Battery condition detecton apparatus

A battery condition detection apparatus comprises at least the first two of a battery discharge current detector, a battery terminal voltage detector, and a battery electrolyte concentration signal detector. The battery condition detection apparatus further comprises a memory circuit for storing detection signals generated by at least the first two detectors and inputted to the battery condition detection apparatus, and a computation device for executing computation processing on output signals from the aforesaid detectors. With the foregoing structure, the battery condition detection apparatus performs computation to obtain at least one of corrected values of the battery terminal voltage and the battery electrolyte concentration in the state where the battery discharge current assumes a predetermined value, and performs the detection of the battery condition and/or the control of power generation of a battery-charging generator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a battery condition detection apparatus 
for determining a charging condition, namely a capacity of an automotive 
battery accurately. 
2. Description of the Related Art 
The specific gravity of the battery electrolyte has conventionally been 
measured by a specific gravity sensor as a means for detecting the battery 
condition (a residual capacity, etc.). The problem of the above-mentioned 
conventional means is that if the battery electrode is deteriorated or if 
a liquid level of the battery drops due to overcharge of the battery, the 
relationship between the specific gravity and the battery capacity is 
changed undesirably from the relationship therebetween under a normal 
condition, thereby making it impossible to measure the battery condition 
(capacity) accurately. 
Another conventional apparatus for detecting the battery condition (a 
residual capacity, etc.) is well known, as disclosed in JP-A-53-127646, in 
which internal impedance of a battery is determined from a battery 
discharge current and a battery voltage, so that the battery charging 
state is detected on the basis of the internal impedance which is 
increased with the deterioration of the battery charging condition (a 
reduction in the residual capacity). 
If the battery condition is to be evaluated accurately, however, it is 
necessary to determine the internal impedance from a battery terminal 
voltage V.sub.S upon conduction of a predetermined reference discharge 
current I.sub.S. A starter current under a cranking operation of an engine 
greatly varies depending on the type and temperature of the engine. The 
aforementioned conventional apparatus, in which the internal impedance is 
determined only from a ratio between a starter current happening to flow 
and the battery terminal voltage at the start of an engine operation, 
poses a problem such that the battery condition cannot be measured 
accurately. 
Another problem is that, even if it is desired to determine the battery 
terminal voltage V.sub.S at a moment when the starter current has reached 
a predetermined reference discharge current level I.sub.S, the starter 
current does not rise up to the reference discharge current level I.sub.S 
due to the engine temperature or the like, thus making the measurement 
impossible. 
Further, there was a further problem that the reference discharge current 
I.sub.S is 150 A to 300 A for an ordinary class of automobiles and 50 A to 
100 A for a light-weight class of automobiles, so that it is necessitated 
to change the setting of the reference discharge current I.sub.S depending 
on the type of an automobile carrying the battery. 
The present invention has been made in order to solve the above-mentioned 
problems of conventional apparatuses. 
SUMMARY OF THE INVENTION 
A first object of the present invention is to provide a battery condition 
detection apparatus which stores the value of one of parameters including 
a battery discharge current, battery voltage and internal resistance 
related to a value of the battery electrolyte concentration together with 
the value of the battery electrolyte concentration per se which provides a 
reference value. Then, when the discharge current exceeds a predetermined 
value, the value of said one parameter is detected. At the same time or 
before or after that time, an electrolyte concentration detection signal 
representing the electrolyte concentration is detected by electrolyte 
concentration signal detection means, and an electrolyte concentration 
signal correction value is obtained from the value of the stored 
electrolyte concentration corresponding to the detected one parameter and 
the electrolyte concentration detection signal. After that, an electrolyte 
concentration signal detected by the electrolyte concentration signal 
detection means is corrected by using the aforementioned electrolyte 
concentration signal correction value, whereby an accurate battery 
condition is detected on the basis of the corrected electrolyte 
concentration signal. 
A second object of the present invention is to provide a battery condition 
detection apparatus in which, in order to obtain an accurate value of the 
internal impedance of a battery, a plurality of values of the battery 
terminal voltage are obtained in the state where a predetermined value of 
battery discharge current is caused to flow, and an average value of the 
battery terminal voltage is calculated, or alternatively, a plurality of 
values of the battery discharge current are obtained successively in the 
state where the battery terminal voltage has a predetermined value, and an 
average value of the battery discharge current is calculated, so that an 
accurate value of the internal impedance of a battery is determined, 
thereby detecting a battery condition. 
A third object of the present invention is to provide a battery condition 
detection apparatus in which, in order to improve the aforementioned 
apparatus for attaining the second object, a reference discharge time 
terminal voltage of a battery is calculated by using a voltage-current 
approximation line obtained from the battery currents and voltages 
detected at a plurality of time points while a starter is actuated, and a 
battery condition is determined on the basis of the reference discharge 
time terminal voltage. 
The battery condition detection apparatus of the present invention has an 
advantage such that an always accurate battery condition is determined by 
making correction of a detected electrolyte concentration signal by using 
a concentration signal correction value which is detected at the time of 
discharge of the battery. 
The battery condition detection apparatus of the present invention has 
another advantage such that accurate internal impedance is determined by 
obtaining accurate corresponding values for the battery voltages and 
battery discharge currents at the time of discharge of the battery, 
thereby making it possible to determine an accurate battery condition 
without using any special additional detectors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will be explained below with 
reference to the accompanying drawings. 
First, an explanation will be made of an embodiment of the present 
invention in which a battery condition is detected by using a corrected 
electrolyte concentration signal. This first embodiment relates to an 
apparatus in which a corrected battery voltage is obtained from a detected 
battery voltage value in the state of a predetermined magnitude of 
discharge current, and a concentration correction value is obtained from a 
reference electrolyte concentration related to the corrected battery 
voltage and an actually measured electrolyte concentration. The 
concentration correction value thus obtained is used to correct the values 
of subsequent actually measured electrolyte concentrations, and further 
the power generation is controlled in such a manner that the value of the 
actually measured electrolyte concentration remains within a predetermined 
range. 
In FIG. 1, reference numeral 1 designates a car battery, numeral 2 a 
starter, numeral 3 a generator, numeral 4 a concentration sensor for 
detecting the concentration of the reactive substance, here sulfuric acid, 
in the battery 1, numeral 5 a starter switch for actuating the starter, 
numeral 6 a current detector for detecting the battery discharge current, 
numeral 7 a microcomputer, numeral 8 an electric load, numeral 9 an 
indicator for indicating the service life of the battery 1, and numeral 10 
a battery voltage detector. 
FIG. 2 is a reference characteristic diagram showing a curve A of a battery 
voltage V against the sulfuric acid concentration S of the electrolyte of 
a new battery, obtained by measuring the battery voltage with the 
discharge current of 150 A sustained for about five seconds for various 
sulfuric acid concentrations of the electrolyte. In this diagram, V.sub.L 
designates a voltage required for driving the starter 2, associated with 
the sulfuric acid concentration S.sub.L of the battery 1. More 
specifically, it is understood that when the sulfuric acid concentration S 
of the battery electrolyte is small, the battery voltage V is low. This 
characteristic is stored in the microcomputer 17. 
Now, the control operation in the microcomputer 7 will be explained 
together with the program shown in FIG. 3. First, upon actuation of the 
starter 2 with the starter switch 5 closed, the discharge current of the 
battery 1 is measured by a current detector 6. When the discharge current 
of 150 A of the battery 1 is detected by first detection means 71, a 
battery voltage detector 10 detects the voltage V providing one of 
parameters indicating the state of the battery 1. 
The reason why the battery voltage is measured when the discharge current 
of the battery 1 reaches 150 A is to secure the battery performance for 
driving the starter in view of the fact that a stable relationship between 
discharge currents and voltages cannot be obtained for the discharge 
current of less than about 30 A of the battery 1 and that the current is 
normally more than 100 A in driving the starter 2. The discharge current 
in measuring the battery voltage, however, is not necessarily limited to 
150 A. 
The recommended time of detecting the sulfuric acid concentration of the 
battery 1 by the concentration sensor 4 is before the state of the battery 
1 changes from that at the time of voltage measurement (for example, 
within 5% in concentration change). The electrolyte concentration may be 
measured before actuation of the starter 2 taking into account the fact 
that the state of the battery 1 remains substantially unchanged even if a 
current of several hundred A is supplied for about one second at the time 
of driving the starter 2. 
The battery voltage V.sub.B obtained in step 1 is corrected at step 2. The 
reason for this correction will be explained below. 
As shown in FIG. 4, the voltage V with the battery 1 discharged decreases 
with time, and reaches a steady level in about five seconds. For this 
reason, the engine is started by driving the starter 2 normally within a 
second. The measurement of the battery voltage at the time of driving the 
starter in step 1 thus indicates a voltage higher than the steady level. 
If the relationship between the battery characteristic and the discharge 
time is determined in advance and the correction value V.sub.S is 
determined by correcting the detection value V.sub.B by applying thereto a 
difference .DELTA.V between the detection value V.sub.B based on a starter 
current and a steady value determined from the time t of detection as 
shown in FIG. 4, it is possible to obtain a voltage-current characteristic 
of the battery with greater accuracy. 
The rate of voltage drop is substantially the same for the charge rate of 
30% or more, and therefore the steady voltage level five seconds later may 
be measured by estimation based on the rate of voltage drop from the time 
of actual battery voltage measurement. 
Then, step 4 performs correction for obtaining a reference specific 
gravity. An explanation will be made with reference to the characteristic 
diagram of FIG. 2. Assume that steps 1 and 2 have determined the 
correction voltage V.sub.S and the concentration S.sub.B of the battery 1 
at the time of driving the starter, that is, the case at point X. In this 
case, the concentration S.sub.B is high as compared with the concentration 
S.sub.A (point Y) for the reference characteristic A, indicating a 
deteriorated condition of the battery 1 (such as a reduced quantity of the 
electrolyte or an exhausted life of the battery 1). 
Under the reference characteristic A, it is possible to drive the starter 2 
as the voltage of the battery 1 is higher than V.sub.L to the extent that 
the concentration of the battery 1 is higher than S.sub.L. If the 
condition of the battery 1 is deteriorated as mentioned above, however, 
the concentration S increases and the battery voltage is apparently 
decided to be high, so that, if a control operation based on the 
concentration S is effected, the concentration S would be regarded as high 
in spite of a low battery voltage, resulting in a starter failure. 
Step 4, therefore, determines the reference battery concentration S.sub.A 
at the battery voltage V.sub.S based on the reference characteristic A 
stored in the microcomputer 7, and calculates a concentration correction 
value .DELTA.S=S.sub.A -S.sub.B from the actually measured concentration 
S.sub.B and the reference value S.sub.A. The above calculation is 
performed at step 4 which is executed in the block 72 in FIG. 1 which 
includes both a second detection means and a concentration correction 
value computation means. 
Step 5 detects the concentration S.sub.r of the battery 1 at predetermined 
intervals of time (while the vehicle is running or in other modes) after 
the engine start by means of the concentration sensor 4. 
Step 6 adds the concentration correction value .DELTA.S obtained at step 4 
to the concentration S.sub.r determined at step 4 to produce a real 
concentration S.sub.r '. Specifically, in view of the fact that a 
deteriorated battery 1 has an increased concentration as shown in FIG. 2, 
it is possible to determine an accurate concentration always for a 
predetermined voltage by correcting the concentration. The correction of 
the concentration obtained by the concentration sensor 4 thus permits 
always accurate detection of the condition (capacity) of the battery 1. 
Since the battery characteristic (the relationship between an electrolyte 
concentration and a voltage at the time of discharge determined by the 
remaining life, electrolyte concentration, etc. of the battery) undergoes 
a gradual change, it is sufficient to measure the concentration correction 
value .DELTA.S at least once when the starter is energized for each time 
of drive. 
An accurate concentration-voltage relationship is always secured by power 
generation control based on the corrected concentration S.sub.r '. As 
shown at step 7, if power generation is controlled in such a manner that 
the corrected concentration S.sub.r ' is always equal to or larger than 
S.sub.L (if S.sub.r '.ltoreq.S.sub.L, the control voltage is increased at 
step 8), therefore, the battery voltage at the time of driving the starter 
is always greater than V.sub.L, thus making an accurate actuation of the 
starter possible. 
Step 9 compares the concentration values S.sub.r ' and S.sub.H on condition 
that step 7 secures the relationship S.sub.r '.gtoreq.S.sub.L. The value 
S.sub.H is determined by the fuel economy or the like and has a 
predetermined margin with respect to S.sub.L. Specifically, if power 
generation is controlled to secure the relationship S.sub.r '&lt;S.sub.H at 
steps 9 and 10, the battery 1 would not be required to be charged more 
than necessary (such a charging would increase an adjustment voltage 
unnecessarily), and the resulting lower adjustment voltage could save the 
load of the generator 3 as compared with that of the engine, thus reducing 
fuel cost. Also, a reduced charge of the battery 1 prevents a drop in 
liquid level of the battery electrolyte. 
In other words, the power generation control to secure the specific gravity 
S.sub.r ' in the range S.sub.L .ltoreq.S.sub.r '.ltoreq.S.sub.H at steps 7 
to 10 maintains the battery in a balanced state, thus assuring smooth 
starting of the vehicle engine (preventing emptying of a battery) while at 
the same time producing the effect of reducing the fuel consumption rate 
and the rate of decrease in electrolyte at the same time. 
These effects could be secured more firmly if the charging capacity is 
improved or discharged is prevented by raising the idling level or cutting 
off the electric load of the engine, in the case where a change in the 
adjustment voltage alone is not sufficient to charge the battery as 
intended due to the capacity of the generator. 
In the method of correcting the concentration mentioned above, the 
concentration detection value S.sub.r is not necessarily corrected by 
S.sub.r '=S.sub.r +.DELTA.S at step 6. Instead, the concentration decision 
values S.sub.H and S.sub.L for power generation control may be corrected 
as new decision values S.sub.H '=S.sub.H -.DELTA.S and S.sub.L '=S.sub.L 
-.DELTA.S respectively to control power generation in such a manner as to 
attain the concentration value S.sub.r at step 5 while holding the 
relations S.sub.L '&lt;S.sub.r &lt;S.sub.H '. 
Further, if the battery voltage V.sub.5 obtained at step 1 is lower than 
V.sub.1 at step 3 regardless of the power generation control mentioned 
above, step 14 may issue an alarm for designating the time of replacing 
the battery. 
Also, in spite of the fact that the decision value V.sub.L (S.sub.L) used 
for power generation control is the same as V.sub.L for life alarm in this 
embodiment, the value V.sub.L2 (V.sub.L2 &gt;V.sub.L) is normally used as the 
decision value V.sub.L for power generation control allowing for a 
predetermined margin. Further, an average of the concentration correction 
value .DELTA.S calculated from several past measurements may be used to 
further improve correction accuracy. 
According to the aforementioned embodiment, the battery characteristic for 
actuating the starter is measured by determining the battery voltage 
V.sub.B at the time of discharge of a predetermined current (150 A) and 
comparing it with the electrolyte concentration S.sub.B. In place of this 
method, however, taking into consideration the relationship E-V=IR (in 
which R designates internal resistance of the battery depending on the 
charging condition, and E is the electromotive force of the battery) 
between the discharge current and the voltage representing the battery 
performance, the discharge current or internal resistance for a 
predetermined battery voltage (say, 9.5 V) may alternatively be detected 
as a battery characteristic as of the time of starter actuation thereby to 
detect the battery condition based on the discharge current and internal 
resistance. 
FIG. 5 shows a characteristic of the battery current versus the electrolyte 
concentration when the battery voltage is maintained to be constant, and 
FIG. 6 shows a characteristic of the internal resistance versus the 
electrolyte concentration. 
A second embodiment of the apparatus according to the present invention is 
shown in FIGS. 7 and 8. According to this embodiment, in order to detect 
the internal resistance R.sub.B of the battery 1, a predetermined 
discharge current is detected by a current detector 6 and a battery 
voltage associated with a predetermined discharge current is determined by 
a battery voltage detector 10. Specifically, the internal resistance R is 
determined from the equation 
##EQU1## 
The reference concentration of battery electrolyte related to the internal 
resistance R.sub.B is then determined from the characteristic B (shown in 
FIG. 6) stored in the microcomputer 7. 
After the reference concentration of battery electrolyte is determined, the 
concentration is corrected as described with respect to the embodiment 
above. 
In the case where the internal resistance R.sub.B remains higher than 
R.sub.H in spite of the power generation control, on the other hand, step 
13 issues an alarm against electrolyte degradation. 
A flowchart of a third embodiment of the apparatus according to the present 
invention is shown in FIG. 9. In this flowchart, as is different from the 
flowchart of FIG. 3, in accordance with the temperature of the battery 1, 
step 14 corrects the battery voltage and step 15 corrects the battery 
electrolyte concentration. 
This is by reason of the fact that the battery characteristic (voltage at 
the time of discharge at step S1) and the electrolyte concentration have a 
temperature depending characteristic. 
Step S14 corrects the battery voltage V.sub.B in accordance with the 
temperature registered at the temperature sensor mounted on the battery 1, 
which voltage is compared with the reference characteristic A of FIG. 2 
stored in the microcomputer 7 as explained with reference to the first 
embodiment above. 
As a consequence, according to the third embodiment, the voltage and 
concentration are corrected in response to the temperature of the battery 
1, thereby providing improved accuracy of detection of the battery 
condition. 
The concentration sensor in the aforementioned embodiment may be of such a 
type as disclosed by JP-A-60-24435 in which the potential difference 
between a lead electrode and a lead dioxide electrode is measured to 
determine the battery electrolyte concentration in terms of a potential. 
Also, as disclosed in JP-A-55-23435, the battery electrolyte concentration 
may be measured indirectly from the transmission time of a sound wave. 
As an alternative, ions caused by dissociation of sulfuric acid may be 
detected by an electrode for detecting the hydrogen ion concentration and 
an auxiliary electrode as taught by JP-A-60-112266. 
Furthermore, the battery electrolyte concentration may be alternatively 
measured indirectly by using refraction, float or the like. 
Now, an explanation will be made of still another embodiment in which 
accurate internal impedance of the battery is obtained from a 
predetermined battery discharge current and a plurality of battery 
voltages associated therewith or from a predetermined battery voltage and 
an average value of a plurality of battery discharge currents associated 
therewith, thereby determining the battery condition. 
As shown in FIG. 12(A), upon a steep stepwise change in battery discharge 
current, the battery voltage undergoes a change with delay time Td1, Td2 
(FIG. 12(B)). At the time of the starter actuation, the battery discharge 
current fluctuates periodically as shown in FIG. 13(A), and therefore the 
battery voltages differ from each other even at points a and b in FIG. 
13(A) where the discharge currents have the same value with each other. 
Specifically, the battery voltage assumes a higher value (V2) in the 
process of a change in the discharge current from a low to high value (at 
point a in FIG. 13(A)), and the battery voltage assumes a lower value (V2) 
in the reverse case (at point b in FIG. 13(A)). The battery discharge 
current at the time of starter actuation, as seen from the same diagram, 
is represented by periodical repetitions of the same waveform, resulting 
in the substantially opposite discharge causation at points a and b. 
In such a situation, each couple of battery voltages has almost the 
opposite discharge causation. By calculating an average of these battery 
voltages, therefore, the effects of the respective discharge causation 
cancel each other to produce a real battery voltage. This battery voltage 
indicates the same value as the battery discharge current and hence the 
internal impedance of the battery, whereby it is possible to determine the 
charging condition of the battery accurately. 
If a plurality of battery discharge currents are detected for the same 
value of battery voltage and an average thereof is calculated, on the 
other hand, the real value of discharge current against the battery 
voltage is obtained, which in turn determines accurate internal impedance, 
thus making it possible to know an accurate charging condition of the 
battery. 
A fourth embodiment shown in FIG. 10 will be explained below as an example 
having the functions mentioned above. 
In FIG. 10, a battery 1 is connected with a charge generator 3, an electric 
load 8 and a starter 2 through a starter switch 5. The voltage across the 
battery 1 is detected by a voltage detector 10 and applied into a computer 
15. The discharge current of the battery 1, on the other hand, is detected 
by a current detector 6 and also inputted into the computer 15. 
Upon turning on the starter switch 5, the starter 2 is energized with power 
supplied thereto from the battery 1, and as shown in FIG. 13, a 
periodically changing discharge current begins to flow, thereby causing 
corresponding fluctuations of the battery voltage. 
The computer 15 includes a memory 51 and a computation unit 52. The memory 
51 reads and stores therein two successive battery voltages V1 and V2 (at 
points a and b in FIG. 13(A)) when the discharge current stands at a 
predetermined value (say, 150 A). The computation unit 52 computes an 
average V.sub.AVE of the battery voltages V1 and V2, and indicates the 
charging condition of the battery on a battery condition indicator 11 on 
the basis of the average V.sub.AVE. 
Now, an explanation will be made of a fifth embodiment in which the 
specific gravity of the electrolyte related to the aforementioned average 
battery voltage is determined and a corrected value of the specific 
gravity is used for deciding the charging condition to control the power 
generation. It should be noted that, in the embodiments of the present 
invention described hereinafter, the detection of the specific gravity of 
the battery electrolyte is used for the detection of the battery 
electrolyte concentration. 
This embodiment represents an application of the present invention to an 
apparatus for detecting the specific gravity of the battery electrolyte 
during engine operation and thus improving the battery charging condition 
on the basis of the detected specific gravity. The specific gravity thus 
detected, which reflects the battery charging condition faithfully, is 
affected by the evaporation of the battery electrolyte or the like 
phenomenon as well as the charging condition, and therefore, it is 
required to be corrected at the time of starting the engine. 
For this purpose, the specific gravity of the battery electrolyte is 
determined in advance as a stoichiometric specific gravity S.sub.A for 
each voltage of a new battery discharged with a predetermined discharge 
current. The specific gravity S.sub.B for the average voltage value 
V.sub.AVE obtained upon actuation of the starter in the same configuration 
as the fourth embodiment is corrected, and the resulting correction value 
is used to correct the specific gravity of the battery electrolyte during 
an engine operation thereby to decide the charging condition. 
A fifth embodiment of the invention will be explained in detail with 
reference to FIG. 11. 
In FIG. 11, a battery 1 is provided with a specific gravity sensor 4 for 
producing the specific gravity of the battery electrolyte, which specific 
gravity is applied to a computer 15. The computer 15 includes voltage 
measuring means 53, specific gravity correction value computation means 
54, specific gravity correction means 55 and power generation control 
means 56. The voltage measuring means 53 has a memory 51 and a computation 
unit 52 as those of the fourth embodiment. This voltage measuring means 53 
is supplied with battery voltages V1 and V2 in the state of the discharge 
current having a predetermined value and produces an average value 
V.sub.AVE of the battery voltages V1 and V2. 
The correction value computation means 54 computes a correction value 
.DELTA.S as a difference between an actually measured specific gravity 
S.sub.B, which is given by a specific gravity corresponding to the average 
value V.sub.AVE of the battery voltage, and a stoichiometric specific 
gravity S.sub.A. 
After the engine is started, a detected specific gravity S.sub.r is 
corrected by using the correction value .DELTA.S to obtain a real specific 
gravity S.sub.r ', and the power generation control means 56 changes the 
adjustment voltage of the charging generator 3 in such a manner as to keep 
the specific gravity S.sub.r ' always in a predetermined range, thereby 
maintaining a proper charging condition of the battery 1. 
In the case where the average value V.sub.AVE is reduced below a voltage 
required for actuating the starter, the life indicator 9 is turned on 
indicating the necessity of changing the battery 1. 
In this way, a real battery voltage is determined by the voltage measuring 
means 53, thereby making it possible to make accurate correction of the 
specific gravity. 
In each of the above-mentioned embodiments, an average value of battery 
voltage is obtained from a couple of voltage measurements. If an average 
value is obtained from further more plural times of voltage measurements, 
however, the accuracy will be improved. 
Instead of calculating an average value of the battery voltages in the 
state of the battery discharge current having a predetermined value, an 
average value of the discharge current in the state of the battery voltage 
having a predetermined value may be computed. In this way, the internal 
impedance of the battery may be obtained in the same way, thereby making 
it possible to make accurate determination of the battery charging 
condition. 
Now, still another embodiment of the present invention will be explained, 
in which an approximation line, which is determined by battery current 
values and voltage values detected at a plurality of time points while the 
starter is actuated, is used to compute the value of a reference discharge 
time terminal voltage of the battery so that the battery condition is 
determined on the basis of the value of the reference discharge time 
terminal voltage of the battery. 
This sixth embodiment is based on the facts that the relationship between a 
discharge current and a terminal voltage of a battery is linear at the 
time of high-rate discharge of a current density of more than about 100 
mA/cm.sup.2 per unit battery electrode as shown in FIG. 16, and that the 
discharge current flowing through the starter when it is actuated is large 
enough to correspond to high-rate discharge and has a large pulsation due 
to load variations. In this embodiment, the terminal voltages and the 
discharge currents having a large pulsation are measured at a plurality of 
(two or more) time points. In the case shown in FIG. 15, for example, the 
discharge currents and the terminal voltages are measured as the current 
I.sub.1 and the voltage V.sub.1 at the time point t.sub.1 and as the 
current I.sub.2 and the voltage V.sub.2 at the time point t.sub.2. These 
currents and voltages generally assume different values because the 
current is pulsating. The reference discharge time terminal voltage 
computation means makes linear approximation of the relationships of the 
measured currents and voltages such as (I.sub.1, V.sub.1), (I.sub.2, 
V.sub.2), computes a reference discharge time terminal voltage V.sub.S in 
the state of a predetermined reference discharge time current value 
I.sub.S by using extrapolation or interpolation as shown in FIG. 17. The 
terminal voltage V.sub.S thus computed coincides substantially with the 
terminal voltage V.sub.S as measured actually by causing the reference 
discharge current I.sub.S to flow in view of the linear current-voltage 
relationship during high-rate discharge. 
A sixth embodiment of the present invention will be explained with 
reference to the accompanying drawings. A configuration of a battery 
condition detection apparatus is shown in FIG. 14. A car battery 1 is 
connected to a given electric load 8 such as a lamp and a generator 3, and 
also to an engine starter 2 through a starter switch 5. The wires leading 
from the battery 1 to the loads 8, 2 are connected to a current detector 6 
including a shunt resistor or the like to detect the discharge current of 
the battery 1. The positive terminal of the battery 1 is connected to a 
voltage detector 10. 
The outputs of the current detector 6 and the voltage detector 10 are 
connected to a microcomputer 18. Upon receipt of signals from the 
detectors 6, 10 at an A/D converter thereof, the microcomputer 18 causes a 
CPU thereof to take the data into a memory. Except for the hardware 
configuration which is well known, means for realizing the processing 
operation in the CPU are shown in this diagram. The microcomputer 18 
includes memory means 81, reference discharge time terminal voltage 
computation means 82 (abbreviated as V.sub.S computation means 82) and 
timer means 83. The output of the microcomputer 18 is connected to a 
battery condition indicator 11. 
The operation of this embodiment will be explained with reference to FIG. 
15. Upon turning on the starter switch to start the engine, the timer 
means 83 detects that the cranking operation is started and continues, by 
a great rise in the current value, and notifies the memory means 81 of a 
plurality of predetermined time points t.sub.1 and t.sub.2 after the start 
of the cranking operation. The memory means 81 stores the current values 
I.sub.1, I.sub.2 and the voltage values V.sub.1, V.sub.2 at the time 
points t.sub.1, t.sub.2. During cranking, the discharge current assumes a 
large value accompanied by a great pulsation, and therefore measurements 
at different time points t.sub.1, t.sub.2 make it possible to measure 
terminal voltages V.sub.1, V.sub.2 for different large currents I.sub.1, 
I.sub.2. 
The V.sub.S computation means 82, as shown in FIG. 17, computes the 
reference discharge time terminal voltage V.sub.S in the state of the 
reference discharge current value I.sub.S by making extrapolation, which 
uses a first-order equation, of a plurality of measured values of 
(I.sub.1, V.sub.1) and (I.sub.2, V.sub.2). The reference discharge time 
terminal voltage V.sub.S provides an index accurately representing a 
condition of the battery 1. When this terminal voltage V.sub.S is smaller 
than a predetermined level, the microcomputer 18 produces a signal to a 
battery condition indicator 11 issuing an alarm to inform the driver of 
the battery capacity shortage. 
Apart from the case of FIG. 17 in which the reference discharge time 
current value I.sub.S is larger than the two current measurements I.sub.1 
and I.sub.2 and extrapolation computation is required, linear 
approximation may also be used to obtain the reference discharge time 
current value I.sub.S by making interpolation in the case where the 
reference discharge time current value I.sub.S falls between two 
measurements I.sub.1 and I.sub.2. 
Although the reference discharge time terminal voltage V.sub.S is computed 
from measured values at the two points in the sixth embodiment described 
above, it is possible to determine a more accurate reference discharge 
time terminal voltage V.sub.S from current and voltage measurements at 
more time points. Also, if points of measurement are increased, it is 
possible to avoid a computation failure which might occur by unexpected 
coincidence of two current or voltage values measured at two different 
predetermined time points. 
Further, instead of the time lengths t.sub.1, t.sub.2 elapsed from the 
start of the cranking operation used in the present embodiment, a change 
in the current value may be used in determining the time points of 
measurement. For example, a voltage may be measured at the second time 
immediately after a change .DELTA.I in the current value from the first 
measuring point. 
Furthermore, it is also possible to improve the computation accuracy of the 
voltage V.sub.S by discriminating a pulsation in the current value and 
making measurement at time points of peak and bottom of the pulsation. 
Instead of alarm indication based on the reference discharge time terminal 
voltage V.sub.S calculated according to the present invention, the amount 
of power generation of the generator 3 may be controlled on the basis of 
the terminal voltage V.sub.S with equal effect. 
A seventh embodiment in which the amount of power generation is controlled 
is shown in FIG. 18. This seventh embodiment has added thereto a specific 
gravity sensor 4 for detecting the specific gravity of the electrolyte of 
the battery 1. The microcomputer 18 includes timer means 83, memory means 
81 and V.sub.S computation means 82. In addition to the V.sub.S measuring 
means 80 for measuring and computing the reference discharge time terminal 
voltage V.sub.S, means 85, 86, 87 are provided for the power generation 
control. 
The process of the power generation control will be explained. The 
reference discharge time terminal voltage (abbreviated as the terminal 
voltage V.sub.S) is measured and computed based on the current pulsation 
occurring at the time of cranking, and the specific gravity of the battery 
electrolyte is measured and compared with the terminal voltage V.sub.S 
thereby to discriminate the battery condition and to effect power 
generation control. 
In addition to the above explanation, FIG. 2 shows a battery voltage curve 
A versus the specific gravity of the battery electrolyte (indicated in the 
parentheses under the abscissa) when the starter 2 is actuated by using a 
new battery 1. 
Assume, for example, that the terminal voltage V.sub.S of the battery 1 and 
the specific gravity S.sub.B are determined at the time of driving the 
starter 2 as shown by a point X. In this case, the specific gravity 
S.sub.B is high as compared with the specific gravity S.sub.A (point Y) 
for the reference characteristic A, indicating that the battery 1 is 
degraded (a reduced quantity of electrolyte or an exhausted life of the 
battery 1, for example). 
Specifically, as long as the specific gravity of the electrolyte of the 
battery 1 is more than S.sub.L with respect to the reference 
characteristic A, the battery voltage exceeds V.sub.L, thus making it 
possible to drive the starter 2. If the battery 1 is degraded as mentioned 
above, however, the specific gravity S is increased, leading to a decision 
that apparently the battery voltage is also high. If the specific gravity 
S is used to effect the control according to the reference characteristic 
A, a low battery voltage in spite of a high specific gravity S would make 
it impossible to drive the starter 2. 
In order to solve this problem, the reference specific gravity S.sub.A of 
battery electrolyte for the battery terminal voltage V.sub.S is determined 
on the basis of the reference characteristic A stored in the microcomputer 
18, and the specific gravity is corrected by using the actual measurement 
of the specific gravity S.sub.B and the reference value S.sub.A, thereby 
making it always possible to obtain accurate specific gravity for a 
predetermined voltage. As a result, an accurate condition of the battery 1 
is always detected by correcting the specific gravity obtained from the 
specific gravity sensor 4. 
If power generation is controlled on the basis of the corrected specific 
gravity S.sub.r ', the battery voltage at the time of starter actuation is 
always higher than V.sub.L, thus permitting the starter 2 to be driven 
always accurately. 
Since there is no need of charging the battery 1 more than necessitated 
(increasing the adjustment voltage to an unnecessary degree), the 
adjustment voltage can be reduced to save the load of the generator 3 on 
the engine, resulting in an improved fuel efficiency. Further, the amount 
of charging the battery 1 is reduced to provide an advantage of preventing 
a reduction in the electrolyte quantity. 
In other words, power generation is controlled in such a manner as to keep 
the corrected specific gravity value S.sub.r ' in the range of S.sub.L 
.ltoreq.S.sub.r '.ltoreq.S.sub.H, so that the battery is maintained in a 
balanced condition while at the same time assuring smooth starting of the 
engine (preventing emptying of a battery) and providing an improved fuel 
efficiency and a lesser rate of reduction in the electrolyte quantity. 
If it is impossible to charge the battery as intended simply by changing 
the adjustment voltage in view of the power generation capacity of the 
generator 3, the above-mentioned effect could be assured to a higher 
degree by improving the charging capacity or preventing discharge, by 
raising the idling speed or cutting off the electric load of the engine. 
The operation of the microcomputer 18 for realizing the aforementioned 
control concept will be explained with reference to FIG. 19. 
Step 1 computes the terminal voltage V.sub.S at the time of reference 
discharge of the battery 1 from a pulsation current occurring when the 
starter 2 is actuated. At the same time, the specific gravity S.sub.B of 
the battery electrolyte is detected by the specific gravity sensor 4 and 
is stored. 
Step 2 checks to see whether the terminal voltage V.sub.S thus measured and 
computed is lower than the lower limit voltage V.sub.L, and, if it is 
lower, indicates that the exhaust of the battery life is approaching, on 
the life indicator 9. 
Step 3 calculates and stores a specific correction value .DELTA.S (=S.sub.A 
-S.sub.B) from the reference specific gravity S.sub.A for the stored 
terminal voltage V.sub.S and the measured specific gravity S.sub.B. This 
process is effected at specific gravity correction value computation means 
85. 
Step 4 detects the specific gravity S.sub.r of the electrolyte of the 
battery 1 by the specific gravity sensor 4 at a predetermined later time 
point (when the vehicle is running, for example). 
Step 5 adds the specific gravity correction value .DELTA.S obtained at step 
3 to the specific gravity S.sub.r determined at step 4, thereby producing 
a real specific gravity S.sub.r '. This process is performed by specific 
gravity correction means 86. 
In view of a steadily changing battery characteristic (represented by the 
relationship between the electrolyte specific gravity and the terminal 
voltage V.sub.S at the time of discharge as determined by the battery 
life, electrolyte quantity, etc.), it is sufficient to measure the 
specific gravity correction value .DELTA.S only at the time of starter 
actuation once for each drive. 
Steps 6 to 9 change the adjustment voltage in such a manner that the 
corrected specific gravity value S.sub.r ' is maintained in the range 
S.sub.L .ltoreq.S.sub.r '.ltoreq.S.sub.H. Specifically, if S.sub.r 
'.ltoreq.S.sub.L, the adjustment voltage is increased at step 7, while if 
S.sub.r '.gtoreq.S.sub.H, the adjustment voltage is decreased at step 9. 
The upper limit value S.sub.H is determined appropriately from the 
viewpoint of fuel efficiency and the like to have a predetermined marginal 
band for the lower limit value S.sub.L. The processes from steps 6 to 9 
are performed by power generation control means 7. 
The vehicle then continues to be driven (step 10). The processes of steps 4 
to 10 are repeated as long as the key switch remains in the "on" state 
(step 11). 
While, in the present embodiment, the discharge current (I.sub.S) providing 
a reference is determined to obtain a terminal voltage V.sub.S, since the 
relation between a discharge current and a terminal voltage of a battery 
is determined by the internal impedance of the battery, a discharge 
current corresponding to a reference terminal voltage or the internal 
impedance obtained from the relationship between the terminal voltage and 
discharge current may obviously be used alternatively to indicate the 
battery condition or to control power generation with equal effect.