U.S. patent application number 11/998732 was filed with the patent office on 2008-06-05 for thermostatic expansion valve for refrigeration or heat-pump circuits with thermally controlled safely function.
Invention is credited to Joan Aguilar, Rainer Maurer.
Application Number | 20080127664 11/998732 |
Document ID | / |
Family ID | 38721421 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080127664 |
Kind Code |
A1 |
Aguilar; Joan ; et
al. |
June 5, 2008 |
Thermostatic expansion valve for refrigeration or heat-pump
circuits with thermally controlled safely function
Abstract
The invention relates to a thermostatic expansion valve having a
valve element (33) which, for the throughflow of the refrigerant,
closes and moves in the opening direction a valve seat (32) of a
passage opening (29) arranged between the supply opening (27) and
the discharge opening (31), and which is assigned to a first
actuating element (36), the first actuating element (36) comprising
a chamber (38) which is delimited with a first active face (37) and
which contains a control charge (41), wherein an actuating element
(46) is provided, which is thermally activated independently of the
high pressure, the actuating movement of which actuating element
(46) is coupled in terms of movement to the first active face (37)
of the first actuating element (36) when a temperature-dependent
actuating movement of the thermally activatable actuating element
(46) acts counter to the actuating movement of the first active
face (37) of the first actuating element (36), with a temperature
threshold value of the thermally activatable actuating element (46)
for an actuating movement being set to an identical value as the
MOT (maximum operation temperature) of the control charge (41) of
the first actuating element (36), which control charge (41) has a
fluid density which lies below its critical density.
Inventors: |
Aguilar; Joan; (Leonberg,
DE) ; Maurer; Rainer; (Pforzheim, DE) |
Correspondence
Address: |
KRIEGSMAN & KRIEGSMAN
30 TURNPIKE ROAD, SUITE 9
SOUTHBOROUGH
MA
01772
US
|
Family ID: |
38721421 |
Appl. No.: |
11/998732 |
Filed: |
November 30, 2007 |
Current U.S.
Class: |
62/210 |
Current CPC
Class: |
F25B 40/00 20130101;
F25B 2309/061 20130101; F25B 2341/063 20130101; F25B 9/008
20130101; F25B 41/31 20210101 |
Class at
Publication: |
62/210 |
International
Class: |
F25B 41/06 20060101
F25B041/06; F25B 41/04 20060101 F25B041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2006 |
DE |
102006057131.2 |
Claims
1. Thermostatic expansion valve for regulating a high pressure of a
refrigeration or heat-pump circuit which is operatable both
transcritically and also subcritically, having a valve housing in
which, at the input side, a high pressure prevails in a supply
opening, and at the output side, a low pressure prevails at a
discharge opening, having a valve element which, for the
throughflow of the refrigerant, closes and moves in the opening
direction a valve seat of a passage opening arranged between the
supply opening and the discharge opening, and which is assigned to
a first actuating element, the first actuating element comprising a
chamber which is delimited with a first active face and which
contains a control charge, characterized in that an actuating
element is provided, which is thermally activated independently of
the high pressure, the actuating movement of which actuating
element is coupled in terms of movement to the first active face of
the first actuating element when a temperature-dependent actuating
movement of the thermally activatable actuating element acts
counter to the actuating movement of the first active face of the
first actuating element, with a temperature threshold value of the
thermally activatable actuating element for an actuating movement
being set to an identical value as the MOT (maximum operation
temperature) of the control charge of the first actuating element,
which control charge has a fluid density which lies below its
critical density.
2. Valve according to claim 1, characterized in that a detachable
mechanical coupling is provided between the first actuating element
and the thermally activatable actuating element, and the thermally
activatable actuating element engages on a first active face of the
first actuating element or on a valve element which is connected to
the first actuating element.
3. Valve according to claim 1, characterized in that the chamber is
embodied in the manner of a diaphragm or bellows and is thermally
conductive in order to absorb the temperature of the
high-pressure-side refrigerant.
4. Valve according to claim 1, characterized in that the critical
temperature of the control charge of the first actuating element
lies above the critical temperature of the refrigerant.
5. Valve according to claim 1, characterized in that the
temperature-independent force of the thermally activatable
actuating element corresponds to the increase of the control charge
of the first actuating element in the superheated state.
6. Valve according to claim 1, characterized in that the thermally
activatable actuating element is embodied in the form of bimetal
elements which are stacked one on top of the other.
7. Valve according to claim 1, characterized in that the thermally
activatable actuating element is embodied in the form of a spring
element which is composed of a shape-memory alloy.
8. Valve according to claim 1, characterized in that the thermally
activatable actuating element is embodied in the form of a filled,
bellows-like spring element.
9. Valve according to claim 8, characterized in that the thermally
activatable actuating element is embodied in the form of a
hydraulically filled bellows-like spring element.
10. Valve according to claim 7, characterized in that the thermally
activatable actuating element is preloaded by a
pressure-independent device.
11. Valve according to claim 10, characterized in that the preload
of the thermally activatable actuating element is set by means of
the pressure-independent device to a temperature threshold value at
which the thermal safety function comes into action.
12. Valve according to claim 10, characterized in that the
pressure-independent device is adjustable.
13. Valve according to claim 1, characterized in that the chamber
or an inner contour of the chamber is guided by a sleeve or
webs.
14. Valve according to claim 1, characterized in that, in a rest
position of the valve element, a predefined minimum passage opening
between the valve element and the valve seat is opened, which
minimum passage opening is externally adjusted during assembly.
15. Transcritical or subcritical refrigeration or heat-pump circuit
having an inner heat exchanger, characterized in that an expansion
valve according to one of the preceding claims is provided.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a thermostatic expansion valve for
a refrigeration or heat-pump circuit as per the preamble of claim
1.
[0002] In transcritical refrigeration or heat-pump circuits, the
high-pressure side dissipation of heat takes place usually above
the critical pressure of the refrigerant which is used. On account
of the resulting temperature gradient in the gas cooler, the
pressure at the gas cooler outlet is a degree of freedom in the
circuit process. Specifically in circuit processes which use
CO.sub.2 as refrigerant, it is highly important to adjust the high
pressure into an optimum-efficiency range as a function of the
ambient or gas-cooler-outlet temperature. In CO.sub.2 air
conditioning systems, usually only fixed throttles or
externally-controlled expansion elements are used in the regulation
of the refrigerant circuit. The former do not permit any adaptation
of the high pressure to the process boundary conditions during
operation. Externally-controlled expansion elements must for this
purpose be regulated by electronic control elements whose
responsiveness is insufficient in particular for automotive
applications. Accordingly, said externally-controlled expansion
elements cannot offer a sufficient level of operating reliability.
Further disadvantages result from a high susceptibility to failure
and high development and purchase costs.
[0003] DE 102 49 950 B4 discloses an expansion valve for
high-pressure refrigeration systems having a valve seat and a valve
element which interacts with the valve seat, and a spring device
which acts on the valve element, and an adjusting device for the
spring arrangement, with the spring arrangement having at least one
first spring and one second spring which act on the valve element.
The first spring defines a working range and the second spring has
a spring force which can be varied by the adjusting device.
[0004] U.S. Pat. No. 6,012,300 discloses an expansion valve which
has a chamber in which refrigerant is enclosed. The chamber is
delimited by a diaphragm which acts indirectly on a valve element.
The diaphragm is however also exposed to the high-pressure-side
refrigerant. In particular, the active faces which are acted on by
the refrigerant which is enclosed in the chamber and the further
active faces which are acted on by the high-pressure-side
refrigerant which passes from the gas cooler are identical. With
the described expansion valve, no safeguard against high pressure
above a maximum permissible value (for example 120 bar) is
possible. In addition, a reliable start-up behaviour is not
possible at inlet temperatures at the expansion valve above the
critical temperature of the refrigerant. An operationally reliable
application therefore cannot be realized with said expansion
valve.
[0005] DE 10 2005 034 709.6 discloses a thermal expansion valve
which has a first and a second active face which are coupled in
terms of movement to a valve element. The first active face is part
of an expandable separating device which comprises a chamber with a
control charge in the thermal head. The temperature of the
high-pressure-side refrigerant can be sensed in this way. By means
of said expandable separating device of the thermal head, the
temperature-dependent pressure of the control charge in the chamber
is transmitted to a temperature-independent spring element which is
connected to the second active face which is also subjected to the
high pressure. By means of said embodiment, it is intended to
obtain a high-pressure limiting function in the supercritical
regulating range.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the invention to further
develop an expansion valve which can adjust the high pressure of a
refrigeration or heat-pump circuit which can be operated
transcritically and also subcritically within an optimum range and
can autonomously prevent an exceedance of a maximum permissible
value.
[0007] Said object is achieved by means of an expansion valve as
per the features of claim 1. By using a thermally controllable
actuating element whose actuating movement is coupled in terms of
movement to a first active face of a first actuating element only
when a temperature-dependent actuating movement of the second, that
is to say of the thermally controllable actuating element acts
counter to the actuating movement of the first active face of the
first actuating element, it is made possible to provide a pressure
limiting function or a safety function for preventing excessively
high operating pressures, which requires no external
activation.
[0008] Here, a temperature threshold value of the thermally
activatable actuating element for an actuating movement is selected
which corresponds to a temperature value of the MOT of the control
charge. The temperature threshold value is the temperature at which
the thermally controllable actuating element generates an actuating
or stroke movement. The working characteristic curve of the
thermally controlled actuating element has the same gradient as the
working characteristic curves of the control charge in the
superheated vapour state, but in the opposite direction. The safety
function is obtained in this way. In addition, an absolute pressure
limitation, that is to say the realization of the MOP function
(maximum operation pressure), is permitted at all temperature
levels. While the first actuating element is acted on with pressure
by a high-pressure-side refrigerant passing from the inner heat
exchanger and absorbs the temperature of said refrigerant, the
working behaviour of the thermally activatable actuating element is
independent of the refrigerant pressure.
[0009] According to a further advantageous embodiment of the
invention, it is provided that a detachable mechanical coupling is
provided between the first actuating element and the thermally
activatable actuating element, and the thermally activatable
actuating element engages on a first active face of the first
actuating element or on a valve element which is connected to the
first actuating element. Said mechanical coupling, which occurs
above a predetermined temperature value, makes it possible, in
normal operation at a conventional temperature threshold range, for
the first actuating element to work independently of the thermally
activatable actuating element, and the first control element is
coupled in terms of movement to the valve element only when a
further temperature rise takes place which demands the use of the
safety function.
[0010] The control charge of the first control element is
preferably provided in a chamber which is embodied in the manner of
a diaphragm or bellows and absorbs the temperature of the
high-pressure-side refrigerant. The active face of the first
actuating element is acted on by the temperature-dependent pressure
of the control charge in the chamber of the actuating element and
also by the high pressure. The resulting pressure difference
generates an adjusting force which sets the valve element in motion
and, as a function of the throttle properties of the associated
valve seat, opens a certain flow cross section.
[0011] It is preferably also possible for an additional, in
particular preloaded spring element to be provided which
intensifies the action counter to the high pressure. This has the
result that an opening movement of the valve element takes place
when the temperature-independent excess force, which is generated
at the active face by the high pressure of the refrigerant system,
is sufficient to overcome the preload of the in particular
preloaded spring element and the force action of the chamber, as a
result of which a passage between the valve seat and the valve
element is opened or the cross section of the passage opening is
enlarged.
[0012] The control charge of the chamber of the first actuating
element preferably has a charge density which lies below its
critical density. It is preferably additionally provided that a
substance mixture is selected for the control charge which has a
critical temperature which lies above the critical temperature of
the refrigerant to be regulated. In this way, the control charge
has, in most temperature threshold ranges, a two-phase state with a
high vapour proportion. Only when the energy absorbed by the
control charge is sufficient to completely evaporate the liquid
phase, which is present as a function of the prevailing filling
density, does the control charge pass into the superheated vapour
state. Under said circumstances, in the event of a further
temperature rise, a control pressure is generated with only a
smaller gradient than in the previous, two-phase state of the
control charge, which gradient is not equal to zero. The
temperature value above which said physical effect occurs is
referred to as MOT (maximum operating temperature). The associated
pressure value for the control charge is referred to as MOP
(maximum operation pressure). It is additionally preferably
provided that the temperature-independent force of the thermally
activatable actuating element corresponds to the increase of the
control charge of the first actuating element in the superheated
state. In the event of a further temperature rise in the
superheated vapour state, the pressure rises with only a
considerably smaller gradient than in the previous, two-phase
state. On account of the adaptation of the thermally activatable
actuating element to said gradient, the safety function is realized
in that the thermally activatable and high-pressure-independent
actuating element acts in the opposite direction with the same
gradient, so that a maximum operating pressure can be set which, in
a desired manner, corresponds to a horizontal pressure profile at a
MOP level.
[0013] Said temperature value or temperature threshold value is
preferably determined by the structural design of the thermally
activatable actuating element. According to a first advantageous
embodiment of a thermally activatable actuating element, it is
provided that bimetal elements, in particular bimetal plates, which
are stacked one on top of the other are provided. Said bimetal
plates are for example arranged in the shape of a bellows. Said
bimetal elements perform an actuating movement only above a certain
temperature, as a function of their pre-setting.
[0014] A second alternative embodiment for the design of a
thermally activatable actuating element provides that a diaphragm,
a bellows or a spring element, in particular a spiral spring or a
spring bellows, is produced from a shape-memory alloy. A
temperature-dependent activation can in turn be made possible in
this way.
[0015] A further alternative embodiment of the actuating element is
provided by a filled, bellows-like spring element which is
preferably filled with a medium which exists in the liquid state of
aggregation above its vaporization pressure or below its saturation
temperature.
[0016] Suitable charge media are for example oil or generally
hydrocarbons with a high boiling point. Said temperature
displacement transducer elements are preferably hermetically
sealingly joined diaphragm, corrugated-tube, bellows elements or
else cylinder-piston units which exert high actuating forces by
means of thermal expansion of their liquid filling. Said elements
can be designed such that their stroke-temperature characteristic
curve begins only above a certain temperature.
[0017] It is preferably provided that the thermally activatable
actuating elements have a pressure-independent device in order to
preload them. It is made possible in this way for the temperature
value at which the thermal safety function of the valve comes into
action to be adjustable. A device of said type is preferably
externally adjustable. An electronic or motor-driven activation can
alternatively also be provided.
[0018] It is additionally preferably provided that the chamber of
the first actuating element, in particular an inner contour of the
chamber, is guided by a sleeve or webs. This makes it possible for
deformations as a result of the action of the control charge to be
prevented.
[0019] In a rest position of the valve element of the thermostatic
expansion valve, it is preferably provided that a minimum passage
opening is opened. This means that, when the temperature- and
pressure-dependent excess force on the underside of the thermally
activatable actuating element is not sufficient to overcome the
preload of the latter, only an expediently predefined throttle
cross section is opened, and the thermostatic expansion valve
functions as a fixed throttle, as a result of which the high
pressure in the circuit itself is set.
[0020] The scope of the present invention therefore encompasses a
transcritical or subcritical refrigeration or heat-pump circuit
with an inner heat exchanger which makes possible a thermostatic
expansion valve with an autonomously settable overflow function or
safety function without for example an additional relocation of
lines at the evaporation inlet. At the same time, the thermostatic
regulating capability of the COP-optimum high pressure can be
maintained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The invention and further advantageous embodiments and
refinements thereof are described and explained in more detail
below on the basis of the examples illustrated in the drawings. The
features which can be gathered from the description and from the
drawings can be applied according to the invention individually or
together in any desired combination. In the drawings:
[0022] FIG. 1 is a schematic illustration of a refrigerant
circuit,
[0023] FIG. 2 shows a state diagram for explaining the function of
a refrigerant circuit having the thermostatic expansion valve as
specified in the introduction,
[0024] FIG. 3 shows a first embodiment of a thermostatic expansion
valve,
[0025] FIGS. 4a,b are a schematic illustration of a control charge
characteristic curve and the action of the thermally activatable
actuating element on the valve opening characteristic curve,
[0026] FIG. 5 shows a state diagram of valve stroke characteristic
curves at different operating pressures,
[0027] FIG. 6 shows a second embodiment of a thermostatic expansion
valve and
[0028] FIG. 7 shows a third embodiment of a thermostatic expansion
valve.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 shows a refrigerant and/or heat-pump circuit 11 of an
air-conditioning system. In a refrigerant compressor 12, a gaseous
refrigerant, in particular CO.sub.2, is compressed. The compressed
refrigerant is supplied to a gas cooler 13 where a heat exchange
takes place between the compressed refrigerant and the environment
in order to cool the refrigerant. The refrigerant which leaves the
gas cooler 13 passes to an inner heat exchanger 14 which is
connected to an expansion valve 15. The expansion valve 15 has the
effect firstly of limiting the pressure of the refrigerant and
secondly of regulating the pressure of the refrigerant at the
outlet of the inner heat exchanger 14. From the expansion valve 15,
the refrigerant passes to an evaporator 16. In the evaporator 16,
the refrigerant absorbs heat from the environment. Arranged
downstream of the evaporator 16 is an accumulator 17 in order to
separate refrigerant of the gaseous phase and of the liquid phase
and at the same time to collect liquid CO.sub.2. The accumulator 17
is in turn connected to the inner heat exchanger 14.
[0030] The mode of operation of the air-conditioning system is now
to be explained on the basis of the state diagram of FIG. 2 in
which the pressure p is plotted against the specific enthalpy H. A
refrigerant, for example CO.sub.2, in the gaseous phase is
compressed in the refrigerant compressor 12 (A-B). The hot,
highly-pressurized, transcritical refrigerant is then cooled in the
gas cooler 13 and in the inner heat exchanger 14 (B-C and C-D). The
pressure is reduced in the expansion valve 15 (D-E) in order to
evaporate the now two-phase (gaseous and liquid phase) refrigerant
in the evaporator 16 (E-F), and to thereby extract heat from the
environment. The COP is determined by means of the ratio of the
enthalpy change .DELTA.i in the step E-F and the enthalpy change
.DELTA.L in the step A-B, that is to say COP=.DELTA.i/.DELTA.L.
[0031] The critical temperature of CO.sub.2 lies at approximately
31.degree. C., which is lower than the critical temperature (often
>100.degree. C.) of fluorohydrocarbons which have hitherto been
used in air-conditioning systems. This has the result that the
temperature of CO.sub.2 at the outlet of the inner heat exchanger
14 can be higher than the critical temperature of CO.sub.2. In said
state, the CO.sub.2 itself does not condense at the outlet of the
inner heat exchanger 14. The pressure at the outlet of the inner
heat exchanger 14 must therefore be regulated. If, therefore, the
external temperature is high, for example in summer, it is
necessary to set a high pressure at the outlet of the inner heat
exchanger 14 in order to obtain a sufficient cooling power. The
outlet temperature at the inner heat exchanger 14 is dependent
inter alia on the refrigerant-side temperature at the gas cooler
outlet, which is in turn dependent on the ambient temperature. This
means that the temperature of the CO.sub.2 at the outlet of the
inner heat exchanger 14 can also be used for the regulation of the
COP-optimized high pressure, which is otherwise dependent on the
refrigerant-side gas cooler outlet temperature.
[0032] In the diagram as per FIG. 2, the characteristic curves 21'
and 21'' illustrate the COP-optimized regulating region. The double
arrow in between denotes a valve stroke range of 0 to approximately
75% of the valve stroke. Illustrated between the characteristic
curve 21'' and the characteristic curve 21''' is the overpressure
regulating region. By means of a further opening of the valve
stroke beyond approximately 75%, an excess pressure can be
dissipated. The characteristic curve 21'''' represents a settable
high-pressure limit for the refrigerant circuit 11 which is to be
regulated. Said high-pressure limit can be designed to be
variable.
[0033] FIG. 3 illustrates a first embodiment according to the
invention of a thermostatic expansion valve 15 which permits
operation of a refrigerant system as per a state diagram in FIG. 2.
The expansion valve 15 comprises a valve housing 26 which has a
high-pressure side supply opening 27 which leads into a
high-pressure space 28. The high-pressure space 28 is connected by
means of a passage opening 29 to a low-pressure side discharge
opening 31. The passage opening 29 has a valve seat 32 in which a
valve element 33 is provided in a closed position and separates the
supply opening 27 with respect to the discharge opening 31.
[0034] Provided in the high-pressure space 28 is a first actuating
element 36 which comprises a first active face 37 on which the
valve element 33 is provided. A chamber 38 engages on said first
active face 37 in the closing direction of the valve element 33,
which chamber 38 is embodied in the manner of a diaphragm or
bellows.
[0035] Additionally provided is a spring element 39 which for
example surrounds the chamber 38 and preferably engages on the
active face 37 in a preloaded manner and in the same force
direction as the chamber 38. In coordination with the size of the
valve element 33 or the length of its shank or a stop element which
is provided in the high-pressure space 28, a preload of the spring
element 39 and/or of the chamber 38 is made possible.
[0036] The chamber 38 is preferably formed from a highly thermally
conductive material. Provided in the chamber 38 is a control charge
41 whose pressure in the chamber 38 is temperature-dependent. When
a high pressure acts on the high-pressure side, said high pressure
acts against the active face 37 and opens the passage opening 29 if
the acting high pressure has an excess force with respect to the
preloaded spring element 39 and the pressure of the control charge
41 in the chamber 38. The opening and closing movement is, in the
COP-optimized regulating range, independent of a thermally
activatable actuating element 46 which is likewise provided in the
high-pressure space 28.
[0037] In the exemplary embodiment as per FIG. 3, the thermally
activatable actuating element 46 engages on the first active face
37 opposite the chamber 38 and the spring element 39, if provided.
Alternatively, the actuating element 46 can also engage on the
valve element 33 or additionally on the valve element 33. The
thermally activatable actuating element 46 is formed from bimetal
plates which are stacked one on top of the other in the shape of a
bellows. The bimetal plates can be preloaded by means of a
pressure-independent device (not illustrated in any more detail),
so that said bimetal places perform an actuating movement or a
stroke movement only once the safety function is required. This is
the case if the temperature of the refrigerant rises above the MOT.
Accordingly, the preload of the bimetal plates or their material
configuration is adapted to a temperature threshold value of said
type.
[0038] In the event of a sufficient excess force of the high
pressure with respect to the pressure force of the chamber 38 and
of the spring element 39, if provided, by means of a predefined
stroke characteristic curve, the optimum cross section is opened
and therefore the optimum high pressure (COP-optimized range) is
set as a function of the high-pressure-side outlet temperature of
the refrigerant at the inner heat exchanger.
[0039] The expansion valve 15 according to the invention makes
possible an autonomously settable overpressure and safety function,
so that the refrigerant circuit can operate with COP-optimized high
pressure. FIG. 4a is a schematic illustration of a characteristic
curve 19 of a control charge in a chamber 38 of the first actuating
element 36, in which the pressure is plotted against the
temperature up to the critical point. Since the control charge,
which is present in two-phase form up to said point, passes into
the single-phase, superheated gaseous state above the MOT value 20
for the circuit 11, the pressure of the control charge continues to
rise with only a considerably shallower gradient. The safety
function can however only be obtained by means of a horizontal
pressure profile from the MOT value 20. Said further
disadvantageous rise is compensated in one expedient embodiment of
the present invention by means of the use of the thermally
activatable actuating element 46, whose characteristic curve is
illustrated with 46' in FIG. 4a. In this way, a valve opening
characteristic curve 22 is obtained which is illustrated in FIG.
4b. Said valve opening characteristic curve 22 with the horizontal
pressure profile at the MOP level leads to a maximum mass flow
generation when the high pressure of the circuit 11 is situated
thereabove, so as to result in a self-inhibiting generation of high
pressure, because the temperature-induced pressure force of the
chamber 38, which acts in the closing direction of the valve
element 33, is compensated. The thermally activatable actuating
element 46 can also act early on the opening cross section of the
passage opening 29, so that a rise of the high pressure above the
MOP value is prevented.
[0040] It is additionally to be mentioned that, although the
refrigerant-side gas cooler outlet temperature is the preferred
regulating temperature in the circuit with regard to COP
optimization, the high-pressure-side outlet temperature at the
inner heat exchanger 14 can likewise be used for the purpose of
regulating the high pressure in a COP-optimum range. For this
purpose, the outlet states at the inner heat exchanger 14 which
correspond to each COP-optimum gas cooler outlet state are
determined either by means of simulation or testing for the circuit
in which the thermostatic expansion valve 15 described by this
invention is used. A COP-optimized pressure profile therefore
results by means of the high-pressure-side outlet temperature at
the inner heat exchanger 14, and said COP-optimized pressure
profile is the aim of the optimum valve stroke characteristic curve
22 as per the state diagram in FIG. 5, in which the mass flow rate
is plotted against the temperature. Said COP-optimum valve stroke
characteristic curve 22 is restricted to one part, which is to be
defined within the context of the application, of the entire valve
stroke range, for example between 0 and 75%. This is illustrated in
FIG. 2 by the characteristic curves 21' and 21''. The double arrow
22 shows the COP-optimized regulating range. Beyond the upper limit
of the latter, the overflow function comes into action. If a mass
flow rate characteristic curve 23 of the throttle point is
designed, above said upper limit, that is to say until 100% of the
total valve stroke range is reached, so as to be sufficiently steep
that such a mass flow rate can flow out from the high-pressure into
the low-pressure side, and therefore a further rise in the high
pressure of the system can be prevented, one obtains the safety
function, as claimed by the present invention, for preventing
excessively high system pressures.
[0041] By means of the arrangement of a thermostatic expansion
valve 15 of said type at the evaporator inlet, one avoids complex
line set relocation, as is necessary for example in the use of a
thermostatic expansion valve as per the patent U.S. Pat. No.
6,012,300, since the valve described therein must absorb the
refrigerant-side outlet temperature at the gas cooler--either by
means of a local arrangement at the gas cooler outlet or by means
of the relocation of a capillary line between the valve and gas
cooler outlet.
[0042] FIG. 6 illustrates an alternative embodiment to FIG. 3. In
contrast to the latter, the thermally activatable actuating element
46 is produced as a spring element from a shape-memory alloy. Said
actuating element 46 can be set in such a way that the stroke
movement takes place only above a predetermined temperature
threshold value. Here, the acting force can additionally also be
determined by means of the cross section of the spring element. In
addition, an electric activation of said thermally activatable
actuating element 46 composed of the shape-memory alloy could also
be possible. The further functions and variants described with
regard to FIG. 3 likewise apply to this embodiment.
[0043] FIG. 7 illustrates a further alternative embodiment of a
thermally activatable actuating element 46 to FIG. 3. In said
embodiment, a hydraulically filled, bellows-like spring element is
provided which permits the overflow function or safety function.
The charges of the thermally activatable actuating element 36
comprise for example different oils and hydrocarbons.
[0044] All of said features are in each case essential to the
invention and can be combined with one another in any desired
manner.
* * * * *