Battery System

An objective of the invention is to deal with difference of the internal resistance of batteries. A battery system (1) including a plurality of battery modules (3) connected, wherein the higher the temperature of the location where the battery module (3) is located becomes, the larger the resistance value of a distribution cable (11) is made. In a chassis (2), the distribution cable (11) located where the temperature is high is made longer and the distribution cable (11) located where the temperature is low is made shorter. More specifically, the distribution cable (11) connected to a battery group (4) located on the upper part of the chassis is made longer and the distribution cable (11) connected to a battery group (4) located on the lower part of the chassis is made shorter. Further, the length of the distribution cable (11) may be adjusted by arranging the output terminal (21) on the lowermost part of the chassis (2).

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a mode for implementing the present invention (called an “embodiment”) will be explained in detail with reference to the drawings. In the drawings, similar symbols are used to denote similar components, and redundant explanations are omitted.

Here, in this embodiment, the battery system is considered as normal when it is in operation in thermally-stable condition.

First Embodiment

FIG. 1is an external perspective view of a battery system according to the first embodiment of the invention.

In a battery system1according to the embodiment, battery modules3including a plurality of cell batteries (not shown) are horizontally stored per each column in the chassis2. Here, a group of battery modules3in each column is called as a battery group4.

On the upper surface of the chassis2, there is provided a fan5for releasing heat generated in the chassis2. The fan5may be omitted as needed.

FIG. 2is a graph which represents the relation between location and temperature of a battery group in a chassis.

The inventor found that, as shown inFIG. 2, the temperature of the battery group4on the uppermost part of the chassis2ofFIG. 1tends to be higher than that of the battery group4on the lowermost part. It is considered to be caused by the upcoming heat generated by the battery module3.

FIG. 3is a graph which represents the relation between the internal resistance and temperature of a cell battery.

As shown inFIG. 3, it is known with respect to a cell battery like a lithium-ion battery that, when the temperature of the cell battery is increased, the viscosity of the solution in the cell battery decreases. Consequently, the mobility of ion increases and the internal resistance decreases.

As explained inFIG. 2, since the temperature of the battery group4on the uppermost part of the chassis2is high, the internal resistance of the battery group4on the uppermost part of the chassis2is small. Further, since the temperature of the battery group4on the lowermost part of the chassis2is lower than that of the battery group4on the uppermost part, the internal resistance is larger than that of the cell battery on the uppermost part of the chassis2.

Therefore in this embodiment, the resistance of the battery groups4on both the uppermost and lowermost parts of the chassis2are equalized by increasing the resistance of the distribution cables11connected to the battery groups4on the uppermost part of the chassis2, and decreasing the resistance of the distribution cables11connected to the battery groups4on the lowermost part of the chassis2.

FIG. 4is a diagram showing a wiring example of the battery system according to the first embodiment.

In the example ofFIG. 4, each battery group4is provided with five battery modules3connected in series. Further, four battery groups4in total are connected in parallel with an output terminal12and stored in the chassis2.

As shown inFIG. 4, the output terminal12which outputs power of the battery groups4is arranged on the lowermost part of the chassis2. Thus, the battery groups4where the temperature is high, i.e. the higher position of the chassis2where the internal resistance of the cell battery is small, are connected by the distribution cable11having the longer length. In other words, with respect to the battery group4a, battery group4b, battery group4c, and battery group4darranged in sequence from the uppermost part of the chassis2as shown inFIG. 4, the length of the distribution cable11of the batteries4are determined so that the following relation is satisfied: battery group4a>battery group4b>battery group4c>battery group4d. Thus, the resistance of the battery groups4is equalized by making the resistance larger of the distribution cable11connected to the battery groups4as the position of the battery group4becomes higher in the chassis2. In other words, the battery group4located on the position having higher temperature is connected by the longer distribution cable11.

FIG. 5is a diagram showing another wiring example of the battery system according to the first embodiment.

InFIG. 5, similarly toFIG. 4, the output terminal12is arranged on the lowermost part of the chassis2. Thus the length of the distribution cable11connected to the battery group4is made longer as the location of the battery group4becomes higher in the chassis2where the internal resistance of the cell battery is small.

However, in contrast to the battery groups4inFIG. 4which are connected in parallel, the battery groups4inFIG. 5are divided into two groups21, and two battery groups4are connected in series in each of the groups21. In addition, two groups21are connected to the output terminal12in parallel. Here, two battery groups4on the upper position and two battery groups4on the lower position constitute the two groups21. The length of each distribution cables11connected to each group are different from each other.

Thus, the resistance of each of the groups21may be equalized by dividing the battery groups4into a plurality of upper and lower groups21, and making the length of the distribution cable11longer for the group21that is located on the higher position and making the resistance larger accordingly.

In other words, assuming that the battery group4a, battery group4b, battery group4c, and battery group4dare defined in the same way asFIG. 4, making the battery group4aand battery group4bas a group21a, making the battery group4cand battery group4das a group21b, then the relation of the length of the distribution cable11to each of the groups21can be represented as group21a>group21b.

Second Embodiment

Hereinafter, a case where the battery modules3are stored vertically as shown inFIG. 6Awill be explained.

In a battery system1ashown inFIG. 6A, the battery modules3are stored vertically. In the example ofFIG. 6A, four battery modules3are vertically connected in series (the connection is not shown inFIG. 6A), and constitute a battery group4. Then, five battery groups4are arranged horizontally.

Here, right and left end parts of the chassis2storing the battery group4are called as a double end part, and a part positioned in the middle of the chassis2in a horizontal direction is called as a central part.

Meanwhile, a fan5may be disposed on the upper surface of the chassis2.

FIG. 6Bis a graph which represents the relation between location and temperature of the battery group4in a case where the fan5is disposed on the upper surface of the chassis2.

In a case where the fan5is disposed on the upper surface of the chassis2(not shown inFIG. 6), the central part of the chassis2can receive large airflow, but the double end part may not receive large airflow. For this reason, as shown inFIG. 6, the temperature of the battery group4on the double end part may rise higher than that of the battery group4on the central part of the chassis2.

FIG. 7is a diagram showing a wiring example of the battery system ofFIG. 6.

In the example ofFIG. 7, five battery groups4(4eto4i) are vertically connected in parallel with the output terminal12.

From the left of the figure, symbols are given as, a battery group4e, a battery group4f, a battery group4g, a battery group4h, and a battery group4i, a distribution cable11aconnected to the battery group4eand the battery group4i, a distribution cable11bconnected to the battery group4f, the battery group4g, and the battery group4h.

Here, the length of the distribution cables11is determined so that the following relation is satisfied: distribution cable11a>distribution cable11b. More specifically, the distribution cable11ais made longer than the distribution cable11bat a position shown with a symbol601.

In other words, the battery group4eand the battery group4iare located where the temperature is high, and the distribution cables11aconnected to these batteries are made long. The battery group4f, the battery group4gand the battery group4hlocated are located where the temperature is low, and the distribution cables11bconnected to these batteries are made short.

By doing so, the distribution cables11aconnected to the battery group4eand the battery group4ilocated on the double end part where the temperature tends to be high are made longer. Thus the resistance thereof is made larger than those of the distribution cables11bconnected to the battery group4f, the battery group4gand the battery group4hlocated on the central part. As a result the resistance of the battery groups4is equalized.

Meanwhile, also in the second embodiment, a plurality of the battery groups4may be grouped such that each of the groups is connected in parallel with the output terminal12.

Further, in the embodiments (the first and second embodiments), although the resistance of the distribution cable11is increased by making the strength longer, the resistance may also be increased by making the distribution cable11thinner, or using material having larger resistance for the distribution cable11, or inserting a resistor element on the way.

In addition, in the embodiments, although the output terminal12is disposed on the lowermost part, it does not necessarily be disposed on the lowermost part as long as the resistance of the distribution cable11connected to the battery group4, which is located on a location where the temperature is high, can be made larger. For example, the output terminal12may be disposed on other location than the lowermost position, if the resistance of the distribution cable11can be made larger by making the distribution cable11thinner, or using material having larger resistance for the distribution cable11, inserting a resistor or coil or the like on the way.

Further, in the embodiments, five battery modules3constitute a battery group4, and four or five battery groups4are stored in the chassis2as shown in the example. In addition, inFIG. 5, two battery groups4are stored in a group21in the example. Of course, these numbers are not limited to these examples.

SUMMARY

In the present embodiments, the resistances of the battery groups4are equalized by making the length longer of the distribution cable11connected to the battery groups4located where the temperature is high, and shortening the distribution cable11connected to the battery groups4located where the temperature is low. In other words, the present invention does not equalize the resister values of the distribution cables11connected to the batteries like the patent documents 1 to 3. Instead, the resister values of the distribution cable11is varied in accordance with the connected battery groups4by design.

Thus, including batteries having the large internal resistance such as a lithium battery, it is possible to equalize the resistance of the battery groups4and prevent load from being concentrated on one battery.

Herewith, it is possible to effectively use the power in the battery systems1and1a, and to prevent the deterioration of the batteries due to load concentration from occurring.

DESCRIPTION OF THE SYMBOLS