Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
2001-04-02
2002-03-26
Toatley, Gregory (Department: 2838)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C320S120000
Reexamination Certificate
active
06362626
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cell voltage measuring device for a cell module comprising a plurality of cells connected together in series.
BACKGROUND OF THE INVENTION
Attention has been directed in recent years to environmental technology with consideration given to global environmental problems such as ozone hole and global warming. In the motor vehicle industry, efforts have been devoted to the development of electric motor vehicles with diminished carbon dioxide emissions. As power sources for such vehicles, cell modules having a great capacity are used in which secondary cells, typical of which are lithium ion cells or nickel hydrogen cells, are connected in series.
Secondary cells, typical of which are lithium ion secondary cells, cause undesirable troubles such as liquid leakage or heat generation if overcharged or overdischarged, so that each cell needs to be checked for voltage by monitoring. Furthermore, handling a cell module of large capacity having great energy requires safety measures such as electrical insulation of the module and the circuit in the vicinity thereof. Accordingly, techniques for measuring the voltage of each cell accurately with safety are important for cell modules of large capacity for use as power sources for electric motor vehicles.
Cell voltage measurement of such cell modules having a great capacity is conventionally done, for example, by dividing the module into blocks of several cells, multiplexing the cell voltages of each block and converting the voltages to digital values, and obtaining cell voltages in terms of digital values as shown in FIG.
2
. However, this method requires many AD converters, and the power sources for the AD converters need to be insulated, consequently entailing the problem of necessitating a complex circuit and a higher cost.
Accordingly, the cell voltage measuring method with use of so-called flying capacitors has attracted attention in recent years. With reference to
FIG. 3
showing an example of arrangement of flying capacitors, indicated at
31
is a cell module, at
32
potential holding means, at
33
cell voltage measuring means, and at
34
control means. With the method of
FIG. 3
, the switches of the potential holding means
32
are turned on first to cause the capacitors of the means
32
to hold potentials of the cell module
31
, and the switches are thereafter turned off to electrically insulate the cell module
31
from the potential holding means
32
. The capacitor corresponding to the cell to be checked for voltage is connected to an A/D converter to measure the cell voltage by the measuring means
33
. The cell voltage of the cell module
31
can be measured by this method, with the module
31
electrically insulated from the cell voltage measuring means
33
.
FIG. 4
shows another example of arrangement of flying capacitors. Indicated at
41
is a cell module, at
42
potential holding means, at
43
cell voltage measuring means, and at
44
control means. With the illustrated construction like that of
FIG. 3
, the cell voltage can be measured based on the potential held in the capacitor of the potential holding means
42
, with the cell module
41
electrically insulated from the cell voltage measuring means
43
.
However, the construction shown in
FIG. 3
requires mounting of many switches, necessitating complex wiring and a higher cost. Although the construction shown in
FIG. 4
is smaller in the number of switches needed, all the capacitors constituting the potential holding means
42
are connected to one another in series, consequently entailing the need for the cell voltage measuring means
43
to handle a high voltage, so that the device is not useful practically. For example, in the case where 40 lithium ion cells are connected in series, a voltage of 3.6 V×40=144 V must be handled, whereas it is difficult to measure with the same accuracy the cell voltages increasing over a wide range of from 0 to 144 V with an increment of about 3.6 V.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a cell voltage measuring device which is reduced in the number of switches, lower in the voltage to be handled and adapted to measure the voltages of a cell module as electrically insulated.
The present invention provides a cell voltage measuring device for a cell module
11
wherein the component cells are theoretically divided into a plurality of (n) cell blocks
111
to
11
n
. A plurality of potential detecting lines extending from respective potential detecting points of each of the cell blocks are provided with potential holding means
12
for holding the potentials of the potential detecting points of the cell block, and cell voltage measuring means
14
for measuring the voltage of the cells based on the potentials of the potential detecting points held by the potential holding means
12
. The potential holding means
12
and the cell voltage measuring means
14
have their operations controlled by control means
17
.
The potential holding means
12
comprises: a plurality of (n) pre-switch blocks
121
to
12
n
connected to the plurality of (n) cell blocks
111
to
11
n
respectively and each comprising a plurality of switches capable of opening or closing the potential detecting lines extending from the cell block, and
a plurality of (n) capacitor blocks
131
to
13
n
connected to the plurality of (n) cell blocks
111
to
11
n
by way of the plurality of (n) pre-switch blocks
121
to
12
n
respectively and each comprising a plurality of capacitors for holding the potentials of the potential detecting points of the cell block. The voltage measuring means
14
comprises:
a plurality of (n) post-switch blocks
141
to
14
n
connected to the plurality of (n) cell blocks
111
to
11
n
respectively by way of the potential holding means
12
and each comprising a plurality of switches for opening or closing the potential detecting lines extending from the cell block, and
a voltage measuring circuit for selecting voltage signals for each cell block from among those obtained by the potential detecting lines via the post-switch blocks
141
to
14
n
to measure the voltage of each cell constituting the cell block.
The voltage measuring circuit can be composed of a difference computing circuit
150
for calculating the potential difference between two potential detecting lines extending from electrode terminals of each cell and included among the potential detecting lines from each cell block, and an AD converter
160
having connected thereto output terminals of the computing circuit
150
.
With the cell voltage measuring device of the invention for the cell module, the cell module is divided into a plurality of cell blocks, and flying capacitors are provided for each cell block. This feature reduces the number of switches, lowers the voltage to be handled and permits voltage measurement with the module in an electrically insulated state, at the same time.
REFERENCES:
patent: 5744936 (1998-04-01), Kawakami
patent: 6239579 (2001-05-01), Dunn et al.
patent: 6249125 (2001-06-01), Haddad et al.
Rader & Fishman & Grauer, PLLC
Sanyo Electric Co,. Ltd.
Toatley Gregory
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