Chemistry: electrical current producing apparatus – product – and – Cell support for removable cell – For plural cells
Reexamination Certificate
2001-10-19
2004-11-02
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Cell support for removable cell
For plural cells
C429S100000, C429S096000, C429S149000, C429S152000, C429S153000, C429S157000, C429S159000
Reexamination Certificate
active
06811921
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a battery pack.
BACKGROUND ART
Conventionally, a backup battery has typically been realized by using a lead battery. In recent years, an alkaline storage battery and a lithium-ion secondary battery are coming into wider use as backup batteries in keeping with growing concern over the environment and an increasing demand for a more compact and lightweight battery. Moreover, as a driving battery, an alkaline storage battery, particularly, a nickel hydrogen storage battery has attracted attention and besides a lithium-ion secondary battery has been put to practical use.
In an enclosed-type nickel hydrogen storage battery, during charging and discharging processes, heat of reaction occurs due to gaseous hydrogen absorbing reaction, as well as Joule heat generated in the battery. This leads to a temperature rise. Thus, in a battery pack, like conventional ones, having a number of batteries arranged in a predetermined space thereof, although it varies with the charging current and thermal radiation characteristics of the battery, the battery temperature might rise up to 80° C. or above. A lithium-ion secondary battery also undergoes heat generation during charging and discharging processes.
Moreover, as described hereinabove, in a battery pack having a number of batteries closely arranged therein, the batteries located at the central part thereof are inhibited from exhibiting satisfactory thermal radiation due to their neighboring batteries and thus suffer from a significant temperature rise, as compared with the neighboring batteries.
Further, a nickel hydrogen storage battery is characterized in that the battery temperature significantly increases with higher ambient temperature. Thus, constituting a battery pack by using nickel hydrogen storage batteries creates substantial problems of, in addition to an undesirable temperature rise, great temperature differences among the individual batteries.
In general, an alkaline storage battery suffers from degradation in charging characteristics as well as degradation in service life characteristics under high temperature conditions. A lithium-ion secondary battery also exhibits poor service life characteristics under high temperature conditions.
To suppress such a temperature rise in a battery, various proposals have been made to date, for example, a method wherein a metal plate is inserted between batteries so as to dissipate heat from its one end (as disclosed in Japanese Patent Publication No. 7-14616), and a method wherein, of a plurality of batteries piled up, only the batteries located at the central part are provided with a heat dissipating plate (as disclosed in Japanese Patent Publication No. 6-223804).
However, the above-described proposals failed to come up with satisfactory solutions to a problem that batteries located at the central part are more susceptible to a temperature rise due to heat generation caused by their neighboring batteries, and to a problem that a heat-collecting effect exerted by a heating element is insufficient.
The present invention has been made to solve the above-described problems, and accordingly its main object is to provide a battery pack in which degradation in the charging and service life characteristics is prevented by suppressing a temperature rise in the battery due to heat generation.
DISCLOSURE OF THE INVENTION
To achieve the above object, a battery pack according to the present invention is characterized by comprising: a battery unit composed of a plurality of batteries arranged flatly, the batteries being electrically connected with one another by either series or parallel connection, or a combination of series connection and parallel connection; a pair of heat transfer plates made of a material exhibiting excellent thermal conductivity and arranged in parallel to a surface where the battery unit is arranged, of which one makes surface contact with the top-surface side of each of the batteries constituting the battery unit, and the other makes surface contact with the back-surface side of each of the batteries constituting the battery unit; and a housing made of a material exhibiting excellent thermal conductivity, the housing accommodating the battery unit and the pair of heat transfer plates and making surface contact with the pair of heat transfer plates.
According to the above-described structure, each of the batteries of the battery unit makes surface contact with the pair of heat transfer plates; the pair of heat transfer plates make surface contact with the housing; and the heat transfer plates and the housing are made of materials exhibiting excellent thermal conductivity. Thus, heat generated in the battery is efficiently transmitted through the housing and is then dissipated, thereby suppressing a rise in the battery temperature within the battery pack.
Although each of the batteries of the battery unit may preferably make surface contact with the pair of heat transfer plates at its substantially entire outer peripheral surface excluding the end faces thereof, it is essential only that at least 60% or more, preferably 75% or more, or optimally 90% or more of the area of the battery be brought into surface contact with the heat transfer plates. Moreover, by forming projections and depressions for dissipating heat, like a cooling fin, on the outer surface of the housing, heat dissipation is further facilitated, thereby suppressing a rise in the battery temperature within the battery pack.
The heat transfer plates and the housing may preferably be made of aluminum, copper, magnesium, or an alloy composed mainly of one of them. This is because these components are excellent in thermal conduction and are thus suited for suppressing a battery temperature rise. The heat transfer plate and the housing may preferably be separately fabricated to obtain as large a contact area therebetween as possible. However, if they are molded in one piece, the contact area is theoretically maximized. This is most desirable. Moreover, the heat transfer plate and the housing may be made of a thermally conductive resin which exhibits excellent thermal conductivity, for example, “SARCON GR-d t2.0” manufactured by Fuji Polymer Industries Co., Ltd. Since the thermally conductive resin in this example show the softness and elasticity, the heat transfer plate, even though it is flat-shaped, can make surface contact with the battery.
In constituting the battery unit, preferably, N pieces of axially connected batteries are integrated together to form a battery module, and the battery modules are arranged in M rows in parallel to each other. By performing temperature and voltage measurements separately for each battery module realized by mechanically and electrically connecting N pieces of batteries in series, discharge control is facilitated.
The present invention is suitably applied to such a battery pack as employs a cylindrical nickel hydrogen storage battery, or a cylindrical lithium-ion secondary battery, in particular.
REFERENCES:
patent: 4314008 (1982-02-01), Blake
patent: 5545491 (1996-08-01), Farley
patent: 6152597 (2000-11-01), Potega
patent: 6326766 (2001-12-01), Small
patent: 6372377 (2002-04-01), Ovshinsky et al.
patent: 6444350 (2002-09-01), Toya et al.
patent: 06-223804 (1994-08-01), None
patent: 07-014616 (1995-01-01), None
patent: 08-212989 (1996-08-01), None
patent: 9-298051 (1997-11-01), None
patent: 9-306447 (1997-11-01), None
patent: 10-154494 (1998-06-01), None
patent: 11-339766 (1999-12-01), None
patent: 2000-14028 (2000-01-01), None
Dansui Yoshitaka
Kasahara Hideki
Bell Bruce F.
Jordan and Hamburg LLP
Matsushita Electric - Industrial Co., Ltd.
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