as "ST1" in the figure) to Step 9 show the control procedures in the initial charging process, Step 10 to Step 13 show the control procedures in the quick charging process, and Step 14 to Step 19 show the control procedures in the final charging process. In the following, the operation of the battery charging apparatus is particularly described according to Fig. 6 and Fig. 7. First, in Step 1 (shown as "ST1" in the figure) of Fig. 6, the CPU 27 judges whether the power is switched on or not, when it is judged "YES", after setting an initial set point TH in the initial charging process in the setter 36 of the control signal generating unit 30, and setting any sufficiently large values in the setters 42, 43 of the period setting unit 31, the CPU turns on the starting signal [4] (refer to Fig. 7 (1)), and starts the timer 24 (Step 2 to Step 4). In Fig. 7, reference character TM1 indicates a start timing of the initial charging process a, thereby the control signal generating unit 30 generates the control signal [3] (refer to Fig. 7 (4)) having the pulse width responsive to the initial set point TH. Though the counter 39 of the period setting unit 31 starts counting operation, since its counted value is smaller than the set points of the setters 42, 43. A comparison output [5] (refer to Fig. 7 (2)) of the first comparator 41 remains as "0", and an AND output [6] (refer to Fig. 7 (3)) of the AND circuit 46 is "1". Thus, the gate circuit unit 32 is maintained in open-state, and in the initial charging process a, the control signal [3] passes through the gate circuit 32 as it is and is given to the control switch 8 as an output signal [7] (refer to Fig. 7 (5)). In the timer 24, the duration time (say 30 seconds) of the initial charging process a is set, and in the next Step 5, it is judged whether the time of the timer 24 is up, and in the following Step 6, it is judged whether a predetermined time has elapsed. When a predetermined time has elapsed, it is judged "YES" in Step 6 and the CPU 27 proceeds to Step 7 to set the next set point TH in the setter 36 of the control signal generating unit 30, and generates the control signal [3] having the pulse width responsive to the set point TH. By renewing the set point TH at every elapse of predetermined time, and generating the control signal having the pulse width responsive to the set point TH until the time of the timer 24 is up, the charging current whose quantity of electricity is increased gradually is obtained. When the time of the timer 24 is up, it is judged "YES" in Step 5 and the CPU 27 proceeds to Step 8 to take in the detected value by the charging current detector 11, and compares with a predetermined reference value. When the detected value is above the reference value, though it is judged "YES" in Step 9 and the CPU 27 moves to the quick charging process b below Step 10, when the detected value is below the reference value, the CPU 27 judges the battery defect and performs extraordinary procedures such as suspension of charging. In the first Step 10 of the quick charging process b, the CPU 27 sets a predetermined set point TH in the setter 36 of the control signal generating unit 30, sets a value corresponding to the continuous charging time T1 in one setter 42 of the period setting unit 31, sets a value corresponding to one cycle length T3 in the other setter 43, and resets the counter 39 of the period setting unit 31. In Fig. 7, reference character TM2 indicates a start timing of the quick charging process b, thereby the control signal generating unit 30 generates the control signal [3] having the pulse width responsive to the set point TH. Though the counter 39 of the period setting unit 31 continues the counting operation, until the counted value reaches the set point of the setter 42 corresponding to the continuous charging period, the comparison output [5] of the first comparator 40 is "0", and the AND output [6] of the AND circuit 46 is "1" (refer to Figs. 7 (2), (3)). Thus, the gate circuit unit 32 is set to open-state, and the control signal [3] passes through the gate circuit unit 32 as it is and is given to the control switch 8 as the output signal [7] (refer to Fig. 7 (5)). When the count value of the counter 39 becomes larger than the set point of the setter 42, the charging suspension period T2 is extended, the comparison output [5] of the first comparator 40 becomes "1" and the AND output [6] of the AND circuit 46 becomes "0" (refer to Figs. 7 (2), (3)). Thereby, the gate circuit unit 32 is set to close-state, the control signal [3] is interrupted by the gate circuit unit 32 and the output signal [7] is "0" (refer to Figs. 7 (4), (5)). When the AND output [6] of the AND circuit 46 falls from "1" to "0", it is detected by the fall-edge detecting circuit 33 and the edge detecting signal is outputted to the CPU 27. Thereby, it is judged "YES" in Step 11, and the CPU 27 takes in the detected value by the terminal voltage detector 12 to compare with the charging end voltage V E (Step 12). When the detected value has reached the charging end voltage V E , though it is judged "YES" in Step 13 and the CPU 27 moves to the final charging process c below Step 14, when the detected value is smaller than the charge-end voltage V E , the CPU 27 returns to Step 11 continue the quick charging process b and stands by for the next edge detecting signal. When the count value of the counter 39 becomes larger than the set point of the setter 43 in the quick charging process b, the comparison output of the second comparator 41 becomes "1", and by this comparison output the counter 39 is reset. As a result, the count value of the counter 39 becomes smaller than the set point of the setter 42, the comparison output of the comparator 40 is changed to "0" and the AND output [6] of the AND circuit 46 becomes "1" (refer to Figs. 7 (2), (3)). Thereby, the gate circuit unit 32 is set to open-state, and the control signal [3] passes through the gate circuit unit 32 as it is and is given to the control switch 8 as the output signal [7], thus returning to the continuous charging period T1 from the charging suspension period T2 (refer to Fig. 7 (5)). While such operation are repetitively executed, when the detected value by the terminal voltage detector 12 reaches the charge-end voltage V E , it is judged "YES" in Step 13, and the CPU 27 moves to the final charging process c below Step 14. In the first Step 14 of the final charging process c, after setting a first set point TH in the final charging process c in the setter 36 of the control signal generating unit 30, and setting any sufficiently large value in the setters 42, 43 of the period setting unit 31, the CPU 27 starts the timer 24 (steps 14, 15). In Fig. 7, reference character TM3 indicates the start timing of the final charging process c, thereby the control signal generating unit 30 generates the control signal [3] having the pulse width responsive to the first set point TH (refer to Fig. 7 (4)). Though the counter 39 of the period setting unit 31 starts counting operation, since the count value is smaller than the set points of the setters 42, 43, the comparison output [5] (refer to Fig. 7 (2)) of the first comparator 41 remains as "0", and the AND output [6] (refer to Fig. 7 (3)) of the AND circuit 46 is "1". Thus, the gate circuit unit 32 is maintained in open-state, and in the final charging process c, the control signal [3] passes through the gate circuit unit 32 as it is and is given to the control switch 8 as the output signal [7] (refer to Fig. 7 (5)). A predetermined duration time of the final charging process c is set in the timer 24, and in Step 16 it is judged whether the time of the timer 24 is up, and in the following Step 17, it is judged whether a predetermined time has elapsed. When the predetermined time has elapsed, it is judged "YES" in Step 17 and the CPU 27 proceeds to Step 18 to set a next set point TH in the setter 36 of the control. signal generating unit 30, and generates the control signal [3] having the pulse width responsive to the set point TH. By generating the control signal having the pulse width responsive to the set point TH at every elapse of predetermined time as renewing the set point TH until the time of the timer 24 is up, the charging current whose volume of electricity is reduced gradually is obtained. When the time of the timer 24 is up, it is judged "YES" in Step 16 and the CPU 27 proceeds to Step 19 to turn off the start signal [4] to finish charging.

Claims: A method of charging a battery (6), comprising: an initial charging step (a) of applying stepwise increasing control pulses to gradually increase the charge rate supplied to the battery (6); a quick charging step (b) of applying control pulses to supply a larger charge rate than that in the initial charging step (a) until the battery terminal voltage has increased to a predetermined charge-end voltage value; and a final charging step (c), wherein said initial charging step (a) comprises a step of carrying out an extraordinary procedure, provided that the charging current is below a predetermined value after the lapse of a predetermined time since the charging has started; and said quick charging step starts when the charging current in the initial charging step is above said predetermined value after the lapse of said predetermined time since the charging has started; characterized in that said final charging step starts when said charge-end voltage value has been reached and comprises applying stepwise decreasing control pulses to finish charging by gradually reducing the charge rate; and in the quick charging step, a step of applying repeated control pulses to continuously charge the battery (6) at the larger charge rate for a certain time, approximately 10 s, and a step of suspending the control pulses for a shorter time, approximately 2 s, than said pulse-supplying time, are done alternately until the battery terminal voltage has increased to said predetermined charge-end voltage value. A battery charging apparatus comprising a charging circuit for causing current to flow through a battery (6); a control switch (8) connected to said charging circuit for selectively passing and cutting off the charging current which flows through said charging circuit; a charging current detector (11) for detecting the current which flows through said charging circuit; a terminal voltage detector (12) for detecting the terminal voltage of the battery (6); a control unit (9, 30, 31) for applying control pulses to said control switch (8) in response to values measured by said charging current detector (11) and terminal voltage detector (12); first signal generating means (9, 30, 32) for generating stepwise increasing control pulses for supplying gradually increasing current to the battery (6); second signal generating means (9, 30, 31, 32) for generating control pulses to supply a larger charge rate to the battery (6) than that obtained by the control pulses of the first signal generating means; and means (9, 24) for carrying out extraordinary procedures, provided that the current detected by said current detector (11) is below a predetermined value after the lapse of a predetermined time since said first signal generating means has started; characterized by third signal generating means (9, 30, 32) for generating stepwise decreasing control pulses to gradually decrease the charge rate; and controlling means (9, 30, 31, 32) for controlling the first through third signal generating means to operate the first signal generating means to start charging of the battery, and for shifting the operating from the first signal generating means to the second signal generating means, provided that the current detected by said charging current detector (11) has increased to said predetermined value after the lapse of said predetermined time since said first signal generating means has started, and for repeating the operation of the second signal generating means after each lapse of a certain pulse suspending time, approximately 2 s, which is shorter than the operating time, approximately 10 s, of the second signal generating means, until the voltage detected by said terminal voltage detector (12) has increased to a charge-end voltage value and, in response thereto, for shifting to operate the third signal generating means to finish charging.

Inventors: SHIMOMOTO KENKICHI, SHIMOMOTO, KENKICHI, SHIMOMOTO, KENKICHI MC JAPAN CO., LTD.
Applicants: HANASHIRO KIYOMI, HANASHIRO, KIYOMI
Application year: 1992
Main classification: H02J7
IPC codes: H02J7