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US 20140007915A1
119) United States
112) Patent Application Publication 110) Pub. No. :US 2014/0007915 A1
Koehne 143) Pub. Date: Jan. 9, 2014
154) THERMOELECTRIC GENERATOR FOR A
VEHICLE AND HEAT STORAGE DEVICE
FOR ATHERMOELECTRIC GENERATOR OF
AVEHICLE
152) U.S.Cl.
CPC .........
USPC
157)
... H01L 35/28 12013.01)
136/205
ABSTRACT
JUI. 3, 2012 1DE) 10 2012 211 466.1
Publication Classification
151) Int. Cl.
H01L 35/28 12006.01)
171) Applicant: Robert Bosch GmbH, Stuttgart 1DE)
172) Inventor: Martin Koehne, Asperg 1DE)
121) Appl. No. :13/934,670
122) Filed: Jul. 3, 2013
130) Foreign Application Priority Data
Athermoelectric generator for avehicle includes agenerator
housing arranged in an exhaust line ofthe vehicle and/or in a
bypass to the exhaust line and at least one thermoelectric
module assigned to at least one first exhaust gas contact
surface. Thermal energy is transferred from the first exhaust
gas contact surface to the thermoelectric module via at least
one heat conduction path and at least one heat storage cham-
ber filled with at least one heat storage material. The heat
storage chamber is assigned at least one second exhaust gas
contact surface from which thermal energy is configured to be
transferred to the heat storage chamber. The heat storage
chamber is arranged outside the heat conduction path from
the first exhaust gas contact surface to the thermoelectric
module. Aheat storage device is provided for the thermoelec-
tric generator ofthe vehicle.
Patent Application Publication Jan. 9, 2014 Sheet 1of 4US 2014/0007915 A1
39
Patent Application Publication Jan. 9, 2014 Sheet 2of 4US 2014/0007915 A1
Patent Application Publication Jan. 9, 2014 Sheet 3of 4US 2014/0007915 A1
Patent Application Publication Jan. 9, 2014 Sheet 4of 4US 2014/0007915 A1
US 2014/0007915 A1 Jan. 9, 2014
THERMOELECTRIC GENERATOR FOR A
VEHICLE AND HEAT STORAGE DEVICE
FOR ATHERMOELECTRIC GENERATOR OF
AVEHICLE
[0001] This application claims priority under 35 U.S.C.
)119to patent application no. DE 102012 211466.1, filed on
Jul. 3, 2012 in Germany, the disclosure ofwhich is incorpo-
rated herein by reference in its entirety.
BACKGROUND
[0002] The disclosure relates to athermoelectric generator
for avehicle. The disclosure furthermore relates to aheat
storage device for athermoelectric generator of avehicle.
[0003] Athermoelectric device having athermoelectric
generator and means for limiting the temperature at the gen-
erator is described in DE 102006 040 853 B3.Athermoelec-
tric generator is formed in the housing ofthe thermoelectric
device, said generator being thermally connected on afirst
side thereof to aheat source and on the second side thereof,
that opposite the first side, to aheat sink. Aheat storage
chamber, which is filled with afusible working medium, is
formed between the heat source and the thermoelectric gen-
erator. Ifthe temperature of the heat source rises above the
melting temperature ofthe working medium, said medium is
at least partially melted, and this is supposed to enable over-
heating ofthe thermoelectric generator to be prevented. Ifthe
temperature of the heat source subsequently falls below the
melting temperature of the working medium, the thermal
energy liberated by the solidifying working medium is at least
partially released to the thermoelectric generator. This is sup-
posed to enable a constant temperature gradient to be main-
tained across the thermoelectric generator.
SUMMARY
[0004] The disclosure provides athermoelectric generator
and aheat storage device for athermoelectric generator ofa
vehicle.
[0005] The present disclosure makes it possible to equip a
thermoelectric generator with at least one heat storage cham-
ber, wherein the thermal energy ofat least one exhaust gas can
be conducted from at least one first exhaust gas contact sur-
face to the at least one thermoelectric module of the thermo-
electric generator via at least one heat conduction path while
bypassing the at least one heat storage chamber. Expressing
this in another way, one can also say that the thermal energy
released by the at least one exhaust gas is deliberately not
transferred via the at least one heat storage chamber to the at
least one thermoelectric module. This transfer ofthe thermal
energy ofthe at least one exhaust gas while bypassing the at
least one heat storage chamber ensures that the thermoelectric
generator has improved thermal resistance.
[0006] The conventional transfer of the thermal energy
released by the at least one exhaust gas via the at least one heat
storage chamber leads to atotal thermal resistance which is
the sum of the thermal resistance both of the at least one
thermoelectric module and of the at least one heat storage
chamber. In contrast, areduced thermal resistance can be
achieved by means ofthe present disclosure as compared with
the prior art.
[0007] It is advantageous if at least one intermediate vol-
ume is situated between the at least one first exhaust gas
contact surface and the at least one associated thermoelectric
module in each case, wherein the at least one heat storage
chamber is arranged outside the at least one intermediate
volume. This ensures reliable transfer of the thermal energy
liberated by the at least one exhaust gas at the at least one first
exhaust gas contact surface to the at least one thermoelectric
module while bypassing the at least one heat storage chamber.
In this way, an advantageous reduced thermal resistance in the
conversion ofthe thermal energy liberated by the at least one
exhaust gas into electric energy is ensured.
[0008] In an advantageous embodiment, thermal energy
can be transferred from the at least one heat storage chamber
to the at least one associated thermoelectric module by means
of at least one heat transfer contact of the thermoelectric
generator, which contact is formed or can be formed. Since, as
aheat transfer point between two solids, the heat transfer
contact has ahigher efficiency than aheat transfer point
between a solid and agas, the thermal energy temporarily
stored in the at least one heat storage chamber can be output
more efficiently to the at least one associated thermoelectric
module. In this way, it is possible to increase the electric
energy that can be obtained from the at least one heated
exhaust gas by means ofthe thermoelectric generator.
[0009] In particular, the at least one heat transfer contact
can be formed by means of at least one switchable heat-
conducting connecting device ofthe thermoelectric genera-
tor, which device can be switched from astate in which it does
not conduct heat to astate in which it conducts heat. Thus, the
at least one switchable heat-conducting connecting device
can be switched on specifically when the energy in the at least
one heat storage chamber has been charged up. At the same
time, switching the at least one switchable heat-conducting
connecting device into the state in which it does not conduct
heat makes it possible to prevent disadvantageous discharg-
ing ofthe at least one heat storage chamber.
[0010] Preferably, the at least one switchable heat-conduct-
ing connecting device of the thermoelectric generator
switches from the state in which it does not conduct heat to the
state in which it conducts heat at atemperature above the
switching temperature, and switches from the state in which
it conducts heat to the state in which it does not conduct heat
at atemperature below the switching temperature. By means
of the control, achievable in this way, of the at least one
switchable heat-conducting connecting device, the advan-
tages described in the preceding paragraph can be reliably
achieved. In particular, the at least one switchable heat-con-
ducting connecting device can be designed in such away that
it automatically performs the transfer from the state in which
it does not conduct heat to the state in which it conducts heat
at the temperature above the switching temperature, while, by
virtue ofits design, the switchable heat-conducting connect-
ing device switches automatically from the state in which it
conducts heat to the state in which it does not conduct heat at
the temperature below the switching temperature. This elimi-
nates the need to equip the thermoelectric generator with a
controller for switching the at least one switchable heat-
conducting connecting device.
[0011] For example, the at least one switchable heat-con-
ducting connecting device of the thermoelectric generator
can expand in such away at the temperature above the switch-
ing temperature that the at least one heat transfer contact
between the at least one heat storage chamber and the at least
one associated thermoelectric module or an at least one heat-
conducting material which makes contact with the at least one
associated thermoelectric module is closed, wherein the at
least one switchable heat-conducting connecting device of
US 2014/0007915 A1 Jan. 9, 2014
the thermoelectric generator contracts in such away at the
temperature below the switching temperature that the heat
transfer contact is interrupted due to an air gap. As explained
in greater detail below, an advantageous embodiment ofthis
kind ofthe at least one switchable heat-conducting connect-
ing device can be formed at low cost by means of simple
production process steps.
[0012] In aparticularly advantageous embodiment, the at
least one switchable heat-conducting connecting device is
formed at least partially from ashape memory alloy. In this
case, at least one component part ofthe at least one switchable
heat-conducting connecting device can automatically expand
in such away at aswitching temperature equal to the associ-
ated shape memory temperature that apreviously existing gap
is closed.
[0013] As an alternative or in addition thereto, the at least
one switchable heat-conducting connecting device can be
formed in such away as an outer casing ofthe at least one heat
storage chamber, which is filled with at least one latent heat
storage material and/or with at least one thermochemical heat
storage material as the at least one heat storage material, that
aphase change ofthe at least one latent heat storage material
at the switching temperature and/or areversible chemical
reaction ofthe at least one thermochemical heat storage mate-
rial at the switching temperature brings about achange in the
shape of the outer casing of the at least one heat storage
chamber. The change in shape too can be used to close a
previously existing gap in such away that the desired heat
transfer contact for transferring the thermal energy to the at
least one thermoelectric module is obtained.
[0014] In an advantageous development, the at least one
switchable heat-conducting connecting device is coated with
acatalyst which reduces asoot burn off temperature. In this
way, soot deposits on the switchable heat-conducting con-
necting device can be prevented. Thus, reliable operation of
the thermoelectric generator is still guaranteed, even during
prolonged operation ofthe thermoelectric generator, despite
said generator being exposed to soot-rich exhaust gases.
[0015] The advantages described in the above paragraphs
can also be achieved by means of acorresponding heat stor-
age device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Further features and advantages ofthe present dis-
closure are explained below with reference to the figures, in
which:
[0017] FIG. 1shows a schematic illustration of afirst
embodiment ofthe thermoelectric generator;
[001S] FIG. 2shows a schematic illustration of asecond
embodiment ofthe thermoelectric generator;
[0019] FIGS. 3a to 3d show schematic partial views
intended to illustrate the operation of athird embodiment of
the thermoelectric generator; and
[0020] FIG.4shows a schematic illustration ofan embodi-
ment ofthe heat storage device.
DETAILED DESCRIPTION
[0021] FIG. 1shows a schematic illustration of afirst
embodiment ofthe thermoelectric generator.
[0022] The thermoelectric generator 10 illustrated sche-
matically in FIG. 1has agenerator housing 12,which can be
arranged in an exhaust line 14 ofavehicle and/or in abypass
to the exhaust line 14. The generator housing 12 can be
arranged in such away in the exhaust line 14 and/or in the
bypass that at least afirst exhaust gas contact surface 16ofthe
thermoelectric generator 10 is exposed for contacting by at
least one exhaust gas 1S.For example, at least one exhaust gas
duct 20 can pass through the thermoelectric generator 10,
through which the at least one exhaust gas 1S can be passed
after arrangement of the thermoelectric generator 10 in the
exhaust line 14.To enlarge the heat exchange surface thereof,
the thermoelectric generator 10can furthermore be designed
with arib structure. However, the thermoelectric generator 10
described here is not limited to aparticular form.
[0023] The thermoelectric generator 10illustrated in FIG. 1
can be divided (schematically) into aheat converter subunit
22 and aheat storage subunit 24. Preferably, the thermoelec-
tric generator 10can be arranged in the exhaust line 14in such
away that the heat storage subunit 24 is situated ahead ofthe
heat converter subunit 22. This can be interpreted to mean
that, after arrangement of the generator housing 12 in the
exhaust line 14 and/or in the bypass, the heat storage subunit
24 is arranged in such away relative to the heat converter
subunit 22 that the at least one exhaust gas 1S is first of all
guided past the heat storage subunit 24 and makes contact
with the at least one first exhaust gas contact surface 16ofthe
heat converter subunit 22 only after passing the heat storage
subunit 24. The construction of subunits 22 and 24 will be
explained in greater detail below.
[0024] The heat converter unit 22 comprises at least one
thermoelectric module 26 assigned to the at least one first
exhaust gas contact surface 16, wherein thermal energy
released by the at least one exhaust gas 1Scan be transferred
from the at least one first exhaust gas contact surface 16to the
at least one thermoelectric module 26 via at least one heat
conduction path. The at least one thermoelectric module 26
can be interpreted to mean aconverter device which converts
aflow ofheat directly into electric power. For this purpose,
the at least one thermoelectric module 26 preferably uses the
Seebeck effect, which results in atemperature gradient in a
thermoelectric material producing thermodi ffusion ofcharge
carriers. In this way, an electric potential difference between
a"hot" side 26a ofthe thermoelectric module 26 and a"cold"
side 26b of the thermoelectric module 26 can form, and this
can be taken off as an electric voltage. The "hot" side 26a of
the thermoelectric module 26 can be interpreted to mean a
side of the thermoelectric module 26 which faces the first
exhaust gas contact surface 16.In acorresponding way, the
"cold" side 26b ofthe thermoelectric module 26 can alterna-
tively be expressed as aside ofthe thermoelectric module 26
which faces away from the hot side 26a.
[0025] The heat conduction path from the at least one first
exhaust gas contact surface 16 to the at least one associated
thermoelectric module 26 can pass via at least one heat con-
duction material 2S. For example, at least one intermediate
volume, which is bounded in each case by afirst exhaust gas
contact surface 16 and by the hot side 26a ofthe at least one
associated thermoelectric module 16, can be filled at least
partially with the at least one heat conduction material 2S.The
at least one intermediate volume is preferably filled com-
pletely with the at least one heat conduction material 2S.This
ensures reliable trans fer ofthe thermal energy liberated by the
at least one exhaust gas 1S at the first exhaust gas contact
surface 26 to the at least one associated thermoelectric mod-
ule 26 so as to ensure ahigh yield ofelectric energy.
[0026] The heat storage subunit 24 has at least one heat
storage chamber 30, which is filled at least partially with at
US 2014/0007915 A1 3Jan. 9, 2014
TH —
Ta ~l+ZT —l
gi1liiX +
TH ~1+ZT +Tg/TH,
(Eq. t)
where qis amaximum material efficiency, T~is the tem-
perature on the hot side 26a, Tis the temperature on the cold
side 26b and ZT is an integral average of the temperature
gradient between sides 26a and 26b. The left-hand fraction in
the equation (Eq. I) indicates the Carnot efficiency q~
[0029] It is expressly pointed out here that the thermoelec-
tric generator 10can still be used, even at ahigh exhaust gas
temperature, despite its relatively low thermal resistance,
without fear of damage to the at least one thermoelectric
module 26. The advantageously arranged at least one heat
storage chamber 30, the at least one second exhaust gas con-
tact surface 32 ofwhich is preferably contacted by the at least
one exhaust gas 1Sfor the at least one first exhaust gas contact
surface 16, can still prevent overheating of the at least one
thermoelectric module 26, even at high/high-energy exhaust
least one heat storage material. In particular, the at least one
heat storage material can be at least one latent heat storage
material and/or at least one thermochemical heat storage
material. The at least one heat storage chamber 30 is assigned
at least one second exhaust gas contact surface 32 of the
thermoelectric generator 10, which surface is exposed for
contacting by the at least one exhaust gas 1S,wherein thermal
energy liberated can be transferred from the at least one
second exhaust gas contact surface 32 to the at least one
associated heat storage chamber 30. Moreover, the at least
one heat storage chamber 30 is arranged outside the at least
one heat conduction path. This can also be expressed by
saying that thermal energy transferred from the at least one
first exhaust gas contact surface 16to the at least one thermo-
electric module 26 is not transferred via the at least one heat
storage chamber 30.In particular, the at least one heat storage
chamber 30 can be situated outside the at least one interme-
diate volume bounded in each case by the at least one first
exhaust gas contact surface 16 and by the hot side 26a ofthe
at least one associated thermoelectric module 26, ofthe asso-
ciated thermoelectric module 26.
[0027] In this way, it is possible to ensure that the at least
one heat storage chamber 30 does not affect athermal resis-
tance during the conversion of thermal energy to electric
energy. It is thus possible to achieve areduced thermal resis-
tance in comparison with the prior art. Whereas, convention-
ally, athermal resistance during conversion ofthermal energy
to electric energy is the sum ofthe thermal resistance of the
least one thermoelectric module 26 and ofthe at least one heat
storage chamber 30, the relevant thermal resistance in the
case ofthe advantageous thermoelectric generator 10in FIG.
1is (virtually) equal to the thermal resistance ofthe at least
one thermoelectric module 26. In the case ofthe thermoelec-
tric generator 10,therefore, an improved yield 10 of electric
energy is obtained in comparison with aconventional genera-
tor.
[002S] By converting the waste heat ofthe exhaust gas 1Sto
electric energy, the thermoelectric generator 10 in FIG. 1
contributes to areduction in the energy consumption and
pollutant emissions of avehicle equipped therewith. Advan-
tages ofalarger temperature gradient between sides 26a and
26b of athermoelectric module 26 lie in high efficiency, as
shown in the equation (Eq. I):
gas volume flows, e.g. those during travel on afreeway. In
particular, the thermoelectric generator 10 can therefore be
designed for maximum efficiency during ajourney with a
relatively low average speed (ke. for amoderate exhaust gas
volume flow), thereby ensuring advantageous efficiency for
energy recovery, even during an urban journey, and simulta-
neously preventing overheating of the at least one thermo-
electric module 26 during ajourney on afreeway.
[0030] Owing to the advantageous interaction ofthe ther-
moelectric generator 10with at least one heat storage cham-
ber 30,the thermoelectric module 26 can also be designed for
an advantageous thermal resistance of the heat conduction
path to the thermoelectric module. Moreover, the temperature
on the hot side 26a ofthe thermoelectric module 26 can be
limited without reducing atotal efficiency ofthe thermoelec-
tric module 26. In particular, heat above atemperature level
which could damage the thermoelectric module 26 can be
converted to atemperature level which is permissible for the
thermoelectric module 26.
[0031] Another advantage ofthe interaction of the at least
one heat storage chamber 30with the at least one thermoelec-
tric module 26 is that the maximum permissible hot side
temperature ofthe hot side 26a ofthe thermoelectric module
26 can be designed to be lower and hence the requirements on
the construction and connection engineering can be reduced
considerably. As aresult, it is also possible to increase the
reliability ofthe at least one thermoelectric module 26 with-
out reducing the power yield.
[0032] Another advantage ofthe interaction of the at least
one heat storage chamber 30with the at least one thermoelec-
tric module 26 is that the transient states outside the permis-
sible temperature range ofthe thermoelectric generator which
are often encountered in normal driving can be accommo-
dated and exploited for energy. Transient states in the ther-
moelectric generator arise, for example, from overtaking
maneuvers, starts fromtraffic signals orhilly sections ofroad,
when the volume and temperature ofthe exhaust gas increase
due to asignificantly higher power output by the vehicle
engine. By means ofthe technology according to the disclo-
sure, however, the thermoelectric generator 10 is protected
even in these situations, and the thermal energy present in the
relatively hot exhaust gas can advantageously be used to
obtain electric energy.
[0033] The at least one latent heat storage material in the at
least one heat storage chamber 30 can be interpreted to mean
at least one heat storage material operating on the principle of
alatent heat store. Above apredetermined limiting tempera-
ture, aheat storage material of this kind undergoes aphase
change and, in this way, absorbs large quantities of energy.
For example, the phase change can be melting ofthe at least
one heat storage material to absorb heat offusion, which can
be liberated again as heat of solidification at atemperature
below the limiting temperature, by solidification of the at
least one heat storage material.
[0034] In aparticularly advantageous embodiment, the at
least one heat storage chamber 30 is filled with at least one
latent heat storage material (phase change material), which
has aheat of fusion of more than 350 I/g and amelting
temperature of less than 600' C. Preferably, the at least one
latent heat storage material is asalt, amixture ofsalts, ametal
and/or ametal alloy. Salts, mixtures ofsalts, metals and metal
alloys can reliably offer ahigh heat of fusion at asuitable
melting temperature.
US 2014/0007915 A1 Jan. 9, 2014
[0035] Filling the at least one heat storage chamber 30with
asalt or amixture of salts furthermore offers the advantage
that arelatively large quantity of energy can be stored tem-
porarily as heat of fusion. Moreover, salts and mixtures of
salts are low cost materials for latent heat storage. By forming
relatively short heat transfer paths in the at least one salt, it is
also possible to maintain low losses over the heat transfer path
where the thermal conductivity of the at least one salt is
relatively low. Moreover, more rapid heat transfer is also
possible in this way.
[0036] In an advantageous development, the at least one
salt can also be embedded/infiltrated into astructure consist-
ing ofathermally conductive material, e.g. at least one metal
and/or graphite. The structure consisting of the at least one
thermally conductive material can be afabric, an open-cell
material and/or afoam, for example. In a particularly advan-
tageous embodiment, the at least one salt is embedded/infil-
trated into an open-cell metal foam, e.g. an aluminum foam.
Thus, despite arelatively low thermal conductivity ofthe at
least one salt, rapid heat transfer can be achieved in asimple
manner.
[0037] As the at least one salt or mixture ofsalts, the at least
one heat storage chamber 30 can contain KCI(54)-46ZnCI~,
KCI(61)-39MgCI„NaCI(48)-52MgCI„KCI(36)-64MgCI„
NaCI(33)-67CaCI„MgCI, (37)-63SrCI„LI,CO,(47)-
53K~CO, LI~CO (44)-56Na~CO, LI~CO (28)-72K~CO,
K,CO, (51)-49Na,CO3, LIF(33)-67KF, NaF(67)-33MgF~,
NaBr(45)-55MgBr~, LIF(20)-80LIH, KCI(25)-27CaCI~-
48MgCI~, KCI(5)-29NaC1-66CaCI~, KCI(13)-19NaCI-
68SrCI~, KCI(28)-19NaC1-53BaCI~, KCI(24)-47BaCI~-
29CaCI„LI,CO,(32)-35K,CO, Na, CO„NaF(12)-59KF-
29LiF, KCI(40)-23KF-37K~CO3, NaF(17)-21KF-62K~CO3,
LI~CO (35)-65K~CO, LI~CO (20)60-Na~CO -20K~CO
and/or Li3CO(22)-16Na~CO3-62K~CO3, for example. How-
ever, the filling ofthe at least one heat storage chamber 30 is
not limited to the salts and mixtures ofsalts enumerated here.
[0038] As an alternative or in addition to at least one salt,
the at least one heat storage chamber 30 can also contain a
metal or ametal alloy as alatent heat storage material. Filling
the at least one heat storage chamber 30with ametal and/or a
metal alloy offers the advantage of high thermal conductivity
ofthe metal filling in the at least one heat storage chamber 30
and ofexternal surroundings ofthe at least one heat storage
chamber 30.This heat transfer is also relatively rapid and, in
particular, does not require an additional structure to improve
thermal conductivity, such as ametal foam.
[0039] As the at least one metal or the at least one metal
alloy, the at least one heat storage chamber 30 can contain
463Mg-53.7Zn, 96Zn-4AI, 34.65Mg-6535AI, 60.8A1-33.
2Cu-6.0Mg, 64.1A1-5.2Si-28.5-Cu2.2Mg, 68.5A1-5.0Si-26.
5Cu, 66.92A1-33.08Cu, 83.14A1-11.
7Si-5.16Mg, 87.76AI-
12.24Si, 463A1-4.6Si-49.1Cu and/or 86.4A1-9.4Si-4.2Sb,
for example. However, the suitability for use ofmetals/metal
alloys for filling the at least one heat storage chamber 30is not
limited to the embodiments enumerated here.
[0040] All the latent heat storage materials enumerated
above have amelting temperature which allows heat storage
at arelatively high exhaust gas temperature. In addition, all
the latent heat storage materials enumerated above have a
high specific thermal storage capacity and ahigh heat of
fusion in order to be able to temporarily store alarge quantity
ofthermal energy, even when the dimensions of the at least
one heat storage chamber 30 are relatively small. In the case
ofaphase change ofthe latent heat storage materials enumer-
ated above, melting is congruent (undissociated). Thus, no
phase separation takes place during melting or solidification,
and therefore astoichiometric composition or inhomogeneity
is prevented. The respective phase changes ofthe latent heat
storage materials enumerated above are reliably reversible
and repeatable. Moreover, the latent heat storage materials
have ahigh thermal conductivity for very low temperature
gradients during heat transfer within the latent heat storage
material (phase change material).
[0041] Another advantage of many latent heat storage
materials enumerated is arelatively small change in volume
during the phase change, something that allows the use of
low-cost outer walls for the at least one heat storage chamber
30.Moreover, the latent heat storage materials mentioned do
not have any pronounced tendency for an undercooled melt.
Owing to the chemical stability thereof, a long service life of
the latent heat storage materials is also guaranteed. In addi-
tion, the latent heat storage materials show no tendency for
chemical reaction with the materials that are generally used to
form an outer casing ofthe at least one heat storage chamber
30. The latent heat storage materials enumerated here are
neither toxic nor easily flammable. The costs associated
therewith are relatively low.
[0042] In aparticularly advantageous embodiment, the at
least one heat storage chamber 30 is at least partially filled
with AISi12 (aluminum containing 12%by mass of silicon).
Such afilling ensures arelatively high heat offusion of 560'
C. Moreover, the advantages of aspecific heat of the melt
which is higher by over 70% than the solid can be exploited.
Thus, after the complete melting ofthe material, more energy
can be absorbed per unit of mass than in the solid. Further
advantageous embodiments of latent heat storage materials
are salts LIF(20)-80LIOH and NaCI(48)-52MgCI~ and the
metal alloys 60.8A1-33.2Cu-6.0Mg and 87.76A1-12.24Si.
[0043] As an alternative or in addition to at least one latent
heat storage material, the at least one heat storage chamber 30
can also be filled with at least one thermochemical heat stor-
age material. The at least one thermochemical heat storage
material can be interpreted to be materials for chemical heat
storage, wherein spent thermal energy can be stored tempo-
rarily by means of areversible chemical reaction. The tem-
porarily stored thermal energy is then liberated again by
means ofat least one reverse reaction.
[0044] The at least one chemical reaction can be arevers-
ible elimination ofwater, for example. For this purpose, the at
least one heat storage chamber 30 can contain the hydrate of
calcium chloride (CaC1~~2H~O~CaCI~~H~O+H~O), cal-
cium hydroxide (Ca(OH)~~CaO+2H~O) and/or magnesium
hydroxide (Mg(OH)~~MgO+H~O) as the thermochemical
heat storage material.
[0045] Ametal hydride can likewise be used as the thermo-
chemical heat storage material in order to store thermal
energy temporarily by means of the reversible decomposi-
tion. Magnesium hydride (MgH~~Mg+H~), in particular, is
very suitable for this purpose.
[0046] The reversible decomposition of salts can also be
used for heat storage, e.g. using ammonium sulfate
(NH~SO~~NH3+H~O+SO3). In addition, the reversible
decomposition of metal carbonates, e.g. iron carbonate
(FeCO3~FeO+CO~) and/or calcium carbonate
(CaCO3~CaO+CO~) can be used for energy storage.
[0047] Moreover, thermal energy can be stored temporarily
by the dilution of acids, wherein sulfuric acid (H~SO~+
xH~O~dilute H~SO~), in particular, can be used. Moreover,
US 2014/0007915 A1 Jan. 9, 2014
the reversible decomposition of alcohols, especially metha-
nol (CH3OH~CO+2H~) can also be used for reversible heat
storage.
[004S] All the examples enumerated here ofthermochemi-
cal heat storage materials that can be used have avery high
heat storage densities for chemical heat storage in their reac-
tions, and these densities can be up to several 1000 kJ/kg.
Owing to the large number ofchemical reactions that can be
used, at least one particularly well-suited thermochemical
heat storage material can be selected for specific heat storage
and temperature requirements.
[0049] The thermoelectric generator described here is also
suitable for use in avehicle with arelatively high curb weight,
e.g. acommercial vehicle. Thus, high pressures may also be
exerted on the at least one thermochemical heat storage mate-
rial, and this increases the available choice of reversible
chemical reactions that can be used. Byvirtue ofthe relatively
high storage density of the thermal heat stores that can be
achieved by this means, it is also possible to compensate for
large load peaks. Thus, the use ofthe thermoelectric generator
10allows an increase in the efficiency ofcommercial-vehicle-
specific processes for waste heat recovery, e.g. cyclical pro-
cesses (organic Rankine, steam turbocharger). Through skil-
ful configuration of the thermoelectric generator 10, in
particular of the at least one heat storage chamber 30, the
proportionate amount of time for which these cyclical pro-
cesses are operated at the point ofmaximum efficiency can be
increased.
[0050] By means ofthe heat storage materials enumerated
above, very high heat storage densities can be achieved.
Moreover, the heat storage materials can also be selected to
release heat at arelatively high temperature, thereby addition-
ally increasing the efficiency of thermoelectric energy gen-
eration. Attention is drawn here, in particular, to the fact that
acombination ofthe principle ofthe latent heat store and the
principle ofthe chemical heat store can be used for temporary
storage ofthermal energy by means of the at least one heat
storage chamber 30.
[0051] The at least one latent heat storage material and/or
thermochemical heat storage material can absorb and tempo-
rarily store thermal energy at afirst exhaust gas temperature,
which is higher than or equal to aspecific limiting tempera-
ture/heat storage temperature ofthe latent heat storage mate-
rial and/or ofthe thermochemical heat storage material. At a
second exhaust gas temperature ofthe at least one exhaust gas
1S,which is less than or equal to the limiting temperature/heat
storage temperature, the at least one latent heat storage mate-
rial and/or thermochemical heat storage material can release
this thermal energy again.
[0052] Ifthe at least one exhaust gas 1S has atemperature
which is higher than alimiting temperature ofthe at least one
heat storage material, thermal energy can thus be absorbed
and temporarily stored by means of aphase change or a
reversible chemical reaction ofthe at least one heat storage
material. In this way, it is possible to ensure that ahot side
temperature ofthe hot side 26a ofthe thermoelectric module
26 remains below the maximum permissible temperature,
even at relatively high exhaust gas temperatures. The at least
one heat storage chamber 30 thus converts aflow ofheat at a
temperature higher than amaximum permissible operating
temperature ofthe thermoelectric generator 10 into aflow of
heat, the temperature of which is below the maximum per-
missible operating temperature ofthe thermoelectric genera-
tor 10.This reduction in the temperature of the flow of heat
takes place continuously until the latent/thermochemical heat
storage material has reached the maximum heat absorption
capacity thereof. Moreover, the reduction in temperature has
no effect on the amount ofheat in the flow ofheat. Ifthe flow
of heat is so great that there is more heat available at areduced
temperature than can flow through the thermoelectric genera-
tor 10, more ofthe instantaneously excess thermal energy is
stored temporarily in the heat storage material. If the tem-
perature in the thermoelectric generator 10 falls below the
temperature at which heat is released from the heat storage
material/limiting temperature, the heat storage material once
again begins to discharge more heat into the thermoelectric
generator. The thermoelectric generator 10 is thus reliably
protected from damage by excessive temperatures from the
exhaust gas flow.
[0053] As asupplementary feature to the components ofthe
thermoelectric generator 10which have been described thus
far, the generator can also be designed with at least one
cooling water duct 34, which is preferably routed along the at
least one cold side 26b of the at least one thermoelectric
module. However, the design potential ofthe thermoelectric
generator 10is not limited to being equipped with the at least
one cooling water duct 34or to aparticular design of the latter.
[0054] The thermoelectric generator 10 illustrated sche-
matically in FIG. 1has an outer thermal insulation 36.In the
thermoelectric generator 10, aregion situated between the at
least one heat storage chamber 30 and the adjacent thermo-
electric module 26 and the associated intermediate volume is
furthermore also filled with athermal insulation 3S.There is
thus no direct heat transfer (fuel solid-body heat transfer)
between the at least one heat storage chamber 30 and the at
least one adjacent thermoelectric module 36.Ifan exhaust gas
temperature ofthe at least one exhaust gas 1S falls below the
limiting temperature, the at least one cooling heat storage
chamber 30 releases the thermal energy being emitted to the
at least one exhaust gas 1Svia the at least one second exhaust
gas contact surface 32. By means ofthe at least one exhaust
gas 1S, the thermal energy is then transmitted to the at least
one first exhaust gas contact surface 16and is then transferred
to the at least one associated thermoelectric module 26. The
thermal energy that is temporarily stored by means of the at
least one heat storage chamber 30 can thus be converted at
least partially into electric energy by the at least one thermo-
electric module 26.
[0055] FIG. 2shows a schematic illustration of asecond
embodiment ofthe thermoelectric generator.
[0056] The thermoelectric generator 10 illustrated sche-
matically in FIG. 2has the components 12, 16 and 20 to 36
already described above. In the thermoelectric generator 10in
FIG. 2, however, aregion situated between the at least one
heat storage chamber 30 and the intermediate volume is not
completely filled with athermal insulation 3S.Instead, aheat
transfer contact 40 between the at least one heat storage
chamber 30 and at least one heat-conducting material 2S in
the respective region is designed in such away that thermal
energy can be transferred directly from the at least one heat
storage chamber 30 to the at least one associated thermoelec-
tric module 26 by means ofthe at least one heat-conducting
material 2S situated therebetween in each case.
[0057] This is advantageous since aheat transfer point
between the solids ofthe at least one heat storage chamber 30
and the at least one heat-conducting material 2S has ahigher
efficiency than asolid/gas heat transfer point. As compared
with the embodiment described above, the heat transfer con-
US 2014/0007915 A1 Jan. 9, 2014
tact 40 can thus replace two solid/gas heat transfer points. The
thermoelectric generator 10 in FIG. 2thus ensures abetter
yield ofthe thermal energy stored temporarily in the at least
one heat storage chamber 30.
[005S] FIGS. 3a to 3d show schematic partial views
intended to illustrate the operation of athird embodiment of
the thermoelectric generator.
[0059] The thermoelectric generator 10 shown schemati-
cally in part by means ofFIGS. 3a to 3d is designed in such a
way that thermal energy can be transferred (directly or indi-
rectly) from the at least one heat storage chamber 30 to the at
least one associated thermoelectric module 26 by means ofat
least one heat transfer contact 40, which can be formed, ofthe
thermoelectric generator 10.The presence of aheat transfer
contact 40 which is formed or can be formed between the at
least one heat storage chamber 30 and the associated thermo-
electric module 26 or the at least one heat-conducting mate-
rial 2S connected thereto is associated with the advantage that
the temporarily stored thermal energy can be fed into the at
least one thermoelectric module 26 from the at least one heat
storage chamber 30 exclusively via a solid-body heat conduc-
tion path. In this way too, the abovementioned solid/gas heat
transfer point can advantageously be circumvented. In this
case, the feeding in ofthe temporarily stored thermal energy
is significantly more efficient.
[0060] Inparticular, the at least one heat transfer contact 40
can be formed by means of at least one switchable heat-
conducting connecting device 42 ofthe thermoelectric gen-
erator 10, wherein the switchable heat-conducting connect-
ing device 42 can be switched from astate in which it
conducts heat to astate in which it does not conduct heat.
Implementing the at least one heat transfer contact 40 by
means ofat least one switchable heat-conducting connecting
device 42 offers the advantage that the heat trans fer contact 40
can be formed selectively when the limiting temperature of
the at least one latent heat storage material and/or thermo-
chemical heat storage material is exceeded. In contrast, the
heat transfer contact 40 which can be formed can be inter-
rupted selectively to the extent that the limiting temperature
has not yet been undershot. In this way, it is possible to
prevent asituation where thermal energy flows from the at
least one heat storage chamber 30 into the at least one ther-
moelectric module 26 even at temperatures below the limiting
temperature.
[0061] The at least one switchable heat-conducting con-
necting device 42 ofthe thermoelectric generator 10 is pref-
erably designed in such away that the at least one switchable
heat-conducting connecting device 42 switches (automati-
cally) from the state in which it does not conduct heat to the
state in which it conducts heat at atemperature above a
switching temperature Ts, and switches (automatically) from
the state in which it conducts heat to the state in which it does
not conduct heat at atemperature below the switching tem-
perature Ts.By means ofthe automatic capacity for switching
of the at least one switchable heat-conducting connecting
device 42, acontrol device for controlling the at least one
switchable heat-conducting connecting device 42 can be
omitted.
[0062] In the case of the thermoelectric generator 10 in
FIGS. 3a to 3d, the at least one switchable heat-conducting
connecting device 42 of the thermoelectric generator 10
expands at atemperature above the switching temperature Ts.
By means ofthe expanded switchable heat-conducting con-
necting device 42, the at least one heat transfer contact 40
between the at least one heat storage chamber 30 and the at
least one associated thermoelectric module 26 or at least one
heat-conducting material 2S which makes contact (directly or
indirectly) with the at least one associated thermoelectric
module 26 is closed. In contrast, the at least one switchable
heat-conducting connecting device 42 ofthe thermoelectric
generator 10 contracts in such away at atemperature below
the switching temperature Ts that the heat transfer contact 40
is interrupted due to an air gap 44.
[0063] In the embodiment in FIGS.3a to 3d, the at least one
switchable heat-conducting device 42 is formed as an outer
casing ofthe at least one heat storage chamber 30, which is
filled with the at least one latent heat storage material and/or
with the at least one thermochemical heat storage material. As
can be seen from FIGS. 3a and 3b, the switchable heat-
conducting connecting device 42 is formed in such away that
aphase change ofthe at least one latent heat storage material
and/or areversible chemical reaction ofthe at least one ther-
mochemical heat storage material brings about achange in
the shape ofthe outer casing of the at least one heat storage
chamber 30.This allows alow-cost design ofthe at least one
switchable heat-conducting connecting device 42 in order to
ensure that it operates in an advantageous manner.
[0064] FIG. 3a shows aswitchable heat-conducting con-
necting device 42 designed as an outer casing ofaheat storage
chamber 30 in the compressed form ofsaid device. The com-
pressed switchable heat-conducting connecting device 42 has
afirst maximum length Ll at afirst temperature less than a
predetermined switching temperature Ts.
[0065] As can be seen from FIG. 3b, an increase in tem-
perature to asecond temperature T2 greater than the switch-
ing temperature Ts brings about an expansion ofthe switch-
able heat-conducting connecting device 42 designed as an
outer casing of the heat storage chamber 30 to asecond
maximum length L2 greater than the first maximum length
Ll. This expansion of the switchable heat-conducting con-
necting device 42 can be used to close the at least one heat
transfer contact 40. For this purpose, the at least one heat
storage chamber 30 is arranged in afree space in the generator
housing 12between at least one supporting wall 46 and the at
least one associated thermoelectric module 26 or the at least
one heat-conducting material 2S making contact (directly or
indirectly) with the at least one associated thermoelectric
module 26, which has an extent in the direction ofthe maxi-
mum length LIor L2 which is greater than the first maximum
length Ll and less than or equal to the maximum length L2.
[0066] Thus, the presence ofthe switchable heat-conduct-
ing connecting device 42 in the compressed state thereof
results in the presence ofat least one air gap 44 between the
heat storage chamber 30 and the adjacent thermoelectric
module 26 or the at least one heat-conducting material 2S
making contact (directly or indirectly) with the module 26
(see FIG. 3c).As can be seen from FIG. 3d, the at least one air
gap 44 is bridged in such away by the expansion of the
switchable heat-conducting connecting devices 42 to at least
the second maximum length L2 at asecond temperature T2
greater than or equal to the switching temperature Ts that the
heat transfer contact 40 is closed.
[0067] The at least one switchable heat-conducting con-
necting device 42 designed as the outer casing ofthe at least
one heat storage chamber 30 can be made of nickel, for
example. This is advantageous, in particular, ifLiOH is used
as the latent heat storage material (phase-change heat store).
The switchable heat-conducting connecting device 42 as the
US 2014/0007915 A1 Jan. 9, 2014
outer casing can likewise contain the high-grade steel 1.4301
(XSCrNi18-10) for encapsulating aphase-change heat store
made of87.76A1-12.24Si and/or AISi12. However, the mate-
rials enumerated here for forming the switchable heat-con-
ducting connecting device 42 acting as the outer casing ofthe
heat storage chamber 30 should be interpreted only as
examples.
[006S] Attention is drawn to the fact that the above-ex-
plained design ofthe switchable heat-conducting connecting
device 42 as the outer casing/encapsulation ofthe at least one
heat storage chamber 30 should be interpreted only as an
example. For example, the at least one switchable heat-con-
ducting connecting device can also be formed at least par-
tially from ashape memory alloy. In this case, atwo-way
shape memory alloy is particularly advantageous, wherein
the switchable heat-conducting connecting device 42 has
both ahigh-temperature and alow-temperature shape.
[0069] The switchable heat-conducting connecting device
42 formed at least partially by ashape memory alloy can be
configured as aspring, for example. When the shape memory
temperature is reached, the switchable heat-conducting con-
necting device 42 designed as aspring in this case assumes
the expanded high-temperature shape thereof and can thus
move aheat storage chamber 30 in the direction ofthe adja-
cent thermoelectric module 26 or the at least one associated
heat-conducting material 2S in such away that the desired
heat transfer contact 40 is closed. In the case of alow-tem-
perature shape ofthe at least one switchable heat-conducting
connecting device 42 designed as aspring, at least one heat
storage chamber 30 can be pushed back into the initial posi-
tion thereof, as aresult ofwhich the heat transfer contact 42 is
interrupted by an air gap 44. Formation of the at least one
switchable heat-conducting connecting device 42 at least par-
tially from ashape memory alloy thus also offers the advan-
tages described above.
[0070] In an advantageous development, the at least one
switchable heat-conducting connecting device 42, which is
designed, for example, as the outer casing ofthe at least one
heat storage chamber 30 and/or is made ofashape memory
material, can be coated with acatalyst which reduces asoot
burn offtemperature. By means ofthe catalytic coating ofthe
switchable heat-conducting connecting device 42, the burn
off temperature ofthe soot can be reduced to such an extent
that the switchable heat-conducting connecting device 42
remains (almost) free from soot, even after prolonged opera-
tion of the thermoelectric generator 10. In this way, it is
possible to prevent asituation where soot is deposited on the
switchable heat-conducting connecting device 42 and hence a
thermal connection between the compressed switchable heat-
conducting connecting device 42 and the outside environ-
ment thereof is formed by soot deposits. Cerium oxide (CeO)
is suitable as acatalytic coating, for example.
[0071] FIG.4shows a schematic illustration ofan embodi-
ment ofthe heat storage device.
[0072] The heat storage device 50 shown schematically in
FIG. 4can interact with athermoelectric generator 52 of a
vehicle. For this purpose, the heat storage device 50 can be
arranged in such away outside agenerator housing 12 ofthe
thermoelectric generator 52, in an exhaust line 14 of the
vehicle and/or in abypass 54 to the exhaust line 14, that
thermal energy can be transferred from the at least one heat
storage chamber 30 of the heat storage device 50 to at least
one thermoelectric module 26 (not shown) ofthe thermoelec-
tric generator 52 by means ofat least one heat transfer contact
40, which is formed or can be formed between the heat
storage device 50 and the thermoelectric generator 52. In this
case too, the at least one heat storage chamber 30 is filled with
at least one heat storage material. In particular, the at least one
heat storage material can be at least one latent heat storage
material and/or at least one thermochemical heat storage
material.
[0073] In the embodiment in FIG. 4, the heat storage device
50 is integrated into abypass 54. The advantage of such an
arrangement ofthe heat storage device 50 is that, in this case,
the exhaust gas heat passed through the bypass 54 at arela-
tively high temperature, which is impermissible for the ther-
moelectric generator 52 for example, can nevertheless also be
used for the thermoelectric generator 52.For this purpose, the
heat ofthe exhaust gas 1Spassed through the bypass 54 can be
stored temporarily by means of the heat storage device 50.
The temporarily stored heat can then be fed into the thermal
generator 52 again as soon as said generator is in the operating
state thereof below the maximum design figure thereof. In
this way, the electric power output ofthe thermoelectric gen-
erator 52 can be additionally increased.
[0074] The bypass 54 is often used to compensate for the
exhaust gas temperature and/or the exhaust gas backpressure
being exceeded at ahigh load, e.g. during ajourney on a
freeway. For this purpose, the bypass 54 is opened when there
is arisk that the thermoelectric generator 52 will overheat due
to the exhaust gas temperature and/or the exhaust gas back-
pressure. Bymeans ofthe bypass 54, the exhaust gas flow can
be routed at least partially around the thermoelectric genera-
tor 52. However, this opening ofthe bypass normally results
in the loss of alarge amount ofthermal energy for the ther-
moelectric generator 52 and hence also for power generation.
In contrast, the heat storage device 50 makes it possible also
to use part ofthe waste heat which would otherwise be lost
through the bypass 54.
[0075] In an advantageous embodiment ofthe heat storage
device 50, the at least one heat transfer contact 40 can be
formed by means ofat least one switchable heat-conducting
connecting device 42 ofthe heat storage device 50. This can
be achieved by the fact that the switchable heat-conducting
connecting device 42 can be switched from astate in which it
does not conduct heat into astate in which it conducts heat.
For this purpose, the switchable heat-conducting connecting
device can, for example, be designed in such away that the at
least one switchable heat-conducting connecting device 42
switches (automatically) from the state in which it does not
conduct heat to the state in which it conducts heat at atem-
perature above aswitching temperature, and switches (auto-
matically) from the state in which it conducts heat to the state
in which it does not conduct heat at atemperature below the
switching temperature. This can be achieved by designing the
switchable heat-conducting connecting device 42 ofthe heat
storage device 50 in such away that it expands at atempera-
ture above the switching temperature, and hence the at least
one heat transfer contact 40 between the at least one heat
storage chamber 30 and the thermoelectric generator 52 or the
at least one thermoelectric module is closed. It is likewise
possible for the at least one switchable heat-conducting con-
necting device 42 to be designed in such away that it contracts
at atemperature below the switching temperature, as aresult
ofwhich the heat transfer contact 42 is interrupted due to an
air gap (not shown).
[0076] To ensure the advantageous mode of operation of
the at least one switchable heat-conducting connecting device
US 2014/0007915 A1 Jan. 9, 2014
42 ofthe heat storage device 50, the at least one switchable
heat-conducting connecting device can be formed at least
partially from ashape memory alloy and/or can be designed
as an outer casing ofthe at least one heat storage chamber 30.
With respect to the possibility of forming the at least one
switchable connecting device 42, attention is drawn to the
statements made above. The at least one switchable heat-
conducting connecting device 42 is preferably protected from
soiling by ahousing.
[0077] The heat storage device 50 illustrated schematically
in FIG. 4can be designed as acompact unit with the thermo-
electric generator 52. Moreover, an outer housing ofthe heat
storage device 50 can be formed integrally with the exhaust
line 14 and/or the bypass 54.
[007S] In particular, the above-described embodiments of
the thermoelectric generator 10and 52 and ofthe heat storage
device 50 can also be integrated into an exhaust catalyzer to
form aunit. In this case, the latent heat storage material and/or
the thermochemical heat storage material can be integrated
into the exhaust catalyzer in such away that the temperature
ofthe catalytically active surface in the exhaust catalyzer can
be limited by means ofthe at least one heat storage chamber
30.In this way, removal ofcatalytically active substance by
an excess temperature can be prevented.
[0079] In particular, the assembly comprising an exhaust
catalyzer, athermoelectric generator 10 or 52 and/or aheat
storage chamber 30/heat storage device 50 can be configured
in such away that, specifically when the catalyzer is in a
high-temperature form, the heat storage chamber 30/heat
storage device 50 forms athermal contact with the catalyzer.
In this way, it is possible to ensure that the catalyzer does not
suffer any heat losses due to the thermoelectric generator 10
or 52 and/or the heat storage chamber 30/heat storage device
50 at low temperatures. Thus, awarm-up time before the
operating temperature of the catalyzer is reached is not
lengthened, despite the formation ofthe assembly.
What is claimed is:
1.Athermoelectric generator for avehicle, comprising:
agenerator housing arranged in one or more ofan exhaust
line ofthe vehicle and abypass to the exhaust line in such
away that at least one first exhaust gas contact surface of
the thermoelectric generator is configured to contact at
least one exhaust gas;
at least one thermoelectric module assigned to the at least
one first exhaust gas contact surface, thermal energy
being configured to be transferred from the at least one
first exhaust gas contact surface to the at least one ther-
moelectric module via at least one heat conduction path;
and
at least one heat storage chamber filled with at least one
heat storage material,
wherein the at least one heat storage chamber is assigned at
least one second exhaust gas contact surface ofthe ther-
moelectric generator, the second exhaust gas contact
surface being configured to contact the at least one
exhaust gas,
wherein thermal energy is configured to be transferred
from the at least one second exhaust gas contact surface
to the at least one heat storage chamber, and
wherein the at least one heat storage chamber is arranged
outside the at least one heat conduction path from the at
least one first exhaust gas contact surface to the at least
one thermoelectric module.
2. The thermoelectric generator according to claim 1,
wherein at least one intermediate volume is situated between
the at least one first exhaust gas contact surface and the at least
one associated thermoelectric module in each case, and
wherein the at least one heat storage chamber is arranged
outside the at least one intermediate volume.
3. The thermoelectric generator according to claim 1,
wherein thermal energy is configured to be transferred from
the at least one heat storage chamber to the at least one
associated thermoelectric module by at least one heat transfer
contact of the thermoelectric generator, the contact being
formed or being configured to be formed.
4. The thermoelectric generator according to claim 3,
wherein the at least one heat transfer contact is configured to
be formed by at least one switchable heat-conducting con-
necting device of the thermoelectric generator, the device
being configured to be switched from astate in which it does
not conduct heat to astate in which it conducts heat.
5. The thermoelectric generator according to claim 4,
wherein the at least one switchable heat-conducting connect-
ing device ofthe thermoelectric generator switches from the
state in which it does not conduct heat to the state in which it
conducts heat at atemperature above aswitching temperature
and switches from the state in which it conducts heat to the
state in which it does not conduct heat at atemperature below
the switching temperature.
6. The thermoelectric generator according to claim 5,
wherein the at least one switchable heat-conducting connect-
ing device ofthe thermoelectric generator expands in such a
way at the temperature above the switching temperature that
the at least one heat transfer contact between the at least one
heat storage chamber and the at least one associated thermo-
electric module or an at least one heat-conducting material
which makes contact with the at least one associated thermo-
electric module is closed, and the at least one switchable
heat-conducting connecting device ofthe thermoelectric gen-
erator contracts in such away at the temperature below the
switching temperature that the heat transfer contact is inter-
rupted due to an air gap.
7. The thermoelectric generator according to claim 6,
wherein the at least one switchable heat-conducting connect-
ing device is formed at least partially from ashape memory
alloy.
S. The thermoelectric generator according to claim 6,
wherein:
the at least one heat storage chamber has an outer casing
into which one or more ofat least one latent heat storage
material and at least one thermochemical heat storage
material are filled as the at least one heat storage mate-
rial, and
wherein the at least one switchable heat-conducting con-
necting device is formed in such away that one or more
of aphase change ofthe at least one latent heat storage
material and areversible chemical reaction ofthe at least
one thermochemical heat storage material brings about a
change in the shape ofthe outer casing ofthe at least one
heat storage chamber.
9. The thermoelectric generator according to claim 4,
wherein the at least one switchable heat-conducting connect-
ing device is coated with acatalyst that reduces a soot burn off
temperature.
10.Aheat storage device for athermoelectric generator of
avehicle, comprising:
US 2014/0007915 A1 Jan. 9, 2014
at least one heat storage chamber filled with at least one
heat storage material,
wherein the heat storage device is configured to be
arranged in such away outside ahousing ofthe thermo-
electric generator, in one or more of an exhaust line of
the vehicle and abypass to the exhaust line, that thermal
energy is configured to be transferred from the at least
one heat storage chamber to at least one thermoelectric
module of the thermoelectric generator by at least one
heat transfer contact, the contact being formed or being
configured to be formed between the heat storage device
and the thermoelectric generator.
11.The heat storage device according to claim 10,wherein
the at least one heat transfer contact is configured to be
formed by at least one switchable heat-conducting connect-
ing device of the heat storage device, the switchable heat-
conducting connecting device being configured to be
switched from astate in which it does not conduct heat into a
state in which it conducts heat.
12.The heat storage device according to claim 11,wherein
the at least one switchable heat-conducting connecting device
ofthe heat storage device switches from the state in which it
does not conduct heat to the state in which it conducts heat at
atemperature above aswitching temperature and switches
from the state in which it conducts heat to the state in which
it does not conduct heat at atemperature below the switching
temperature.
13.The heat storage device according to claim 12,wherein
the at least one switchable heat-conducting connecting device
of the heat storage device expands in such away at the
temperature above the switching temperature that the at least
one heat transfer contact is closed, and the at least one swit-
chable heat-conducting connecting device ofthe heat storage
device contracts in such away at the temperature below the
switching temperature that the heat transfer contact is inter-
rupted due to an air gap.
14.The heat storage device according to claim 13,wherein
the at least one switchable heat-conducting connecting device
ofthe heat storage device is one or more of formed at least
partially from ashape memory alloy and designed as an outer
casing ofthe at least one heat storage chamber that is filled
with the at least one heat storage material.
15.The heat storage device according to claim 11,wherein
the at least one switchable heat-conducting connecting device
is protected from soiling by ahousing.