DE102011000719A1 - Method for operating electric heater for heating airflow in air-conditioning system of car, involves reading temperature of resistor heating elements based on resistance, and changing electric power of heating elements based on temperature - Google Patents

Abstract

The method involves storing a resistance-temperature-characteristic curve of resistor heating elements (28, 30, 32) in a data memory of a power electronics (4), where the electronics controls a heating circuit of an electric heater (1). Resistance of the heating elements is determined during operation of the heater, where the heating elements are made from strip material. Temperature of the heating elements is read based on the resistance, and electric power of the heating elements is changed based on the temperature. An independent claim is also included for an electrical heater for heating fluid stream for a car.

Description

The invention relates to a method for driving an electric heater and a heater for heating a fluid flow, which can be operated by such a method.

The basic structure of such heaters for motor vehicles is for example in the EP 0 350 528 B1 the applicant described. This document discloses a PTC air heater for the air conditioning of a motor vehicle, wherein PTC resistors are used to generate heat, which have self-regulating properties due to their temperature-increasing resistance, so that overheating of the PTC resistor can be relatively easily prevented. The PTC resistors are thermally connected in the known solution with heat distribution elements / radiator elements, which consist for example of meandering curved band material. By this corrugated-shaped heat distribution elements a plurality of fins are provided, which are flowed through by the medium to be heated - in the present case air - it is important that the heat distribution elements and the PTC resistors are sufficiently thermally contacted in order to achieve the highest possible effective performance guarantee.

In the EP 1 407 907 B1 an air heater is disclosed in which the resistance element and the heat distribution element are integrally formed. In this known solution, a plastic material with PTC properties is used, for example, polypropylene or EVA can be used, which is added to improve the conductivity with carbon black.

In the EP 1 967 398 A1 an air heater is disclosed in which instead of the lamellar heat distribution elements described above stamped and bent parts are used, are introduced into the flow openings for the medium to be heated and then bent in a U-shape and contacted with PTC resistor elements.

In the EP 1 852 878 A1 Applicant proposes to use resistance wires wound on an electrically insulating support instead of PTC heating elements.

The advantage of such heaters with WDERstandsheizelementen over the solutions described above is that the resistance heaters are much cheaper than the PTC resistor elements, so that a very cost-effective production is possible. The disadvantage, however, is that such resistance heating elements do not or only to a significantly lesser extent have the self-regulating properties of the PTC resistance elements, so that a suitable control to avoid overheating must be provided. These resistance heating elements can be produced, for example, as a resistance wire, expanded or stamped metal or from a suitable plastic, for example carbon fiber. Applications are possible in both high-voltage and low-voltage ranges.

After applying the voltage, the full heating power is initially applied during operation of the heater. The medium to be heated, for example air, cooling water, fuel or the like flows through the heater and is warmed up accordingly. If there is a tearing of the media flow, for example due to the failure of a fan, a pump or a leak in the system, there is a risk that the resistance heating elements overheat. In the best case, the heating element burns through, so that the power supply is interrupted. In the worst case, the current flow remains, so that it can lead to overheating or inflammation surrounding material - a corresponding damage result is the result. In particular, in interior heaters of a motor vehicle, such a damage event due to the endangerment of the vehicle user or the environment in any case to avoid. It is therefore necessary to provide a suitable fuse element, via which the temperature can be detected and to reduce via the power electronics, the registered electrical power to prevent overheating.

Such a fuse element may for example be a thermocouple, for example an NTC element, via which the temperature of the medium to be heated is recorded. However, the use of such a thermocouple has serious disadvantages. On the one hand, it is necessary to guide the connections of the thermocouple to the power electronics of the heater, which must be paid to a sufficient seal and the leads must be routed so that no cable break is to be feared during operation. On the other hand, via the thermocouple, only a local temperature detection conclusions on the total temperature in the heater, d. H. the temperature of the resistance heating element or the medium to be heated, are difficult.

In contrast, the invention has for its object to provide a method for driving an electric heater and a heater operable by such a method, with the overheating can be reliably prevented when using a resistance heating.

This object is achieved with regard to the method by the combination of features of claim 1 and with respect to the electric heater by the feature combination of the independent claim 6.

Advantageous developments of the invention are the subject of the dependent claims.

The electrical heater controlled via the method according to the invention has power electronics, via which at least one heating circuit is controlled. This heating circuit has a resistance heating element which is contacted with the power electronics. According to the invention, a resistance-temperature characteristic of the resistance heating element is stored in a data memory of the power electronics.

During operation of the heater, the resistance of the resistance heating element is determined, for example, by measuring the current at a predetermined voltage, and read in dependence on this currently determined resistance on the characteristic curve, the actual temperature. The electrical power is then modulated by the power electronics as a function of this actual temperature and possibly the heater or a heating circuit is switched off when a maximum temperature is exceeded. Ie. According to the method according to the invention, a power modulation takes place as a function of the temperature determined via the characteristic curve.

Accordingly, the electric heater according to the invention is designed with power electronics, via which at least one heating circuit can be controlled. This has a resistance heating element with an approximately linear in the operating temperature range resistance-temperature characteristic, which is electrically contacted with the power electronics. This has a data memory for storing the characteristic curve and is designed such that an actual resistance of the resistance heating element determined and depending on this actual resistance an actual temperature can be read from the data memory and then the control of the resistance heating element in dependence on this -Temperature takes place.

By means of this method according to the invention and the corresponding heater, an extremely cost-effective temperature monitoring can be realized practically without additional components, wherein an advantage lies in the fact that the entire resistance heating element itself acts as a temperature sensor and thus an integral temperature determination is also made possible. The temperature signal obtained by the method according to the invention can then be used to control the heater, for example to switch off the entire heater or to switch off individual heating circuits or for power modulation.

In a variant of the invention, it is assumed that the characteristic curve runs approximately linearly in the operating temperature range, so that the detection of the characteristic curve is simplified. In principle, it is of course also possible to use an exact characteristic curve with a non-linear course.

With an approximately linear characteristic curve, the calibration before starting the heater is relatively simple, since, for example, at given reference temperatures, the resulting resistance is measured and then from the resistance / temperature values and the assumption of an approximately linear characteristic curve, the slope is calculated.

Calibration is even easier if one assumes that the slope of the characteristic curve of the resistance material remains the same even in the case of manufacturing and material fluctuations and the respective characteristic curves are merely shifted in parallel, depending on material and manufacturing variations. In this case, it is sufficient to carry out a single measurement at a given reference temperature and to determine the position of the characteristic with a predetermined slope from the resulting value pair (resistance, temperature).

In the heater according to the invention, a control of the power electronics for switching or controlling the Widerstandsheizelementes also be designed for measuring the current, so that at a given operating voltage (low voltage about 13.5 V, high voltage between 1 about 120 V and about 450 V) and off the measured current strength of the actual resistance of the resistance heating element can be determined.

The structure of the electric heater is particularly simple if the resistance heating element of a heating circuit is made of a strip material.

The one or more resistance heating elements are preferably held in a frame, while the connection can be made by latching, so that the assembly is simplified.

The heater has a compact design, if the power electronics is attached to the side of a frame.

The electrical contacting of the control can be done via a plus bolt and ground bolt, which protrude laterally at a parallel distance from the frame.

In a variant of the invention, the heater has a multi-part control housing which contains a power electronics board, a ground plate contacted with the ground pin and a seal for sealing the power electronics to the environment.

In order to avoid a thermal overload of the power electronics, a circuit board with cooling elements can be cooled, which protrude through the control housing into a flow cross-section of the heater.

In a very simple construction of the embodiment of the heater, the contacting of the resistor element via connection pins, which are either electrically connected to a ground plate or enforce this without electrical contact.

A seal then surrounds the said connection pins and the cooling elements.

The assembly is particularly simple when a control housing is clipped on the side of a resistance heating elements receiving frame.

A timing case cover may be latched to a frame-side timing case bottom.

Preferred embodiments of the invention are explained in more detail below with reference to schematic drawings. Show it:

1 a three-dimensional view of a heater according to the invention for the air flow of an automotive air conditioning system;

2 another view of the heater off 1 ;

3 a detailed view of the heater according to the 1 and 2 ;

4 a longitudinal section through the heater according to the 1 and 2 ;

5 an exploded view of a control of the heater;

6a . 6b Characteristics of resistance heating elements and

7 a highly simplified process scheme of the control of the heater according to 1 ,

1 shows a three-dimensional representation of a heater 1 which is used as a heater in the air conditioning system of a motor vehicle to heat an air flow. Such a heater 1 can be designed for operation on a low-voltage or high-voltage vehicle electrical system.

The in 1 illustrated heater 1 has a radiator 2 , which is flowed through by the air to be heated and a laterally attached to the radiator power electronics 4 in a control box 6 is included, with the power supply of the power electronics 4 over a plus bolt 8th and a ground bolt 10 that takes off from the radiator 2 side facing away from the control housing 6 protrude. The radiator 2 is executed in the illustrated embodiment with three heating circuits, each heating a heating module 12 . 14 . 16 assigned. The three heating modules 12 . 14 . 16 are in a frame 18 of the radiator 2 recorded, this in 1 approximately in the horizontal direction extending longitudinal beams 20 . 22 . 24 . 26 has, whose from the power electronics 4 distant end portion in a side rail 27 enters, leaving three compartments to accommodate the heating modules 12 . 14 . 16 be formed. In each of these subjects is a meandering curved, in the illustration according to 1 indicated by dark solid lines resistance heating element 28 . 30 respectively. 32 taken, the concrete structure will be explained in more detail below. The three heating modules 12 . 14 . 16 can about the power electronics 4 be controlled independently of each other to the power input by connecting or disconnecting individual heating modules 12 . 14 . 16 to vary. Of course, about the power electronics 4 also the heat output through individual control of each heating module 12 . 14 . 16 adjustable. This will be explained in more detail below.

The control housing 6 has a caseback 34 that with a housing cover 36 is locked. This Verrasterung is done via a variety of locking tongues 38 on the housing cover 36 which engage in corresponding snap-in shots 40 of the case bottom 34 engage the control box 6 to close. According to the rear view in 2 is on the case back 34 at the back a frame flange 42 trained in the the frame 18 can be used. In the illustration according to 2 you can also see another side panel on the side of the housing 44 that the longitudinal spars 20 . 22 . 24 . 26 connects with each other, so that the frame-like structure arises. At the respective outer side surfaces of the longitudinal bars 20 . 22 are each locking lugs 46 formed in corresponding breakthroughs 48 on side cheeks of the frame flange 42 snap into place, leaving the frame 18 Reliable with the control housing 6 connected is. In this rest position is also the radiator 2 electrically with the power electronics 4 contacted.

As in particular from 2 shows are on the side surfaces of the frame flange 42 a series of recesses 43 executed, which ensure that the heated air flow and the connection area between the frame 18 and the power electronics 4 flows around and thus cools this area with.

Further details of the heater 1 arise from the 3 and 4 , in which 3 a detail X of the heater 1 out 2 and 4 a longitudinal section through this heater 1 shows. From this longitudinal section, the structure of the radiator opens up 2 , in particular the frame construction with the outer longitudinal beams 20 . 26 , the two lateral side rails 27 . 44 and the two inner longitudinal beams 22 . 24 about which the three heating modules 12 . 14 . 16 are spaced from each other. The frame 18 is made as an injection molded part, wherein to avoid mass accumulation in the outer longitudinal beams 20 . 26 and in the outer side rail 27 cavities 50 are formed, over which the wall thickness of the frame is largely made uniform, so that the injection molding process improved and on the other hand, the injection weight is minimized.

In the illustration according to 4 you can clearly see the meandering curved resistance heating elements 28 . 30 . 32 whose end sections through the longitudinal spar 44 are passed through and bent at right angles fittings 52 . 54 (please refer 4 above), which are on the outer end face of the side spar 44 issue. These fittings 52 . 54 are with a plus pin 56 or with a ground connection pin 58 contacted, in turn, electrically with the power electronics explained in more detail below 4 are connected. At the in 4 illustrated embodiment is each heating module 12 . 14 . 16 via such connection pins 56 . 58 contacted. For the mechanical guidance of the resistance heating elements 28 . 30 . 32 are in the frame 18 parallel to the longitudinal bars 20 . 22 . 24 . 26 running walls 60 . 62 arranged, of which in 4 only two are provided with these reference numerals. These walls 60 . 62 extend alternately from side spar 44 away to a small distance to the other side spar 27 or from this external side rail 27 to a predetermined distance to the other side spar 44 , so that the band-shaped resistance heating element 28 . 30 . 32 each through the resulting gap 64 through between the wall 60 . 62 and the adjacent side rail 27 . 44 can be guided around. In this way, each leg of the resistance heating element 28 . 30 . 32 between two wall sections of the frame 18 arranged so that a short circuit is excluded. In the illustrated embodiment, each heating module 12 . 14 . 16 with seven such walls 60 . 62 executed, so that the resistance heating element 28 . 30 . 32 corresponding to eight parallel to the longitudinal beams 20 . 22 . 24 . 26 extending leg sections within the frame 18 extends zigzag, said leg portions are connected via short at right angles thereto angled connecting portions extending through the above-mentioned gaps 64 extend through.

As already explained, the end sections of the resistance heating elements 28 . 30 . 32 each on the inner side rail 44 anchored. Another position fixation takes place in the region of the outer side member 27 about a Verrasterung. According to the detail X in 3 is in the process from the side rail 44 away walls 60 in each case a freely cut latching tongue 66 formed, in which the area lying there of the band-shaped resistance heating element 28 . 30 . 32 can be clipped, with a snap hook 68 the side edge of the respective resistance heating element (here 32 ) engages behind, so that this is reliably fixed in position. Of course, there are more snap hooks 68 along the walls 60 . 62 be provided to the resistance heating element 28 . 30 able to fix.

Details of the power electronics are described below with reference to 4 and 5 explained.

5 shows some items of power electronics 4 or the receiving this control housing 6 , You can see the frame 18 with the latched housing bottom 34 , This is from the aforementioned connection pins 56 . 58 interspersed, with the connecting pins 56 with the plus bolt 8th and the connection pins 58 with the ground bolt 10 are electrically connected. These, with the corresponding end portions of the resistance heating elements 28 . 30 . 32 connected connection pins 56 . 58 enforce according to the 4 and 5 corresponding holes 70 . 72 one the electronic components of power electronics 4 receiving board 74 and are electrically connected to it, for example by welding, crimping or soldering. The board 74 is in the case back 34 used.

To dissipate the waste heat of highly thermally stressed components of the board 74 is the heater according to the invention with, for example, three approximately cylindrical heat sinks 76 executed, of which in the illustrations only one example by the reference numeral 76 is provided. These heatsinks 76 enforce the case back 34 and are on the one hand thermally contacted with the thermally loaded electronic component and collar on the other hand according to the sectional view in 4 in the frame flange 42 encompassed area, these end portions 78 by suitable design with a comparison with the cylindrical board-side end portions enlarged heat exchange surface are formed in order to dissipate the heat in an optimal manner. The end portions designed with the enlarged heat exchange surface 78 the heat sink 76 protrude into the area, with the recesses 43 is provided so that a good flow is ensured.

The earth connection of the board 74 via a ground plate 80 , which in contrast angled connection lug 82 which, as shown in FIG 4 with the ground bolt 10 is contacted. The ground plate 80 has three each one of the ground connection pins 58 associated, beaded clamp receptacles 84 through which pass the corresponding ground connection pins 58 extend and over which these are connected to ground. In the ground plate 80 are further through holes 86 . 88 for the plus connection pins 56 or the heat sink 76 provided, wherein the respective diameter is selected so that no contact with the terminal pin 56 / Heatsink 76 he follows. The ground plate 80 is also still with a variety of spring tongues 90 executed, over which a fixation in the housing bottom 34 he follows.

For sealing the power electronics 4 opposite the environment is between the ground plate 80 and the caseback 34 a seal 92 provided with the same hole pattern as the ground plate 80 is executed and the openings surrounds sealingly and on the other hand sealingly on a pins 56 . 58 and the heatsinks 76 encompassing sealing ring 94 of the case bottom 34 rests so that the power electronics 4 to the radiator 2 is sealed off. To optimize the sealing effect are on the sealing element 92 even more sealing fields 96 . 98 formed, with the sealing fields 96 each the breakthroughs 86 . 88 and the circular sealing fields 98 the associated terminal receiving 84 embrace.

The board 74 as well as the ground plate 80 and the seal 92 are via suitable fixing and support webs within the housing bottom 34 and the clipped housing cover 36 fixed in position, so that even with vibrations or excessive accelerations a reliable relative positioning of these components is present.

At the bottom of the case 34 are also still connection areas 100 for fixing the heater 1 provided on a support or the like.

As mentioned above, the resistance heating element 28 made of a material having an approximately linear RT characteristic in an operating temperature range. For the control of the heater explained in more detail below 1 The knowledge of this characteristic is important, so before putting the heater 1 During production, a calibration or measurement of the individual characteristic curve of the respective heating module 12 . 14 . 16 should be done.

6a shows a way to measure such a characteristic. In this case, at two predetermined reference temperatures T _R1 , T _R2 and predetermined operating voltage (high-voltage, low-voltage), the resulting corresponding resistors R ₁ , R _{2 of} the resistance heating 28 recorded and then from these two pairs of values according to the linear assumed characteristic 6a determined, which passes through the two value pairs. In this way, the characteristic for each resistance heating element can be 28 Determine so that manufacturing inaccuracies and material variations by this calibration of each resistance heating element 28 can be compensated.

The characteristic curves measured in this way are then stored in a data memory of the power electronics.

In the calibration procedure described above, for each resistance heating element 28 . 30 . 32 at least two measurements are carried out.

6b shows a simplified calibration, assuming that the. Increase in the characteristic even in production and material fluctuations remains the same and, if necessary, a parallel displacement of the characteristics is carried out to determine only a single measurement is required. Ie. it is at a given reference temperature T _{R1 of} the self-adjusting resistance of the respective resistance heating 28 . 30 . 32 determined, so that then also given slope, the actual characteristic (dashed in 6b ) and in the data memory of the power electronics 4 can be stored.

In knowledge of these characteristics, the control of the heater takes place 1 then according to the highly simplified flowchart in 7 ,

When the vehicle is put into operation, the heater for heating the air flow is first turned on at full power or according to the specifications of the air conditioning control with reduced power, for example, in some switched-off heating circuits.

Via a switching or control element which controls the respective heating circuit and that on the circuit board 74 is installed, can then be suitable Design also take a current measurement, so that, depending on the given on-board voltage. (High voltage, low voltage) and the measured current, the resistance of the respective resistance heating element 28 . 30 . 32 can be determined.

In response to this resistance is then from the stored characteristic of each resistance heating element 28 . 30 . 32 an actual temperature T _{IST is} read and this temperature of the resistance heating element 28 with one in the power electronics 4 stored maximum temperature T _Max compared.

In the case where the actual temperature exceeds the predetermined maximum temperature, the heater becomes 1 switched off or at least one of the heating circuits switched off.

In the case where the actual temperature is below the maximum temperature, via the power electronics 4 a power modulation as a function of the actual temperature in order to optimize the warming of the air flow, with sufficient power input, the electrical power supplied to the individual heating circuits can be reduced and / or individual heating circuits can be switched off, so that the load of the heater 1 is always reduced to an optimum, in which a minimum consumption is accompanied by a sufficient warming of the air flow.

In the illustrated embodiment is for the resistance heating elements 28 . 30 . 32 used a material that has a slight PTC characteristic. However, this PTC effect is by no means comparable to that of a true PTC resistor, but is sufficient to determine the temperature of the heating element as a function of the resistance.

Disclosed are a method for driving an electric heater and a heater operable by such a method, wherein it is designed with at least one resistance heating element, which itself acts as a thermocouple, so that its temperature can be used to drive the heater.

LIST OF REFERENCE NUMBERS

1

stoker

2

radiator

4

power electronics

6

control housing

8th

plus bolts

10

earth stud

12

heating module

14

heating module

16

heating module

18

frame

20

longitudinal beam

22

longitudinal beam

24

longitudinal beam

26

longitudinal beam

27

side rail

28

resistance

30

resistance

32

resistance

34

caseback

36

housing cover

38

locking tongues

40

locking receivers

42

frame flange

43

recess

44

another side rail

46

locking lug

48

breakthrough

50

cavity

52

connector

54

connector

56

connector pin

58

connector pin

60

wall

62

wall

64

gap

66

catch tongue

68

snap hooks

70

hole

72

hole

74

circuit board

76

heatsink

78

end

80

ground plate

82

terminal lug

84

terminal receiving

86

breakthrough

88

breakthrough

90

spring tongue

92

poetry

94

seal

96

sealing field

98

sealing field

100

lands

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0350528 B1 [0002]
• EP 1407907 B1 [0003]
• EP 1967398 A1 [0004]
• EP 1852878 A1 [0005]

Claims (19)

Method for driving an electric heater ( 1 ) for vehicles, with power electronics ( 4 ), via which at least one heating circuit can be controlled, which is a resistance element ( 28 . 30 . 32 ), which is connected to the power electronics ( 4 ), comprising the steps of: - storing an RT characteristic of the resistance heating element ( 28 . 30 . 32 ) in a data memory of the power electronics ( 4 ); Determining the resistance (R) of the resistance heating element ( 28 . 30 . 32 ) during operation of the heater ( 1 ); - Reading a temperature (T _actual ) as a function of the resistance (R) and - Changing the registered electrical power as a function of the temperature (T _actual ). The method of claim 1, wherein the resistance is determined from the applied voltage and the current. Method according to claim 1 or 2, wherein a resistance heating element ( 28 . 30 . 32 ) is used with approximately linear characteristic in the operating temperature range. Method according to claim 3, wherein the resistance heating element ( 28 ) before putting the heater into operation ( 1 ) is calibrated by determining the resistance (R) at two predetermined reference temperatures (T _R ) and then calculating the slope of the characteristic curve from the two resistance values. Method according to claim 3, wherein the resistance heating element ( 28 . 30 . 32 ) before putting the heater into operation ( 1 ) is calibrated by the resistance (R) is determined at a predetermined reference temperature (T _R ) and the characteristic curve is calculated at a predetermined slope. Electric heater, for heating a fluid flow, in particular for a vehicle, with power electronics ( 4 ), via which at least one heating circuit can be controlled and which has a data memory for storing an RT characteristic, wherein the power electronics ( 4 ) for determining an actual resistance (R _IST ) and for reading out an actual temperature (T _IST ) as a function of the actual resistance and for driving the resistance heating element ( 28 . 30 . 32 ) is designed as a function of the actual temperature (T _actual ). Heater according to claim 6, wherein a control of the power electronics ( 4 ) for switching or regulating the resistance heating element ( 28 . 30 . 32 ) is also designed to measure the current (I). Heater according to claim 6 or 7, wherein the resistance heating element ( 28 . 30 . 32 ) is made of a strip material. Heater according to claim 8, wherein the at least one resistance heating element ( 28 . 30 . 32 ) in a framework ( 18 ) is held. Heater according to claim 9, wherein the resistance heating element ( 28 . 30 . 32 ) at least in sections by latching in the frame ( 18 ) is held. Heater according to claim 9 or 10, wherein the power electronics ( 4 ) on the side of the frame ( 18 ) is set. Heater according to one of the claims 6 to 11, wherein the electrical contacting of the power electronics ( 4 ) via a plus and a ground pin ( 8th . 10 ), which protrude laterally in the parallel distance. Heater according to one of the claims 6 to 12, wherein the power electronics ( 4 ) in a multi-part housing ( 34 . 36 ) and a board ( 74 ), one with the ground bolt ( 10 ) contacted ground plate ( 80 ) and a seal ( 92 ) contains. A heater according to claim 13, wherein the board ( 74 ) over heat sink ( 76 ) cooled from the housing ( 34 ) out into a flow cross-section of the heater ( 1 ) protrude. Heater according to claim 13 or 14, wherein the contacting of the resistance heating element ( 28 ) via connection pins ( 56 . 58 ), one of which is connected to the ground plate ( 80 ) is electrically connected and the other part of the housing ( 34 . 36 ) interspersed without contact. Heater according to claim 14 and 15, wherein a seal ( 92 ) the connection pins ( 56 . 58 ) and the heat sink ( 76 ) surrounds. Heater according to one of the claims 13 to 16 , where the housing ( 34 . 36 ) of the power electronics ( 4 ) to a frame ( 18 ) is clipped. Heater according to one of the claims 6 to 17 , with a housing cover ( 36 ), which with a frame-side housing bottom ( 34 ) is locked. A heater according to any one of claims 6 to 18, wherein the fluid flow is an airflow.

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