FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
AND
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10; rule 13)
TITLE OF THE INVENTION THERMAL MAPPING METHOD AND APPARATUS
APPLICANT
Tata Motors Limited
Of Bombay House, 24 Homi Mody Street,
Mumbai 400001, Maharashtra, India;
An Indian Company;
&
Tata Motors European Technical Centre plc,
Of 18 Grosvenor Place, London, SW1X 7HS, London, United Kingdom
Nationality: United Kingdom
INVENTOR
BALL, Robert of Tata Motors European Technical Centre plc,
Commercial Department, International Automotive Research Centre,
University of Warwick, Coventry-CV4 7AL, United Kingdom
Nationality: United Kingdom
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner
in which it is to be performed.

TECHNICAL FIELD
The present disclosure relates to a thermal mapping method and apparatus. More particularly, the present disclosure relates to a method and apparatus for generating a thermal map for estimating an internal temperature of a battery module. The present disclosure also relates to a battery module incorporating the thermal map. The battery module can form part of a traction battery for a vehicle, but the disclosure is not limited in this respect.
BACKGROUND
A battery module typically comprises a plurality of electrically connected battery cells. In use, the temperature of the battery module tends to increase, for example during charging and discharging. It is important to monitor the temperature of the constituent battery cells. The battery cell temperature is used to estimate accurately the state of charge (SOC); and to ensure that battery cells do not exceed safe temperature limits.
One technique would be to incorporate a plurality of temperature sensors throughout the battery module. The battery module could then be operated and the temperature recorded with respect to time. The repeated operation of the battery module would produce a set of time histories of individual temperatures at many locations in the cells throughout the battery module, as represented by a chart 100 in Figure 1. However, using a fully-instrumented battery module is impractical, because of the number of sensors required, the cost of the sensors and the instrumentation circuits needed to monitor them. The instrumentation required to perform this monitoring is complex and bulky and cannot readily be used in a production implementation of the battery module.
An alternative to directly measuring the internal temperature of the battery module is to build a thermal model of the battery structure. A small number or temperature sensors are provided on the periphery of the battery module and a transfer function is used in a temperature estimation function of the Battery Management System (BMS). The thermal model can define a mathematical transfer function to relate the measured temperatures to the internal temperatures of the battery module. This technique is complicated, takes skill to generate and uses memory and processor resources in the BMS during execution of the routine.

SUMMARY OF THE INVENTION
Aspects of the present invention relate to a method of generating a thermal map; to a battery module incorporating a thermal map; to a traction battery; and to a vehicle.
According to a further aspect of the present invention there is provided a method of generating a thermal map for estimating internal temperatures of a battery module; the method comprising:
performing a plurality of cycling operations on a battery module comprising one
or more battery cell;
during said cycling operations, measuring a plurality of first temperatures at first
locations and one or more second temperature at one or more second locations;
and
cross-plotting the first temperatures measured at said first locations with the
second temperatures measured at the one or more second locations.
The thermal map can be generated in dependence on the cross-plotting of said first and second temperatures. At least in certain embodiments, the thermal map is more straightforward to generate than a mathematical transfer function, typically requiring less testing. The first and second locations are different from each other. By cross-plotting the first and second temperatures, the resulting thermal map can provide a transfer function relating temperatures in different locations in the battery module. The first locations can be disposed in an interior of the battery module, for example between adjacent battery cells or within one or more battery cells. The second locations can be disposed at a periphery of the battery module to provide a measurement of an external temperature of the battery module. The thermal map can thereby provide a transfer function which allows temperature measurements at said second locations on the periphery of the battery module to be used to estimate the temperature at said first locations inside the battery module. At least in certain embodiments, the thermal map can be evaluated relatively quickly to enable a transfer function to be implemented relatively quickly and easily. The thermal map can, for example, be implemented as a series of look-up tables (‘worst-case cell temperature’, ‘average cell temperature’, etc.).

The temperature can be measured at fewer of said second locations than at said first locations. A relatively small number of temperature sensors can be disposed at said second locations to estimate the temperature at said first locations.
The cross-plotting of the first and second temperatures can generate a scatter-plot. The thermal map can be generated from said scatter-plot. The method can comprise performing statistical analysis of the scatter-plot to generate the thermal map. For example, the method can comprise performing statistical analysis on the measured first temperatures for a given second temperature. A first maximum temperature can be estimated for each second temperature in a range. A first average temperature can be estimated for each second temperature in a range. The estimated first maximum temperature and/or the estimated first average temperature can be extracted from the scatter-plot to form the thermal map. For example, the thermal map can comprise a look-up table which defines the estimated first maximum temperature and/or the estimated first average temperature for a series of second temperatures. A look-up table can be defined for each said second temperature sensor. In use, the look-up table can be accessed in dependence on a temperature measured by the corresponding second temperature sensor.
The first temperatures can define a dependent variable in the thermal map. The second temperatures can define an independent parameter in the thermal map.
The method can comprise, in dependence on the measured first temperatures, determining a maximum first temperature estimate for a given second temperature. The maximum first temperature estimate can be defined for a range of second temperatures measured at said one or more second location.
The method can comprise, in dependence on the measured first temperatures, determining an average first temperature estimation for a given second temperature. Other types of statistical analysis can be performed on the measured first temperatures, for example to determine a median value for a given second temperature.
The operating cycles can comprise at least first and second different operating cycles to generate a range of said first and second temperatures. The operating cycles can comprise one or more of the following: warm-up, charging, discharging, pull-down and heat soak.

The first locations can be disposed within the battery module. The first locations comprise one or more of the following: between adjacent battery cells; and inside one or more of said battery cells.
The one or more second locations can be external to the battery module. For example, the one or more second locations can be disposed on an external surface of the battery module; or connected to an external component.
The method can comprise measuring more first temperatures at said first locations than second temperatures at said second locations.
According to a further aspect of the present invention there is provided a thermal map generated by implementing the method described herein.
According to a still further aspect of the present invention there is provided a battery monitoring system having at least one electronic processor coupled to system memory, wherein a thermal map as described herein is stored in said system memory.
The at least one electronic processor can be configured to receive a temperature signal from one or more temperature sensors. The at least one electronic processor can be configured to estimate an internal temperature of the battery module in dependence on the received temperature signal and the thermal map.
According to a further aspect of the present invention there is provided a battery comprising at least one first battery module connected to a battery monitoring system as described herein.
Each first battery module at least substantially corresponds to the battery module used to generate the thermal map.
The first battery module can comprise one or more temperature sensor disposed at said one or more second location.

The one or more temperature sensor can be thermally connected to a bus bar of the at least one battery module.
According to a still further aspect of the present invention there is provided a battery module comprising at least one battery cell, and a battery monitoring system as described herein. The at least one first battery module can at least substantially correspond to the battery module used to generate the thermal map.
According to a yet further aspect of the present invention there is provided a vehicle comprising a battery as described herein.
According to a further aspect of the present invention there is provided a battery module comprising:
one or more battery cell;
a battery monitoring system having at least one electronic processor coupled to system memory;
one or more temperature sensor configured to measure an external temperature of said battery module;
wherein the at least one electronic processor is configured to access a thermal map stored in the system memory to estimate an internal temperature of the battery module in dependence on the measured external temperature of said battery module. The thermal map can correlate the external temperature of the battery module to the internal temperature of the battery module. The thermal map can comprise a look-up table. The thermal map can be generated using the techniques described herein.
According to a still further aspect of the present invention there is provided a method of estimating an internal temperature of a battery module, the method comprising: measuring an external temperature of said battery module; and accessing a thermal map to determine the internal temperature of the battery module in dependence on the measured external temperature of said battery module. The thermal map can comprise a look-up table correlating the measured external temperature to the internal temperature of the battery module. The thermal map can correlate the external temperature of the battery module to the internal temperature of the battery

module. The thermal map can comprise a look-up table. The thermal map can be generated using the techniques described herein.
The battery monitoring system described herein may suitably comprise a control unit or computational device having one or more electronic processors. Thus the system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. A first control unit may be implemented in software run on one or more processors. One or more other control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.
Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.
BRIEF DESCRIPTION OF THE DRAWINGS
One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows thermal testing results for a set of time histories for a battery module using known techniques;
Figure 2 shows a perspective view of a battery module configured to access a stored thermal map to estimate internal operating temperatures in accordance with an embodiment of the present invention;
Figure 3 shows a schematic representation of the battery monitoring system for the battery module shown in Figure 2;
Figure 4 shows a horizontal section through the battery module shown in Figure 2;
Figure 5 shows a vertical section through the battery module shown in Figure 2;
Figure 6 shows a sectioned perspective view of the battery module shown in Figure 2;
Figure 7 shows a thermal map generated in accordance with an embodiment of the present invention; and
Figure 8 shows a schematic representation of a vehicle incorporating a plurality of battery modules in accordance with the present invention.
DETAILED DESCRIPTION
A method and apparatus for generating a thermal map 1 to estimate internal temperatures of a battery module 2 in accordance with an embodiment of the present invention will now be described with reference to the accompanying Figures 2 to 8. A battery module 2 incorporating the thermal map 1 to estimate internal temperatures will also be described.
As described herein, the thermal map 1 is generated through experimental analysis of the thermal behaviour of a test battery module 2. The thermal map 1 is subsequently used by a production version of the same battery module 2 to estimate internal temperatures. The configuration of the battery module 2 will now be described and the differences between the test and production versions outlined.
A perspective view of the battery module 2 is shown in Figure 2. The battery module 2 comprises a plurality of battery cells 3-n and a Battery Monitoring System (BMS) 4. As shown in Figure 3, the BMS 4 comprises one or more electronic processor 5 coupled to system memory 6. In the present embodiment, the battery cells 3-n are lithium ion cells

but other cell compositions are also contemplated. The battery cells 3-n can have various configurations, including cylindrical, rectangular (prismatic) and pouch cells. In the present embodiment the battery cells 3-n are pouch cells each having a pouch formed from a flexible material. As shown in Figure 4, the battery cells 3-n each comprise first and second major surfaces 7-1, 7-2 which are generally rectangular in shape and have a relatively large surface area to facilitate cooling. The battery cells 3-n are mounted in a housing 8 in a uniform array and are each connected to a respective bus bar 9. The battery cells 3-n are disposed in the housing 8 such that the first and second major surfaces 7-1, 7-2 of adjacent battery cells 3-n are arranged in a face-to-face arrangement.
During normal operation of the battery module 2, the battery cells 3-n generate heat in dependence on the current supplied and other factors, such as the cell temperature, state of charge (SOC) and state of health (SOH). Heat transfer plates 10 are sandwiched between pairs of the battery cells 3-n. As shown in Figure 4, the heat transfer plates 10 each comprise a lateral flange 11. The heat transfer plates 10 provide a thermally conductive path to transfer thermal energy from the battery cells 3-n to a cooling plate 12 positioned along a lateral side of the housing 8. The cooling plate 12 is externally cooled by a liquid coolant pumped through a coolant supply conduit 13. The lateral flange 11 is disposed in contact with the cooling plate 12 to establish a thermally conductive connection.
The test battery module 2 is used to generate the thermal map 1 and comprises first temperature sensors 14-n and second temperature sensors 15-n. The first temperature sensors 14-n are disposed internally within the battery module 2 at known first locations and are configured to measure an internal temperature of the battery module 2. A schematic representation of the first temperature sensors 14-n within the test battery module 2 is shown in Figure 5. The first temperature sensors 14-n generate first temperature measurements T1. In the present embodiment, the first temperature sensors 14-n are disposed between adjacent battery cells 3-n within the battery module 2. Alternatively, or in addition, one or more of the first temperature sensors 14-n can be disposed inside a battery cell 3-n of the test battery module 2. The second temperature sensors 15-n are configured to generate second temperature measurements T2 at said second locations. The second temperature sensors 15-n are disposed externally of the test battery module 2 at known second locations. The first and second temperature sensors 14-

n, 15-n can, for example, be thermistors, thermocouples or resistance temperature detectors (RTDs). In the test battery module 2, the first temperature sensors 14-n can be thermocouples for instrumentation; and the second temperature sensors 15-n can be thermistors for outputting temperature measurements to the BMS. As shown in Figure 6, the test battery module 2 in the present embodiment comprises three of said second temperature sensors 15-1, 15-2, 15-3 fixedly mounted to respective bus bars 9. In use, the temperature of the bus bars 9 increases due to internal resistance, both within the battery cells 3 and the bus bars 9, in dependence on the current supplied (Joule or Ohmic heating determined by the resistance (R) squared times the current (I)). The temperature of the respective bus bars 9 are measured by said second temperature sensors 15-1, 15-2, 15-3.
The first temperature sensors 14-n are omitted from the production battery module 2. Instead, the production battery module 2 uses the thermal map 1 to estimate internal temperatures in dependence on the measured external temperatures. The production battery module 2 comprises said second temperature sensors 15-n disposed at said second locations to measure the external temperature of the battery module 2. The second temperature sensors 15-n are coupled to the BMS 4. The second temperature sensors 15-n generate second temperature measurements T2 which are transmitted to said one or more electronic processor 5 in the BMS 4. The one or more electronic processor 5 is configured to cross-reference the second temperature measurements T2 with the thermal map 1. The arrangement of the second temperature sensors 15-n is the same in the test and production versions of the battery module 2. Thus, the second temperature sensors 15-n are disposed at the same second locations in said test and production battery modules. In the present embodiment, the production battery module 2 comprises three of said second temperature sensors 15-1, 15-2, 15-3 fixedly mounted to respective bus bars 9. The second temperature sensors 15-n are configured to measure an exterior temperature of the battery module 2 at said second locations during operation of the battery module 2.
The thermal map 1 is generated by performing a plurality of cycling operations on the test battery module 2. The cycling operations represent a range of normal operating conditions of the battery module 2 and can include one or more of the following: warm-up, charging, discharging, pull-down and heat soak. It will be understood that the cycling operations can be performed under different operating conditions and/or different ambient conditions.

During the cycling operations, the temperatures measured by each of the first temperature sensors 14-n and each of the second temperature sensors 15-n are recorded. The resulting first and second temperature measurements T1, T2 are re-plotted from a ‘time-history’ format into a ‘cross-plot’ format. The first and second temperature measurements T1, T2 can thereby be displayed in a scatter-plot 16. The first temperatures T1 define a dependent variable; and the second temperatures T2 define an independent parameter. The thermal map 1 is generated in dependence on the scatter-plot 16.
A scatter-plot 16 is shown in Figure 7 by way of example. The first temperature measurements T1 (measured by the first temperature sensors 14-n) are plotted on the Y-axis and all of the second temperature measurements T2 (measured by the second temperature sensors 15-n) for each first measured temperature are plotted on the X-axis. Thus, for a given first measured temperature, the scatter-plot 16 comprises a range of second temperature measurements T2. In the scatter-plot 16 shown in Figure 7, for a second measured temperature of 30°C there is a corresponding range of first temperature measurements T1 from approximately 16°C to approximately 26°C. It will be appreciated that the scatter-plot 16 is provided by way of example and will vary for different battery modules 2. For a given second temperature, there is a maximum first temperature. In the above example for a second measured temperature of 30°C, there is a maximum first measured temperature of approximately 26°C.
The scatter-plot 16 can be analysed to determine an estimated first maximum temperature T1MAX for a given second temperature. The estimated first maximum temperature T1MAX can be determined for each first temperature in a range (typically corresponding to a temperature range for normal operation of the battery module 2). The scatter-plot 16 can be analysed to determine an estimated first average temperature T1AVG for a given second temperature. The estimated first average temperature T1AVG can be determined for each first temperature in a range (typically corresponding to a temperature range for normal operation of the battery module 2). Thus, the estimated first maximum temperature T1MAX and/or the estimated first average temperature T1AVG can be generated from the first and second temperature measurements T1, T2. It will be appreciated, therefore, that the estimated first maximum temperature T1MAX and/or the estimated first average temperature T1AVG can be extracted from the scatter-plot 16 to form the thermal map 1.

The thermal map 1 can comprise a look-up table which defines the estimated first maximum temperature and/or the estimated first average temperature for a given second temperature. A look-up table can be defined for each said second temperature sensor. Thus, the thermal map 1 can comprise multiple look-up tables. In use, the one or more look-up table can be accessed in dependence on a temperature measured by the corresponding second temperature sensor.
With reference to the scatter-plot 16, a second measured temperature of 30°C corresponds to an estimated first maximum temperature T1MAX of 26°C and an estimated first average temperature T1MAX of approximately 23°C.
The thermal map 1 is stored in the system memory 6 and can be accessed by said one or more electronic processor 5. In dependence on the thermal map 1 and the measured second temperatures, the BMS 4 is configured to estimate the internal temperature of the battery module 2. In particular, the one or more electronic processor 5 receives the second temperature measurements T2 from said second temperature sensors 5-n and accesses the thermal map 1 to identify the estimated first maximum temperature T1MAX and/or the estimated first average temperature T1AVG. The estimated first maximum temperature T1MAX can be used to monitor operation of the battery module 2, for example to determine if the internal temperature exceeds a predetermined operating threshold. The estimated first average temperature T1AVG can be used, for example, to determine a state of charge (SOC) of the battery module 2.
The method of generating the thermal map 1 comprises measuring the temperature at fewer of said second locations than said first locations. The test battery module 2 comprises more of said first temperature sensors 14-n than said second temperature sensors 15-n. The resulting thermal map 1 enables a relatively small number of said second temperature sensors 15-n to be used to estimate the temperature within the battery module 2. This simplifies the fabrication of the production battery module 2 since fewer of said second temperature sensors 15-n are required.
The battery module 2 can, for example, form part of a traction battery 17 for supplying electrical energy to one or more electric machine 18 to propel a vehicle 19, such as an

automobile. A schematic representation of the vehicle 19 incorporating traction battery 17 comprising a plurality of said battery modules 2 is shown in Figure 8. The battery modules 2 are electrically connected to each other to power the one or more electric machine 18. The thermal map 1 can be stored in the BMS 4 associated with each of the battery modules 2.
It will be appreciated that various changes and modifications can be made to the method and apparatus described herein without departing from the scope of the present invention. The thermal map 1 is described herein as being generated for a single test battery module 2, but a thermal map 1 could be generated for a plurality of test battery modules 2 or for the assembled traction battery 17.

WE CLAIM
1. A method of generating a thermal map (1) for estimating internal temperatures of
a battery module (2); the method comprising:
performing a plurality of cycling operations on a battery module (2) comprising one or more battery cell;
during said cycling operations, measuring a plurality of first temperatures (T1) at first locations and one or more second temperature (T2) at one or more second locations; and
cross-plotting the first temperatures (T1) measured at said first locations with the second temperatures (T2) measured at the one or more second locations.
2. A method as claimed in claim 1, wherein the first temperatures (T1) define a dependent variable in the thermal map (1); and the second temperatures (T2) define an independent parameter in the thermal map (1).
3. A method as claimed in claim 1 or claim 2 comprising, in dependence on the measured first temperatures (T1), defining a maximum first temperature estimate (T1MAX) for a given second temperature (T2).
4. A method as claimed in claim 3, wherein said maximum first temperature estimate (T1MAX) is defined for a range of second temperatures (T2) measured at said one or more second location.
5. A method as claimed in any one of the preceding claims comprising performing statistical analysis on the measured first temperatures (T1) for a given second temperature (T2).
6. A method as claimed in claim 5 wherein the statistical analysis comprises determining an average first temperature estimation (T1AVG) for a given second temperature (T2).

7. A method as claimed in any one of the preceding claims, wherein said operating cycles comprise at least first and second different operating cycles to generate a range of said first and second temperatures (T1, T2).
8. A method as claimed in any one of the preceding claims, wherein said operating cycles comprise one or more of the following: warm-up, charging, discharging, pull-down and heat soak.
9. A method as claimed in any one of the preceding claims, wherein said first locations are disposed within the battery module (2).
10. A method as claimed in claim 9, wherein said first locations comprise one or more of the following: between adjacent battery cells; and inside one or more of said battery cells.
11. A method as claimed in any one of the preceding claims, wherein the one or more second locations is external to the battery module (2).
12. A method as claimed in any one of the preceding claims, wherein more first temperatures (T1) are measured at said first locations than second temperatures (T2) are measured at said second locations.
13. A thermal map (1) generated by implementing the method claimed in any one of the preceding claims.
14. A battery monitoring system (4) having at least one electronic processor (5) coupled to system memory (6), wherein a thermal map (1) as claimed in claim 12 is stored in said system memory (6).
15. A battery monitoring system (4) as claimed in claim 14, wherein the at least one electronic processor (5) is configured to receive a temperature signal from one or more temperature sensors (15).

16. A battery monitoring system (4) as claimed in claim 15, wherein the at least one electronic processor (5) is configured to estimate an internal temperature of the battery module (2) in dependence on the received temperature signal and the thermal map (1).
17. A battery comprising at least one first battery module (2) connected to a battery monitoring system (4) as claimed in any one of claims 14, 15 or 16.
18. A battery as claimed in claim 17, wherein the first battery module (2) comprises one or more temperature sensor (15) disposed at said one or more second locations.
19. A battery as claimed in claim 18, wherein said one or more temperature sensor (15) are thermally connected to one or more bus bar (9) of the at least one battery module (2).
20. A battery module (2) comprising at least one battery cell, and a battery monitoring system (4) as claimed in any one of claims 14, 15 or 16.
21. A vehicle (19) comprising a battery as claimed in any one of claims 17, 18 or 19.
22. A battery module comprising a battery monitoring system (4) having at least one electronic processor (5) coupled to system memory (6), wherein a thermal map (1) as claimed in claim 12 is stored in said system memory (6).
23. A battery module (2) comprising:
one or more battery cell (3);
a battery monitoring system (4) having at least one electronic processor (5) coupled to system memory (6);
one or more temperature sensor (15) configured to measure an external temperature of said battery module (2);
wherein the at least one electronic processor (5) is configured to access a thermal map (1) stored in the system memory (6) to estimate an internal temperature of the battery module (2) in dependence on the measured external temperature of said battery module (2).

24. A method of estimating an internal temperature of a battery module (2), the
method comprising:
measuring an external temperature of said battery module (2); and
accessing a thermal map (1) to determine the internal temperature of the battery
module (2) in dependence on the measured external temperature of said battery module
(2).
25. A method substantially as herein described with reference to figures 2 to 8.
26. A battery module (2) substantially as herein described with reference to figures 2 to 8.