Patent Application
20110298472
Not Applicable.
Not applicable.
1. Field of the Invention
This invention relates to battery systems and specifically to a battery connection failure detection system.
2. Description of the Problem
Battery packs are generally made from a number of individual cells that are connected in series to provide higher voltages and/or parallel to provide higher current. A number of inventions address the fundamental issue of how to connect such cells including bolting, soldering, friction and welding methods.
A disadvantage of the existing connection methods is that they may all, at some point, be prone to failure. This can be caused by corrosion, physical impact, vibration or components coming loose. If bolts securing the cells become lose resistance increases and so does connection temperature. This could cause a fire. This is particularly troublesome in hybrid vehicles using high capacity and high voltage electrical storage systems for electrical motors.
Battery safety systems employ thermal sensors placed near the battery cells which are used to detect thermal runaway events where cells have experienced a catastrophic failure. This failure can occur during charging or discharging. It is hoped that electrically disconnecting the battery would halt further heating and prevent fire from occurring. Such sensors often operate based on a single temperature threshold, for example 80 degrees centigrade, as a point where battery operation is considered unsafe.
Battery safety systems occasionally include thermal sensors located on the electronic components that are used to carry the battery power. These components are often rated to withstand up to 175 degrees centigrade. Therefore, the temperature threshold used to determine mis-operation of such devices is usually set in excess of 100 degrees centigrade.
There remains a need for a battery safety system that can determine the health of the battery connections and can therefore take preventative action when such connections are found to be unhealthy. There further exists a need for such detection methods to be predictive of such failure before it reaches catastrophic levels.
In a preferred embodiment of the invention the system is composed of a current sensor capable of monitoring current flow into and out of the battery and multiple temperature sensors arranged to sense various positions of the battery pack including at a minimum one sensor on the cell body and one sensor near the cell connections. During normal operation the temperature of the cell connections would be similar to the temperature of the body of each cell.
Large battery packs with many cells would include more temperature sensors to ensure that an individual cell failure or an individual connection failure could be detected.
Under high load, when a connection is failing, the resistance of the connection will rise. This increase in resistance will cause the temperature near the cell connection to rise beyond the levels normally expected for that given load. Comparing the cell temperature, the current flow, and the temperature near the cell connections will allow a simple software algorithm to determine if the cell connection temperature is higher than expected and therefore if the connection is degraded. This ensures that any degradation in the cell connection will be detected before the resistance climbs to the point where the heat generated is sufficient to cause a fire.
In an alternative embodiment of the invention, the system is composed of multiple temperature sensors arrange to sense various positions of the battery pack including at a minimum one sensor for the ambient environment and one sensor near the cell connections. In this way, large temperature differences between the cell temperature and the connection temperature will indicate localized production of heat near the cell connection and therefore a degradation of that connection. This can be done without knowing the actual current flow of the battery.
A third embodiment of the invention would include at least two temperature sensors located near the cell connections. In this embodiment, which is especially useful on larger batteries, the temperature of several different cell connections can be monitored and compared against each other. Since the current flowing through the battery is expected to be equal through cells connected in series, any individual cell connection exhibiting higher than expected temperatures with respect to other connections would be suspected to be in a degraded connection.
In all of the above embodiments, the primary detection threshold for a degraded cell connection is based on at least a temperature difference between two different temperatures. This improves the system safety as a degraded connection can be detected with temperature differences of only a few degrees centigrade, even in cold environments.
Similar detection methods can be accomplished with a variety of temperature sensing technologies including resistance transducers, thermocouples, infrared and semiconductor junctions. The use of any particular technology, thermal monitoring, current monitoring or power monitoring methods would still employ the fundamental aspect of seeking to qualify cell connection health based on the energy being lost at a degraded connection that has some amount of current flowing through it.
Electrical connections in general can use this method of detecting failure. This method is not limited to batteries and could be applied to other fields including capacitors, generators, switches and terminal blocks.
Referring to
Although the description above contains much specificity, these should not be construed as limiting the scope of the invention but as merely providing illustrations of the presently preferred embodiment of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents.
