Protective battery casing

A casing has an interior space in which a battery can be fitted. The casing comprises a plurality of walls that encapsulate the interior space. A wall comprises an assembly of wall elements arranged as layers. This wall assembly includes a protective wall element comprising electrically conductive material, such as, for example, carbon fibers. The wall assembly further includes a set of electrically insulating wall elements located between the protective wall element and the interior space.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This is a National Stage Entry into the United States Patent and Trademark Office from International PCT Patent Application No. PCT/EP2015/051420, having an international filing date of Jan. 23, 2015, which claims priority to European Patent Application No. EP 14305099.5, filed Jan. 23, 2014, the entire contents of both of which are incorporated herein by reference.

FIELD OF THE INVENTION

An aspect of the invention relates to a casing having an interior space in which a battery can be fitted. The casing may be included in, for example, a vehicle for housing a battery capable of electrically propelling the vehicle. Other aspects of the invention relate to an assembly comprising a casing and a battery fitted within the casing, and to an electrically propelled vehicle.

BACKGROUND OF THE INVENTION

A vehicle, such as, for example, a car, may be propelled electrically. This requires the vehicle to have an electrical energy source, which is typically in the form of a battery. The battery may be fitted in a protective casing that provides fire protection. There may be a risk that the battery catches fire if, for example, the battery is overcharged or malfunctions otherwise. The protective casing may prevent this fire from reaching combustible material in the vehicle, or even explosive material such as, for example, fuel.

A protective battery casing should preferably be lightweight for reasons of, for example, power efficiency. Light weight may also contribute to performance, in terms of speed and acceleration. Carbon fiber-based composites are relatively lightweight and relatively heat resistant, and also relatively strong and stiff. A protective battery casing may thus comprise carbon fiber-based composites. For example, a protective battery casing may comprise walls that have a layered structure including carbon fibers in epoxy resin.

SUMMARY OF THE INVENTION

There is a need for a solution that alto is satisfactory protection against electrocution.

In order to better address this need, the following points have been taken into consideration. A battery in an electrically propelled vehicle may provide a relatively high output voltage, which could electrocute a person if he or she were to contact an element receiving this high output voltage. A carbon fiber-based composite may provide some electrical insulation although carbon fibers are electrically conductive. For example, carbon fibers may be embedded in epoxy resin, which can be considered as an electrically insulating material.

However, a protective battery casing comprising carbon fibers, or another conductive material, may get damaged in, for example, an accident. A wall of the protective battery casing may structurally degrade such that some carbon fibers are at least partially denuded, that is, are no longer embedded in epoxy resin or other insulating material. These denuded carbon fibers may contact the battery directly, or indirectly through a conductive element that electrically contacts the battery. A person who touches the protective battery casing may thus risk touching denuded carbon fibers that electrically contact the battery. These touchable carbon fibers may therefore be under relatively high voltage. There is thus risk of electrocution.

In accordance with an aspect of the invention, there is provided a casing having an interior space in which a battery can be fitted, the casing comprising a plurality of walls that encapsulate the interior space, whereby a wall comprises an assembly of wall elements arranged as layers, the assembly including:a protective wall element comprising electrically conductive material; anda set of electrically insulating wall elements located between the protective wall element and the interior space and bounding the interior space, the set of electrically insulating wall elements comprising:a flexible electrically insulating wall element; anda rigid electrically insulating wall element located between the flexible electrically insulating wall element and the interior space, so that the flexible electrically insulating wall element is sandwiched between the protective wall element and the rigid electrically insulating wall element.

Other aspects of the invention concern an assembly comprising a casing as defined hereinbefore and a battery fitted within this casing. Yet another aspect of the invention concerns an electrically propelled vehicle comprising a casing as defined hereinbefore.

In each of these aspects, the set of electrically insulating wall elements provides protection against electrocution following, for example, an accident as described hereinbefore. Moreover, the set of electrically insulating wall elements provide protection against a dielectric breakdown in the casing, which also presents a risk of electrocution. In addition, the set of electrically insulating wall elements may prevent a short circuit in the battery if, for example, a battery cell breaks away due to, for example, a shock. The battery cell will collide with the set of electrically insulating wall elements, rather than with a conductive part that could cause a short circuit.

An embodiment of the invention may comprise one or more additional features defined in the dependent claims, which are appended to the description.

For the purpose of illustration, a detailed description of some embodiments of the invention is presented with reference to accompanying drawings.

DETAILED DESCRIPTION

FIG. 1schematically illustrates an electrically propelled vehicle100, which is represented in a block diagram. The electrically propelled vehicle100comprises a chassis101, a wheel drive mechanism102, an electric motor103, and a battery104that is fitted in a casing105. The casing105may form a structural part of the chassis101of the electrically propelled vehicle100.

The electrically propelled vehicle100basically operates as follows. The electric motor103draws electrical power from the battery104, which is fitted in the casing105. This allows the electric motor103to deliver mechanical power to the wheel drive mechanism102, which may set the electrically propelled vehicle100in motion, or may keep the electrically propelled vehicle100in motion.

There is a risk that the electrically propelled vehicle100is involved in an accident. The casing105should therefore preferably be resistant against shock and penetration of objects, which may hit the casing105in an accident. Yet, the casing105should preferably be lightweight for reasons of, for example, power efficiency. Light weight also contributes to performance, in terms of speed and acceleration.

In particular, there is a risk of electrocution when the battery104provides a relatively high output voltage. For example, the battery104may comprise150lithium-ion cells arranged in series. Such a cell may provide an output voltage of approximately 3 volt. This implies that the battery104may provide an output voltage in the range of, for example, 300 to 1000 volt.

FIG. 2schematically illustrates the casing105. The casing105is represented in a cross-sectional diagram. The casing105provides satisfactory protection against electrocution, in addition to being resistant against shock and penetration of objects.

The casing105has an interior space201in which the battery104can be fitted. The casing105comprising a plurality of walls202-205that encapsulate the interior space201. These walls include a bottom wall202, a top wall203, and two side walls204,205, which will be referred to individually as left side wall204and right side wall205for reasons of convenience. There may be two further side walls, a front wall and a rear wall, which are not visible inFIG. 2.

The top wall203forms a primary lid part206of the casing105, which is detachably fastened to a primary lid receiving part207that includes the bottom wall202and the two side walls204,205. The top wall203comprises a secondary lid part208and a secondary lid receiving part209, which are detachably fastened to each other. In fact, the secondary lid part208is a lid-forming portion of the top wall203. The secondary lid receiving part209is a remaining, lid receiving portion of the top wall203.

The left side wall204comprises an assembly of wall elements210-213arranged as layers. This assembly includes a protective wall element210, which comprises electrically conductive material, and a set of electrically insulating wall elements211,212. The set of electrically insulating wall elements211,212are located between the protective wall element210and the interior space201. The others walls, including the bottom wall202, the top wall203, and right side wall205have a similar structure.

The protective wall element210should preferably be relatively lightweight for reasons mentioned hereinbefore. Yet, the protective wall element210should preferably confer sufficient mechanical strength to the casing105, so that the casing105can be part of the chassis101of the electrically propelled vehicle100illustrated inFIG. 1. The chassis101should be able to resist to forces of acceleration and, to a certain extent, to forces that may occur in an accident.

The protective wall element210may be carbon fiber-based. For example, the protective wall element210may have a layered structure that includes carbon fibers. For example, the protective wall element210may comprise a core layer in the form of a honeycomb structure panel of relatively lightweight metal, such as, for example, aluminum, or an alloy. This core layer may be sandwiched between two carbon fiber layers that comprise carbon fibers embedded in a resin, such as, for example, an epoxy resin. Such a structure can indeed be relatively lightweight and provide sufficient mechanical strength.

The set of electrically insulating wall elements211,212may comprise a flexible electrically insulating wall element211and a rigid electrically insulating wall element212. The rigid electrically insulating wall element212is located between the flexible electrically insulating wall element211and the interior space201. This implies that the flexible electrically insulating wall element211is sandwiched between the protective wall element210and the rigid electrically insulating wall element212. This is a general structure of the set of electrically insulating wall elements211,212. In this general structure, the flexible electrically insulating wall element211may be thicker than the rigid electrically insulating wall element212.

The flexible electrically insulating wall element211may comprise wool-like electrically insulating material, such as, for example, Calcium-Magnesium-Silicate wool, or Calcium-Magnesium-Zirconium-Silicate wool, or a combination of both. These examples of wool-like electrically insulating material are commercialized under the name “Superwool™”, Superwool being a trademark of The Morgan Crucible Company plc.

The rigid electrically insulating wall element212may comprise electrically insulating fibers, such as, for example, glass fibers, or aramid fibers. A fiber of so-called S2 glass can be a suitable choice. “Kevlar®” is an example of a suitable aramid fiber, Kevlar being a registered trademark of E. I. du Pont de Nemours and Company or its affiliates.

The set of electrically insulating wall elements211,212should be sufficiently thick to prevent dielectric breakdown. Dielectric breakdown, which causes arcing, may potentially occur due to the relatively high output voltage of the battery104. The set of electrically insulating wall elements211,212should therefore preferably have a thickness that is greater than a critical thickness at which a dielectric breakdown would occur if a maximum output voltage of the battery104were applied to the assembly of wall elements210-213.

An appropriate thickness of the set of electrically insulating wall elements211,212can be determined by means of a dielectric test. The standard IEC 60664-1: 2007 (incorporated herein by reference) defines a suitable dielectric test. Such a dielectric test can reveal a level of electrical insulation that the set of electrically insulating wall elements211,212provides for a given thickness.

The assembly of wall elements210-213includes an EMC shield213, EMC being an acronym of Electro Magnetic Compatibility. The casing105may include this particular shield because the protective wall element210may not provide sufficient EMC shielding, although this wall element comprises conductive material.

The EMC shield213is located between the protective wall element210and the set of electrically insulating wall elements211,212. The set of electrically insulating wall elements211,212thus form a barrier between the EMC shield213and the battery104. This prevents the EMC shield213from causing a short circuit in the battery104in case, for example, a battery cell breaks away from the battery104due to, for example, a shock. The battery cell will collide with the set of electrically insulating wall elements211,212, rather than with the EMC shield213, or another conductive part that could cause a short circuit.

The EMC shield213may comprise an electrically conductive fabric.FIG. 2illustrates an embodiment in which the various protective wall elements210are covered with the electrically conductive fabric on their respective inner sides. The electrically conductive fabric may comprise fibers, such as, for example, polyester fibers coated with an electrically conductive material, such as, for example, Nickel.

The casing105comprises a primary interconnection member214that equipotentially bonds together the EMC shield213in the primary lid part206, which is formed by the top wall203, and the EMC shield213in the primary lid receiving part207, which includes the two side walls204,205. The primary interconnection member214is provided with a primary shield connector215. The primary shield connector215allows equipotentially bonding the primary interconnection member214to a ground terminal200, as schematically illustrated inFIG. 2. The EMC shield213is thereby also equipotentially bonded to the ground terminal200. Equipotential bonding is achieved by means of a conductive path having relatively low impedance, which typically involves use of relatively wide and thick conductive elements.

In more detail, the primary lid part206has a circumferential rim216over which the EMC shield213extends. The primary lid receiving part207also has a circumferential rim217over which the EMC shield213extends.FIG. 2illustrates a state in which the primary lid part206and the primary lid receiving part207are fastened to each other. In this state, the circumferential rim216of the primary lid part206and the circumferential rim217of the primary lid receiving part207face each other.

The primary interconnection member214is sandwiched between the aforementioned extending portions of the EMC shield213, which comprise the electrically conductive fabric in this example. The electrically conductive fabric on the circumferential rim216of the primary lid part206is pressed against the primary interconnection member214. The same applies to the electrically conductive fabric on the circumferential rim217of the primary lid receiving part207, which is also pressed against the primary interconnection member214.

Near the circumferential rim216of the primary lid part206, the set of electrically insulating wall elements211,212may have a structure that is different from the general structure described hereinbefore. Near the circumferential rim216, the set of electrically insulating wall elements211,212may comprise the rigid electrically insulating wall element212only, as illustrated inFIG. 2. In the structure near the circumferential rim216, the rigid electrically insulating wall element212is significantly thicker than in the general structure. This ensures a satisfactory degree of electrical insulation.

Near the circumferential rim217of the primary lid receiving part207, the structure of the set of electrically insulating wall elements211,212also differs from the general structure in a manner as described hereinbefore. It can be further noted that the circumferential rim217of the primary lid receiving part207comprises a flange-like extension218alongside the protective wall element210of the left side wall204and the right side wall205. This flange like extension218may comprise a same material as the rigid electrically insulating wall element212.

The casing105comprises a secondary interconnection member219that equipotentially bonds together the EMC shield213in the secondary lid part208and the EMC shield213in the secondary lid receiving part209, which parts form part of the top wall203. The secondary interconnection member219is provided with a secondary shield connector220that allows equipotentially bonding the secondary interconnection member219to a ground terminal200, as schematically illustrated inFIG. 2.

The remarks hereinbefore with regard to the primary lid part206and the primary lid receiving part207also generally apply to the secondary lid part208and the secondary lid receiving part209, respectively. The secondary interconnection member219may press against the conductive fabric that is present on a circumferential rim221of the secondary lid part208, as well as against the conductive fabric that is present on a circumferential222of the secondary lid receiving part209, as illustrated inFIG. 2.

The casing105comprises an interior fastening structure223to fasten the battery104within the interior space201. The interior fastening structure223may comprise, for example, conductive base members224,225, studs226,227, screws228-231, and battery cell supports232, as illustrated inFIG. 2. The battery cell supports232may mechanically be interconnected with each other by means of screeds. The conductive base members224,225, studs226,227, screws228-231may be of metal. In this figure, two conductive base members224,225are visible, which will be referred to individually as left conductive base member224and right conductive base member225.

In this example, the left conductive base member224is fixed in a through hole in the bottom wall202and traverses this wall. This implies that an intermediate portion of the left conductive base member224is embedded in the assembly of wall elements210-213that form the bottom wall202. The right conductive base member is fixed in a recess of the bottom wall202; which implies that a bottom portion of this member225is embedded in the assembly of wall elements210-213that from the bottom wall202.

The interior fastening structure223allows fastening a battery104within the interior space201so that there is a gap233of between the battery104and any of the walls that forms the casing105. This gap233contributes to providing protection against electrocution. The gap233is preferably sufficiently wide to prevent a dielectric breakdown in a space between the battery104and any of the protective wall elements210, or the electrically conductive fabric that forms the EMC shield213. The gap233may be, for example, at least 1 millimeter (mm).

The casing105comprises a connector box234located in a through hole in the assembly of wall elements210-213that form the bottom wall202. The connector box234comprises a set of connectors236,237that allow electrically connecting the battery104, which is fitted in the interior space201of the casing105, to an electrical device exterior to the casing105, such as, for example, the electric motor103of the electrically propelled vehicle100illustrated inFIG. 1.

The connector box234comprises a ground connector237that allows equipotentially bonding the connector box234to the ground terminal200. The left conductive base member224and right conductive base member225are each equipotentially bonded to the connector box234, as illustrated inFIG. 2. Consequently, these conductive base members224,225are equipotentially bonded to the ground terminal200if the connector box234is equipotentially bonded to the ground terminal200, as illustrated inFIG. 2.

The casing105comprises an exterior fastening member238that allows fastening the casing105to, for example, other structural elements that form part of the chassis101of the electrically propelled vehicle101illustrated inFIG. 1. The exterior fastening member238may be in the form of, for example, a mounting bush, which may have a threaded internal cylindrical wall. The exterior fastening member238may be electrically conductive because, for example, this element is made of metal.

The exterior fastening member238is anchored in the protective wall element210. That is, a base portion of the exterior fastening member238is embedded in the protective wall element210. A remaining portion of the exterior fastening member238protrudes outwardly from the casing105as illustrated inFIG. 2.

The fastening member238need not be equipotentially bonded to the signal ground terminal200. This is because this element is relatively strongly electrically insulated from the battery104, contrary to, for example, the conductive base members224,225. The set of electrically insulating wall elements211,212provide protecting against an electrical contact between the fastening member238and the battery104in case of an accident.

FIG. 3provides a schematic perspective view of the casing105. In this figure, like elements are denoted by like reference signs.

The detailed description hereinbefore with reference to the drawings is merely an illustration of the invention and the additional features, which are defined in the claims. The invention can be implemented in numerous different ways. In order to illustrate this, some alternatives are briefly indicated.

The invention may be applied in numerous types of products or methods that involve a battery fitted within a casing. For example, the invention may be applied in any type of battery powered structure or system, which need not be a vehicle. It should further be noted that the term “vehicle” should be understood in a broad sense. The term may embrace any type of propelled device, including devices capable of flying. The term “battery” should be understood in a broad sense. The term may embrace any type of electrical energy source that may potentially cause electrocution. The term “set of electrically insulating wall elements” should be understood in a broad sense. Such a set may comprise a single electrically insulating wall element only, such as for example, the rigid electrically insulating wall element described hereinbefore.

In general, there are numerous different ways of implementing the invention, whereby different implementations may have different topologies. In any given topology, a single module may carry out several functions, or several modules may jointly carry out a single function. In this respect, the drawings are very diagrammatic.

The remarks made hereinbefore demonstrate that the detailed description with reference to the drawings is an illustration of the invention rather than a limitation. The invention can be implemented in numerous alternative ways that are within the scope of the appended claims. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. Any reference sign in a claim should not be construed as limiting the claim. The word “comprising” does not exclude the presence of other elements or steps than those listed in a claim. The word “a” or “an” preceding an element or step does not exclude the presence of a plurality of such elements or steps. The mere fact that respective dependent claims define respective additional features, does not exclude combinations of additional features other than those reflected in the claims.