Cognition Device for Battery Residual Capacity

1. Field of the Invention

The present invention relates to a cognition device for battery residual capacity, especially useful for portable wireless equipment or office automation equipment.

2. Description of the Prior Art

Conventional cognition devices for battery residual capacity have used a device which directly measures the residual capacity or a device in which residual capacity is obtained from consumed electric power obtained by integrating current during the time which a battery is used with a timer.

In conventional cognition devices for battery residual capacity as described above, there has been a problem that battery residual capacity cannot be measured accurately due to changes in battery voltage resulting from changes in ambient temperature or load.

Japanese Patent Application laid-open No. 218077/85 describes a method of temperature correction for such a condition. In this method, a correction factor is calculated by using the temperature difference between the ambient reference temperature of 20.degree. C. and the ambient temperature at that time, but the correction for the temperature changes is too rough to obtain accurate residual capacity.

The present invention is directed toward solving such problems as described above. It is therefore an object of the invention to provide a cognition device for battery residual capacity with which the battery residual capacity at any arbitrary point of time can be determined correctly without being influenced by ambient temperature or load.

The cognition device for battery residual capacity comprises, in one embodiment of the invention, an A/D converter to convert the voltage information of the battery and the ambient temperature information of the battery into digital signals, and a central control circuit which corrects the voltage information with the load information and reads out the data conforming to the ambient temperature information from the discharge characteristic data previously stored in memory to compare the data with the voltage information after correction and calculate battery residual capacity based on the comparison data.

Other objects and advantages of the present invention will be made clearer by the following detailed description with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a cognition device for battery residual capacity according to one embodiment of the present invention;

FIG. 2 is a discharge characteristic chart of a battery voltage;

FIG. 3 is a flow chart explaining the operation of the device shown in FIG. 1; and

FIG. 4, FIG. 5 and FIG. 6 are block diagrams showing cognition devices for battery residual capacity according to other embodiments of the present invention.

In FIG. 1, a secondary battery 1, for example, of a Ni--Cd type is connected to supply a load 2, which may be, for example, the internal circuit of an electronic device. An electronic switch 3 is connected between the battery 1 and the load 2. A temperature sensor 4 is provided physically close to the battery 1. An A/D (analog-digital) converter 5 for converting the outputs of the battery 1 and of the sensor 4 comprises an analog switch section 5a having a plurality of selectively connectable switch nodes and which switches over to the output of the battery 1 or that of the temperature sensor 4. An A/D converter section 5b, which performs A/D conversion, is connected to the analog switch section 5a.

A component part 6 is a microprocessor which reads data from the A/D converter 5 and controls the electronic switch 3. A nonvolatile memory 7 (hereinafter referred to as a memory) in which a program for normal operation of the electronic device and the discharge characteristic data of the battery are stored and a display 8 which displays battery residual capacity are connected to the microprocessor 6.

FIG. 2 shows the discharged capacity as a function of battery voltage at temperature differences of 10.degree. C. apart for a Ni--Cd secondary battery. In FIG. 2, the battery voltage is the open-circuit voltage at no load and discharged capacity values at 10% capacity intervals are plotted with marks o's.

A table shown below expresses the characteristics shown in FIG. 2 in a matrix form in which battery voltages (V.sub.NM) corresponding to individual temperatures at intervals of 10.degree. C. and discharged capacity values at intervals of 10% are plotted. The voltage data in matrix form as mentioned above are stored in a specific address area of the memory 7 shown in FIG. 1. In the example shown in the table, 10.times.10 data are shown.

Following is the explanation of operation in the embodiment as described above referring to the flow chart shown in FIG. 3. The microprocessor 6 controls the analog switch section 5a of the A/D converter 5 to measure a battery voltage (step ST1), controls the A/D converting section 5b as to perform A/D conversion, and reads converted data (step ST2).

The value of the read converted data is denoted V.sub.0. At this point, the control condition of the switch 3 shall be judged (step ST3), if it is in ON state, a voltage drop due to a load shall be used to correct the value of open-circuit voltage. The corrected voltage V.sub.1, which is the open-circuit voltage, is obtained from the equation

where

R is the load resistance and r is the internal resistance of a battery.

On the other hand, if the electronic switch is in the OFF state:

At step ST6, the A/D converter is set to read the temperature from the output of the temperature sensor 4. The measured temperature T is compared with stored data for stored temperature values T1, T2, T3, . . . successively, to retrieve T.sub.N which is the closest to the measured data (steps ST7 to ST11). The measured data T.congruent.T.sub.N, is obtained, and battery voltages V.sub.NO to V.sub.N9 corresponding to the memorized data TN on the table are read from the memory 7 (step ST12). The read data are compared successively with the above mentioned corrected measured voltage V.sub.1 to retrieve V.sub.NM (steps ST13 to ST15). The discharged capacity is equal to M.times.10(%) and this value is displayed on display 8 at step ST16. The residual capacity is, therefore, obtained in the expression 100-M.times.10(%).

An example is shown in the following. In FIG. 2, for example, when T.congruent.-30.degree. C., a point to be V.sub.l on the line of -30.degree. C. is shown with x.

By successive comparison of voltage as described in the above, the voltage value becomes V.sub.02, and the discharge capacity is 20%. The residual value is, therefore, 80%.

The microprocessor 6 displays the battery residual capacity thus obtained in the display 8 in the form of a digital value or of a bar graph or the like.

The operation of cognition and display of battery residual capacity may be renewed at regular intervals of time or when a user executes a specific operation. For example, during normal program execution of the electronic device, the microprocessor may be switched to a mode of battery residual capacity cognition and display by an interrupt control.

In the above example, 10 temperature parameters and 10 discharge parameters for a total of 10.times.10=100 voltage data are used, but to upgrade precision, for example, if 20 temperature parameters, in the range of -30 to +55.degree. C. at intervals of 5.degree. C. and 20 discharge capacity parameters at intervals of 5%, that is, a total of 20.times.20=400 voltage data are used, a measurement can be made with double the precision for temperature and also for load.

FIG. 4 shows an embodiment in which the battery 1 and the memory 7 are integrated into a single case 9 made attachable to and detachable from the electronic device shown as a load 2. According to this example, the discharge characteristic data conforming to the type of battery 1 can be stored in the memory 7, so that a battery can be selected and exchanged freely out of various kinds of batteries for electronic devices. The remaining capacity cognition components can be provided with the electronic device.

FIG. 5 shows an embodiment in which a plurality of loads 2a-2c are connected to a battery 1 in parallel through respective independent electronic switches 3a-3c for exclusive use. In this case, all electronic switches 3a-3c are controlled by microprocessor 6. The microprocessor 6 can, therefore, always recognize an overall load based on the state of electronic switches 3a-3c controlled by the microprocessor, and the battery voltage can be corrected accordingly.

FIG. 6 shows an embodiment in which a memory 7a storing a control program and a memory 7b storing discharge characteristics are independently provided. In this case, if the memory 7b has read-write capability to store external input data through the microprocessor 6, the exchange of discharge characteristics is easily done according to the type of battery utilized at any given time.

The detailed drawings of A/D converters 5 in the embodiments shown in FIG. 4-FIG. 6 are omitted since each of them comprises an analog switch section 5a and an A/D conversion section 5b as shown in FIG. 1.

According to the present invention, a measured battery voltage can be corrected by load information and the corrected voltage is compared with the temperature correlated data read from the discharge characteristic data of a battery stored in a memory to determine the discharged capacity of the battery. Correct cognition of battery residual capacity can be performed based on the determined discharged capacity.