Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
2002-11-27
2004-12-21
Le, N. (Department: 2858)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C324S503000, C324S511000
Reexamination Certificate
active
06833708
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to leak detecting circuits for power source devices for use in electric motor vehicles and the like, and more particularly to a leak detecting circuit for a power source device having a cell unit comprising a plurality of cells.
2. Description of the Related Art
Electric motor vehicles such as hybrid cars are provided with a cell unit serving as a power source for the drive motor and comprising a plurality of secondary cells connected in series. Such a cell unit produces a high voltage, for example, of at least 240 V, so that if a leak occurs, a leakage current flowing portion is likely to provide an electric shock to the person by contact, posing the problem of bringing a danger to the human body. Accordingly, it is conventional practice to provide a circuit for detecting leaks, as shown in
FIG. 5
, to notify a control system or the driver of the occurrence of a leak upon detecting the fault. The leak detecting circuit of
FIG. 5
has a cell unit Vb which comprises about 200 nickel-hydrogen cells NiMH connected in series, and an output voltage, which is usually about 240 V, is available across a positive (P) terminal and a negative (N) terminal. Voltage dividing resistors R
1
and R
2
(R
1
=R
2
) of high resistance value are connected between the P and N terminals, and the midpoint between the two resistors is grounded via a resistor R
3
. The voltage between the opposite ends of the resistor R
3
is detected by a voltmeter V. In the case of electric motor vehicles, “grounding” means connection to the chassis (vehicle body).
When no leak occurs, no current flows through the resistor R
3
, with the result that the voltmeter V delivers zero output. If a leak occurs in the line P, the line P is grounded via a ground-fault resistance RL in the resulting equivalent circuit as indicated in a broken line in the diagram. Formed in the equivalent circuit is a current path of line P→ resistance RL→ resistor R
3
→ resistor R
2
→ line N, and a voltage is produced between the opposite ends of the resistor R
3
. The leak can be detected by detecting the voltage thus produced by the voltmeter V. The voltmeter V has the function of measuring the voltage in detecting the leak and judging whether the measurement is not lower than a predetermined value or below the predetermined value, and can therefore be provided by a voltage comparator.
In
FIG. 5
, the resistors R
1
, R
2
, R
3
provide insulation resistance for the cell unit against ground, and the combined resistance value of these resistors is substantially an insulation resistance value. Usually the circuit is so desired that the combined resistance value will not be less than 1 M&OHgr;. Assuming that the input impedance of the voltmeter V is Zv, the insulation resistance value Rz in
FIG. 5
is calculated from Mathematical Expression 1.
Rz=R
1
·R
2/(
R
1
+R
2)+
R
3
·Zv
/(
R
3
+Zv
) (Mathematical Expression 1)
When the resistance values of the resistors R
1
, R
2
are small, the cell voltage Vb remains applied to the resistors R
1
and R
2
to discharge the cell unit at all times, so that the resistors R
1
, R
2
have a relatively high resistance value. For example, in the case where the cell voltage is 240 V and the limit value for the allowable discharge current is 100 &mgr;A, the combined resistance value of the resistors R
1
, R
2
is at least 2.4 M&OHgr;. Accordingly, the resistors R
1
, R
2
have a high resistance value with reference to this resistance value. As a result, the insulation resistance value Rz of Mathematical Expression 1 is such that the first term becomes predominant which makes it possible to provide a sufficiently great value to the insulation resistance value Rz even if the resistance R
3
and impedance Zv of the second term have relatively small values. Usually, the resistor R
3
is designed to have a small resistance value so that the input impedance Zv of the voltmeter V is negligible.
FIG. 6
shows the construction of another conventional leak detecting circuit. The circuit has voltage dividing resistors R
1
and R
2
of high resistance value connected between P and N terminals. The midpoint between the two resistors is grounded. The potential difference between the line P and the grounded point is detected by a voltmeter V
1
, and the potential difference between the line N and the grounded point by a voltmeter V
2
. To afford a sufficiently great insulation resistance, the resistors R
1
, R
2
have a high resistance value, for example, of at least 2.2 M&OHgr;.
In the leak detecting circuit of
FIG. 6
, a high voltage of Mathematical Expression 2 below is steadily applied to the voltmeters V
1
, V
2
even in the event of no leak occurring.
V
1
=V
2=(1/2)
Vb
(Mathematical Expression 2)
If a leak occurs in the line P, the line P is grounded via a ground-fault resistance RL in the resulting equivalent circuit as indicated in a broken line in the diagram. Accordingly, the leak is detectable from a decrease in the voltage detected by the voltmeter V
1
or an increase in the voltage detected by the voltmeter V
2
.
Power source devices comprising a cell unit include those which require detection of the “degree” of leaks. In the event of a leak occurring, for example, there arises a need to judge whether a countermeasure should be taken urgently or in due time in accordance with the “degree” of the leak. Stated more specifically, a judgement is made in accordance with the magnitude range of ground-fault resistance RL as shown in FIG.
7
. The value of ground-fault resistance RL, when not smaller than a threshold value RL
2
, indicates occurrence of no leak, hence safety. If the value RL is within the range of a threshold value RL
1
to the value RL
2
, this indicates the occurrence of a leak, which nevertheless is not dangerous to the human body. When up to the threshold value RL
1
, the value RL is interpreted as indicating a danger to the human body. For example, if resistance values dangerous to the human body are up to about 100 &OHgr;/V (at least 10 mA calculated as current), the threshold value RL
1
is 24 k&OHgr; when the output voltage is 240 V. However, if the threshold values RL
1
, RL
2
are great, an increased impedance will result, causing the circuit to make an error in detection, so that the threshold values RL
1
, RL
2
are determined in the range of 50 to 70 k&OHgr;, with an allowance made for the value 24 k&OHgr;.
FIG. 8
shows the leak detecting circuit of
FIG. 5
when R
1
=R
2
=2.2 M&OHgr;, R
3
=10 k&OHgr; (Zv is sufficiently great relative to R
3
), and Vb=240 V. In the case where the ground-fault resistance RL has varying values of 0 &OHgr;, 50 k&OHgr;, 70 k&OHgr;, 1 M&OHgr;, 2 M&OHgr; and ∞, the voltage values to be detected by the voltmeter V are listed in Table 1.
TABLE 1
Ground-fault
resistance RL
0 &OHgr;
50 k&OHgr;
70 k&OHgr;
1 M&OHgr;
2 M&OHgr;
∞
Voltage to be
1.081 V
1.034 V
1.017 V
0.569 V
0.386 V
0 V
detected V
With reference to
FIG. 8
, two voltmeters VA, VB connected in parallel with the resistor R
3
are for use in detecting leaks when the ground-fault resistance is up to 70 k&OHgr; and up to 50 k&OHgr;, respectively. The voltmeter VA is adapted to detect leaks at not lower than 1.017 V, and the voltmeter VB operates for detection at not lower than 1.034 V as will be described below more specifically.
(1) Neither of the voltmeters VA, VB operate for detection at not higher than 1.017 V. This case is interpreted as indicating occurrence of no leak.
(2) The voltmeter VA operates for detection when the voltage to be detected is in the range of 1.017 to 1.034. The voltage is interpreted as indicating the occurrence of a leak in the precaution range shown in FIG.
7
.
(3) Both the voltmeters VA, VB operate for detection when the voltage to be detected is at least 1.034 V. The voltage is interpreted as indicating the occurrence of a leak in the dangerous range shown in FIG.
Armstrong Kratz Quintos Hanson & Brooks, LLP
Le N.
Nguyen Vincent Q.
Sanyo Electric Co,. Ltd.
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