GB2087605A

GB2087605A - Limiting the Variation in Gassing Current in Batteries

Info

Publication number: GB2087605A
Application number: GB8132737A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1980-11-03
Filing date: 1981-10-30
Publication date: 1982-05-26
Also published as: GB2087605B; FR2493627A1; FR2493627B1; DE3041200A1

Abstract

A regulator (1) for a three-phase generator (2) in a motor vehicle or the like effects temperature-dependent limitation of the variation of the gassing current of a starter battery (B) dependent upon age and variations in operating characteristics. The battery charging current and the battery voltage (UB) are measured by means of a measuring shunt RSh in the connection lead (5) between the generator (2) and the battery (B) and are utilised by the regulator, such that high gassing currents are reduced and low gassing currents are increased by varying the output voltage (UG) of the generator. A sensor (8) responds to battery temperature and a temperature-dependent desired voltage of the battery is combined with the adjusting voltage from the battery voltage and charging current in a Schmitt trigger which controls the generator field current. The regulator de-energizes the three-phase generator in the event of overvoltage as sensed at the output D+ used also as a source for the generator field current. <IMAGE>

Description

SPECIFICATION A Method Of, and a Regulator For, Limiting the Gassing Current in Batteries The invention relates to a limitation of the charging current in starter batteries for I C engines driving a generator which charges the battery and more particularly to a limitation in accordance with variation of the gassing current dependent upon age and variations in the operating characteristics, particularly in motor vehicles.

Despite the high demands made on them, it is known to influence current generators, which serve to supply voltage to a vehicle electrical system, preferably three-phase generators in motor vehicles and the like, by regulating the excitation current fed thereto such that the generator output voltage is maintained at a substantially constant, desired level.

The excitation current, and thus the excitation field in the rotor of the generator, are thus controlled in dependence upon the voltage generated in the generator, such that the generator terminal voltage remains constant up to the maximum current despite a rotational speed which varies considerably between idling speed and full load, and despite considerable fluctuations in the load on the generator. Mechanical single-contact regulators or multi-contact regulators are known. Regulators normally used nowadays are chiefly electronic transistorised regulators which regulate the generator voltage by periodic attenuation of the excitation current, normally by periodically switching it on and off, since the voltage generated in the generator is substantially proportional to the product of the rotational speed and the excitation current.

Problems in this connection arise particularly with respect to charging the starter battery of the motor vehicle, particularly in winter or in town traffic, since the internal resistance of the battery increases to a considerable extent at low temperature, so that there can be a considerable reduction in the cold-starting performance of the battery, while the charging current generated at low rotational speeds is very frequently inadequate. In order to reach a compromise between the demands made by the voltage-sensitive loads of the vehicle electrical system on the one hand and, on the other hand, the charging requirements of the battery, the generator voltage produced by the three-phase generator, which is virtually identical to the charging voltage of the battery, is regulated to a constant value by the field regulator.

However, this can be disadvantageous in starter batteries for mobile units, normally in lead storage batteries for motor vehicles and the like, since batteries of this kind require a highly temperature-dependent voltage in order to charge them fully, the voltage at which gassing of the batteries sets in also being dependent upon the age of the battery in addition to being dependent upon the temperature of the battery, and also being subjected to variations in operating characteristics. By way of example, the possible range of variation of the voltage a't which gassing sets in can lie between 12.7 and 16.0 V in the case of a normally hot battery having conventional data (approximately 400C for a 12 V, 55Ah battery).Thus, in the case of a battery having an internal resistance of approximately 0.1 Ohm in the gassing range, a difference of 33 A in the gassing current is possible for a given voltage applied.

In this connection a further compromise between the requirement of a constant load voltage and the variable desired battery voltage in a motor vehicle, leading to so-called kinked characteristic regulation, is known although this readily leads to excessive gassing at high temperatures ((p > 350C), and to a poor state of charge of the battery at low temperatures ((p < 50C).

Thus, the use of a kinked characteristic regulator which does not take account of the specific requirements of the battery at any given time, is less helpful, and a further disadvantage is that in the case of old, hot batteries, there is the risk of excessive gassing during long journeys at high speed, irrespective of whether the voltage of the vehicle electrical system is regulated to a constant value or whether kinked characteristic regulation is used, since the temperature of batteries of this kind is further increased by a high gassing current, so that the voltage of these batteries is decreased to an even greater extent.

There is a need for regulation which is able to protect starter batteries, particularly in motor vehicles, against disadvantageously high voltages and high gassing currents caused thereby.

The present invention provides a method of limiting the variation in the gassing current in a starter battery for an internal combustion engine dependently upon age and variations in operating characteristics, in which the battery is charged by an electrical generator driven by the internal combustion engine, and in which the charging current flowing into the battery at any given time is measured, and the generator voltage and thus the charging voltage, are reduced in dependence upon the measured charging current, such that, taking into account the prevailing internal resistance of the battery, high gassing currents are reduced and low gassing currents are increased.

The invention includes a regulator for limiting the age dependent and characteristic dependent variation in the gassing current of a starter battery charged from a generator which is driven by an internal combustion engine, which regulator comprises means for adjusting the excitation current to be fed to the excitation winding of the generator, a measuring shunt to be connected between the battery and the generator output terminal supplying an electrical load, a first function block containing an amplifier to which the two voltages tapped at the measuring shunt are fed, such that the battery voltage and the battery charging current are determined in this single amplifier, a threshold-vaiueresponsive circuit to one input of which the output of the first functional block is connected, and a characteristic block for feeding a temperature-dependent desired battery voltage to the other input of the threshold-value-responsive circuit.

This has the advantage that the possible range of variation of the gassing current in starter batteries is reduced and, in particular, high gassing currents are avoided in the case of old batteries during long journeys at high speed.

It is particularly advantageous if, in addition to taking into account the charging current effectively flowing to the battery, the temperature of the battery is also included in the regulation of the generator output voltage.

In addition to the individual regulation of the generator output voltage and its adjustment to the existing battery and to the age and temperature of the battery, a particularly advantageous possibility is that of regulating the voltage of the generator of the vehicle electrical system in conformity with an optimum charging characteristic, the charging voltage being reduced rapidly in the first instance and then slowly as the charging current rises, so that a discharged battery can be charged rapidly, while a fully charged battery gasses to only a slight extent.

The invention is further described, by way of example, with reference to the drawings, in which: Fig. 1 is a block circuit diagram of the electrical distribution system of a motor vehicle and the connection of the protective regulator, in accordance with the invention, to the vehicle electrical system fed by a three-phase generator, Fig. 2 is a block circuit diagram of the regulator, Fig. 3 shows a possible embodiment of the block circuit diagram in greater detail, and Fig. 4 is a graph of the generator voltage plotted against the battery charging current in two possible embodiments.

The basic idea of the present invention resides in adjusting the charging current individually to an existing battery, particularly in the case of starter batteries of motor vehicles and the like, by influencing the generator voltage which feeds the vehicle electrical system to which the battery is connected, such that the possible range of variation of the gassing current is reduced, that is to say, high gassing currents are reduced and low gassing currents are increased.

Fig. 1 shows the connection of the regulator 1, on which the invention is based, to the vehicle electrical system, the basic principle of the two-state switching regulator being retained, that is to say, in the regulator in accordance with the invention, regulation is also effected such that the excitation current appearing at the output terminal DF of the regulator is periodically and rapidly switched on and off, and the generator voltage is thereby adjusted. The generator 2 for the vehicle electrical system is generally a three-phase generator having a rectified output and is accordingly hereinafter referred to only as a "three-phase generator". The terminal of the three-phase generator carrying output voltage is designated B+. The resistor R, represents all the loads of the vehicle electrical system.The starter for the internal combustion engine is designated A and is connected to the battery B by way of a separate switch 3. It will be seen that-a series or shunt resistor Rsh is connected between the battery terminal 6 and the lead 5 which carries the generator voltage and which is connected to the loads R, of the vehicle electrical system by way of a switch 4, so that the generator output voltage UG and the battery voltage UB are fed at the same time to the regulator 1 when the ignition switch 7 is closed. A further regulator terminal is designated Uv and is connected to a temperature sensor 8, such as a NTC probe, associated with the battery B.A further regulator terminal is the negative pole D- and, finally, the output signal D+ of the three-phase generator 2 is fed to the regulator 1, that is to say, for the purpose of limiting over-voltage when, for example, the connection lead between the generator and the battery is interrupted, as will be further described below as well, as well as for supplying the power for the field current.

The block circuit diagram of the regulator 1 of Fig. 1 is illustrated in Fig. 2 and comprises a first main function block 9 which comprises a comparator 9a in the form of an operational amplifier, and a summation point 9b. The generator voltage U, and the battery voltage UB are fed to the two inputs of the operational amplifier 9a, so that a signal which corresponds to the voltage drop across the shunt resistor Rush, i.e. to the battery charging current IBT and to which a battery voltage signal is added, appears at the output of the operational amplifier.The output of the function block 9 is then combined at a second summation point 11 with the output signal of a characteristic block 12 which produces the desired temperature-dependent charging voltage characteristic Uo ((p). The summation point 11 can be part of a following threshold value amplifier 13, such as an operational amplifier wired as a Schmidt trigger, by which the desired voltage Uo ((p) and the actual voltage UG+Ri. IB, corrected by the amount of the charging current component, are compared, Ri being the internal resistance of the battery and 1B being the battery current. The output signal from the Schmidt trigger 13 is applied to a following driver circuit 14 on which the output signal DF of the regulator appears and is fed to the excitation winding 1 5 of the three-phase generator.

It will be seen from the detailed illustration of the field regulator 1 of Fig. 3, that the generator voltage Ue present at the input side of the shunt resistor Rush, is fed to the operational amplifier 9a via a voltage divider connected to earth and comprising resistors R3, R5 with a potentiometer P 1 and via a series resistor R7, and that the battery voltage UB is fed to the operational amplifier 9a via a voltage divider connected to earth and comprising resistors R4, R6, and via a series resistor R8. For the purpose of smoothing ripple, the input circuit of the operational amplifier 9a also includes capacitors C1 and C2 connected to earth.The inverting input (negative input) of the operational amplifier 9a is connected to the following summation point 9b by way of a series combination comprising a resistor R9 and a resistor wired as a potentiometer P2, and a capacitor C5 is connected in parallel with this series combination. The battery voltage and the battery current are measured in the amplifier 9a by means of a circuit of this kind, the voltage tapped from the measuring shunt Rsh being fed to the differential inputs of the amplifier by way of two voltage dividers R3, P 1, R5 and R4, R6 respectively which are set to slightly differing values. A change in the output voltage of the amplifier is thus effected by an equal change in the voltage at the two terminals of the measuring shunt Rsh (in-phase amplification) and also by opposing changes in the voltage (push-pull amplification).In-phase amplification and push-pull amplification can be established separately by way of the potentiometer P1 in the input circuit of the operational amplifier 9a and by way of the potentiometer P2 in the feedback path. Thus, by means of a circuit of this kind, it is possible to avoid greatly differing consumptions of charging current, caused by variations in the operating characteristics and/or the effects of age, by measuring the battery current and the corresponding "statics" of the field current regulator.The reduction of the generator voltage UG with increasing battery charging current IBL is effected in accordance with the equation UG=UGOR1 1BL A regulating characteristic of this kind is shown by a curve I in Fig. 4 in which the generator voltage UG is plotted against the battery charging current IBL- Temperature dependence is taken into account at the following second operational amplifier 16, to the negating input of which is fed the output signal of the first operational amplifier 9a at the summation point 9b by way of a resistor R1 5.

The battery temperature signal Uv is fed to the other input by the characteristic block 12 and, for the purpose of adjusting the threshold value, is mixed with a bias voltage signal from a voltage divider comprising a potentiometer P4 in series with a resistor R1 7. The characteristic block 12 comprises the NTC resistor R1 2 sensing the battery temperature and at least one Zener diode Z4 which is connected in parallel with the resistor R1 2 and which can be connected in series with two diodes D2 and D3. This circuit is connected to the supply current bus carrying a stabilized voltage Ust by way of a parallel combination comprising a potentiometer P3 and a resistor R1 1.

The stabilized voltage is produced by a supply block 1 7 which, in a known manner, produces the stabilized voltage from the generator voltage UG by means of a series transistor T1 1 and at least one Zener diode Z1 , Z2.

The output signal of the Schmidt trigger 13 is applied by way of a series Zener diode Z5 to a, preferably integrated, Darlington transistor circuit T3 having a driver transistor T2 connected to the input thereof in a conventional manner, the excitation coil 1 5 of the three-phase generator being connected to the interconnected collectors of the Darlington transistor circuit and to earth. A reverse biassed diode D4 is connected in parallel with the excitation coil 1 5 for conducting the decaying field current when the Darlington circuit T3 is switched off.

In an advantageous development of the invention, a diode D5 is connected in parallel in the input region of the first operational amplifier 9a, and, in the illustrated embodiment, the diode D5 is connected between the junction of the potentiometer P 1 with the resistor R7 and the junction of the resistor R4 with the resistor R6 in the other branch of the voltage divider. The diode D5 only has a low threshold voltage and reduces the push-pull amplification when a predetermined differential voltage on the measuring shunt Rsh is exceeded, so that the charging voltage drops rapidly in the first instance and then slowly in accordance with the curve II of Fig. 4 as the charging current increases, so that a discharged battery can be rapidly charged, and a fully charged battery only gasses to a slight extent.

Otherwise, it is quite possible to use a portion of the battery lead to the ignition lock as a measuring shunt. Thus, it is unnecessary to provide a separate resistor in the present case. The resistance value of the measuring shunt can be, for example, 4m Ohm.

A further advantageous development of the present invention resides in providing an overvoltage protection which becomes effective when, for example, the connection lead between the generator and the battery is interrupted. This overvoltage protection resides in likewise applying the generator output voltage D+, required in Fig. 1 for activating the charging pilot lamp 10, to the junction between the potentiometer P 1 and the resistor R7 in the voltage divider branch for the generator voltage UG by way of a resistor R10 connected in series with at least one Zener diode Z3 and, in the illustrated embodiment, in series with a further diode Dl.The diode D1 thereby blocks the flow of current in a negative direction, so that the voltage on the terminal D+, generated to provide the source of excitation current also influences the field current regulator by way of the first operational amplifier 9a at a voltage in excess of the forward voltage of the Zener diode Z3, such that the operational amplifier de excites the generator. The voltage on the terminal D+, generated for the excitation, is also fed as a supply voltage to the output stage of the field current regulator in a conventional manner.

The following data ensued in a field current regulator, constructed in accordance with the invention, for three-phase generators rated at 14 V: Principle: Two-state switching regulator Supply: By way of the excitation diodes of the three-phase generator Regulating variable: Generator voltage according to characteristic UG=UO ((p) -Ri. 1B Statics: Ri adjustable 50.... 200 < nOhm Measured variables: Battery temperature PB=20 ... +600C Battery current 1,=--50 .... +50A Adjusting variable: Excitation voltage: 0 or UG; Excitation current: 0... 4A Overvoltage protection: Becomes effective upon interruption of the connection lead between the generator and the battery.

Claims

1. A method of limiting the variation in the gassing current in a starter battery for an internal combustion engine dependently upon age and variations in operating characteristics, in which that battery is charged by an electrical generator driven by the internal combustion engine, and in which the charging current flowing into the battery at any given time is measured, and the generator voltage and thus the charging voltage, are reduced in dependence upon the measured charging current, such that, taking into account the prevailing internal resistance of the battery, high gassing currents are reduced and low gassing currents are increased.

2. A method as claimed in claim 1, in which the battery charging current is adjusted taking into account the prevailing battery temperature.

3. A method as claimed in claim 1 or 2, in which the charging voltage is reduced rapidly in the first instance and then subsequently slowly when the charging current is increasing, such that a discharged battery is charged rapidly and a fully charged battery only gasses to a small extent.

4. A regulator for limiting the age-dependent and characteristic dependent variation in the gassing current of a starter battery charged from a generator which is driven by an internal combustion engine, which regulator comprises means for adjusting the excitation current to be fed to the excitation winding of the generator, a measuring shunt to be connected between the battry and the generator output terminal supplying an electrical load a first function block containing an amplifier to which the two voltages tapped at the measuring shunt are fed, such that the battery voltage and the battery charging current are determined in this single amplifier, a threshold-value-responsive circuit to one input of which the output of the first functional block is connected and a characteristic block for feeding a temperature-dependent desired battery voltage to the other input of the threshold-value-responsive circuit.

5. A regulator as claimed in claim 4, in which the amplifier of the first functional block is an operational amplifier to the two inputs of which the voltages tapped from the measuring shunt are fed by way of voltage dividers set at values slightly different from one another, such that the output voltage of the amplifier is varied by equal variation of the voltages in the sense of in-phase amplification and also by opposed variation of the voltages in the sense of push-pull amplification.

6. A regulator as claimed in claim 5, in which a first potentiometer is disposed in at least one of the input voltage dividers, and a second potentiometer is disposed in a feedback network connecting the battery voltage input voltage divider to the output of the operational amplifier for the purpose of separate adjustment of the in-phase amplification and the push-pull amplification.

7. A regulator as claimed in claim 6, in which the junction between the feedback network and the output of the operational amplifier is connected to one input of a second operational amplifier which is wired as a Schmidt trigger and whose other input is fed with the temperature-dependent desired battery voltage from the characteristic block.

8. A regulator as claimed in claim 7, in which the characteristic block includes a temperaturedependent NTC resistor for detecting the battery temperature, and a Zener diode.

9. A regulator as claimed in claim 8, in which the NTC resistor and the Zener diode are connected in parallel and are connected in series with a \'arable resistor and in which the output of the characteristic block is connected to the input of the second operational amplifier by way of an adjustable voltage divider.

10. A regulator as claimed in any of claims 5 to 9, in which the input voltage divider circuits for the generator voltage and the battery voltage on the measuring shunt are bridged by a diode having a low threshold voltage, such that the push-pull amplification is reduced in order to obtain a kinked characteristic of the charging voltage when a predetermined differential voltage is exceeded.

1 A regulator as claimed in any of claims 4 to 10, in which overvoltage protection is provided by feeding the excitation supply voltage on an output terminal of the generator by way of a Zener diode and a further diode to one of the terminals of the operational amplifier of the first function block such that the generator is deenergized at a voltage in excess of the forward voltage of this Zener diode.

12. A method of limiting the variation in the gassing currents of IC engine starter motors, substantially as herein described with reference to the drawings.

1 3. A regulator for limiting the variation in the gassing current of a starter battery, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.