U.S. patent application number 15/317528 was filed with the patent office on 2017-05-18 for branching means for a refrigerant flow of a refrigerant circuit.
This patent application is currently assigned to VALEO KLIMASYSTEME GMBH. The applicant listed for this patent is VALEO KLIMASYSTEME GMBH. Invention is credited to Roland Haussmann.
Application Number | 20170138651 15/317528 |
Document ID | / |
Family ID | 53476896 |
Filed Date | 2017-05-18 |
United States Patent
Application |
20170138651 |
Kind Code |
A1 |
Haussmann; Roland |
May 18, 2017 |
BRANCHING MEANS FOR A REFRIGERANT FLOW OF A REFRIGERANT CIRCUIT
Abstract
A branching means for a refrigerant flow of a refrigerant
circuit (10), in particular of a battery cooler circuit (30), has
an inlet (52) and at least two outlet lines (58) which lead to two
cooling branches (34, 36), wherein at least one throttle stage is
integrated into the branching means (44).
Inventors: |
Haussmann; Roland;
(Wiesloch, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VALEO KLIMASYSTEME GMBH |
Bad Rodach |
|
DE |
|
|
Assignee: |
VALEO KLIMASYSTEME GMBH
Bad Rodach
DE
|
Family ID: |
53476896 |
Appl. No.: |
15/317528 |
Filed: |
June 23, 2015 |
PCT Filed: |
June 23, 2015 |
PCT NO: |
PCT/EP2015/064105 |
371 Date: |
December 9, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 9/008 20130101;
F25B 2500/18 20130101; F25B 2500/31 20130101; F25B 5/02 20130101;
F25B 2700/21174 20130101; F25B 2309/061 20130101; F25B 40/00
20130101; F25B 40/06 20130101; F25B 39/028 20130101; F25B 43/003
20130101; F25B 2600/2519 20130101; F25B 39/00 20130101; F25B 40/02
20130101; F25B 2700/21175 20130101; F25B 41/062 20130101 |
International
Class: |
F25B 39/00 20060101
F25B039/00; F25B 9/00 20060101 F25B009/00; F25B 40/06 20060101
F25B040/06; F25B 43/00 20060101 F25B043/00; F25B 40/00 20060101
F25B040/00; F25B 40/02 20060101 F25B040/02; F25B 5/02 20060101
F25B005/02; F25B 41/06 20060101 F25B041/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2014 |
DE |
102014108989.8 |
Claims
1. A branching means for a refrigerant flow of a refrigerant
circuit for a battery cooler circuit, comprising: an inlet; and at
least two outlet lines which lead to two cooling branches, wherein
at least one throttle stage is integrated into the branching
means.
2. The branching means as claimed in claim 1, wherein the throttle
stage is arranged upstream of a branching point to the two outlet
lines.
3. The branching means as claimed in claim 2, wherein a filter is
arranged downstream of the throttle stage.
4. The branching means as claimed in claim 1, wherein the throttle
stage is arranged downstream of a branching point to the two outlet
lines.
5. The branching means as claimed in claim 4, wherein the throttle
stage has a constriction in each of the outlet lines.
6. The branching means as claimed in claim 1, wherein the throttle
stage has a throttle point which is formed by a calibrated
bore.
7. The branching means as claimed in claim 6, wherein the
calibrated bore is formed so as to directly adjoin a branching
point of a main line.
8. The branching means as claimed in claim 1, wherein the throttle
stage has a throttle point which is formed by an inserted pipe with
calibrated internal diameter.
9. The branching means as claimed in claim 8, wherein the pipe is
inserted into a threaded sleeve or plug-in sleeve which is screwed
or plugged into a body of the branching means.
10. The branching means as claimed in claim 1, wherein a first
throttle stage is arranged upstream of the branching point and a
second throttle stage is arranged downstream of the branching
point.
Description
[0001] The invention relates to a branching means for a refrigerant
flow of a refrigerant circuit, in particular of a battery cooler
circuit.
[0002] In electrically operated vehicles or in hybrid vehicles, the
battery modules generate heat during operation, which heat is often
dissipated by way of a cooling circuit. Here, for the cooling of
the battery modules, it is expedient to use a cooling sub-circuit
of a vehicle air-conditioning system that is already provided in
the vehicle.
[0003] Since most battery cells are combined to form separate
battery modules which are thermally decoupled from one another,
such that no heat is exchanged between the individual battery
modules, the battery cooler circuit is often split into multiple
cooling branches which are assigned to in each case one or more of
the battery modules. In this case, it is the intention for the
cooling branches to be flowed through in parallel by the
refrigerant.
[0004] It is known for the battery cooler circuit to be assigned a
dedicated expansion device which is provided between an outlet of
the gas cooler and an inlet into a branching means which splits the
refrigerant into the individual cooling branches. Here, as an
expansion device, use is made of a known thermostatic expansion
valve (TXV) which controls the refrigerant throughflow in
accordance with the conditions in the battery cooler circuit. In
this case, the pressure drop in the thermostatic expansion valve
accounts for approximately 60 to 95% of the total pressure
difference, whereas the pressure drop in the branching means
amounts to merely 3 to 10%. A reason for this is that the pressure
difference between the high-pressure branch and the low-pressure
branch of the vehicle air conditioning system is considerably
greater in the presence of high ambient temperatures than in the
presence of low temperatures. The thermostatic expansion valve must
however supply an adequate amount of refrigerant, that is to say an
adequate refrigerant flow, to the evaporator even in the presence
of the minimum operating temperature and thus a minimal pressure
difference; this is possible only if the pressure drop in the
branching means is small. Therefore, known branching means are
configured for a small pressure drop.
[0005] To ensure the longest possible service life of the
individual battery cells, it must be ensured that only a very small
temperature difference of no more than 5 K prevails between the
individual battery cells. The small pressure drop across the
branching means however makes it difficult to realize a homogenous
distribution of the refrigerant, which in the presence of
relatively high temperatures is always present in a liquid-gaseous
mixture upstream of the branching point, to the various cooling
branches.
[0006] Owing to the phase mixture in the branching means, it is
also necessary for the known branching means to be installed in an
exactly vertical orientation in order, even in the presence of a
small throughflow, to realize as homogenous as possible a
distribution of the two-phase mixture to the various outlet
lines.
[0007] Furthermore, in the case of the cooling of battery modules,
a cooling arrangement must function even in the presence of low
ambient temperatures of, for example, down to -10.degree. C. or
below, by contrast to a passenger compartment cooling arrangement,
which is normally deactivated in the presence of such
temperatures.
[0008] In the presence of such low temperatures, however, the
fraction of liquid refrigerant upstream of the branching means is
substantially 100%, for which the known branching means are not
configured.
[0009] It is an object of the invention to ensure homogenous
cooling performance in a battery cooler circuit over the entire
range of ambient temperatures of both summer and winter, wherein at
the same time the costs and the structural size of the system are
reduced.
[0010] Said object is achieved by means of a branching means for a
refrigerant flow of a refrigerant circuit, in particular of a
battery cooler circuit, having an inlet and having at least two
outlet lines which lead to two cooling branches, wherein at least
one throttle stage is integrated into the branching means. Owing to
the fact that the functions of the distribution of the refrigerant
and the pressure reduction are combined in one component, the
structural size and manufacturing costs are reduced. In relation to
known arrangements, the distance between the expansion device, that
is to say the pressure reducer, and the branching means in the
individual cooling branches can be reduced considerably, which
leads to a more uniform distribution in particular of the liquid
fractions of the refrigerant to the individual cooling branches.
Thus, a uniform and adequate supply of liquid refrigerant to the
individual cooling branches of the battery cooler circuit is also
ensured.
[0011] In a preferred embodiment, the throttle stage is arranged
upstream of a branching point to the individual outlet lines,
wherein the throttle stage is in particular situated directly
upstream of the branching point. Owing to the spatial proximity of
the throttle point to the splitting of the refrigerant flow to the
individual outlet lines, the liquid phase and the gas phase in the
refrigerant flow remain fully mixed downstream of the throttle
point, thus ensuring a homogenous distribution of the refrigerant,
including the liquid fractions of the refrigerant, to the
individual outlet lines. Since the cooling performance is primarily
linked to the evaporation of the liquid phase of the refrigerant,
it is thus possible to attain highly homogenous cooling performance
in both cooling branches.
[0012] With the use of a throttle stage upstream of the branching
point, it has proven to be expedient for a filter to be used
directly downstream of the throttle stage in order to keep the
liquid phase and the gas phase and the refrigerant well mixed and
realize the best possible homogenization of the two phases during
the splitting to the individual outlet lines.
[0013] In another preferred embodiment, the throttle stage is
arranged downstream of a branching point to the two outlet lines.
The pressure at the inlet of the branching means may then continue
to correspond approximately to the pressure of the high-pressure
side in the refrigerant circuit, and the thermodynamic state of the
refrigerant remains supercritical at least in the presence of high
ambient temperatures. At the branching point itself, the
refrigerant is present in a single-phase state, and can thus be
easily distributed uniformly to the individual outlet lines,
without the known problems with regard to the distribution of a
two-phase mixture being encountered.
[0014] The throttle stage preferably has a throttle point, that is
to say a constriction of the flow cross section, each of the outlet
lines, said throttle points being in particular of identical form
such that the same conditions prevail in all of the outlet lines
and in all of the cooling branches supplied from said outlet
lines.
[0015] It is possible for the throttle point of the throttle stage
to be formed by a calibrated bore. The calibrated bore is
preferably formed directly in a body of the branching means and
forms an integral constituent part either of a main line upstream
of the branching point or of in each case one of the outlet lines
downstream of the branching point. The length and internal diameter
of the calibrated bore can be defined very precisely and
manufactured reproducibly, such that the pressure drop across the
throttle point can be precisely set. Furthermore, there is no need
to use additional components.
[0016] If the throttle stage is provided in the outlet lines, the
calibrated bore may be formed so as to directly adjoin the
branching point of the main line, in order to keep the structural
length of the branching means small.
[0017] In another preferred embodiment, the throttle stage has a
throttle point which is formed by an inserted pipe with calibrated
internal diameter. In this case, in accordance with the known
principle for pressure reduction, a separate pipe is inserted into
the inlet, the main line and/or or the outlet lines, in order to
realize a precise reduction of the flow cross section at the
throttle point. Such pipes can be prefabricated in a simple and
inexpensive manner and with high accuracy, and can be inserted and
fastened at a suitable location in the branching means.
[0018] For the fastening of the pipe in the body of the branching
means, the pipe may for example be inserted into a threaded sleeve
which is screwed into the body of the branching means. This is
conceivable both for throttle points in the region of the inlet or
of the main line of the branching means and for throttle points in
the region of the outlet lines. Thus, easy exchange and simple
maintenance of the throttle point is also possible.
[0019] It is expedient to provide an end stop on the threaded
sleeve, which end stop ensures precise positioning of the pipe
within the body of the branching means.
[0020] Suitable internal diameters for the throttle point, both for
a calibrated bore and for a pipe with calibrated internal diameter,
for example between 0.2 and 1.0 mm, and a suitable length lies
between 10 and 40 mm. With increasing length of the throttle point,
the flow becomes more stable, and the sensitivity to the generation
of vibrations in the flow is reduced.
[0021] To prevent contamination of the throttle points, a filter is
preferably arranged upstream of the throttle point.
[0022] In one possible embodiment, a two-stage pressure reduction
is provided by way of two throttle stages which are in series in
terms of flow, which throttle stages each have a throttle point.
Here, a first throttle stage may be provided, upstream of the
branching point, in a main line or in the region of the inlet of
the branching means, and a second throttle stage may be arranged,
downstream of the branching point, in the outlet lines.
[0023] The internal diameter of the throttle points is in each case
fixedly predefined and cannot be varied without structurally
exchanging the branching means for the inserted pipe.
[0024] The desired pressure drop across the branching means is set
by way of the design of the throttle points, specifically the
arrangement, cross section and length thereof.
[0025] The branching means may effect for example 10 to 50% of the
total pressure drop.
[0026] In the presence of ambient temperatures of approximately
between 20 and 40.degree. C., that is to say under summer
conditions, the refrigerant is preferably still substantially in
the supercritical or liquid state, with only a single phase, at the
inlet of the branching means.
[0027] In the presence of low ambient temperatures of approximately
-10 to 0.degree. C., that is to say during winter usage, the
refrigerant is preferably entirely in its liquid phase at the inlet
of the branching means. In this case, too, a homogenous
distribution to the two outlet lines is possible without
problems.
[0028] It is preferably the case that the refrigerant flow does
not, in any operating state, have clearly separated phases
downstream of the branching point, such that a homogenous
distribution of the refrigerant flow to the two outlet lines is
always realized. Thus, uniform cooling of the battery modules in
the two cooling branches is always ensured. Furthermore, the
sensitivity with respect to a deviation from a vertical
installation position is greatly reduced.
[0029] In a preferred embodiment, the branching means has two
outlet lines. It would self-evidently be possible for three or more
outlet lines to be provided in the branching means instead of two
outlet lines. Equally, it is possible for a further battery cooler
circuit of identical or similar construction to be connected in
parallel with respect to a battery cooler circuit having a
described branching means.
[0030] The invention will be described in more detail below on the
basis of multiple exemplary embodiments and with reference to the
appended figures. In the drawings:
[0031] FIG. 1 is a schematic illustration of a vehicle
air-conditioning system having a battery cooler system with a
branching means according to the invention;
[0032] FIG. 2 shows a schematic sectional view of a branching means
according to the invention in a first embodiment;
[0033] FIG. 3 shows a schematic sectional view of a branching means
according to the invention in a second embodiment;
[0034] FIG. 4 shows a schematic sectional view of a pressure
reducer having a branching means according to the invention in a
third embodiment;
[0035] FIG. 5 is a schematic illustration of a switching cycle of a
shut-off valve of a pressure reducer of the battery cooler
system;
[0036] FIG. 6 is a diagrammatic illustration of the maximum
pressure difference at the pressure reducer of the battery cooler
system as a function of the ambient temperature;
[0037] FIG. 7 is a diagrammatic illustration of the enthalpy
difference for the evaporation of R744 as a function of the ambient
temperature; and
[0038] FIG. 8 shows a Mollier diagram of the refrigerant R744,
showing the working range of the battery cooler system in the
presence of low and high ambient temperatures.
[0039] FIG. 1 shows a refrigerant circuit 10 of a vehicle
air-conditioning system (not illustrated in any more detail). A
refrigerant, in this case R744, flows through multiple cooling
sub-circuits. Said refrigerant is compressed in a compressor 12
before being cooled in a gas cooler 14, for example by cooling by
means of ambient air. The gaseous, highly pressurized refrigerant
subsequently passes through an inner heat exchanger 16, in which it
releases some of its heat energy to expanded refrigerant on a
return flow path.
[0040] In a first cooling sub-circuit 18, the refrigerant flow is
through an evaporator 20 of the vehicle air conditioning system, by
means of which a vehicle interior compartment is cooled, for
example.
[0041] Upstream of the evaporator 20 there is arranged a shut-off
valve 22 by means of which the cooling sub-circuit can be shut off
when cooling is not required. In this example, the shut-off valve
22 comprises a pressure reduction stage in the form of an opening
of reduced cross section, which acts as a throttle point and which,
by way of the pressure reduction, effects a partial expansion of
the refrigerant.
[0042] The pressure reduction from the high-pressure side to the
low-pressure side is realized here by way of a fixedly predefined
cross-sectional constriction, such as is known for R744 refrigerant
circuits. The diameter of said throttle point is selected inter
alia in a manner dependent on the required performance of the
evaporator.
[0043] The shut-off valve 22 is bridged by way of a bypass line 24
with a safety valve 26. The safety valve 26 is configured so as to
permit a refrigerant flow through the cooling sub-circuit 18 when a
critical pressure threshold is reached at the safety valve 26,
which critical pressure threshold may for example be approximately
120-150 bar (12-15 MPa).
[0044] In general, when using R744 as refrigerant, the refrigerant
circuit must be protected against overpressure. This is realized in
this case by way of the safety valve 26, which in the event of a
sudden increase in pressure opens a flow connection from the
high-pressure side to the low-pressure side of the refrigerant
circuit. Said bypass function is in this case available under all
operating conditions. Such a pressure rise may occur for example in
the event of intense vehicle acceleration, in the case of which the
compressor throughput cannot be regulated downward rapidly enough,
such that a large amount of gas is conducted into the gas cooler
14.
[0045] The refrigerant flowing back from the evaporator 20 passes
through the inner heat exchanger 16 again and through an
accumulator 28, in which any liquid refrigerant that is present is
separated off, before the refrigerant flows back to the compressor
12.
[0046] In parallel with respect to the first cooling sub-circuit
18, the refrigerant flows through a battery cooling circuit 30,
which is part of a battery cooler system 32. The battery cooler
circuit may have a cooling power of approximately 0.5 to 2 kW.
Battery cells of a hybrid or electric vehicle (not illustrated in
any more detail here) are in this case arranged in multiple
modules, which are cooled by two cooling branches 34, 36 connected
in parallel. Thus, in this case, the battery cooler circuit 30 is
divided into two cooling branches 34, 36 which, after passing
through the battery modules, open into a common return suction line
38. The cooling branches 34, 36 serve as evaporators, in which the
liquid refrigerant situated therein absorbs the heat from the
battery cells and thus changes into the gaseous state.
[0047] Downstream of the outlet of the evaporator 20, the first
cooling sub-circuit 18 opens into the return suction line 38.
[0048] A pressure reducer 40 is arranged upstream of the two
cooling branches 34, 36. In the variant illustrated here, the
pressure reducer 40 has a shut-off valve 42 which is arranged
upstream of a branching means 44.
[0049] In a possible embodiment which will be described further
below (see FIG. 4), the shut-off valve 42 and the branching means
44 are combined in a single component. They may however also be
formed as separate components. It would also be possible to
dispense with the shut-off valve 42 and to realize the pressure
reduction entirely by way of the branching means 44.
[0050] The shut-off valve 42 is connected to a controller 46 which
can define the opening state of the shut-off valve 42. In this
example, the shut-off valve 42 can assume only the two control
states "open" and "closed".
[0051] In this example, directly downstream of the shut-off valve
42, there is arranged a temperature sensor T.sub.1 which is
likewise connected to the controller 46. Here, a second temperature
sensor T.sub.2, which is likewise connected to the controller 46,
is provided directly at the connecting point 48 of the two cooling
branches 34, 36.
[0052] FIGS. 2 to 4 show various embodiments of the branching means
44. For clarity, the reference sign 44 has been used for all three
embodiments.
[0053] The branching means 44 illustrated in FIG. 2 has a body 50
into which there is recessed an inlet 52 which transitions into a
main line 54. At the end of the main line 54 there is situated a
branching point 56, proceeding from which the main line 54 splits
into two outlet lines 58, which in these examples are in each case
of identical form. Each of the outlet lines 58 transitions into an
outlet 60, by means of which the respective outlet line 58 is
connected to one of the two cooling branches 34, 36 of the battery
cooler circuit 30.
[0054] A throttle stage is integrated into the branching means 44,
which throttle stage has a constriction which acts as a throttle
point and which thus effects a pressure reduction downstream of the
throttle point.
[0055] In the example shown in FIG. 2, the throttle stage is
realized, by way of in each case one calibrated bore 62 of fixedly
predefined diameter and length, in each of the outlet lines 58. In
this case, the calibrated bore 62 directly adjoins the branching
point 56, and is thus situated directly downstream of the main line
54 as before.
[0056] Instead of a branch into two outlet lines 58, it would also
be possible to provide a branch into more than two outlet lines 58.
Equally, it would be possible for multiple distributors 44 to be
provided in further battery cooler circuits (not shown) connected
in parallel with respect to the battery cooler circuit 30.
[0057] In this example, the throttle stage is provided downstream
of the branching point 56. This has the effect that the
refrigerant, which in the main line 54 is present entirely or
substantially entirely in a single phase (supercritical or liquid
depending on the ambient temperature, as will be described in more
detail below), is split uniformly to the two outlet lines 58. Owing
to the uniform state of aggregation, a non-vertical installation
position of the branching means 44 also does not pose any
problems.
[0058] Here, there is provided within the inlet 52 a filter 64
which prevents contamination of the branching means 44.
[0059] In these examples, the inlet 52 is formed in a connector
piece 66 by way of which the branching means 44 can be connected to
the pipelines of the battery cooler circuit 30 or to the shut-off
valve 42 (see FIG. 4).
[0060] The calibrated bore 62 has for example a diameter of 0.2-1.0
mm and a length of 10-40 mm, wherein, with increasing length of the
throttle point, the flow becomes more stable, and the tendency for
the generation of vibrations in the flow is also reduced.
[0061] FIG. 3 shows an embodiment of a branching means 44 in which
the throttle stage is provided in the region of the main line 54.
In this case, the pressure reduction takes place already upstream
of the branching point 56.
[0062] Downstream of the throttle point there is arranged a filter
68 which homogenizes the refrigerant downstream of the throttle
point by virtue of the liquid and gaseous fractions being
thoroughly mixed, such that a homogenous distribution to the two
outlet lines 58 is realized.
[0063] In the example of FIG. 3, the throttle point is formed by a
separate, inserted pipe 70 with a calibrated internal diameter.
Internal diameters and lengths may be selected in the same way as
in the case of the calibrated bore 62 of the preceding exemplary
embodiment.
[0064] To fasten the pipe 70 in the body 50 of the branching means
44, there is provided a threaded sleeve 72 which is screwed into
the connector piece 66 of the inlet 52. Instead of the threaded
sleeve 72, it would also be possible for use to be made of a
plug-in sleeve which is plugged into the connector piece 66.
[0065] The threaded sleeve 72 has an end stop 74 which serves for
precise positioning of the pipe 70 in the main line 54.
[0066] At the inlet side, the pipe 70 is covered by a filter 64
which prevents contamination of the branching means 44.
[0067] The calibrated internal diameter of the inserted type 70 can
be produced with high precision as a bore.
[0068] Instead of the inserted pipe 70, it would also be possible
in the main line for a bore to be formed in the body 50, as has
been described for example with regard to FIG. 2 for the outlet
lines 58. Analogously, in the embodiment illustrated in FIG. 2, it
would also be possible, instead of the calibrated bores 62, for in
each case one pipe 70 with calibrated internal diameter to be
inserted into the outlet lines 58.
[0069] Furthermore, it is possible to provide in the branching
means 44 not only one throttle point but two throttle points which
are in series in terms of flow, wherein the first throttle point is
arranged in the main line 54 and the second throttle point is
formed by in each case one constriction in each of the outlet lines
58.
[0070] FIG. 4 shows a pressure reducer 40 which has two throttle
stages in series in terms of flow.
[0071] The pressure reducer 40 is in this case composed of a
branching means 44 and of a shut-off valve 42, these being screwed
together by way of the connector piece 66 of the branching means
44. In this example, the branching means 44 corresponds to the
branching means illustrated in FIG. 2. It would however also be
possible for use to be made of a branching means as per the
embodiment illustrated in FIG. 3, or some other suitable branching
means 44.
[0072] In this example, the shut-off valve 42 is switched by way of
an electromagnet 76 which is connected to the controller 46 of the
battery cooler system 32. By means of the electromagnet 76, the
shut-off valve 42 is switched between its two switching states
"open" and "closed", wherein the refrigerant flow through the inlet
78 of the shut-off valve 42 is either permitted in full or is
completely stopped.
[0073] Directly downstream of a valve seat 80 of the shut-off valve
42, a first throttle stage is realized, in this case by way of a
calibrated bore 82, which constitutes a constriction of the
throughflow cross section for the refrigerant. The cross section of
the calibrated bore 82 is narrowed in relation to the cross section
of the inlet 78 and also in relation to the cross section of the
adjoining inlet 52 of the branching means 44. In this way, a first
expansion of the refrigerant, and a first pressure reduction, is
effected in the calibrated bore 82.
[0074] In the branching means 44, a second throttle stage is
formed, in this case by way of the constrictions formed by the
calibrated bores 62 in the outlet lines 58, which effect a second
pressure reduction and a further expansion of the refrigerant.
[0075] Instead of the calibrated bore 82 in the body of the
shut-off valve 42, it would also be possible for a calibrated bore
or a pipe 70 with calibrated internal diameter to be provided in
the inlet 52 of the branching means 44. In this way, the
construction of the shut-off valve 42 can be further
simplified.
[0076] From the outlet lines 58, the refrigerant flows into the two
cooling branches 34, 36 of the battery cooler circuit 30.
[0077] In the embodiment illustrated in FIG. 1, the battery cooler
system 32 is configured such that, in the presence of low ambient
temperatures under "winter conditions", that is to say in the
presence of temperatures between approximately -10 and 0.degree.
C., a pressure difference of approximately 10 bar and an enthalpy
difference of approximately 240 kJ/kg are attained across the
pressure reducer. The pressure difference may also be configured
with regard to a pressure difference between the high-pressure side
and the low-pressure side of the overall refrigerant circuit 10.
These parameters are attained through the specific design of the
throttle stages of the pressure reducer 40.
[0078] It is important that the refrigerant flow realized through
the cross-sectional constrictions in the throttle stages is great
enough to provide adequate cooling performance for the battery
modules in the battery cooler circuit 30 even in the presence of
low ambient temperatures. Under these ambient conditions, the phase
boundary to the supercritical state is overshot by only
approximately 1 to 5 Kelvin (see also FIG. 8).
[0079] In the presence of the ambient temperatures that prevail in
summer, that is to say temperatures up to approximately +40.degree.
C., a considerably greater pressure difference prevails between the
high-pressure side and the low-pressure side of the refrigerant
circuit 10 and of the battery cooler circuit 30. To prevent an
excessively large flow rate of liquid coolant through the branching
means 44 under such conditions, which would not be able to be fully
evaporated in the cooling branches 34, 36 and would thus reduce the
cooling performance of the evaporator 20 for the air conditioning
of the passenger compartment, the shut-off valve 42 is operated in
pulsed fashion.
[0080] This is illustrated schematically in FIG. 5. The solid curve
indicates that, in the presence of high ambient temperatures, the
shut-off valve 42 is, by way of the controller 46, operated with
pulse width modulation in such a way that the cooling performance
is optimized. The opening duration of the shut-off valve 42 is
calculated by the controller 46 from the values signaled by the
temperature sensor T.sub.1 and T.sub.2, that is to say from the
refrigerant temperature at the inlet 52 of the branching means 44
and the refrigerant temperature after said refrigerant has passed
through the cooling branches 34, 36 of the battery cooler circuit
30.
[0081] The time period for which the shut-off valve 42 remains
closed between two opening states may amount to 30 seconds or more;
this also applies to the time period for which the shut-off valve
42 is open between the closed phases. This is possible because the
battery cooler circuit 30 with the battery modules has a higher
thermally active mass than, for example, the evaporator 20 of the
vehicle air-conditioning system.
[0082] In winter, that is to say in the presence of low ambient
temperatures and a small pressure difference, it is by contrast the
case that the shut-off valve 42 is continuously open (see dashed
line in FIG. 5).
[0083] FIGS. 6 and 7 show the pressures prevailing on the
high-pressure side of the refrigerant circuit 10 and on the
low-pressure side thereof as a function of the ambient temperature.
The pressure profile of the high-pressure side is denoted by
rhombuses, whereas the pressure profile on the low-pressure side is
denoted by squares. It can be read from FIG. 6 that, in the
presence of winter conditions between -10 and 0.degree. C., a
pressure difference of between 7 and 9 bar (0.7 to 0.9 MPa) is to
be expected, whereas, in the presence of summer conditions between
25 and 40.degree. C. ambient temperature, considerably higher
pressure differences prevail, for example 35 to 65 bar (3.5 to 6.5
MPa), wherein a pressure difference of even 90 bar may prevail.
[0084] From such a measurement, it is possible, for an existing
battery cooler system 32 in a refrigerant circuit 10, to calculate
the optimum configuration of the pressure reducer 40. For this
purpose, it is also necessary to take into consideration the
enthalpy difference during the evaporation of the refrigerant, in
this case R744, which is plotted as a function of the ambient
temperature in FIG. 7.
[0085] The pressure difference between the high-pressure side and
low-pressure side greatly increases with rising ambient
temperature. Since the mass flow that is generated changes
approximately with the square root of the pressure difference, it
is the case for example that, for an ambient temperature of
-10.degree. C., the possible cooling performance of the battery
cooler circuit 30 is reduced by approximately 40% in relation to an
ambient temperature of +40.degree. C. If the battery cooler system
32 and in particular the pressure reducer 40 are optimized for
operation in the presence of low ambient temperatures, this has the
effect that, during operation in the presence of high ambient
temperatures, the shut-off valve 42 should be closed for
approximately 30-90% of the time.
[0086] The configuration of the rest of the refrigerant circuit 10,
in particular of the cooling sub-circuit 18, which serves for the
vehicle air-conditioning system evaporator 20, are not affected by
these considerations, as only the pressure reducer 40 in the
battery cooler circuit 30 has to be configured correspondingly.
[0087] FIG. 8 shows, on the basis of a Mollier diagram, the cycles
that are passed through for operation of the refrigerant circuit 10
under some conditions (high ambient temperatures) and winter
conditions (low ambient temperatures).
[0088] The upper cycle in the graph, with the points A to G,
describes the operation in the presence of high ambient
temperatures.
[0089] The high-pressure side, which in this case is preferably at
between 80 and 120 bar, is operated in the supercritical range.
From point A to point B, the compression of the refrigerant in the
compressor 12 takes place. From point B to point C, the
supercritical refrigerant is cooled in the gas cooler 14. From
point C to point D, further cooling on the high-pressure side of
the refrigerant circuit 10 is realized by way of the inner heat
exchanger 16. From point D to point E, a pressure reduction takes
place in the first throttle stage of the pressure reducer 40,
wherein the pressure reduction takes place at most as far as the
liquid boundary, such that the refrigerant remains in only
single-phase form, or is in the supercritical state, when it enters
the branching means 44. From point E to point F, the further
pressure reduction in the second throttle stage of the pressure
reducer 40 takes place, in this case in the outlet lines 58 of the
branching means 44. From point F to point G, the cooling of the
battery modules in the cooling branches 34, 36 of the battery
cooler circuit 30 takes place, wherein the refrigerant is
evaporated and absorbs the heat from the battery modules. Finally,
from point G to point A, the refrigerant flows via the return
suction line 38, passing through the inner heat exchanger 16, back
to the compressor 12, wherein said refrigerant absorbs heat from
the high-pressure branch.
[0090] In winter operation (lower cycle in FIG. 8, with points
a-f), the same cycle is performed below the critical point. From
point a to point b, the refrigerant is compressed, and from point b
to point d, said refrigerant is cooled. After the expansion of the
refrigerant in the first throttle stage of the pressure reducer 40
(point d to point e), the refrigerant is entirely in the liquid
phase. Only when it passes through the second throttle stage (point
e to point f) can the refrigerant have gaseous fractions.
[0091] In the example described here, the refrigerant is however
still in only single-phase form when it the branching means 44. In
this way, a homogenous distribution to the two cooling branches 34,
36 is possible more easily than in the presence of a phase
mixture.
* * * * *