Device for determining the charge condition of a secondaryelectric storage battery

The invention relates to an electrical display device for the state of charge of a secondary battery, with a correct charging and discharging the secondary battery detected

Integrator in the form of a pulse generator, the frequency of which is proportional to the battery current and is followed by a controlled depending on the Batteryurrrichtungrichtung up and down counter.

Display devices of this type can, as described in the AT-PS Nr.331357, be designed for motor vehicle batteries so that they show the battery still each removable amount of Ah analogous to a gasoline watch, or even so that they can detect timely whether the battery still removable Ah amount is sufficient to allow a safe starting of the motor vehicle.

It has now been found that display devices of the type described in long-term operation due to unavoidable, albeit very small error in the derivation of the battery current proportional variable and in the conversion of this variable in counts and temperature changes of the switching elements used for the integration of all these errors over provide a long integration time false readings, to avoid a readjustment of the device is required. In addition, even when replacing the battery, the count must be adjusted to the state of the new battery, so the display device to be adjusted.

The invention is therefore concerned with the task of designing a device of the type specified in the introduction in such a way that it allows automatic adjustment or readjustment.

This object is achieved according to the invention in that the forward-backward counter via a switching device for meter reading correction in place of the battery current controlled pulse generator an Justierimpulsgenerator is connectable, and that for the pulse control of the forward-backward counter by the Justierimpulsgenerator this one is also preceded by the counting direction controlling comparator, on which are present as comparison variables a counter value indicating the respective counter status and a control signal supplied by a function generator programmed in accordance with the battery type, which control signal is proportional to the respective state of charge of the battery as a function of its idling voltage and its temperature.

The invention is based on the known fact that the open circuit voltage of a secondary battery at a predetermined temperature after the minimum time after the last charge or discharge, which is sufficient for decaying associated with the change in the state of charge diffusion processes is a measure of the respective state of charge, so that with the help of a function of the temperature and the open circuit voltage of a secondary battery controlled and programmed according to the battery type function transmitter the state of charge of the battery can be displayed. However, this indication is valid only under the conditions mentioned above, ie in particular after long sleep periods of the battery, and no longer when the battery is charged or discharged constantly or at relatively short intervals.

When the adjustment pulse generator is briefly switched on with the switchover device provided according to the invention after expiration of the decay time for susceptible diffusion processes in the battery, the counter reading is corrected, so that cumulative errors in the display are switched off. In most cases, this adjustment requires several hours of rest of the battery. Since a premature actuation of the switching device would cause a misalignment, serves in a preferred embodiment of the invention as a control stage for the actuation of the switching device by switching off the battery inevitable in going settable timer, which can be reset automatically both by restarting the battery before the delay time and by ending the adjustment of the forward-backward counter after the delay time.

As an embodiment, the application of the invention in a device according to the AT-PS no. 331357 is described, which is shown schematically in the drawing.

The drawing shows a starter battery -1-, in whose circuit -2- a measuring resistor -3- is located, from which a measuring voltage is tapped and a measuring amplifier -4- is supplied. The output voltage of the measuring amplifier -4-- acts on a pulse generator -5- in the form of a voltage-frequency converter, which provides in its output a pulse train with a frequency proportional to the input side voltage. This pulse generator -5- has an actuator -6-, with the function of the charging factor (efficiency) of the battery -1- the output frequency in

- 3 No. 346429 can be influenced to such extent that the charging current exerts a smaller effect on the output frequency than the discharge current by an amount corresponding to the charge factor.

The output line -7- of the pulse generator --5- is connected to the one input of a switch - "8-, the output line -12- is connected to a forward-backward counter -11- having, for example, four Zähldekaden. This counter -11- counts backward on charge and on discharge so as to provide and store a digital output signal indicative of the resulting Ah pick, starting from a predetermined full charge state. In order to control the counting direction of the counter -11- in response to the charging or discharging operation, the forward-backward control input -13- is preceded by a polarity comparator -14-, which detects the sign of the output voltage of the measuring amplifier --4--. Further, between this comparator -14- and the counter -11- another switch -8A-.

In the output of the counter -11- there is a digital-to-analog converter -15-, which supplies an analog voltage corresponding to the digital content of the counter. This voltage has the value 0 at full charge of the battery -l- and increases with increasing discharge.

To the measuring amplifier -4- also a load current function generator -18- is connected, which operates according to the combination of discharge, temperature and Ah-removal and on the one hand at an input -19- of the measuring amplifier -4- corresponding to the respective discharge current and on the other hand at an input -20- from a temperature sensor -21- corresponding to the operating temperature of the battery -1- is guided so that it provides at its output -22- an analog voltage, which indicates the removable at the respective discharge current and at the effective temperature Ah amount.

In the output -22- of the function generator -18- is a Differenzanzeigeinstrument -23-, with which the output of the digital-to-analog converter -15- is connected and analogous to a gasoline watch indicates the battery still removable Ah amount. Moreover, in the output -22- of the function generator -18- there may be another function generator -26- which operates according to the combination of minimum Ah requirement and temperature and is guided at a second input -28- by the temperature sensor -21-. The analog signal in the output -29- of this function transmitter -26- acts on the input -29- of an Ah comparator -23A- whose other input is also acted upon by the digital-to-analog converter -15- and in whose output a tiltable switching stage - 30- which responds when the comparison signals are the same size or their difference is less than 0 and then provides an output indicative of an indicator -31-; which, for example, provides an 'audible or visual warning signal when the battery can only cover minimum Ah demand. When used on motor vehicles, the driver is thus warned in good time of exhaustion of the battery which impairs the ability to start.

In order to ensure in long-term operation that in the timing chain of the device parts -3, 4, 5 and 11- is not due to integration of small errors gradually a significant error-prone counter reading in counter -11- comes, a Justierimpulsgenerator -9- is provided by means of the switch -8- instead of the pulse generator -5- to the counter -11- can be turned on. The pulse transmission from the generator -9- to counter -11- is either, as indicated in the drawing, by direct control of the generator -9- or by using a gate in the output of the same under the control effect of a Hilfskomparators -16-, which from the Converter -15- converted into an analog signal counter reading of the counter -11- with the output signal of another function transmitter -10- compares. This function generator -10- is controlled via a line -32- from the open circuit voltage of the battery -1- and another line -33- from the temperature sensor -21- and is programmed according to the battery type, that it depends on the measured variables indicates the state of charge of the battery indicating signal. If the two input signals of the comparator -16- have different size, there is a signal from the pulse generator -9- via the switch -8- to the counter -11-, this counter is additionally from the comparator -16- via the switch -8A- accordingly the sign of the comparison result is controlled, so that depending on the size and direction of the deviation of the count of the value specified by the function generator -10- adjustment pulses are fed into the counter -11-.

Switching over the turnouts -8 and 8A- takes place advantageously with the aid of a time switch -17-, which is set to a switching time of several hours, for example 8 hours, in order thereby to ensure that the switching to adjustment takes place in each case only after the diffusion processes in the battery have subsided after their last charge or discharge is possible. This timer -17- is activated upon opening a switch coupled to the operating switch in the battery circuit -35- and, as already mentioned, performs its switching function preparatory to a few hours, if it has not previously been closed by prematurely closing the switch -35- is reset. As soon as the battery circuit is then closed again, the switches -8 and 8A- switch over in a short time, the readjustment of the counter -11-, and after completion of this process, the timer -17- is reset in a manner not shown, which is a Resetting the turnouts -8 and 8A- and a shutdown of Justierimpulsgenerators -9- and thus has the transition of the display device to normal operation result.