Patent Application
20180040864
The present invention relates to a battery pack for a handheld machine tool.
Generally, electrical handheld machine tools such as impact wrenches, drilling machines, angle grinders, jigsaws, circular saws or planing machines for the craftsmen or do-it-yourselfer use either an alternating current motor or a direct current motor as drive motor. While the former is usually supplied with an alternating current from the grid via a mains cable, the electrical energy for the supply of the direct current motor normally comes from what is known as a battery pack, i.e., a rechargeable accumulator in a housing that is able to be coupled with the housing of the handheld machine tool and is electrically connected to the current supply lines of the direct current motor when the two housings are coupled.
Such conventional battery packs include rechargeable accumulators, normally a plurality of battery cells connected in a parallel and/or series circuit. Herein, such a battery pack therefore denotes a battery pack that is preferably made up of a plurality of electrically interconnected battery cells. This battery pack is able to store electrical energy, supplies the energy for the operation of the handheld machine tool, and is accommodated in an exchangeable manner in a chamber, an interface or the like of the handheld machine tool. The allocation of the battery pack to the handheld machine tool is implemented by inserting or sliding the battery pack into a complementary insert bushing of the device housing. The battery pack is able to be coupled with the device housing of the handheld machine tool in such a way that the electric tool is electrically coupled with the battery pack and mechanically locked when the two housings are coupled. The electrical contacting normally takes place in the region of the locking device.
The battery packs have the disadvantage that each battery cell experiences heat losses both during the current delivery and the current draw, which may lead to an increased temperature of the entire battery block. To prevent damage to the battery cell and/or the battery block, heat losses must be dissipated in a reliable manner on the one hand, and heating of the battery pack at low outside temperatures must be possible on the other, which is advantageous especially in the case of cells that are chemically based on lithium.
In addition, such battery packs have housings that are made of plastic materials for the most part. Plastic materials generally used for battery pack housings include acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), or polyamide (PA). These plastic materials have excellent mechanical properties and adequate thermal conductivity, which makes them suitable for use as battery pack housings for most of the battery cells that are currently on the market, such as lithium-ion cells. However, these have the disadvantage of providing good thermal insulation. This is not desired in a battery pack inasmuch as the heat created during the operation or charging of the battery pack is to be dissipated as quickly as possible.
Moreover, the development of more recent battery packs goes in the direction of a greater power output, meaning that the heat losses are becoming greater as well; as a result, more heat is generated in the interior of the housing and must be dissipated into the environment more rapidly so as to avert overheating of the battery cells.
In addition, more and more battery pack housings are developed in tightly sealed form for the most part in order to prevent the entry of moisture, which means that the heat dissipation must take place through the wall of the housing.
It is an object of the present invention to mitigate the aforementioned disadvantages and to provide a battery pack for a handheld machine tool that features a more optimal dissipation of the generated heat losses. The battery pack according to the present invention may also offer excellent ergonomics and assembly capabilities and have a cost-effective and uncomplicated structure.
Advantageous refinements, variants and further developments of the present invention are described herein.
According to the present invention, an example battery pack for a handheld machine tool includes a cell holder and at least one battery cell; the cell holder accommodates the at least one battery cell, and the battery cell has a lateral area that extends parallel to a longitudinal axis x. The lateral area is delimited by two end faces disposed at a right angle to longitudinal axis x, at which the electrical poles of the battery cell are situated. At least one elastic, heat-conductive insert is disposed between at least one end face of the battery cell and a wall of the battery pack housing extending essentially parallel to the end face of the battery cell. The elastic, heat-conductive insert is in thermal contact with the end face of the battery cell and dissipates heat from the battery cell in the direction of the wall of the battery pack housing. It is advantageously provided that the elastic, heat-conductive insert is situated between the end face of the battery cell and a wall of the battery pack housing that is situated essentially at a right angle to longitudinal axis x of the battery cell.
In one particularly preferred specific embodiment of the present invention, at least one heat distribution element is disposed between the at least one elastic, heat-conductive insert and the wall of the battery pack housing, in the region of the at least one end face of the at least one battery cell. The heat distribution element is in thermal contact with the elastic, heat-conductive insert and with the wall of the battery pack housing and ensures an even application of heat to the wall of the battery pack housing.
It may be advantageous to produce the at least one heat-conductive insert at least partially from a thermally conductive material that belongs to at least one of the material groups of elastomers, thermo-plastic elastomers, or carbon fibers. The plastic materials such as acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), or polyamide (PA), e.g., PA6 or PA12, usually have good mechanical properties and an adequate thermal conductivity of 0.17 W/mK (ABS), 0.21 W/mK (PC), and 0.29 W/mk (PA6). This makes them suitable for use as battery pack housings for most of the battery cells that are currently on the market. According to the present invention, the heat-conductive insert has a thermal conductivity that is greater than 0.15 W/mK, and preferably greater than 0.20 W/mK, and most preferably, lies between 0.20 W/mK and 0.50 W/mK. If the thermally conductive insert has a wall thickness of less than 1 mm, the thermal conductivity may also be less than 0.15 W/mK, and preferably may amount to exactly 0.15 W/mK. Preferably, the heat-conductive insert has a Shore hardness of less than 50 Shore A, and preferably of between 20 Shore A and 45 Shore A.
According to an example embodiment of the present invention, the heat distribution element is at least partially made of a metal, preferably an aluminum or a magnesium alloy, or of a heat-conducting plastic. The heat distribution element advantageously is a planar component having a length L, a width B, and a thickness D. Thickness D is small in comparison with length L and width B, and heat distribution element has a plurality of recesses distributed across its surface. This makes it possible to dissipate the heat to be carried away in an especially advantageous manner such that it is distributed across the battery pack housing.
In one preferred specific embodiment, the heat distribution element is developed as a metal foil having a thickness of between 0.1 mm and 0.5 mm, and preferably of between 0.01 mm and 0.3 mm, or it is developed as a graphite layer at a thickness of between 0.1 mm and 0.5 mm, and preferably of between 0.01 mm and 0.1 mm.
Therefore, it is especially advantageous if the heat-conductive insert is developed as an elastic foil having a thickness of between 0.1 mm and 1.4 mm, preferably of between 0.2 mm and 1.2 mm, and most preferably, of between 0.3 mm and 1.0 mm. This is advantageously in particular if the heat-conductive insert and the heat distribution element are developed as a composite part, and especially as a foil composite part.
In an advantageous manner, the cell holder at least regionally forms an outer side of the first housing component and/or the second housing component of the battery pack housing. In an especially preferred specific embodiment, the cell holder forms the second housing component in its entirety. Here, the battery pack housing preferably has at least two side components, which keep the first housing component and the second housing component together in the assembled state of the battery pack in such a way that a detachment of the first housing component from the second housing component, or vice versa, is prevented.
In this context it is possible that the side components are at least partially made from a metal, preferably an aluminum or a magnesium pressure casting. In this case, a reliable insulation insert has to be used between the battery cells and the side components; it is possible, for example, to use the elastic, heat-conductive insert as insulation inserts.
In another further development of the present invention, the battery pack has two elastic heat-conductive inserts. A heat-conductive insert together with a side component is produced by a 2K injection molding method in each case, preferably in a common working step and in integrated form, in particular. It is advantageous here if the side components are made of the same material as the rest of the battery pack housing, preferably a polyamide.
The cell holder advantageously accommodates two or more battery cells, which are connected by at least one cell connector in a parallel and/or series circuit. The at least one cell connector is situated between an end face of the battery cells and the elastic, heat-conductive insert.
The at least one cell connector advantageously connects at least two or more battery cells, and preferably four battery cells, and most preferably, six battery cells to one another. In a preferred embodiment variant, the cell connector has a large surface such that the cell connector essentially covers the end faces of the battery cells that are connected to each other, and in this way assumes the function of the heat distribution element. It is possible in this context that the heat distribution element and the cell connector are developed as a composite part, and as an integrally developed composite part, in particular. In areas in which no heat transfer is desired and in which a heat transfer is to be prevented as far as possible, the cell connector includes slot-type recesses, so that the heat losses transferred from the battery cells to the cell connectors in a pointwise manner are able to be distributed to the entire surface and are transferred to the elastic element and/or to the side components. In an especially advantageous further development, the elastic, heat-conductive insert is at least regionally in direct thermal contact with the cell connectors.
The battery pack according to the present invention may be connected to a handheld machine tool in a detachable manner. Accordingly, provided it is connected to a battery pack according to the present invention, a handheld machine tool constitutes another subject matter of the present invention. The battery pack used in the handheld machine tool is employed as a drive of the handheld machine tool.
Lithium-ion cells, in particular, may be used as battery cells because in the case of lithium-ion cells, in particular, it is possible to combine a plurality of battery cells into battery cell blocks in which multiple battery cells are connected in a parallel circuit. It is especially advantageous here that the cell holder is able to accommodate battery cells having different diameters and lengths, thereby allowing the cell holder or the cell carrier to be used in a variety of battery packs.
Within the framework of the present application, a handheld machine tool generally denotes all handheld machine tools having a tool carrier that is able to be set into rotation or translation and is able to be driven directly by a drive motor via a transmission or a planetary gear, e.g., straight drills, cordless drills, impact wrenches, multi-function tools, saws, scissors, grinders and/or combination drills, for example. In this context, the transmission of electrical energy is to be understood specifically in such a way that the handheld machine tool is supplied with energy by way of the battery pack.
Additional features, application possibilities and advantages of the present invention result from the description of the exemplary embodiments of the present invention below, which are depicted in the figures. It should be noted that the illustrated features are merely of a descriptive nature and may also be used in combination with features of other further developments described in the previous text. They are also not intended to limit the present invention in any shape or form.
The present invention is described in greater detail in the below on the basis of preferred exemplary embodiments, where the same reference numerals have been used for the same features.
When battery pack 100 is mounted on handheld machine tool 300, receiving means provided on handheld machine tool 300, e.g., guide grooves and guide ribs, are brought into engagement with corresponding guide elements 110 of battery pack 100. For this purpose, battery pack 100 is inserted in a sliding direction y along the receiving means of handle 315. Battery pack 100 is slipped into the battery pack receptacle of a handheld machine tool 300 along a lower outer surface 316 of handle 315, said surface being aligned essentially at a right angle to the longitudinal direction of handle 315. In the position shown in
For the detachable mounting of battery pack 100 on a handheld machine tool 300 or on a charge device, battery pack 100 is equipped with an interface 180 for a detachable mechanical and electrical connection to a corresponding interface 380 of handheld machine tool 300 or to a corresponding interface of the charge device. When battery pack 100 is mounted, receiving means, e.g., guide grooves and guide ribs, of handheld machine tool 300 or of the charge device, for the accommodation of the corresponding guide elements of battery pack 100, are brought into an engagement therewith, battery pack 100 being inserted in a contacting direction y along the receiving means, and interface 180 of battery pack 100 being inserted into corresponding interface 380 of handheld machine tool 300 or into the corresponding interface of the charge device. Via interfaces 180, 380, battery pack 100 is able to be allocated to handheld machine tool 300 and/or the charge device.
For the locking of battery pack 100 on handle 315, battery pack 100 is slipped along handle 315 in a sliding direction y, i.e. along a lower outer surface of handle 315 that is aligned essentially at a right angle to the longitudinal direction of handle 315. In the position shown in
As is shown in
In the specific embodiment shown in
In addition, cell connectors 500, by which an electrical connection of battery cells 400 among one another in a parallel and/or series circuit is able to implemented, are shown in
It can furthermore be gathered from
In those regions where the heat transfer is undesired and is to be prevented as much as possible, heat distribution element 660 includes a plurality of recesses 665. These recesses are distributed across the entire surface of heat distribution element 660, one recess 665 being provided for each battery cell 400 in the illustrated specific embodiment. This makes it possible to ensure that the heat losses transferred in a pointwise manner from battery cells 400 to elastic element 650, which is in thermal contact with battery cells 400, are able to be transferred directly to immediately adjoining heat distribution element 660, which is in thermal contact with elastic element 650. Because of recesses 665, heat distribution element 660 distributes the heat losses, which are transferred in a relatively punctual manner, to the entire surface of respective side components 125 of battery pack housing 110, heat distribution element 660 also being in direct thermal conduct with respective side component 125.
Elastic element 650 may be in direct thermal contact with respective side component 125. As can be gathered from
As is clear from
In the large-surface cell connectors shown in
In addition to the described and illustrated specific embodiments, additional specific embodiments that may encompass additional modifications as well as combinations of features are possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 204 055.0 | Mar 2015 | DE | national |
| 10 2015 218 261.4 | Sep 2015 | DE | national |
| 10 2016 203 424.3 | Mar 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/054506 | 3/3/2016 | WO | 00 |
