BATTERY ASSEMBLY BASE PORTION

A battery assembly base portion, comprising a base plate comprising a base plate top surface and side edges, and a siderail comprising a siderail top surface and an inner edge. A weld groove is formed in one of the inner edge of the siderail and a side edge of the base plate. The siderail is attached to the base plate by a weld bead formed along the weld groove such that the base plate top surface and the siderail top surface are flush with one another.

TECHNICAL FIELD

The present disclosure relates to a battery assembly base portion in which a siderail is attached to a base plate by a weld bead. First and second siderails may be attached on opposed sides of the base plate. The present disclosure also relates to a battery assembly comprising such a base portion and a sealant layer disposed over the weld beads. In particular, but not exclusively, the battery assembly may relate to a high voltage battery of a fully electric or hybrid vehicle. Thus, in addition, the present disclosure relates to a vehicle comprising a battery assembly as disclosed. The present disclosure also relates to methods of assembling a battery assembly base portion and methods of assembling a battery comprising such a base portion.

BACKGROUND

High voltage batteries are incorporated into fully electric and hybrid vehicles as either a primary or secondary energy source.

Such high voltage batteries typically comprise a base portion and a lid portion, together providing a cavity. The high voltage batteries may be releasably mounted to a vehicle, such as to a sill of the vehicle.

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a battery assembly base portion and a method of assembling a battery assembly base portion. Aspects and embodiments of the invention also provide a method of assembling a battery assembly comprising the battery assembly base portion. Aspects and embodiments of the invention further provide a vehicle comprising a body component, and a battery assembly secured to the vehicle body component.

According to an aspect of the present invention there is provided a battery assembly base portion, comprising: a base plate comprising a top surface and side edges; and a siderail comprising a siderail top surface and an inner edge. A weld groove is formed in one of the inner edge of the siderail and a side edge of the base plate. The siderail is attached to the base plate by a weld bead formed along the weld groove such that the base plate top surface and the siderail top surface are flush with one another.

The inventors have determined that the weld beads could be left undressed if a weld bead protrudes sufficiently shallowly above the top surfaces of the base plate and the siderail such that a sealant layer retains a sufficient sealing performance, and this is achieved through the formation of the weld groove along which the welding then takes place. The weld groove may be formed in either one of the side edges of the base plate or the inner edge of the siderail, in either case at the respective edge thereof that lies adjacent the corresponding side edge of the other, where they form an interface.

The weld groove may be formed at an angle of approximately 35° relative to an interface between the inner edge of the siderail and the side edge of the base plate. Advantageously, this angle has been shown to minimise the height of protrusion of the resulting weld bead above the top surfaces.

The weld groove may be approximately 2 mm deep.

In certain embodiments, the weld groove further comprises a flat bottom portion adjacent said interface. Providing a flat bottom portion may help to mitigate undercutting of the weld.

The weld bead may have a maximum height above the top surfaces of the base plate and the siderail of <1.5 mm.

In certain embodiments, the battery assembly base portion comprises siderails attached to each of the base plate side edges, each including an interface between the inner edge of the respective siderail and the side edge of the base plate and an associated weld groove.

According to aspects of the invention, there is provided a battery assembly comprising the base portion as described above and a sealant layer disposed over the weld beads.

The sealant layer may comprise a modified silane polymer adhesive, such as Teroson MS 930. Adhesives in this class cure via exposure to moisture (e.g. atmospheric moisture) and are thus applied in liquid form, which is tolerant to the presence of minor protrusions in the surface to which it is applied. Moreover, such sealants are tolerant of impurities in the weld bead surface due to sooting.

Optionally, the battery assembly may further comprise a lid portion secured to the base portion, the lid portion including a flange circumscribing a lower end thereof and overlying the weld beads when secured in place.

vehicle comprising a body component; and a battery assembly as described above secured to the body component.

According to aspects of the invention, there is provided a method of assembling a battery assembly base portion, the method comprising: providing a base plate having a top surface and side edges; providing a siderail having a siderail top surface and an inner edge; forming a weld groove in one of the inner edge of the siderail and a side edge of the base plate; aligning the siderail and the base plate such that the base plate top surface and the siderail top surface are flush with one another; and attaching the siderail to the base plate by forming a weld bead along the weld groove.

Optionally, the base plate has first and second opposed side edges; providing a siderail comprises providing a first siderail having a first siderail top surface and a first siderail inner edge, and providing a second siderail having a second siderail top surface and a second siderail inner edge; forming a weld groove comprises forming a first weld groove in one of the first siderail inner edge and the first side edge of the base plate, and forming a second weld groove in one of the second siderail inner edge and the second side edge of the base plate; aligning the siderail and the base plate comprises aligning the first and second siderails and the base plate such that the base plate top surface and the respective first and second siderail top surfaces are flush with one another; and attaching the siderail comprises attaching the first and second siderails to the base plate by forming respective first and second weld beads along the respective first and second weld grooves. Thus, a battery base portion comprising a base plate and two siderails on opposed side edges of the base plate can be constructed.

Optionally, forming the weld groove comprises forming the weld groove at an angle of approximately 35° relative to an interface between the inner edge of the siderail and the side edge of the base plate.

Forming the weld groove may comprise forming the weld groove to a depth of approximately 2 mm.

Forming the weld groove may comprise forming a flat bottom portion adjacent said interface.

According to certain embodiments, the weld bead has a maximum height above the top surfaces of the base plate and the siderail of <1.5 mm.

Forming the weld bead may comprise arc welding. The weld bead is thus typically continuous along the length of the weld groove.

According to aspects of the invention, there is provided a method of assembling a battery assembly, the method comprising: assembling a battery assembly base portion as described above—optionally where the battery base plate is attached to first and second siderails on opposed sides thereof; and disposing a sealant layer over the weld beads.

The disposing of the sealant layer over the weld beads may be done without prior dressing of the weld beads. Due to the relatively low protrusion height of the weld beads, the sealant layer is able to accommodate the height variation in the top surfaces to which it is applied without compromising on seal integrity.

The method of assembling a battery assembly may further comprise securing a lid portion to the base portion, the lid portion including a flange circumscribing a lower end thereof and overlying the weld beads when secured in place. Thus a battery assembly may be constructed using the techniques described above for constructing the battery assembly base portion.

DETAILED DESCRIPTION

A high voltage battery assembly10typically comprises a base portion12and a lid portion14, together defining a cavity16for receiving battery cells (not shown), as illustrated by reference toFIG.1. The base portion12may comprise a substantially planar base plate20surrounded by a plurality of base frame members22. The lid portion14typically comprises a substantially planar top portion30, substantially parallel to the base plate20, and substantially vertical walls32extending downwardly therefrom towards the base plate. A flange or rim34extends outwardly from a bottom end32aof the walls32, circumscribing the bottom end of the lid portion14. Fasteners (not shown) secure the lid portion14to the base portion12. A layer of sealant50is sandwiched between the base portion12and the lid portion14in order to ensure the integrity of their affixation and to seal the cavity16.

Such a high voltage battery assembly10may be releasably mounted to a vehicle (not shown), such as to body component102—typically a sill, and may form part of the vehicle structure. A releasable mounting provides for ease of servicing and replacement of the battery assembly10. One convenient mechanism for releasably mounting the battery assembly10to the body component102is to use threaded fasteners60, such as bolts62and associated nuts64, as shown in schematic form in the accompanyingFIG.1. Conventionally, this has been done by passing a series of bolts62through associated holes66in the base frame members22, through corresponding holes68in the body component102(e.g. the sill) and threading a nut64on to the threaded end62aof each bolt, torquing to predefined specifications. A defined separation ‘S’ between a bottom surface103of the body component102and an upper surface23of the underlying base frame members22is necessary to provide space in which to accommodate, for example, the heads of the fasteners securing the lid portion14to the base portion12, manufacturing tolerances, panel overlaps, different thicknesses of the sealant layer50, etc. Moreover, a certain separation S is required in order to allow access for a cutting tool to cut through the sealant layer during servicing operations. This defined separation S is ensured by placing collars80of defined height in the gap between the battery assembly10and the body component102.

It is important for the battery base portion12to be well constructed, particularly if to be used as an integral part of a vehicle's structure when mounted. Accordingly, the attachment of the siderails22to the base plate20must be solid. For this reason, the siderails22are normally attached to the base plate20by continuous weld beads, formed by an arc-welding operation.

However, the resulting weld beads are variable and can lie significantly proud (i.e. >1.5 mm) of the respective upper surfaces21,23of the base plate20and the siderails22, which can cause problems for the integrity of the seal provided by the sealant layer50as applied over that region. Accordingly, to date, prior to application of the sealant layer and assembly of the lid portion14to the base portion12, the weld beads have been ‘dressed’—i.e. ground back to provide a substantially flush upper surface at an interface between the sides of the base plate20and the respective siderails22. The grinding back may be done via CNC machine operation, but there are significant hardware costs and associated space requirements. Alternatively, the weld beads may be ground down manually, for example through use of an angle grinder tool, but this requires a tool operator and an associated workstation on the assembly line. Dressing the weld beads also removes impurities (‘sooting’) deposited on the weld bead surface during the arc welding process. Thus, the sealant layer laid over the resulting dressed weld beads can take many different compositions and forms, including both wet and dry scaling media.

FIG.2shows a cross-section through a nominal welded joint100attaching a siderail22to a base plate20. The joint100comprises a weld bead130along a half-V weld groove150formed at a lateral edge20aof the base plate. The weld groove150may be approximately 2 mm deep. The weld groove150has a 45° angle to a plane of intersection170between the base plate20and the siderail22. For a nominal welded joint100where there is zero gap between the base plate20and the siderail22, a nominal volume of weld material is required in order to fill the weld groove150such that an upper surface132of the weld bead130is flush with the respective upper surfaces21,23of the base plate20and the siderail22.

However, due to variations in manufacturing and assembly and associated tolerances, there may be a small gap175at the interface between the base plate20and the siderail22. A gap175of up to approximately 1.2 mm can be within tolerance. When such a gap175is present, an additional quantity of weld material134is needed for the weld bead130to fill the gapped joint110, as illustrated by reference toFIG.3.

It is typical for the welding process to attach the siderail22to a base plate20to be at least semi-automated. Accordingly, a nominal volume of weld material is required to be determined so that the automated process may be carried out effectively. To this end, the determined volume must account for gapped joints110as well as for nominal joints100with no gap. Thus, the nominal volume of weld material may be calculated as the sum of the volume required to fill the weld groove150to be flat—i.e. flush with the respective upper surfaces21,23of the base plate20and the siderail22—then plus the volume required to fill the maximum allowable gap175.

As illustrated by reference toFIGS.4A and4B, where that determined nominal volume of weld material is applied to a nominal joint100with no gap present, the additional volume of weld material134is effectively displaced to lie on top of the weld groove150. InFIG.4A, the additional weld material is modelled as deposited in the form of an ideal rectangle134′. With a weld groove150having a 45° angle, the height of that additional rectangle of material134′ above the respective upper surfaces21,23of the base plate20and the siderail22is the same as the width of the maximum permissible gap175—i.e. up to approximately 1.2 mm. InFIG.4B, the additional weld material is modelled as deposited in the form of an ideal semi-circle134″, which represents a worst case scenario in respect of additional height of weld material. For the same conditions, the height of that additional semi-circle of material134″ above the respective upper surfaces21,23of the base plate20and the siderail22is up to approximately 1.53 mm.

A steeper weld groove150with an angle of approximately 35° relative to the plane of intersection170between the base plate20and the siderail22mitigates the risk of a welding undercut and minimises the height of protrusion of the resulting weld bead130above the flush surfaces21,23when welding a joint110having a maximum permissible joint gap175. In certain embodiments, the weld groove further comprises a flat bottom portion152adjacent the joint interface, and thus takes the form of a stepped weld groove150′.FIGS.5to7B, which mirrorFIGS.2to4Billustrate such a groove150′.

As shown inFIG.5, as applied to a nominal joint100with no gap at the plane of intersection170, the volume of weld material can be calculated based on the cross-sectional area of the stepped weld groove150′, and in this instance comprises a first portion130aassociated with filling the triangular region above the 35° side of the groove, and a second portion130bassociated with filling the rectangular region above the flat bottom portion152. For a weld groove depth of 2 mm, and with a flat bottom portion152that is 1 mm in width, the width of the top of the groove150′ at the upper surfaces21,23is 2.4 mm. Thus, the area of the first portion130ais 1.4 mm2and the area of the second portion130bis 2.0 mm2, resulting in a total cross-sectional area of 3.4 mm2. Where, as shown inFIG.6, a joint110has a maximum permissible gap175of 1.2 mm, an additional quantity of weld material134is needed for the weld bead130to fill the gapped joint110. In this instance, the cross-section of the additional quantity of weld material134is 2.4 mm2.

As illustrated by reference toFIGS.7A and7B, where the associated determined nominal volume of weld material is applied to a nominal joint100with no gap present, the additional volume of weld material134is effectively displaced to lie on top of the weld groove150′. InFIG.7A, the additional weld material is modelled as deposited in the form of an ideal rectangle134′. Since the width of the weld groove150′ at the upper end, flush with the respective upper surfaces21,23of the base plate20and the siderail22is 2.4 mm, the height of that additional rectangle of material134′ above the respective upper surfaces21,23is approximately 1.0 mm. InFIG.7B, the additional weld material is modelled as deposited in the form of an ideal semi-circle134″, which represents a worst case scenario in respect of additional height of weld material. For the same conditions, the height of that additional semi-circle of material134″ above the respective upper surfaces21,23of the base plate20and the siderail22is up to approximately 1.27 mm.

FIG.8is a photograph of a cross-section through a test weld200along a weld groove150having a 35° angle to a plane of intersection170between first and second test components202,204. It can be seen that the resulting weld bead130projects only very shallowly above the respective upper surfaces203,205of the test components.

Preparing the geometry of the joint region by providing a half-V weld groove150or a stepped half-V groove150′ in this manner allows for a strong weld joint to be formed whilst minimising the height of the associated weld bead130. The maximum height of the weld bead130above the respective top surfaces21,23of the base plate20and the siderail22can thus be kept below approximately 1.5 mm.

With such a minimised weld bead height and by using a selected class of sealant that is applied in liquid form over the resulting joint100;110and which is thus tolerant to the presence of minor protrusions in the surface to which it is applied, the resulting sealant layer50retains a sufficient sealing performance even if the weld bead130is not machined or ground back to being flush with the respective upper surfaces21,23of the base plate20and siderail22. A modified silane polymer adhesive, such as Teroson MS 930 has been determined as suitable. Moreover, such sealants are tolerant of impurities in the weld bead surface due to sooting.

The sealing performance is tested according to industry standard pressure tests that apply a positive pressure to the cavity16of an assembled battery assembly10.

FIG.1illustrates just one side of a battery assembly, and the associated attachment of a single siderail22to one lateral side edge of the base plate20. It will be appreciated that the battery assembly may be substantially symmetrical, with the base plate20having first and second siderails22attached thereto on opposed side edges thereof. The attachment of the second siderail22would be as described above by reference to the single siderail. Furthermore, additional battery base portion components, such as cross members (not shown) may be attached to the base plate20in an analogous manner.

Whereas the weld groove150;150′ has been described as being formed in the side edge20aor edges of the base plate20, it will be understood that it could instead be formed in the facing inner edge22aof the or each siderail22.

As illustrated by reference toFIG.9, a battery assembly base portion12may thus be assembled using a method900comprising: providing902a base plate20having a top surface21and side edges20a; providing904a siderail22having a siderail top surface23and an inner edge22a; forming906a weld groove150;150′ in one of the inner edge22aof the siderail22and a side edge20aof the base plate20; aligning908the siderail22and the base plate20such that the base plate top surface21and the siderail top surface23are flush with one another; and attaching910the siderail22to the base plate20by forming a weld bead130along the weld groove150;150′.

Once the battery assembly base portion12has been constructed, the sealant layer50may be applied, in liquid form. The method900thus may further comprise disposing912a sealant layer over the weld bead130. Optionally, the battery assembly10may further comprise a lid portion14secured to the base portion12, the lid portion14including a flange34circumscribing a lower end32athereof and overlying the weld beads130when secured in place. Accordingly, the method900may further comprise securing914a lid portion14to the base portion12. Securing914the lid portion14to the base portion12sandwiches the sealant layer50between the flange34and the welded joint region. Thus, the method900may comprise a method of assembling a battery assembly10.

A corresponding method1000of assembling a battery assembly base portion12having both first and second siderails22is illustrated by reference toFIG.10. The base plate20has first and second opposed side edges20a. The method1000corresponds to the method900described by reference toFIG.9, but providing1002a siderail22comprises providing a first siderail22having a first siderail top surface23and a first siderail inner edge22a, and providing a second siderail22having a second siderail top surface23and a second siderail inner edge22a; forming1004a weld groove150;150′ comprises forming a first weld groove150;150′ in one of the first siderail inner edge22aand the first side edge20aof the base plate, and forming a second weld groove150;150′ in one of the second siderail inner edge22aand the second side edge20aof the base plate; aligning1006the siderail and the base plate comprises aligning the first and second siderails22and the base plate20such that the base plate top surface21and the respective first and second siderail top surfaces23are flush with one another; and attaching the siderail comprises attaching the first and second siderails22to the base plate20by forming respective first and second weld beads130along the respective first and second weld grooves150;150′. Thus, a battery base portion12comprising a base plate20and two siderails22on opposed side edges of the base plate can be constructed.

As with the method ofFIG.9, once the battery assembly base portion12has been constructed, the sealant layer50may be applied, in liquid form. The method1000thus may further comprise disposing1012a sealant layer over the weld beads130. The method1000may likewise further comprise securing1014a lid portion14to the base portion12. Securing1014the lid portion14to the base portion12sandwiches the sealant layer50between the flange34and the welded joint regions. Thus, the method1000may comprise a method of assembling a battery assembly10.

In either instance, the weld beads130may be formed by arc welding.

The disposing912;1012of the sealant layer50over the weld beads130may be done without prior dressing of the weld beads. Due to the relatively low protrusion height of the weld beads, the sealant layer is able to accommodate the height variation in the top surfaces21,23to which it is applied without compromising on seal integrity.

The completed battery assembly10may be secured to a vehicle, for example by securing to a body component thereof.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.