Patent Application
20220123412
This application relates to a battery pack, and in particular to a power tool battery pack having a structure for effective cooling of battery cells.
Electric tools include an electric motor and require a source of electricity to power the motor. Electric tools may be broken down into two groups: (1) corded electric tools that source electricity through a cord plugged into a source of alternating current and (2) cordless electric tools that source electricity from a battery. Cordless electric tools may be broken down into two groups: (1) tools that use an internal, integrated battery and (2) tools that use a removable battery pack.
The cordless electric tools that use a removable battery pack and the removable battery pack that provides electricity (energy/power) to a cordless electric tool requires an interface between the tool and the pack. The tool includes a tool portion/aspect/element of the combination interface and the pack includes a pack portion/aspect/element of the combination interface. The interface allows the tool and the pack to couple/mate and decouple/unmate with each other such that when the tool and the pack are coupled/mated the pack will provide power to the tool and will stay affixed to the tool during operation of the combination.
The interface is configured and defined such that only tools and packs that are intended to work with each will be able to fully couple/mate. Particularly, different tool and pack manufacturers configure and define the interface between their tools and packs such that a tool of one manufacturer will not fully couple/mate with a battery pack of another manufacture. In some configurations, the interface may include one or more guide rails that allow insertion of the battery pack along a receiving axis until electrical contact is made between battery terminals and a terminal block of the tool.
A battery pack typically includes a series of battery cells connected in a series, parallel, or series/parallel configuration. The battery cells may be electrically connected in series to increase the voltage rating of the battery pack, in parallel to increase the current and/or charge capacity of the battery pack, or a combination of series and parallel configuration. For example, a battery pack marketed as a 20V Max battery pack in the power tool industry with a nominal voltage of approximately 18V may include a single string of five battery cells (5S1P), or multiple such strings of five battery cells connected in parallel (5SxP, where x>1). The battery pack current capacity may be increased by increasing the number of parallel strings of battery cells. In this example, the parallel connections are made at the ends of the strings, though it should be understood that parallel connections may be made at any point within the strings or even between each cell. In an embodiment, the battery pack may be a convertible battery pack where the strings of cells may be switchable configured in series or parallel depending on the voltage requirement of the power tool. U.S. Pat. No. 9,406,915, which is incorporated herein by reference in its entirety, describes examples of such a convertible battery pack.
Battery cells may be made of, for example, lithium or lithium ion material. Battery cells are typically cylindrical in shape and are arranged in parallel within the battery pack housing. Battery cells generate heat during use, particularly in applications where the power tool draws significant amount of current from the battery pack. A thermistor is typically provided within the battery pack to monitor the temperature of the battery cells. The thermistor may generate a voltage signal corresponding to the temperature. This signal may be sent to the power tool to cut off battery pack discharge, or it may be sent to a switch provided within the battery pack to cut off flow of current, when the battery pack temperature exceeds a temperature threshold. However, with increased use of battery packs with high-power power tools and increase in manufacturing of higher current and higher capacity battery cells, the temperature of the battery pack can frequently exceed the temperature threshold of the cells prior to completely discharging the cells. When this condition occurs, the battery pack must cool down prior to being used or charged. Therefore, an effective mechanism for thermal management and proper cooling of the battery cells within the battery pack is needed.
An aspect of the present invention includes a battery pack. An exemplary embodiment of the battery pack includes features for addressing increases in temperature of the battery pack and battery cells housed in the battery pack.
A first embodiment of a battery pack may include a housing, a battery core, positioned in the housing. The battery core may include a set of battery cells and a battery cell holder. The battery cell holder may include a set of battery cell receptacles, a set of halfpipes, and a set of channels. The set of battery cells may be received in the set of battery cell receptacles. Each battery cell receptacle of the set of battery cell receptacles may include a planar base. The set of halfpipes may be arranged adjacent to the planar base. A channel of the set of channels may be formed between adjacent halfpipes.
The aforementioned first embodiment may include a configuration wherein a channel of the set of channels is formed on both sides of each halfpipe of the set of halfpipes.
The aforementioned first embodiment may include a configuration wherein the battery cells of the set of battery cells have a longitudinal axis and a length along the longitudinal axis, at least one of the halfpipes of the set of halfpipes have a length approximately equal to the length of the battery cells, and at least one of the channels of the set of channels have a length approximately equal to the length of the battery cell and the length of the halfpipe.
In the aforementioned first embodiment the at least one of the channels of the set of channels has a substantially triangular cross section.
In the aforementioned first embodiment each battery cell is in direct contact with at least one of the battery cell receptacles of the set of battery cell receptacles.
In the aforementioned first embodiment the at least one battery cell receptacle of the set of battery cell receptacles includes an upper portion and a lower portion.
In the aforementioned first embodiment the upper portion faces the lower portion.
In the aforementioned first embodiment the halfpipes of the upper portion and the halfpipes of the lower portion form cylindrical chambers sized to form-fittingly receive at least one battery cell of the set of battery cells.
In the aforementioned first embodiment the set of battery cell receptacles has two battery cell receptacles.
In the aforementioned first embodiment at least one channel of the set of channels is formed adjacent to the planar base.
In the aforementioned first embodiment at least one channel of the set of channels extends along the length of the halfpipe and between lower portions of adjacent halfpipes.
In the aforementioned first embodiment the phase change material is Polyethylene Oxide (PEO).
In the aforementioned first embodiment the phase change material is paraffin wax.
The aforementioned first embodiment may also include a set of plugs, a plug of the set of plugs plugged into an end of at least one of the channels of the set of channels.
In the aforementioned first embodiment the phase change material is Polyethylene Oxide (PEO).
In the aforementioned first embodiment the phase change material is paraffin wax.
In the aforementioned first embodiment the phase change material is a solid material having a melting temperature below a maximum temperature rating of the battery cells of the set of battery cells.
The aforementioned first embodiment may also include at least one channel of the set of channels being closed-ended on a first end and open-ended on a second end to receive the phase change material.
In the aforementioned first embodiment the phase-change material is pre-molded as an elongated bar with a substantially triangular cross-sectional shape and sized to be form-fittingly received at least one of the channels of the set of channels.
In the aforementioned first embodiment the phase-change material is poured into at least one channel of the set of channels in liquid form and allowed to solidify.
The aforementioned first embodiment may also include a set of plugs, a plug of the set of plugs plugged into the open-ended second end of the at least one channel of the set of channels.
These and other advantages and features will be apparent from the description and the drawings.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of this disclosure in any way.
The following description illustrates the claimed invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the disclosure, describes several embodiments, adaptations, variations, alternatives, and uses of the disclosure, including what is presently believed to be the best mode of carrying out the claimed invention. Additionally, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
In this conventional battery core 52, each of the battery cells 50 is in physical contact with the main housing 54 (including the posts 68) on one end and the battery cap 65 (including its posts) on the other end. The remaining surface area of each battery cell 50, which constitutes the significant majority of the surface area, is surrounded by air contained within the battery core 52. Air has been found to have a relatively low thermal conductivity and a relatively low specific heat capacity. Thermal conductivity refers to a measure of the ability of the material to conduct heat, and specific heat capacity refers to the amount of heat required to raise the temperature of a unit of mass of a given material by a given amount. The higher the thermal conductivity of a material, the quicker it can transfer heat away from one medium to another. The higher the specific heat capacity of a material, the more heat it can absorb from the surrounding medium. Air therefore is not very effective at carrying heat away or absorbing heat from the battery cells 50 in the conventional battery core 52 described above. In fact, it has been found that even materials such as plastic, that are commonly considered to be thermally insulative have much greater thermal conductivity and specific heat capacity than air and are better suited to carry heat away or absorb heat from the battery cells.
An obvious solution is to place metal heat sinks in contact with battery cells within the battery pack. However, metals are electrically conductive and undesirable in low impedance circuits present in lithium battery packs, where the presence of a metal may cause interference and/or electrical shortage. Also, metals such as brass have very high level of thermal conductivity and very low specific heat capacity, and therefore can reach the temperature level of the battery cells too quickly and without absorbing significant heat from the battery cells. Such metals can only be effective for heat transfer if they are exposed to outside environment via, for example, a heat sink including external fins on the battery pack housing. Even then, due to very high thermal conductivity of the heat sink, the fins need be shielded from direct contact by the user.
Embodiments of the invention as described in this disclosure offer solutions for capturing battery cells in material having suitable levels of thermal conductivity and/or specific heat capacity to improve thermal performance of battery packs.
An embodiment of the invention is described herein with reference to
As shown in these figures, the cell holder 110 (and the battery cell receptacles in particular) is sized and shaped to be in direct contact with the battery cells 50. The upper portion 111a and the lower portion 111b of the cell holder 110 are stacked to form cylindrical battery cell chambers sized to form-fittingly receive the battery cells 50 therein. The cell holder 110, particularly the battery cell receptacles 111, increases the surface contact of the battery cells 50 with plastic material rather than air, thus increasing the overall thermal efficiency of the battery pack.
In an example embodiment, a set of two battery cell receptacles 111 are provided for two rows of battery cells 50. As the upper portion 111a and the lower portion 111b of the battery cell receptacle 111 are generally the same, only the lower portion 111b will be described in detail below. These elements may also be found on the upper potion 111a. The lower portion 111b of the battery cell receptacles 111 include a planar base 112 and a set of halfpipes 114 arranged adjacently on the planar base 112. The elongate channels 116 may be formed between two adjacent halfpipes 114. The elongate channels may be formed adjacent to the planar base 112. The channels 116 have substantially triangular cross-sectional shapes and extend between lower portions of adjacent halfpipes 114. The upper portion 111a and the lower portion 111b of the cell holders 110 are stacked with halfpipes 114 facing each other forming cylindrical chambers sized to form-fittingly receive the battery cells 50. For a battery pack including multiple rows of battery cells 50, two battery cell receptacles 111 may be stacked on top of each other.
This arrangement significantly reduces, and in fact almost eliminates, surface contact between the battery cells 50 and air within the battery core 100. In an embodiment, the battery cell receptacles 111 are made of plastic material that possess material strength to provide structural support for the battery cells 50, but also possess thermal properties for efficient cooling of the battery cells. An example of such material is HDPE (High Density Poly-Ethylene), which has a thermal conductivity of 0.42 W/mK and specific heat capacity of 2.25 J/gK. By comparison, air has a thermal conductivity of 0.025 W/mK and specific heat capacity of 1 J/gK. Other examples of preferred plastic material for this application include GFN (Glass-Filled Nylon), which has a thermal conductivity of 0.35 W/mK and specific heat capacity of 1.5 J/gK, and PC-ABS (Polycarbonate/Acrylonitrile-Butadiene-Styrene Terpolymer Blend), which has a thermal conductivity of 0.2 W/mK and specific heat capacity of 2 J/gK. It was found that use of any of these materials, in particular HDPE, significantly improves thermal efficiency of the battery pack.
In an embodiment, the channels 116 may be provided as air pockets. Alternatively, the channels 116 may be filled with any of the plastic material described above. In an example embodiment, the plastic material within the channels 116 may be the same as or different from the plastic material used for construction of the battery cell receptacles 111.
In yet another example embodiment, as described herein with reference to
In an example embodiment, the phase change material is a solid material having a melting temperature below the maximum temperature rating of the battery cells 50. In an example embodiment, the phase change material also includes a high heat of fusion (also known as enthalpy of fusion), which enables it to absorb a significant amount of heat from the battery cells 50 when its melting temperature is reached. An example of such material is paraffin wax, which has a melting point of approximately between 46° C. to 68° C., preferably approximately 50° C. to 55° C. Paraffin wax has a thermal conductivity of approximately 0.18 W/mK to 0.25 W/mK, which is lower than the plastic material discussed above, and a specific heat capacity of 2.1 J/gK to 3.26 J/gK, which is higher than most of the plastic material discussed above. Importantly, paraffin wax has a heat of fusion of between 200 J/gK to 270 J/gK, allowing it to absorb a significant amount of heat at approximately its melting point.
As shown in these figures, the channels 116 of the battery cell receptacle 111b may be closed-ended on a first end and open-ended on a second end to receive the phase change material 126 therein. In an example embodiment, the phase-change material 126 may be pre-molded as elongated bars with substantially triangular cross-section shapes and sized to be form-fittingly received in the channels 116. Alternatively, the phase-change material 126 may be poured into the channels 116 in liquid form and allowed to solidify.
In an example embodiment, an end cap 120 is mounted at the second end of the battery cell receptacle 111b to seal the phase-change material 126 within the channels 116. In an example embodiment, the end cap 120 includes a set of plugs 122 shaped to be securely plugged into second, open-ends of the battery cell receptacle 111b to form a liquid-tight seal around the phase-change material 126.
As discussed above, the phase-change material 126 may be any material having a melting temperature below the maximum temperature rating of the battery cells 50. While paraffin wax and similar phase-change material are highly effective in absorbing heat from the battery cells 50 at their melting points, they are susceptible to high thermal expansion in liquid form. Paraffin wax can expand by approximately 10% in volume when changing phase and becomes a low viscosity fluid. In an example embodiment, the length and/or volume of the phase-change material 126 within each of the channels 116 is approximately 50% to 90% smaller, preferably 60% to 80% smaller, than the length and/or volume of each of the channels 116 to provide air pockets for expansion of the phase-change material 126. Disposition of the phase-change material 126 within the channels 116 in this manner allows for controlled expansion of the material without potential damage to the battery cells 50 or the battery pack housing.
Another example embodiment may use a composite phase change material which is shape stable, such as polyethylene glycol (PEG). A formed geometry of this or other phase change material can be disposed within the channels 116 to absorb significant heat from the battery cells. An advantage of this design is to utilize the improved structure of the cell holder 110 to mechanically support the battery cells while also transferring heat effectively to the phase change material.
Another example embodiment may use heat absorbing materials such as graphite, metals or composites disposed within the channels to absorb heat without directly touching the battery cells. These materials can also be designed to transfer heat to external surfaces of the battery pack where there are more substantial surface areas and exposure to cooling air.
In another example embodiment, the heat absorbing materials used to fill the channels 116 may vary based on the channel location within the cell holder. Alternatively, some of the channels may remain unpopulated. In other words, these channels are filled with air or filled with the plastic material of the cell holder 110 during the molding/forming process.
An alternative example embodiment of the invention is described herein with reference to
As shown in these figures, the circuit board 230 includes a series of slots that allow the connectors 232 and 234 to project upwardly therethrough. The periphery of the connectors 232 and 234 may be soldered or glued to provide an airtight and/or watertight seal between the connectors 232 and 234 and the circuit board 230.
In an embodiment, two connectors 232a, 232b are coupled to B+ and B− nodes of the battery cells 242, respectively and each connector 234a, 234b, 234c, 234d is coupled to one the nodes between electrically adjacent battery cells 242 to sense voltages of each of the battery cells 242. In an embodiment, each of the connectors 232 and 234 are coupled to ends of the battery cells 242, extend over the battery core 240, and extend perpendicularly upwardly through the slots of the circuit board 230. In this manner, connectors 232 and 234 have some flexibility to move away from the battery core 240 with upward movement of the circuit board 230.
In an embodiment, the circuit board 230 also includes a series of peripheral slots 236 that improves molding of the flexible inner wall 220 around the circuit board 230. In an embodiment, the molding process of the flexible inner wall 220 forms a groove 226 around the opening 222 that receives the peripheral area (slots/wall/rails) of the circuit board 223 and allows the mold material to flow through the peripheral slots 236. This arrangement provides an airtight and/or watertight seal between the circuit board 230 and the flexible inner wall 220.
In an embodiment, the lower housing 202 includes an upper peripheral groove 218 that receives a peripheral wall 224 of the flexible inner wall 220, forming an airtight and/or watertight tongue and groove seal between the lower housing 202 and the flexible inner wall 220.
In an embodiment, the phase-change material 250 may be poured into the lower housing 202 in liquid form and allowed to solidify around the battery core 240. Alternatively, the phase-change material 250 may be pre-molded around the battery core 240 prior to insertion into the lower housing 202. In yet another embodiment, the phase change material 250 may be pre-molded in a shape capable of receiving the battery core 240 therein in the assembly process.
While phase-change materials such as paraffin wax are highly effective for thermal management of battery cells, sealing and containment of the material to account for thermal expansion does present challenges and added costs. In the embodiment of
To overcome these challenges, in an embodiment, the phase-change material may be crystalline-to-amorphous phase-change material having a crystalline-to-amorphous transition point that is lower than the maximum temperature rating of the battery cells 50. An example of such material is Polyethylene Oxide (PEO). PEO has a specific heat capacity comparable to paraffin wax, but it has significant heat of fusion of approximately 120 J/gK, which is approximately half that of paraffin wax. Although PEO is not as effective at absorbing heat from the cells, its volumetric expansion is small and almost negligible. This allows PEO to be used in fixed volume containers without risking damage due to pressure caused by the volume change when changing phase.
Referring once again to
In an alternative embodiment, as described herein with reference to
As shown in these figures, the main housing 310 of the battery core 300 includes a rear wall 312 having a set of openings 314 aligned with a set of terminals 332 of the battery cells 330. The set of openings 314 may have a smaller area than a cross-sectional area of the battery cells 330 such that the peripheral body of each battery cells 330 comes into contact with the rear wall 312. Similarly, a core cap 320 includes a front wall 322 having a set of openings 324 aligned with the set of terminals 332 of battery cells 330. The openings 324 have a smaller area than a cross-sectional area of the battery cells 330 such that the peripheral body of each of the battery cells 330 comes into contact with the front wall 322.
In an embodiment, positioned between rows of battery cells 330 on one end (i.e., a rear end) are a series of annular rims 316a provided on the main housing 310 offset with respect to the openings 314. Similarly, positioned between rows of battery cells 330 on the other end (i.e., front end) are a series of annual rims 326a provided on the core cap 320 offset with respect to the openings 324. Further, positioned between the walls of the main housing 310 and the rear end of the battery cells 330 are a series of semi-annular rims 316b offset with respect to the openings 314. Similarly, positioned between the walls of the core cap 320 and the front end of battery cells 330 are a series of semi-annular rims 326b offset with respect to the openings 324. The rims 316a and 316b are sized to axially project into the gap between the battery cells 330 by approximately 1-2 mm on the rear end of the battery cells 330, and the rims 326a and 326b are sized to axially project into the gap between the battery cells 330 by approximately 1-2 mm on the front end of the battery cells 330. The rims 316a, 316b, 326a, and 326b cooperate structurally to support the battery cells 330 within the battery core 330 while maintaining openings between adjacent battery cells 330.
In an embodiment, the phase-change material 350 is provided within the battery core 300 for absorption of heat directly from the battery cells 330 without an intermediary plastic component. In an embodiment, the phase-change material 350, as discussed above, is preferably crystalline-to-amorphous phase-change material such as PEO with limited thermal expansion. In an embodiment, the phase-change material 350 is pre-molded in the shape depicted in
In an embodiment, the core cap 320 is then mounted on the open end of the main housing 310 to form an enclosure around the battery cells 330 and the phase-change material 350. Once the core cap 320 is mounted, the battery cells 330 make direct contact with the rear wall 312 of the main housing 310 and the front wall 322 of the core cap 320. This contact forms a seal tight enough to prevent flow of the phase-change material 350 out of the battery core 300 even in its amorphous state. In an embodiment, a glue or other sealant may be provided to strengthen the seal between the battery cells 330 and the rear and front walls 312 and 322.
As background, each of the battery packs uses the same type of Li-Ion battery cell—these example battery packs use Samsung 50S battery cells. These battery cells have an undervoltage or discharge threshold of approximately 2 volts, under load. Other battery cells may have other discharge thresholds. Such battery cells are within the scope of this application. These example battery cells are connected in a 5S2P configuration. As such, a battery pack having five of these cells in series will have an undervoltage or discharge threshold of approximately 10 volts. This undervoltage or discharge threshold is the value at which when the battery pack discharges through this threshold, the battery pack is configured to shut itself down so that the battery pack, and more specifically, the battery cells are not damaged by over discharging. As described above, the battery pack is also configured to shut itself down if the temperature of the pack or the cells exceeds a temperature threshold, for example 70° C. Also, as discussed above, if the battery pack or battery cells exceed the temperature threshold—and therefore shuts down—before the battery pack delivers or discharges its capacity, i.e., reaches its undervoltage threshold, the pack is effectively leaving energy unused. This reduces the efficiency of the user. As such, it is very desirable to have a battery pack that reaches its discharge threshold before it reaches its overtemperature threshold.
These example battery packs may be discharged at a 30-ampere constant current using a Kikusiu PLZ 1004W electronic load in relatively still ambient air of approximately 20° C.
The first example battery pack is a conventional battery pack (F) of the type described above and illustrated in
The second example battery pack is an HDPE type battery pack (G) of the type described above and illustrated in
The third example battery pack is a PEO plug-type battery pack (H) of the type described above and illustrated in
The fourth example battery pack is a PEO filled cell holder type battery pack (I) of the type described above and illustrated in
The fifth example battery pack is a wax potted type battery pack (J) of the type described above and illustrated in
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
Numerous modifications may be made to the exemplary implementations described above. These and other implementations are within the scope of this application.
This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63/094,445, filed Oct. 21, 2021, titled “Battery Pack.”
| Number | Date | Country | |
|---|---|---|---|
| 63094445 | Oct 2020 | US |
