Patent Application
20220255395
The present invention relates to a coolant housing for an electric machine, preferably for automotive use.
The present invention hence finds application in the field of mobility, particularly sustainable mobility, more particularly in the construction of high-performance electric vehicles, which are highly demanding and stressful for the electric traction units.
In such applications, in fact, electric motors are generally subject to serious imbalances in performance, resulting in a very irregular trend in the temperature profiles of machines, which is characterised by rapid transients under both heating and cooling conditions.
Therefore, even in the absence of endothermic engines, the most extreme automotive applications required the adoption of special cooling systems and equipment which, notwithstanding the obvious temperature differences involved, recall those used for combustion engines.
Therefore, there is a growing need in the field to provide systems which allow the management of temperature transients in high-performance electric vehicles and thus prevent performance degradation, malfunction or breakdown.
For example, systems are known in which a metal case, typically made of aluminium, is arranged around the stator of the electric machine and internally run through by a liquid cooling duct.
This liquid cooling system is certainly functional for endothermic engines, in which temperature transients are usually very slow, but not very suitable for regulating the temperature of an electric machine in high performance automotive applications, in which, as mentioned, temperature transients are generally short and very fast.
Furthermore, the arrangement of channels circulating cooling liquid around an electric machine entails problems related to size, safety and consumption/emissions, which is why the market demands an ever-increasing limitation thereof.
Therefore, the object of the present invention is to provide a coolant housing for an electric machine, preferably for automotive use, which overcomes the above-mentioned drawbacks of the prior art.
More precisely, the object of the present invention is to provide a coolant housing for an electric machine, which is highly efficient in managing temperature transients.
A further object of the present invention is to provide a coolant housing for an electric machine, which is capable of optimizing temperature control according to the operating conditions of the motor.
Said objects are achieved by means of a coolant housing for an electric machine having the features of one or more of the subsequent claims, as well as by an electric machine, preferably for automotive use, having the features of claim 19.
In particular, the housing comprises a hollow body extending around its own central axis and provided with a radially internal wall, delimiting a reception volume of an electric machine, and a radially external wall.
In other words, the hollow body has a conformation which is at least partially tubular around the central axis, delimiting a central volume for receiving the electric machine.
Furthermore, a cavity is preferably defined between the radially internal wall and the radially external wall.
Therefore, the thickness of the hollow body between the two walls is not completely “full”, but has one or more void portions represented, at least in part, by said cavity.
According to one aspect of the invention, the housing comprises at least one latent heat storage element arranged inside the cavity.
Advantageously, in this way, the sudden temperature changes of the motor can be absorbed while keeping the temperature of the coolant housing substantially unchanged, thus improving the stability of the system and preventing the temperature control system from continuously pursuing unstable references.
In this regard, it should be noted that the expression “latent heat storage element” as used herein is intended to define any material or component capable of absorbing/releasing heat from a source at a predetermined temperature, while maintaining its own temperature unchanged, but responding to this storage or release with a phase transition.
Preferably, the at least one latent heat storage element comprises a predetermined quantity of a phase-change material (PCM) distributed in the cavity.
Advantageously, in this way, the phase-change material interfaces with the electric motor, in particular the stator, absorbing and releasing heat without affecting the temperature of the housing, thereby mitigating the temperature transients.
Preferably, the phase-change material (PCM) comprises a mixture (or composition) of at least two waxes belonging to the class of the phase-change materials (or wax-based PCMs) with different melting temperatures as the latent heat storage element in an electric machine, preferably for automotive use.
This composition is characterised by having a wide melting temperature range of 60 to 120° C., preferably 70 to 105° C.
Said composition comprises a mixture of at least two wax-based PCMs selected from the group consisting of:
In particular, the composition can comprise a mixture of two, three or four of the aforementioned waxes, and can be used as the latent heat storage element over a wide temperature range defined by the melting temperatures of the waxes used therein.
These features and the inherent technical advantages will become more apparent from the following exemplary, therefore non-limiting, description of a preferred, thus not exclusive, embodiment of a coolant housing for an electric machine, preferably for automotive use, as shown in the accompanying drawings, wherein:
With reference to the accompanying figures, the numeral 1 indicates a coolant housing for an electric machine 100 according to the present invention.
For the purposes of the present invention, the terms “paraffin wax”, “paraffin” or “paraffin hydrocarbons” are used as perfectly interchangeable synonyms and indicate a class of saturated aliphatic hydrocarbons (n-alkanes) having the general formula CnH2n+2, whose number of carbon atoms is greater than 20. Exemplary paraffin waxes are Fischer-Tropsch waxes, that is, a mixture of saturated aliphatic hydrocarbons produced by Fischer-Tropsch synthesis, which involves carbon monoxide polymerization under conditions of temperature between 170 and 220° C. and pressure between 1 and 10 atmospheres.
The terms “wax” or “wax-based PCM”, used as perfectly interchangeable synonyms, refer to waxes as defined above belonging to the class of Phase-Change Materials (PCMs).
The term “Phase-Change Material (PCM)” as used herein is intended to define a material that stores latent heat, in particular a wax, which uses the phase transition phenomenon to absorb the incoming energy flows, thus storing a large amount of energy and keeping its own temperature substantially constant.
For the purposes of the present invention, the terms “melting temperature” and “activation temperature”, referred to wax-based PCMs, are used as perfectly interchangeable synonyms.
It should also be noted that the expression “coolant housing” as used herein is not intended to refer to absolute temperature values of the housing, but is preferably intended to define a housing capable of counteracting increases in the temperature of the electric machine, while maintaining its own temperature around optimal operating values.
This coolant housing 1 is preferably to be used for an electric machine 100 in automotive application, comprising at least one stator 101 inside which a rotor 102 rotates coaxially.
An example of such an electric machine 100 could be the traction of electric cars.
The coolant housing 1 comprises at least one hollow body 2 extending around its own central axis “A”.
This hollow body 2 has an axial extension along said central axis “A”, between a first end portion 2a and a second end portion 2b.
Preferably, the hollow body 2 is shaped to contain, on the inside, the stator 101 of the electric machine 100.
In the preferred embodiment, therefore, the hollow body 2 has a substantially tubular shape.
In particular, the hollow body 2 is provided with a radially internal wall 3 and a radially external wall 4, where the term “radially” preferably refers to a central reference defined by the central axis “A”.
The radially internal wall 3 extends around the central axis “A” and perimetrically delimits a reception volume 5 for the electric machine 100.
In other words, the radially internal wall of the hollow body 2 delimits a central opening 5a, preferably a through opening, sized to accommodate the electric machine 100 on the inside.
In the preferred embodiment, the radially internal wall 3 has a substantially cylindrical shape complementary to the stator 101 of the electric machine 100.
The radially external wall 4 also extends around the central axis “A” and preferably has a substantially cylindrical shape, with a larger diameter than that of the radially internal wall 3.
In the illustrated embodiment, the radially internal wall 3 and the radially external wall 4 are coaxial with each other.
It should be noted that, preferably, the hollow body 2 is made of a metallic material, preferably aluminium.
Other materials that can be used for the construction of the housing are for example aluminium alloys, metals and alloys whose thermal conductivity is greater than or equal to 90 W/mK.
At least one cavity 6 is preferably formed between the radially internal wall 3 and the radially external wall 4.
The term “cavity” as used herein refers to any lack of material between the radially internal wall 3 and the radially external wall 4 such as to define a space suitable for housing a different material from that of the hollow body 2.
According to one aspect of the invention, in fact, the housing 1 comprises at least one latent heat storage element 7 arranged right inside the cavity 6.
Advantageously, the storage of latent heat allows the housing to absorb the thermal transients by means of a phase change, without affecting the temperature of the housing 1 itself, and therefore of the electric machine.
Preferably, the latent heat storage element 7 comprises a predetermined quantity of a phase-change material (or PCM composition) distributed in the cavity 6.
The PCM composition is preferably in the solid state at room temperature, but when the latter rises and exceeds a certain transition threshold, the composition melts by storing heat (latent heat of melting) which is removed from the electric machine. Similarly, when the temperature drops, the melted composition solidifies and releases heat (latent heat of solidification).
Furthermore, the phase-change material can be mixed with a thermally conductive additive, such as for example graphite (in particular lamellar graphite), thereby allowing its latent heat storage capacity to be further increased and optimized during the use thereof.
Structurally, the cavity 6 of the housing 1 is filled with the PCM composition (in any one of the embodiments described herein), which therefore has such an arrangement as to be shaped complementarily to the cavity 6 itself.
In accordance with a possible embodiment, shown in particular in
In other words, the casing 20 defines a seat within which the phase-change material can be placed.
Preferably, in order to optimize the heat exchange capacity of the housing 1, a plurality of casings 20 are distributed around the central axis “A”, preferably in a uniform manner.
Each one of the casings is filled with the phase-change material.
More preferably, the casings are angularly equally spaced apart around the central axis “A”.
In accordance with a particular aspect, the housing 1 comprises at least one cartridge 22 containing the phase-change material, which can be coupled or is couplable to a respective casing 20.
In other words, the housing 1 preferably comprises one or more cartridges 22, each inserted in a respective casing 20 to allow the phase-change material to be correctly contained therein and/or to optimize the same.
In particular, each cartridge 22 is preferably shaped complementarily to the respective casing 20 so as to define therewith a shape coupling in a configuration of use of the housing 1.
Each cartridge 22 can therefore be coupled and constrained to the respective axial casing 20 by mechanical interference (promoted by the aforementioned shape coupling) or by gluing or welding, both in a reversible and irreversible manner.
For example, the housing 1 can be heated, thus causing an expansion of the casing 20 and allowing the respective cartridge 22 to be inserted therein.
Once the casing 20 returns to its original temperature, the cartridge 22 becomes constrained by mechanical interference without the possibility of detachment.
Structurally, each cartridge 22 on the inside comprises a mesh or grid structure 23 defining a plurality of interstices for retaining the phase-change material.
In accordance with a preferred embodiment, the mesh or grid structure 23 has a honeycomb shape defining a plurality of cells for retaining the phase-change material.
Advantageously, in this way, the material is held in position even during the solid-liquid transition, preventing its migration inside the container from compromising future performance.
In greater detail, each cartridge 22 is preferably made of aluminium or aluminium alloy, or a combination of the two in all its parts (i.e. both in the walls defining the cartridge 22 itself, and in the mesh or grid structure contained therein).
Preferably, moreover, the housing 1 comprises at least one fluid cooling circuit 12 complementary to the cavity 6.
In other words, the hollow body 2 preferably comprises, between the radially external wall 4 and the radially internal wall 3, both the cavity 6 and a cooling circuit 12 distributed along the central axis “A”.
Advantageously, in this way the performance of the housing is optimized, maximizing both the advantages in the use of a phase-change material and those of a liquid cooling system.
In accordance with a possible embodiment, shown in
Furthermore, in order to define the cooling circuit 12, each axial portion 21 is joined with the adjacent axial portions 21 at respective opposite ends.
In other words, the coil 13 extends so as to run around the casings 20, exchanging heat therewith in an optimal way.
The cooling circuit 12 therefore defines a circuit in which the cooling fluid can flow around the casing 20 so as to maximize heat exchange with the latter.
In accordance with a further aspect, the cooling circuit 12 comprises a plurality of coils 13, each extending between an inlet port 13a and an outlet port and comprising one or more axial portions 21.
In general, the cooling circuit 12 is made so as to have a plurality of axial portions 21 (belonging to the same or different coils 13) arranged and distributed around the central axis “A”, preferably in a uniform manner and equally spaced apart from each other.
Preferably, the casings 20 and the cooling circuit 12 are arranged so that each casing 20 is interposed between two adjacent axial portions 21 of the coil 13.
In this way, in fact, the two cooling systems, complementary to each other, work accurately on shared areas of the stator, maximizing performance.
In accordance with a further possible embodiment, shown in
The fins 24 therefore radiate from the radially external wall 4, each extending in a radial-longitudinal plane, preferably parallel to the central axis “A”.
Therefore, the radially external wall bears fins that significantly increase the exchange surface, thereby allowing a cooling fluid, generally air, to efficiently remove heat from the housing 1.
In particular, the heat dissipation fins 24 are arranged so as to be aligned with, preferably parallel to, the at least one casing 20 and extend between opposite ends of the radially external wall 4, that is to say that they extend over its full length along the central axis “A”.
In accordance with a further aspect of the present invention, the cavity 6 has at least one annular channel 8 extending around the central axis “A”. This annular channel 8 is filled with said latent heat storage element 7, in particular with the PCM composition.
It should be noted that the expression “annular channel” does not necessarily mean that the channel extends in a circle with its two ends joining, but is simply intended to mean that it extends, totally or partially, around the central axis “A”.
Preferably, the annular channel 8 on the inside has a plurality of radial side-by-side protrusions 9 distributed along the length of said channel 8.
These radial protrusions 9 define a corresponding plurality of interstices 9a for retaining the PCM composition.
In other words, the annular channel 8 has a toothed (or comb-like) lateral wall so that each pair of successive radial protrusions 9 delimits a portion for retaining the material making up the PCM composition, which is prevented by said portion from migrating along the channel, even following a solid-liquid transition.
In the preferred embodiment, each radial protrusion 9 is less than 1 cm, preferably less than 5 or 6 mm, away from the adjacent one.
Advantageously, considering the strong thrusts to which an electric machine in automotive use is subjected, this “comb-like” structure facilitates the maintenance of the original distribution of the PCM composition, and consequently maintains the performance and efficiency of the motor unchanged.
Preferably, the cavity 6 comprises a plurality of annular channels 8 (or coils) arranged in succession along the central axis “A”, each filled with the PCM composition.
Advantageously, this allows a plurality of small-sized annular channels 8, that is, with limited cross-section dimensions, to be distributed in the hollow body 2, thus favouring the stability of the material therein.
Preferably, the annular channel 8 has a section with a diameter/width between 10 and 30 mm, preferably of about 20 mm.
More preferably, the annular channels 8 (or coils) are connected to each other and define a helical channel 10 extending along the central axis “A”, around it.
Advantageously, in this way, the cavity 6 extends continuously along the hollow body 2, thus maximizing performance from the thermal point of view.
In this regard, it should be noted that the PCM composition is preferably introduced into the cavity 6 in the form of a liquid, from a filling port 11, so as to allow the complete filling of the same before it solidifies.
Preferably, the filling of the cavity with the phase-change material occurs by gravity.
In this case, the coolant housing 1 also comprises at least one fluid (in particular liquid) cooling circuit 12 complementary to said cavity 6.
In this context, the cooling circuit 12 comprises a helical coil 13 extending between an inlet port 13a for a cooling fluid and an outlet port for said cooling fluid and provided with a plurality of annular turns 13c arranged around said central axis “A”.
A pumping unit 14 associated with the cooling circuit 12 and configured to move the cooling fluid inside the helical coil 13 is also provided.
Preferably, the helical coil 13 of the cooling circuit 12 and the helical channel 10 of the cavity 6 are angularly offset from each other so as to define a double helix structure, thus maximizing the homogeneity of the structure and the distribution of the channels along the length of the hollow body 2.
In other words, the cavity 6 and the cooling circuit 12 are arranged so that each annular channel 8 of the cavity 6 is axially interposed between two annular turns 13c of the helical coil 13, and vice versa.
Alternatively, in this case too, the cooling of the housing 1 could be promoted by creating fins on the radially external wall 4 similarly and equivalently as above.
In the preferred embodiment, the phase-change material used in the PCM composition is of the organic type, more preferably a paraffin or paraffin mixture.
Preferably, the PCM composition comprises a mixture of at least two wax-based PCMs with different melting temperatures. Said composition therefore has a wide melting temperature range.
Said melting temperature range is comprised between 60 and 120° C., preferably between 70 and 105° C.
In one embodiment of the invention, the PCM composition comprises a mixture of at least two wax-based PCMs with different melting temperatures, which are selected from the group consisting of:
In the preferred embodiment, said waxes are selected from the group consisting of:
In one embodiment of the invention, the composition is a “two-wax composition” comprising a mixture of two of the wax-based PCMs listed above.
Said two-wax composition can therefore be advantageously used as a latent heat storage element over a wide temperature range, which is defined by the melting temperatures of the waxes used therein.
For example, if the composition comprises a mixture of “wax 1” with “wax 2”, said composition can be used as a latent heat storage element in a temperature range of 60 to 85° C., preferably of around 70 to around 80° C., and so forth for the other possible combinations.
In a preferred embodiment, the composition comprises a mixture of “wax 2” with “wax 3”. Said composition can therefore be advantageously used as a latent heat storage element in a temperature range of 76 to 102° C., preferably of around 80 to around 100° C.
In another preferred embodiment, the composition comprises a mixture of “wax 2” with “wax 4”. Said composition can therefore be advantageously used as a latent heat storage element in a temperature range of 76 to 120° C., preferably of around 80 to around 105° C.
Preferably, the two-wax composition for use according to the present invention comprises one wax in an amount of 40 to 60% by weight, preferably 45 to 55% by weight, and the other wax in a complementary amount of 40 to 60% by weight, preferably 45 to 55% by weight.
In one embodiment of the invention, the composition is a “three-wax composition” comprising a mixture of three of the wax-based PCMs listed above.
Said three-wax composition can therefore be advantageously used as a latent heat storage element over a wide temperature range, which is defined by the melting temperatures of the waxes used therein.
For example, if the composition comprises a mixture of “wax 1”, “wax 2” and “wax 3”, said composition can be used as a latent heat storage element in a temperature range of 60 to 102° C., preferably of around 70 to around 100° C., and so forth for the other possible combinations.
In a preferred embodiment, the composition comprises a mixture of “wax 2”, “wax 3” and “wax 4”. Said composition can therefore be advantageously used as a latent heat storage element in a temperature range of 76 to 120° C., preferably of around 80 to around 105° C.
Preferably, the three-wax composition for use according to the present invention comprises one wax in an amount of 20 to 60% by weight, preferably 30 to 50% by weight, and the two other waxes in complementary amounts, i.e. one wax in an amount of 20 to 60% by weight, preferably 20 to 40% by weight, and the other wax in an amount of 20 to 60% by weight, preferably 20 to 40% by weight.
In one embodiment of the invention, the composition is a “four-wax composition” comprising a mixture of all of the four wax-based PCMs listed above.
Said four-wax composition can therefore be advantageously used as a latent heat storage element over a wide temperature range, which is defined by the melting temperatures of the waxes used therein.
In this case, said four-wax composition can be used as a latent heat storage element in a temperature range of 60 to 120° C., preferably of around 70 to around 105° C.
In a preferred embodiment, the composition of the invention comprises 40 to 60% by weight, preferably 45 to 55% by weight, of a mixture of “wax 2” with “wax 4”, and 40 to 60% by weight, preferably 45 to 55% by weight, of a mixture of “wax 1” with “wax 3”. Said composition therefore comprises wax 1 in an amount of 10 to 30% by weight, preferably 15 to 25% by weight, wax 2 in an amount of 15 to 35% by weight, preferably 20 to 30% by weight, wax 3 in an amount of 20 to 40% by weight, preferably 25 to 35% by weight, and wax 4 in an amount of 15 to 35% by weight, preferably 20 to 30% by weight.
In a further preferred embodiment, the composition of the invention comprises 40 to 60% by weight, preferably 45 to 55% by weight, of a mixture of “wax 1” with “wax 2”, and 40 to 60% by weight, preferably 45 to 55% by weight, of a mixture of “wax 3” with “wax 4”. Said composition therefore comprises wax 1 in an amount of 10 to 30% by weight, preferably 15 to 25% by weight, wax 2 in an amount of 20 to 40% by weight, preferably 25 to 35% by weight, wax 3 in an amount of 20 to 40% by weight, preferably 25 to 35% by weight, and wax 4 in an amount of 10 to 30% by weight, preferably 15 to 25% by weight.
Preferably, the four-wax composition for use according to the present invention comprises a first wax in an amount of 10 to 40% by weight, preferably 15 to 35% by weight, and the three other waxes in complementary amounts, i.e. one wax in an amount of 10 to 40% by weight, preferably 15 to 35% by weight, another wax in an amount of 10 to 40% by weight, preferably 15 to 35% by weight, and the further wax in an amount of 10 to 40% by weight, preferably 15 to 35% by weight.
The characteristics of the waxes used in the following embodiment examples are schematically shown in the table below (Table I).
These waxes were characterized by the Differential Scanning calorimetry (DSC) technique, which allows the start and end temperatures of each transition (melting during heating and solidification during cooling) to be determined.
The characteristics of the mixtures used according to one embodiment of the present invention are schematically shown in the table below (Table II).
The various wax mixtures used herein (mixture 1, mixture 2, mixture 3, mixture 4 and mixture 5) were characterized by the Differential Scanning calorimetry (DSC) technique in order to determine the activation temperatures of each mixture and observe the peak changes in the temperature range of interest, i.e. from 60 to 120° C.
The curves in
It can also be observed that, by using mixtures of wax-based PCMs with different activation temperatures, the temperature profile changes in a different way according to the relative concentrations (% amount of the at least two waxes that make up each mixture) and the melting temperatures characteristic of each wax (shown in Tables I and II), making it possible to select the most suitable mixture for the thermal profile to be managed.
The invention achieves the intended objects and attains important advantages.
In fact, the use of a latent heat accumulator, in particular a phase-change material, inside the body of the housing allows the rapid temperature transients which electric motors in automotive applications undergo to be slowed down, thus allowing the temperature of the assembly to be maintained as much as possible in the vicinity of optimal values for driving.
Moreover, the use of a cavity with phase-change material together with and complementary to a fluid cooling circuit allows the response of the system to be optimized, even in the cooling phase.
It should be noted that an advantage related to the use of a PCM composition mixing several waxes is that, unlike the use of a single type of wax-based PCM, the two (or more) different melting temperatures allow the range in which the phase change takes place and the mixture absorbs the latent heat of the system to be expanded (see the comparison between
The fact that the shape of the melting peak is “quadrangular” instead of “triangular” advantageously causes said mixtures to be consistently active in a temperature range, unlike the use of a single wax, which exhibits localized temperature transients.
Another advantage related to the use of the PCM composition as a latent heat storage element is that the combination of at least two of the wax-based PCMs with different activation temperatures, as described above, in the operating temperature range of an electric machine, allows part of the mixture to be in the solid state, thus maintaining a level of viscosity suitable for its use inside the coolant housing, even in the event that one or more of the other waxes in the mixture are completely melted.
Since the viscosity of the composition for use according to the present invention depends on the type of the at least two waxes in the mixture and on their relative concentrations (% amount), according to the different thermal profiles to be managed, the composition for use according to the present invention can therefore be modified by mixing the different types of wax-based PCMs in different amounts as described above. Advantageously, this makes it possible to limit or even completely prevent segregation phenomena in the mixture and/or losses of material, thus maintaining the original and homogeneous distribution of the composition. The composition for use according to the present invention therefore exhibits high stability and allows high performance even after several thermal cycles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102019000013146 | Jul 2019 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/057131 | 7/29/2020 | WO |
