EP2828955A2

EP2828955A2 - Electrical machine with pcm for absorbing temperature peaks

Info

Publication number: EP2828955A2
Application number: EP13702957.5A
Authority: EP
Inventors: Joerg Heyse; Uwe Knappenberger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-03-20
Filing date: 2013-01-28
Publication date: 2015-01-28
Also published as: WO2013139511A2; WO2013139511A3; DE102012204422A1

Abstract

The invention presents an electrical machine (1) for motor vehicles. The electrical machine (1) has a rotor (3) and a stator (5). A phase-change material is arranged on the rotor (3) and/or on the stator (5). In this case, the phase-change material is an alditol (7).

Description

description

Electric machine with PCM to catch temperature peaks

State of the art

Electric machines, such as Electric motors of motor vehicles, warm in operation and must be sufficiently cooled. For this purpose often a ventilation or a water cooling is used.

In some applications, especially in motor vehicles, pure air cooling may not be sufficient. Water cooling can be more efficient, but also more costly. On the other hand, cooling may only be required intermittently in certain applications of the electric machine.

Disclosure of the invention

There may therefore be a need for an improved efficient refrigeration capability for electric machines in automobiles.

This need can be met by the subject matter of the present invention according to the independent claims. Advantageous embodiments of the present invention are described in the dependent claims.

In the following, features, details and possible advantages of a device according to embodiments of the invention will be discussed in detail.

According to a first aspect of the invention, an electric machine, in particular an electric motor for motor vehicles is presented, which has a rotor, a stator and a phase change material. The

Phase change material is an alditol, which is arranged on the rotor and / or on the stator. In other words, the idea of the present invention is based on

Temperature peaks on electrical machines intercept that the

Melting enthalpy of a reversible thermodynamic change of state of a storage medium, namely alditol, is exploited for storing thermal energy.

By introducing the phase change material directly into the electric machine, temperature peaks, e.g. arise when accelerating a motor vehicle in the electric machine are intercepted by the phase change material. Alditol is particularly good as a phase change material for

Electric machinery suitable in motor vehicles, as it is an optimal

Has melting temperature at high enthalpy of fusion. For example, the melting temperature of the alditol may be close to but below the allowable limit temperature of components of the electric motor for motor vehicles.

At the same time, the melting enthalpy of the alditol is compared with others

Phase change materials, relatively high.

By using alditol as a phase change material in

Electric machines can preset temperature limits within the

Electric machine can be maintained cost-effectively. This contributes significantly to maintaining the strength and life of the electric machine. Furthermore, the power density with respect to waste heat and size of an electric machine can be maximized with the aid of Alditol. Space and weight of the electric machine can be reduced here. Furthermore, through the use of

Alditol as phase change material the duration of a maximum allowable load, i. maximum heat generation can be extended. This may for example be of particular importance in electric vehicles in which the

Electric machine not in contrast to a hybrid vehicle because of

Overheating hazard may be abgeregelt.

Furthermore, the use of alditol as phase change material makes it possible to dispense with costly structural measures for reducing thermal resistances in the interior of the electric machine. Furthermore, a

cost-effective air cooling sufficient for optimal cooling when to

Cooling additionally alditol is used as a phase change material. The electric machine can be eg an electric motor or an electric generator. It can be used in vehicles, especially in motor vehicles such as cars or trucks. Alternatively, the electric machine as

Industrial motor can be used. The electric machine can be designed as a synchronous or asynchronous machine and has a rotor and a stator. The rotor can be rotatably mounted in the stator. Alternatively, the rotor may be rotatably mounted around the stator.

The phase change material, also referred to as PCM (English Phase Change Material), is used to store thermal energy. The latent one

Heat of fusion, solution heat or heat of absorption of

Phase change material is significantly larger than the heat that the

Phase change material can save due to its normal specific heat capacity. Thus, the phase change material, and especially the alditol, can absorb large amounts of thermal energy at an almost constant temperature as soon as it reaches a temperature at which the phase state of the material changes. In this case, the phase change material takes up so long thermal energy without a significant change in temperature until the complete phase change material, for example, has gone from the solid to the liquid phase. When the ambient temperature of the liquefied phase change material drops, the phase change material changes to the solid phase and returns the stored heat to the environment. The phase transitions of the phase change material and in particular the

Alditol, for example, from solid to liquid, i. Solidification and melting are reversible. This can be repeated in a small by the

Melting temperature of the alditol fixed temperature range much

Heat energy can be stored in relatively little mass. For example, with a melting enthalpy of about 250 kJ / kg in 0.5 kg of Alditol, a waste heat of 3 kW can be stored for 40 seconds. It can to the

appropriate places of the electric machine according to the expected duration of a peak load the appropriate amount of Alditol be used.

The alditol used as phase change material may also be referred to as sugar alcohol and is a non-cyclic polyol, for example structurally derived as a reduction product of a carbohydrate. Alditols can have the following structural formula:

In particular, the following alditols can be used: mannitol, isomalt, lactitol, sorbitol, xylitol, threitol, erythritol, glycerol and arabitol. Erythritol may also be referred to as erythritol and has the following structural formula:

Among organic substances and especially among sugar alcohols erythritol has the highest storage density (J / m ³ ) and suitable for electrical machines melting temperature, for example, about 120 ° C. Erythritol is particularly well suited for electric machines as the melting temperature of erythritol is below the maximum temperature limit of building components of the

Electric machine is located. For example, the melting temperature of erythritol is below a limit temperature of 140 ° C. at the stator inlet or at the winding head. At the same time, the melting temperature is high enough to be at minimum

Material to be melted only at maximum occurring waste heat. Furthermore, the specific storage capacity of erythritol is optimal for electric machines in motor vehicles.

According to a further embodiment of the invention, the

Electric machine at least a range of highest temperature. The phase change material is in direct thermal contact with the highest temperature region. A region of highest temperature, also referred to as hot spot, may be, for example, a point or a component of the electric machine, at which higher temperature values may occur than at other points or components of the electric machine. For example, these areas may be windings or winding carriers or rotor magnets. The phase change material is in direct thermal contact with these areas, ie it is close to the place or applied directly to the areas of highest temperature.

According to a further exemplary embodiment of the invention, the region of highest temperature is at least one region from the following group: an electrical winding of the stator or an electrical winding of the rotor, a permanent magnet of the electric machine or a rotor cage.

In this case, the stator may have a laminated core with grooves on which

Windings are provided. The windings can be combined to form individual winding heads. The alditol can be applied directly to the windings. Alternatively or additionally, the alditol may be attached to a

Permanent magnet can be arranged on the stator or on the rotor. Furthermore, the alditol may alternatively or additionally be applied directly to a rotor cage when the electric machine is designed as an asynchronous machine.

According to a further embodiment of the invention that is

Phase change material between a winding head of the stator and a stator housing introduced. In this case, the phase change material can be in direct thermal contact with the winding head and with the stator housing. The individual windings may, for example, comprise copper and, as mentioned above, be arranged in grooves of a laminated core. In this case, individual windings can be combined to form winding heads. The

Stator housing may for example correspond to a housing of the electric machine and e.g. Have aluminum. By introducing the

Phase change materials between the winding head of the stator and the stator can be ensured in addition to the storage of thermal energy and a connection of the winding overhang to the housing for heat dissipation. That is, the winding head of the stator is thermally connected by means of the phase change material to the good thermal conductivity housing so that the heat from the winding over the housing can be dissipated.

According to a further embodiment of the invention that is

Phase change material on or in an axial bore in the rotor of

Electric machine introduced. For example, this can already be done on the rotor provided for weight reasons provided axial bores. The phase change material can be filled in the axial bores and then sealed with a closure material. In this case, the closure material may be an electrically non-conductive material having a higher melting point or a higher melting temperature than the alditol.

For example, this plastic can be used. By the

Closure material may leak the melted

Phase change material can be prevented.

According to a further embodiment of the invention, the

Electric machine also on a capsule material. The capsule material is electrically insulating and has a higher melting temperature than that

Phase material, especially as the alditol on. The phase change material is surrounded by the capsule material. The capsule material may be, for example, a plastic, in which the phase change material is filled. In this way, cartridges can be provided which prevent leakage of the phase change material in the liquid phase.

According to a further embodiment of the invention is on

Phase change material provided at least one expansion element. According to a further embodiment of the invention, the expansion element comprises a gas. The expansion element is carried out by a thermal

Expansion of the phase change material to be compressed. The

Expansion element can be, for example, a sponge-like element directly on the phase change material. Furthermore, the expansion element can correspond to an air content in the encapsulated phase material. For example, may be contained in the sealed by the closure material axial bores a certain amount of air or gas, so that the phase change material during

Phase change can expand and contract. Furthermore, in the cartridges described above, a gas or air portion may also be provided.

According to a second aspect of the invention, a method of manufacturing an electric machine as described above is presented. The method comprises the following steps: providing a stator and a rotor and Introducing an alditol to absorb thermal energy in the

Electric machine directly to the rotor and / or directly to the stator.

According to a third aspect of the invention, the use of alditol for receiving thermal energy in an electric machine of a

Motor vehicle presented.

Other features and advantages of the present invention will become

Expert from the following description of exemplary

Embodiments, which should not be construed as limiting the invention, with reference to the accompanying drawings.

Fig. 1 shows the melting temperature and the enthalpy of fusion of different heat storage substances

Fig. 2 shows the melting temperature and the storage density of different organic substances

Fig. 3 shows an evaluation of different heat storage substances with respect to an application in motor vehicles

Fig. 4 shows a cross section through an electric machine according to a

Embodiment of the invention

Fig. 5 shows a detail of a plastic representation of a

Electric machine according to an embodiment of the invention

Fig. 6A shows a cross section through the electric machine shown in Fig. 5 parallel to a plane of the rotor

Fig. 6B shows a cross section through a cartridge with alditol according to a

Embodiment of the invention

Figures 7A, 7B show a comparison of the temperature of electrical windings over a drive cycle, viewed with and without the use of alditol All figures are merely schematic representations of devices according to the invention or of their components according to embodiments of the invention. In particular, distances and size relationships are not shown to scale in the figures. In the various figures, corresponding elements are provided with the same reference numbers.

In Fig. 1, the melting temperature in ° C of different heat storage substances is plotted on the X-axis. On the Y-axis is a

Enthalpy of fusion of the heat storage substances in kJ / mol applied.

The graph shows both a temperature range and a melting enthalpy range for the following heat storage substances: gas hydrates A, aqueous salt solutions B, water C, fatty acids D, paraffins E, salt hydrates F, sugar alcohols G, nitrates H, hydroxides J, chlorides K, carbonates L and fluorides M. The melting temperature of the sugar alcohols or alditols used in the electric machine according to the invention is in the range of about 50 to 200 ° C. The melting enthalpy of the sugar alcohols is in a range of about 250 to 450 kJ / mol. Thus, the melting temperature is in the range of the maximum temperature of components of the electric machine. Furthermore, the alditols 7 can absorb a high energy at a relatively small mass. Other heat storage, such as Chloride K or Carbonate L are not suitable for use in electric machines, because, for example, their melting temperature is much higher than the maximum temperature of components of the electric machine.

In Fig. 2, on the X axis, the storage density in MJ / m ^{3 is} the respective one

Heat storage substance applied. On the Y-axis is the

Melting temperature in ° C applied. In this case, in Fig. 2 are organic

Heat storage substances shown.

The heat storage substances shown in Fig. 2 are organic

Substances. Various polyglycols a, dimethyl sulfoxide (DMS) b, various paraffins c, biphenyl d, naphthalene e, water and water-ethylene glycol mixtures f and erythritol g are shown. Among the organic substances shown, erythritol has the highest storage density at a suitable melting temperature of about 120 ° C. The melting temperature of Erythrit is suitable for electric machines where the limit temperature of the components, for example at the stator inlet, is approx. 140 ° C.

At the same time, the melting temperature of erythrol is high enough, in favor of minimal material use, only at maximum occurring waste heat

to be melted. This is advantageous because, for example, stator and

Rotor of the electric machine in regular operation, i. For example, do not constantly come to their limit temperature in typical driving. There are always cooling phases at lower load. With the help of phase change material is generated under highest load

Waste heat in the phase change material in particular in alditol and preferably stored in erythritol by its melting and released in the phases of low load by its solidification. As a result, a further increase in temperature is suppressed in a phase of higher load from reaching the melting temperature of the phase change material. The electric machine is thus reliable under higher loads, in particular with regard to strength and service life, so that high power densities are made possible without further measures. In Fig. 3 are different characteristics of different

Heat storage substances compared with respect to an application in motor vehicles. The first column summarizes the assessments of water. The second, third and fourth columns show the suitability of salt hydrates for use in motor vehicles. The second column shows sodium acetate trihydrate, the third column magnesium nitrate hexahydrate and the fourth column magnesium chloride hexahydrate. The fifth column shows the suitability of a eutectic mixture of salt and salt hydrate. In this case, 14% LiN0 ₃ with 86% Mg (N0 ₃ ) ₂ and 6 H ₂ 0 were used. The sixth column shows the organic substance erythritol, which according to the invention in

Electric machines can be used advantageously. The seventh and the eighth

Columns show commercial phase change materials. It is shown in the seventh column GR80 and in the eighth column RT82. In the first row, the different phase change materials are specific to their specifics

Heat capacity evaluated. In the second row, the respective cycle stability or service freedom of the respective phase change material is assessed. The third

Series represents the toxicity or environmental compatibility and safety of the opposite material. A plus indicates a particularly good suitability for use in motor vehicles, a zero a neutral suitability and a minus a bad suitability for use in motor vehicles. As can be seen from the evaluation in Fig. 3, erythritol is all three

best suited for use in motor vehicles.

4 to 6 different sections of electric machines 1 are shown according to embodiments of the invention. The electric machines 1 shown in FIGS. 4 to 6 are designed as permanent-magnet synchronous machines (PSM) with permanent magnets or permanent magnets 13. An electric machine 1 can also be designed as an asynchronous machine with a rotor cage not shown in the figures.

The electric machine 1 has a rotor 3 and a stator 5. In this case, the electric machine 1 or the stator 5 is surrounded by a stator housing 19. Between stator 5 and rotor 3, an air gap 27 is provided. The rotor 3 is further connected to a shaft 33, which is arranged on a ball bearing 31. At the electric machine 1 is phase change material,

especially Alditol 7 provided. The arrangement of alditol 7 at the

Electric machine 1 is shown only schematically. The alditol 7, which is preferably erythritol, is provided at areas 9 highest temperature. These areas 9 are e.g. Permanent magnet 13 on the rotor 3, as seen for example in Fig. 5. Furthermore, these areas may correspond to electric windings or a stator winding head 17. For example, the stator winding head 17 may be enclosed by a ring of Alditol 7. For this purpose, about 0.5 kg Alditol can be used. Furthermore, a region of highest temperature may correspond to a rotor cage, which is not shown in the figures. The alditol 7 is introduced, for example, between the winding head 17 and the stator housing 19. Furthermore, the Alditol 7 can directly on the

Permanent magnet 13 may be applied. Axial bores 21 are provided on the rotor 3 and continue in a balancing disk 29 arranged on the rotor 3. Alditol 7 may be inserted directly into these axial bores 21.

FIG. 6B shows a cross section through a cartridge or a capsule with Alditol 7, which can be arranged, for example, in the axial bores 21 shown in FIGS. 5 and 6A. The cartridge or a shell of the cartridge has a Capsule material 23, which is electrically insulating and a higher

Melting temperature than the Alditol 7 has. This capsule material 23 prevents outflow of the alditol 7 in the liquid state from the

Axial bore 21. At the Alditol 7, for example, between the alditol 7 and the capsule material 23, an expansion element 25 is provided. The expansion element can be, for example, an air fraction in the encapsulated Alditol 7. This allows expansion and contraction of the alditol 7 during melting and solidification. Furthermore, the capsule material 23 may have an elastic stretching region, indicated by an arrow in FIG. 6B, which can be stretched by the alditol.

FIGS. 7A and 7B show temperature profiles on the winding head 17 and on the winding head 17, respectively

Stator pass over a driving cycle of 1800 seconds. The time in seconds is plotted on the X axis and a temperature in K on the Y axis. 7A shows the temperature profile at the stator inlet without the use of Alditol 7 as the phase change material in the electric machine 1. FIG. 7B shows the temperature profile at the stator pass with the use of Alditol 7. As can be seen in FIG. 7A, after a travel time of approximately 800 seconds a temperature peak, for example by a

Acceleration process. Fig. 7B shows that when using Alditol 7, for example, between the stator housing 19 and end winding 17, the

Temperature peak is caught by melting the alditol 7 and is only a plateau. The arrow in Fig. 7B marks a time when the Alditol 7 is completely melted.

In conclusion, it should be noted that terms such as "comprising" or the like are not intended to exclude that other elements or steps may be envisioned.Furthermore, it should be understood that "a" or "an" does not exclude a multitude It should further be noted that the reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

claims

1 . Electric machine (1) having the electric machine (1)

a rotor (3);

a stator (5); and

a phase change material disposed on the rotor (3) and / or on the stator (5);

characterized in that

the phase change material is an alditol (7).

2. Electric machine (1) according to claim 1,

wherein the alditol (7) is erythritol.

3. Electric machine (1) according to one of claims 1 and 2,

wherein the electric machine (1) has a region (9) of highest temperature;

wherein the alditol (7) is in direct thermal contact with the highest temperature region (9).

4. Electric machine (1) according to claim 3,

wherein the highest temperature region (9) is selected from the group consisting of electric windings (1 1) of the stator (5) or rotor (3), a permanent magnet (13) of the electric machine (1) or a rotor cage.

5. Electric machine (1) according to one of claims 1 to 4,

wherein the alditol (7) is introduced between a winding head (17) of the stator (5) and a stator housing (19).

6. Electric machine (1) according to one of claims 1 to 5,

wherein the alditol (7) in an axial bore (21) on the rotor (3) is introduced.

7. An electric machine (1) according to any one of claims 1 to 6, further comprising a capsule material (23);

wherein the capsule material (23) is electrically insulating and a higher

Melting temperature than the alditol (7);

wherein the alditol (7) is surrounded by the capsule material (23).

8. Electric machine (1) according to one of claims 1 to 7,

wherein on the alditol (7) an expansion element (25) is provided;

wherein the expansion element (25) is carried out by a thermal

Extending the alditol (7) to be compressed.

9. Electric machine (1) according to claim 8,

wherein the expansion element (25) comprises a gas.

10. A method for producing an electric machine (1) according to one of

Claims 1 to 9, the method comprising the following steps

Providing a stator (5) and a rotor (3);

the method characterized by further comprising the following step

Introducing an alditol (7) for absorbing thermal energy into the electric machine (1).

1 1. Use of Alditol (7) in an electric machine (1)

Motor vehicle.