FR3141007A1 - MOTOR VEHICLE COMPRISING BUS BARS EQUIPPED WITH A DYNAMIC BEATER, AND PROCESS ON THE BASIS OF SUCH A VEHICLE - Google Patents

Abstract

The invention relates to a motor vehicle comprising: a battery pack which comprises:- battery modules connected by at least one bus bar (B);- said bar (B) which has attachment to at least one module;- at least one dynamic beater (BD) between said bar (B) and said module, comprising: - an attachment zone (ZA) receiving a strand of said bus bar (B); - a sensitive zone (ZS) having a hardness of Shore A elastomer between 50A and 120A;- a shoulder zone (ZE) having the shape of a widening frustoconical sail;- a retaining stud (TR);- a ballast (MB) covering and being retained by said stud (TR) with a mass between 10g and 25g; - an insertion needle (AI) fixing said beater (BD) to said module. The invention makes it possible to absorb the modes of said bar (B). Figure 4

Description

MOTOR VEHICLE COMPRISING BUS BARS EQUIPPED WITH A DYNAMIC BEATER, AND METHOD BASED ON SUCH A VEHICLE

The invention relates to the field of motor vehicles comprising a powertrain powered by a battery pack comprising battery cell modules. The invention relates more particularly to the protection of battery modules and cells.

The use of electric vehicles requires the integration of a battery pack comprising a specific assembly of electric modules, which are positioned on thermal plates whose role is to ensure the cooling, heating or maintenance of the temperature of the modules.

The “physical” electrical links that connect the modules together are provided by copper “blades” covered with plastic protection, often orange in color, which are called ombinus bars (or “BUSBARS” in English).

Finally, these ombinus bars are generally connected to the M modules, at each end, using screws (tightening 8N.m), and MC shim foam, inserted between the top of the M module and the B ombinus bars on the fixing side, as illustrated in .

This MC shim foam is supposed to restrict the movement of the B ombinus bars, and thus reduce the constraints at the embedding points (under the screw head). Unfortunately, the addition of such a solution does not seem sufficient since deterioration of B ombinus bars has been observed on several occasions during vibration tests in screw fixing areas.

These rupture phenomena are induced by the presence of a significant deformation gradient (and therefore stress gradient) at an embedding point. This gradient is a function of a continuous component, linked to the tightening of the fixing screw and a dynamic component specific to the geometry of the ombinus B bar model (and therefore directly linked to the modal behavior of the ombinus B bars).

The fixing screw generates breakage zones at the ends of the bus bar.

The ombinus bar naturally deforms at different critical frequencies that are stressed by road excitations. The effect of its natural resonances is to amplify the excitations which generates significant stresses, particularly near a fixing on one side, at the ends and in a central deformation zone. These areas are critical areas.

Given the safety nature of this component, and as a result of the complex and time-consuming validation phases that result from it, it is not possible to redesign the bus bar or modify the arrangement of the modules, and even less to make significant modifications to the fixing elements.

It is therefore possible to add other interfaces (foam type) to block, or more precisely stiffen the bus bar, but in this case we would observe a simple frequency shift of the natural modes of the bus bar, without the result being truly dimensioning.

Another clip-type solution allowing the lower part of the bus bar to be clamped to the thermal plate was considered, but with strong constraints for large-scale implementation.

The ideal would be to interact directly and almost exclusively on the modal behavior of the bus bar in order to reduce its movements on the one hand and not have to restart a validation phase which would be prohibitive in terms of time.

For this purpose, the invention proposes a motor vehicle comprising a battery pack which comprises:
- battery modules comprising battery cells, connected together by means of at least one bus bar;
- said bus bar which comprises an attachment at at least one end for attaching said end to at least one battery module;
characterized in that the battery pack further comprises at least one dynamic beater between the bus bar and said battery module, said dynamic beater comprising:
- a hooking zone receiving a strand of said bus bar;
- a sensitive area connected to the gripping area, the sensitive area having a Shore A elastomer hardness of between 50A and 120A;
- a shoulder area connected to the sensitive area, the shoulder area having a truncated cone shape widening away from the sensitive area;
- a retaining nipple connected to the shoulder area;
- a ballast covering the retaining nipple, said ballast being retained on the dynamic beater by the retaining nipple, and having a mass of between 10g and 25g;
- an insertion needle connected to the retaining pin, the insertion needle allowing the dynamic beater to be attached to the drum module.

Advantageously, the invention makes it possible to use a mechanical solution (spring/mass type) which is fixed directly to the bus bar so as to minimize the effect of the bending moment of the bus bar strand which enters into resonance when some of its natural modes are excited. This solution is simple to implement, of low mass, and has a footprint representative of the space available under the battery cover, without there being any need to call into question the tightening constraints and the validation phases already carried out.

Furthermore, the invention makes it possible to reduce the mechanical stresses located at the incriminated embedding point which lead to deterioration of the bus bar following a realistic endurance cycle.

We add directly to the busbar a dynamic beater (mass-spring type) at the end of the longest busbar strand, so that it absorbs the energy dissipated at the resonance frequencies of certain natural modes of the busbar, in particular busbar number 11 of the models marketed by the applicant.

The technical interest of the invention is notably linked to the facts that:
- the incriminated modes of the bus bar are treated;
- no questioning of the previous validation phases is necessary;
- the added mass is low, around 17.5 g;
- the size is small, equivalent to a cylinder with a diameter of 15 mm and a length of 30 mm;
- this results in an 80% attenuation of the vibration amplitudes associated with the incriminated modes (because the solution is multiaxial).

According to one variant, the sensitive zone has a Shore A elastomer hardness of between 70A and 90A, preferably 80A.

This allows for an elasticity corresponding to the majority of busbar modes. The elasticity at 80A corresponds to all modes.

According to one variant, said dynamic beater has a length of between 5 mm and 12 mm, preferably 8 mm, and an overall mass of between 15 g and 20 g, preferably 17.5 g.

This allows to have parameters corresponding to the environment of the bus bar, and an overall mass allowing to implement the bus bar in the best conditions. A length of 8mm and an overall mass of 17g are ideal in the tests.

According to one variant, the ballast has a mass of between 12g and 16g, preferably 14g.

This allows for the best physical properties for the dynamic beater. A mass of 14g has ideal physical properties for the dynamic beater.

According to one variant, said dynamic mixer is made of thermoplastic polyurethane elastomer.

This makes it possible to implement elasticity easily with materials that are readily available in large quantities.

According to one variant, the attachment zone has a diameter between 3mm and 9mm, preferably 6mm.

This allows for a size that matches the busbar environment without taking up significant space. A diameter of 6 mm is optimal in testing.

According to one variant, said dynamic beater has connection radii of between 2 mm and 5 mm, preferably 3 mm.

This allows the mass to be received and a mass stop to be implemented.

Alternatively, the nipple is positioned at a distance from the shoulder area of between 3 mm and 7 mm, preferably 5 mm.

This allows to have a sufficient mass size to have an optimal mass value. A distance of 5mm is ideal in the tests.

According to one variant, the needle has a diameter between 2 mm and 6 mm, preferably 4 mm.

This provides a good compromise between needle rigidity and fixation strength. A diameter of 4 mm is ideal for testing.

The invention further relates to a method for mounting at least one bus bar of a motor vehicle according to the invention, characterized in that it comprises the following steps:
- placing said dynamic drummer between said bus bar and the battery module;
- place said strand of said bus bar in the attachment area.
- attach the insertion needle to the battery module.

The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which:
- schematically illustrates a bus bar in a mounting position with a foam spacer according to the prior art;
- schematically illustrates an experimental setup for applying excitations to a busbar assembly on battery modules, and for verifying the mechanical modes and stresses on the busbar;
- schematically illustrates a side view of a dynamic mixer for a vehicle according to the invention, with ballast on the left and without ballast on the right;
- schematically illustrates a sectional view along IV-IV of the ; And
- schematically illustrates graphs showing the gain achieved with the invention, for each mode, as a function of the speed on a logarithmic scale (top), or as a function of the displacement on a linear scale (bottom).

The development of this solution requires understanding the modal behavior of the B busbar (or “BUSBAR” in English) in real assembly conditions. This concerns in particular the busbar number 11 of the models marketed by the applicant.

For this, it is important to use and position two electrical modules, on which this element is fixed. In addition, there are also embedding conditions, linked to tightening constraints, identical to series life, i.e. a tightening torque of 8N.m as well as the presence of the MC foam type interface. The experimental assembly thus produced is shown in .

Excitation also plays a fundamental role, since it is absolutely necessary to not inject disturbances from the assembly hosting the exciter E, at the risk of interacting with the element to be characterized, and consequently of harming the interpretation of its natural modes.

In particular, the electrodynamic exciter E (vibrating pot) is decoupled from the lifting plate by 4 elastomer pads (not shown). A force sensor is connected to the top of the moving part of the vibrating pot (reference sensor), as well as to the marble above it. This same marble is mounted on air cushions, which allows it to be decoupled from its frame. Two crosspieces are, for their part, held rigidly on this marble, and the electrical modules are fixed, and tightened to a torque of 10 N.m, directly on these crosspieces.

Finally, we use a single-point 3D laser vibrometer as the measuring means, which ensures that there are no interactions between the sensor and the structure to be measured.

All these precautions are important to approach the real modal behavior of the bus bar mounted in a battery pack.

From the experimental protocol point of view, this assembly is subjected to a "random burst" type signal (or white noise bursts) whose useful frequency band corresponds to 500Hz. The spectral resolution, which therefore corresponds to the frequency step, is 0.5Hz, which allows us to very correctly assess the resonance frequency of each of the modes.

Finally, to better understand how busbar B deforms at each of these resonance frequencies, thirty equidistant measurement points are distributed over the surface of the busbar in order to best describe its geometry.

Thus, using this experimental representation and the tests carried out, we obtain 6 natural modes on the frequency band [10,160] Hz. It is not necessary to extend our analysis beyond this since the real excitation of the battery pack mainly corresponds to road loads (frequencies < 100 Hz).

Each of these modes describes a particular way of deforming the bus bar B, we then speak of modal deformation. Some of these deformations induce a displacement, more or less marked, at the end of the longest strand (bus bar) in two preferred directions.

These tests perfectly show the incriminated modes and the orientation taken by the longest strand of bus bar B for each of them. This area is therefore heavily stressed for modes 2, 4, 5 and 6, with pure deflection in a first plane for mode 2, then combined deflections in the first plane, and in a second plane perpendicular to the first plane, for the other 3 modes. Thus, to effectively deal with this problem, it is important to deploy a multiaxial solution, in the form of a dynamic beater.

The solution considered was to design a dynamic BD mixer to operate on its own modes in order to absorb the energy associated with the incriminated modes of the bus bar B. This is a promising solution which allows interaction on several modes of the bus bar B, but whose physical development is complex.

The invention relates to a motor vehicle comprising at least one dynamic drummer BD in the assembly of the bus bar B on a battery module M.

This solution is retained, in particular because of its ability to move in several directions and therefore to interact directly on the modes of the bus bar B to be processed, but also because the development of the body of the BD beater will be optimized by 3D printing and stereolithography. Indeed, the use of such processes makes it possible to use different materials and to produce this element extremely quickly, which makes it possible to carry out several iterations in order to work on certain parameters of its geometry. The design of the elastomer element, which ensures the connection between the bus bar B and the ballast MB on the one hand, and the role of a spring on the other hand, is sized as described below.

The specific features of the BD dynamic drummer illustrated in figures 3 and 4 are as follows:

A ZA attachment zone perfectly matches the section of the bus bar B. A ZS sensitive zone whose geometry requires a parametric study by varying the diameter and length of the pylon, as well as the connecting radii of the foot and the shoulder (ZE shoulder zone). Thus, the adjustment of the rigidity and the cylindrical aspect of this ZS sensitive zone agrees with the frequency of the first mode at 45Hz on the one hand, and allows the beater to evolve in said first and second planes to reach its optimal gain.

The ZE shoulder zone secures the MB ballast to its elastomer support, which makes it possible to prioritize the movements in the sensitive ZS zone and therefore to activate its natural modes.

The T nipple holds the MB ballast at the end of the beater, without it being able to escape during dynamic stresses.

Needle A facilitates the insertion of the MB weight and its mechanical tensioning.

Finally, the size in a longitudinal direction is a parameter which allows to maintain sufficient contact between the ballast MB and the shoulder zone ZE.

This test campaign, for the optimal sizing of this solution, made it possible to compare 3 types of materials: TPU shore 60A - TPU shore 70A - TPU shore 80A. For information, the first two materials require the use of a 3D printer while the last one relies on stereolithography. Two MB ballasts were also tested to tune this BD beater (14 g then 19 g) under the shoulder zone ZE and several values associated with the parameters of the sensitive zone ZS were used. The final solution required the development of 15 BD beaters.

The solution chosen is therefore a dynamic beater developed around a TPU shore 80A elastomer, with a pylon diameter of 6 mm, a length of 8 mm, connection radii of 3 mm, the nipple is positioned 5 mm from the shoulder, with a needle diameter of 4 mm. The inert mass of the ballast is 14 g, and the overall mass of the BD beater is 17.5 g.

There illustrates results obtained using this solution. The original busbar B0 (with higher amplitudes on the curves), from the busbar B equipped with the dynamic mixer BD (with lower amplitudes on the curves). The upper graph represents the gain achieved, for each mode, as a function of the speed (logarithmic scale), and the lower graph represents the gain achieved, for each mode, as a function of the displacement (linear scale).

The gain thus obtained using this solution makes it possible to reduce the amplitude of the deflection by 80%, and resolves the problem of breakage of bus bar B.

Finally, a more advanced solution, in terms of industrialization, is currently being developed. This final step will be carried out by injection using a specific ceramic mold that will allow the entire MB ballast to be embedded in the elastomer material. It is also planned to use this elastomer material in its recycled form.

This solution guarantees the durability of the battery packs, since it effectively addresses the problem of vibration build-up, thus avoiding having to consider its disassembly/reassembly in case it is necessary to replace this B busbar. It could also be applied to any large B busbar on any battery pack.

This solution is simple to implement and integrates perfectly and quickly on the B bus bar without compromising the safety validations previously obtained.

Claims (10)

Motor vehicle comprising a battery pack which includes:
- battery modules (M) comprising battery cells, connected together by means of at least one bus bar (B);
- said bus bar (B) which comprises a fixing at at least one end for fixing said end to at least one battery module (M);
characterized in that the battery pack further comprises at least one dynamic beater (BD) between the bus bar (B) and said battery module (M), said dynamic beater (BD) comprising:
- a hooking zone (ZA) receiving a strand of said bus bar (B);
- a sensitive zone (ZS) connected to the grip zone (ZA), the sensitive zone (ZS) having a Shore A elastomer hardness of between 50A and 120A;
- a shoulder zone (ZE) connected to the sensitive zone (ZS), the shoulder zone (ZE) having the shape of a truncated sail widening away from the sensitive zone (ZS);
- a retaining nipple (TR) connected to the shoulder zone (ZE);
- a ballast (MB) covering the retaining nipple (TR), said ballast (MB) being retained on the dynamic beater (BD) by the retaining nipple (TR), and having a mass between 10g and 25g;
- an insertion needle (AI) connected to the retaining pin (TR), the insertion needle (AI) allowing the dynamic beater (BD) to be attached to the drum module (M). Motor vehicle according to claim 1, characterized in that the sensitive zone (ZS) has a Shore A elastomer hardness of between 70A and 90A, preferably 80A. Motor vehicle according to any one of claims 1 to 2, characterized in that said dynamic beater (BD) has a length of between 5 mm and 12 mm, preferably 8 mm, and an overall mass of between 15 g and 20 g, preferably 17.5 g. Motor vehicle according to any one of claims 1 to 3, characterized in that the ballast (MB) has a mass of between 12g and 16g, preferably 14g. Motor vehicle according to any one of claims 1 to 4, characterized in that said dynamic beater (BD) is made of thermoplastic polyurethane elastomer. Motor vehicle according to any one of claims 1 to 5, characterized in that the attachment zone (ZA) has a diameter of between 3 mm and 9 mm, preferably 6 mm. Motor vehicle according to any one of claims 1 to 6, characterized in that said dynamic beater (BD) has connection radii of between 2 mm and 5 mm, preferably 3 mm. Motor vehicle according to any one of claims 1 to 7, characterized in that the stud (TR) is positioned at a distance from the shoulder zone (ZE) of between 3 mm and 7 mm, preferably 5 mm. Motor vehicle according to any one of claims 1 to 8, characterized in that the needle (AI) has a diameter of between 2 mm and 6 mm, preferably 4 mm. Method for mounting at least one bus bar of a motor vehicle according to any one of claims 1 to 9, characterized in that it comprises the following steps:
- place said dynamic drummer (BD) between said bus bar (B) and the battery module (M);
- place said strand of said bus bar (B) in the attachment zone (ZA).
- attach the insertion needle (AI) to the battery module (M).