DE102018205169A1 - Method for controlling an air conditioning device of a motor vehicle and air conditioning device for a motor vehicle with a heat pump unit - Google Patents

Abstract

A method for controlling an air conditioning device of a motor vehicle having a heat pump unit with a refrigerant refrigerant circuit, wherein the refrigerant circuit comprises at least a first heat exchanger, an expansion valve, a compressor, an evaporator overflowed by ambient air and a fan is characterized by the steps
a. Determining a surface temperature of the evaporator
b. Determining a dew point temperature of the ambient air
c. Determine whether icing of the evaporator threatens with the aid of the determined surface temperature of the evaporator and the determined dew point temperature of the ambient air, and
d. Take measures to increase the surface temperature of the evaporator if icing of the evaporator threatens.
Furthermore, an air conditioning apparatus is described which has a control unit configured to carry out such a method.

Description

The invention relates to a method for controlling an air conditioning device of a motor vehicle, comprising a heat pump unit with a refrigerant refrigerant circuit, wherein the refrigerant circuit comprises at least a first heat exchanger, an expansion valve, a compressor, an overflowed by ambient air evaporator and a fan, and an air conditioning device for a motor vehicle having a heat pump unit, which has a refrigerant circuit carrying a refrigerant, wherein the refrigerant circuit comprises at least one evaporator overflowed by ambient air, an expansion valve, a compressor and a fan.

Such an air conditioning device or such a method is increasingly used in electrically driven vehicles lately. Unlike conventional vehicles with internal combustion engines, new concepts have to be developed here, especially for heating the vehicle interior, since the electrified drive components operate very efficiently in comparison with the internal combustion engine and therefore generate relatively little freely available waste heat. In particular, the waste heat is available only on a very low compared to the internal combustion engine temperature level. For this reason, heat pump concepts are increasingly used that use enthalpy from the ambient air for heating the vehicle interior. In this case, existing anergy in the ambient air is used as a source of evaporation for the refrigerant used to heat the interior. As a result, the outdoor heat exchanger in the form of an evaporator is inevitably cooled to a temperature below the ambient temperature, so that it can come to auskondensierender humidity, which can then settle on the heat exchanger in the form of an ice or frost layer.

When this condition continues for a long time, a critical tire degree is exceeded, and as a result, the air side pressure loss is greatly increased and the air side power supply is significantly reduced. The ice or frost layer increases on the one hand the thermal resistance, which is to overcome heat exchange between the heat exchanger over flowing ambient air and the heat exchanger itself, and on the other hand, the available free cross section is reduced, so that only a smaller amount of air reaches the heat exchanger at all, which also reduces the amount of heat exchanged. An iced outdoor evaporator is then no longer available as an energy source for heating the vehicle or the vehicle interior.

To solve the problem, a de-icing process with a process reversal or external heat is cyclically initiated in many cases after a predetermined time. For active deicing by external heat is usually used an electrical heating resistor for heating the evaporator network. During the process reversal, the refrigeration cycle is switched over and the evaporator is operated as a condenser or as a condenser. Such an active defrosting process requires a considerable expenditure of energy which impairs the efficiency and the performance of the entire system. At the same time, the heating of the vehicle interior is affected because in the defrosting the heat pump is not available for heating the interior. The heating of the vehicle interior is correspondingly so severely impaired that it comes for a user to noticeable loss of comfort. To compensate for this, additional components for heating can be installed during the defrosting process, which in turn causes costs and also reduces the efficiency of the system.

Added to this is the problem that with such a cyclic defrosting process there is the risk that the above-mentioned disadvantages are accepted, even if no relevant icing of the evaporator is present.

From the DE 10 2011 051 285 A1 It is known to operate an air conditioning device of a vehicle with a heat pump so that on the one hand in the evaporator always a slight overheating of preferably 0 K is present, so the entire refrigerant is here in the gaseous state. On the other hand, it is proposed to keep the difference between the ambient temperature and the saturation temperature of the refrigerant as small as possible, in particular less than 4 to 6 K. Since an overheating of about 0 K is present within the evaporator, the saturation temperature of the refrigerant here corresponds to the surface temperature of the evaporator. In other words, it is therefore attempted to keep the temperature difference between the surface of the evaporator and the ambient air, which enthalpy should be withdrawn, as small as possible, so as to prevent icing of the evaporator. Such a procedure, on the one hand, reduces the efficiency of the heat pump and, at the same time, can not reliably prevent icing of the evaporator, since the absolute temperature of the superheated refrigerant can also be below the dew point temperature of the ambient air.

The object of the present invention is therefore to provide a method and a device that allow heating of a vehicle interior by means of a heat pump cycle, without that the used evaporator ices, wherein At the same time, the overall efficiency of the system should be as high as possible.

• a. Ermitteln einer Oberflächentemperatur des Verdampfers
• b. Ermitteln einer Taupunkttemperatur der Umgebungsluft
• c. Ermitteln, ob eine Vereisung des Verdampfers droht unter Zuhilfenahme der ermittelten Oberflächentemperatur des Verdampfers sowie der ermittelten Taupunkttemperatur der Umgebungsluft, und
• d. Ergreifen von Maßnahmen zum Erhöhen der Oberflächentemperatur des Verdampfers, falls eine Vereisung des Verdampfers droht,

sowie durch eine Klimatisierungsvorrichtung für ein Kraftfahrzeug mit einer Steuerungseinheit, die zum Durchführen eines entsprechenden Verfahrens eingerichtet ist.The invention solves the problem by a generic method with the steps

• a. Determining a surface temperature of the evaporator
• b. Determining a dew point temperature of the ambient air
• c. Determine whether icing of the evaporator threatens with the aid of the determined surface temperature of the evaporator and the determined dew point temperature of the ambient air, and
• d. Take measures to increase the surface temperature of the evaporator if icing of the evaporator threatens

and by an air conditioning device for a motor vehicle having a control unit configured to perform a corresponding method.

According to the invention, it has been recognized that icing of the evaporator only threatens if the temperature of the surface of the evaporator is below the dew point temperature of the ambient air. By taking measures to prevent icing only if it is determined that icing is actually at risk, it can be ensured that no such measures are taken in situations which are not critical with respect to icing of the evaporator. It thus avoids an unnecessary reduction in the efficiency of the air conditioning device.

In an advantageous development of the method according to the invention, it is provided that in step c. Based on a difference between the surface temperature of the evaporator and the dew point temperature of the ambient air is determined whether an icing of the evaporator threatens. A simple difference between the two mentioned temperatures is the easiest way to determine a reliable estimate of the risk of icing of the evaporator.

It can also be advantageously provided that the actual dew point temperature is modified with an offset, before it is determined whether an icing of the evaporator threatens.

In other words, therefore, the determined dew point temperature is not used for the further method, but a dew point temperature which is slightly above the determined dew point temperature. It is set such a safe distance and icing of the evaporator particularly safe prevented because minor inaccuracies in the determination of the dew point temperature and / or in determining the surface temperature of the evaporator are tolerable by this safety margin. In particular, in this case an incipient icing of the evaporator is already avoided since countermeasures are already started when the surface temperature of the evaporator comes only in the vicinity of the dew point temperature of the ambient air. Since, however, in many situations, countermeasures are already taken because of the offset, although the surface temperature of the evaporator is still above the dew point temperature, the offset should be as small as possible. Possible values for the offset are, for example, 1 K, 2 K or 3 K. The offset can also be configured as a function of the value of the outside temperature. At higher outside temperatures of, for example, 0 ° C even a slight drop below the dew point temperature can lead to a relatively large separated mass of water or frost, whereas colder air is usually drier and thus can not lose so much water. The selected offset should then be greater at higher ambient air temperatures than at lower ambient air temperatures, since in these even with a smaller offset icing of the evaporator can be reliably prevented.

Advantageously, the dew point temperature of the ambient air can be determined from a temperature of the ambient air and a humidity of the ambient air. The necessary sensors are standard in most vehicles today. Alternatively, reference values that can be obtained, for example, from an online database can also be used.

An easy way to determine the surface temperature of the evaporator results when the surface temperature of the evaporator is determined from a pressure of the refrigerant in the refrigerant circuit. Also, the necessary sensor is usually already available. The relationship between the pressure of the refrigerant and the surface temperature of the evaporator is particularly simple, especially in the two-phase region, ie in the simultaneous presence of liquid phase and gaseous phase. Alternatively, the surface temperature can be measured with its own temperature sensor, or the temperature of the refrigerant at the refrigerant outlet, ie at the outlet of the heat exchanger, is determined. This agrees approximately with the surface temperature of the evaporator.

An advantageous development of the invention provides that as a primary measure for Increasing the surface temperature of the evaporator increases the mass air flow through the evaporator. This reduces the likelihood that the air flowing past the evaporator will be cooled to a temperature below the dew point temperature, since a larger heat flow is transmitted at the same temperature difference.

In order to prevent an acoustic comfort impairment of the occupants, the maximum air mass flow may be dependent on the current driving speed of the vehicle. It is thus achieved that the fan noise at any time unpleasant over the already existing driving noise. These driving sounds increase with increasing speed, so that at a higher speed, a higher noise level caused by a higher fan speed will not be noticed negatively.

In particular, when the air mass flow has reached the maximum value possibly modified by the current driving speed, the refrigerant mass flow through the evaporator can be reduced to increase the surface temperature of the evaporator. It is thus removed from the passing air less heat, so that in this way a drop in the temperature of the passing air is avoided to a value below the dew point temperature. By reducing the refrigerant mass flow flowing through the heat exchanger, the heat flow that can be absorbed by the refrigerant decreases. As a result, under otherwise identical conditions, the superheating and / or the pressure level in the heat exchanger increases, so that the average surface temperature of the component increases and falls below the dew point temperature is reduced.

It may be provided that to increase the surface temperature of the evaporator, a portion of the refrigerant mass flow through a second evaporator, which does not interact with the ambient air, is directed to continue to guarantee the required heat flow for conditioning of the interior.

In particular, the second evaporator can be part of a circuit for cooling traction components of the vehicle, such as battery, engine and power electronics, as is usually the case with electrically driven vehicles. Such a second evaporator is often referred to as a "chiller". Other sources of heat can also be used here, if any.

An advantageous development of the invention provides that a temperature gradient of the coolant in the circuit for cooling of traction components is monitored, and that, as soon as this gradient is negative, a desired outlet temperature is lowered until a positive gradient is measured again. The temperature gradient is in particular a time-related gradient. In other words, the temporal evolution of the temperature of the coolant is monitored.

In the event that the measures mentioned so far are not sufficient or in the event that, in order to reliably prevent icing, forcibly the power of the heat pump cycle must be reduced to such an extent that the vehicle interior can no longer be kept at the desired temperature, An additional electric heater can be activated.

• 1: Einen schematischen Aufbau einer Klimatisierungsvorrichtung zur Durchführung eines erfindungsgemäßen Verfahrens,
• 2: eine schematische Darstellung der Regelarchitektur zur Steuerung des Klimageräts, und
• 3: eine weitere vereinfachte schematische Darstellung eines erfindungsgemäßen Verfahrens

Embodiments of the invention will be explained in more detail with reference to the drawings and the description below. Show it:

• 1 FIG. 1 shows a schematic structure of an air-conditioning device for carrying out a method according to the invention, FIG.
• 2 a schematic representation of the control architecture for controlling the air conditioner, and
• 3 : a further simplified schematic representation of a method according to the invention

1 schematically shows the structure of an air conditioning device 2 for carrying out the method according to the invention. In the upper left area is the compressor 4 can be seen, which draws on its right side low pressure and low temperature refrigerant, this compressed and on the left side, which is the high pressure side, with higher pressure and higher temperature again. Pressure and temperature are determined by the first pressure / temperature sensor 5 measured. The first shut-off valve 6 is closed, so that the refrigerant from the compressor 4 through the open second shut-off valve 7 through moved to the right and then through the direction indicated by the dashed box air conditioner 8th arranged first heat exchanger 10 flows. Through the first expansion valve 12 , which is fully open in the state shown, the refrigerant then flows through the second heat exchanger 14 , The second shut-off valve 15 as well as the third shut-off valve 16 are closed so that the refrigerant flow is completely through the second heat exchanger 14 of the air conditioner 8th flows. In the air conditioner 8th finds a heat exchange between the indicated by arrows, intended for the interior air 17 and the heat exchanger 10 . 14 flowing refrigerant instead. Accordingly, the refrigerant after leaving the second Heat exchanger 14 already cooled a bit, resulting in the second pressure / temperature sensor 18 is registered.

At the division point 20 the refrigerant flow is now divided. Depending on the position of the second expansion valve 22 and the third expansion valve 24 In this case, different partial mass flows can be directed through the other parts of the arrangement. The through the second expansion valve 22 flowing partial mass flow flows through a battery that is not necessary for the described method 26 and then into the front gas cooler 28 , which in turn is used in the described method as an evaporator. The battery 26 is a large-volume element for storing heat energy. At the entrance of the third heat exchanger in the form of the front gas cooler 28 is the third pressure / temperature sensor 30 arranged.

This is after flowing through the second expansion valve 22 Refrigerant at a low temperature level comes in the front gas cooler 28 in thermal contact with the ambient air 32 holding the front gas cooler 28 flows through. The refrigerant absorbs enthalpy from the ambient air 32 and warms up. Due to the optional roller blind 34 In this case, the geometry or the open area of the front gas cooler can be influenced. Through the open fourth shut-off valve 36 the refrigerant flows to the merge point 38 , Here it hits the refrigerant partial flow that passes through the third expansion valve 24 and the fourth heat exchanger in the form of the so-called chiller 40 has flowed and combines with this again to a total refrigerant mass flow. Pressure and temperature are here once again by the fourth pressure / temperature sensor 44 measured. After the total refrigerant mass flow again the battery 26 has passed through it flows to the entrance of the compressor 4 where the fifth pressure / temperature sensor 46 again measures pressure and temperature. All sensors and valves are connected to a control unit, not shown, and are controlled by this.

2 shows a schematic representation of the control architecture for controlling the air conditioner. The first nonlinear member NL1 calculated from the input variables of the humidity of the ambient air φ and the ambient air temperature outside the current dew point temperature τ , Addition of an offset of a few K results in the weighted dew point temperature τ * which is used for further regulation. In the first computer M1 is the difference between that of the third nonlinear member NL3 based on the refrigerant pressure p determined surface temperature T _surface of the evaporator and the rated dew point temperature τ * calculated. This difference serves as a measure of the strength of the necessary intervention. If the difference is positive, the surface temperature of the evaporator is T _surface ie above the rated dew point temperature τ * , so no intervention is necessary. If the difference is equal to zero or even negative, then the surface temperature of the evaporator must be T _surface be increased to prevent icing of the evaporator. The greater the amount of the negative difference, the stronger the intervention. The regulator R1 regulates the fan power and optionally the refrigerant mass flow as described above, so that it comes to a heating of the surface of the evaporator. The second nonlinear member NL2 represents the controlled system. The manipulated variable change of the fan speed ( n ) caused in superposition with the caused by the vehicle speed back pressure on the heat exchanger changed suction pressure conditions, which represent the measured output of the controlled system. There, the operating parameters of the refrigerant circuit are further adapted to the modified by the adjusted fan power air mass flow, so that at the second heat exchanger of the refrigerant circuit, which tempered the indoor air, regardless of the measures to prevent icing a constant amount of heat can be removed.

3 shows a further simplified schematic representation of the method according to the invention. In step S10 the support is regulated by the air mass flow in the front heat exchanger. The controlled variable is the surface temperature of the evaporator, the reference variable is the weighted dew point of the ambient air, and the manipulated variable is the fan output of the associated fan. In the event that this manipulated variable is limited, since due to the current driving speed, the passengers acoustically no higher fan speed can be expected, is in step S20 as a further measure to increase the surface temperature of the evaporator reduces the outlet temperature of the temperature-controlled air in the vehicle interior. The controlled variable is in turn the surface temperature of the evaporator, the reference variable is also the weighted dew point temperature of the ambient air and the manipulated variable is the target outlet temperature to the vehicle interior.

As soon as the fan speed command value limit is no longer active, you can go to step S30 be continued and it will increase the blow-out temperature again. The controlled variable, reference variable and manipulated variable correspond to the respective variables in step S20 , As soon as neither the manipulated variable limit for the fan nor the reduction of the blow-off temperature are active, it is possible again with step S10 be continued. On the other hand, if the manipulated variable limit for the fan speed is reactivated, for example, because the vehicle speed is reduced, so after step S30 again with step S20 continued.

LIST OF REFERENCE NUMBERS

2

Air conditioning device

4

compressor

5

first pressure / temperature sensor

6

first shut-off valve

7

second shut-off valve

8th

air conditioning

10

first heat exchanger

12

first expansion valve

14

second heat exchanger

15

second shut-off valve

16

third shut-off valve

17

air

18

second pressure / temperature sensor

20

dividing point

22

second expansion valve

24

third expansion valve

26

battery pack

28

front gas cooler

30

third pressure / temperature sensor

32

ambient air

34

roller blind

36

fourth shut-off valve

38

rallying point

40

Chiller

42

heat flow

44

fourth pressure / temperature sensor

46

fifth pressure / temperature sensor

48

additional heating

NL1

first nonlinear member

NL2

second non-linear member

NL3

third nonlinear member

M1

first computing element

R1

first controller

φ

humidity

_Outside

Temperature of the ambient air

τ

dew point temperature

τ *

rated dew point temperature

n

Fan speed

v

Driving speed of the vehicle

p

Pressure of the refrigerant

T _surface

Surface temperature of the evaporator

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

• DE 102011051285 A1 [0006]

Claims (10)

A method for controlling an air conditioning device (2) of a motor vehicle having a heat pump unit with a refrigerant refrigerant circuit, wherein the refrigerant circuit at least a first heat exchanger (10), an expansion valve (12, 22, 24), a compressor (4), one of Surrounding air overflowed evaporator (28) and a fan comprises, with the steps a. Determining a surface temperature T _{surface of} the evaporator b. Determining a dew point temperature τ of the ambient air c. Determine whether icing of the evaporator (28) threatens with the aid of the determined surface temperature T _{surface of} the evaporator and the determined dew point temperature τ of the ambient _air , and d. _Take measures to increase the surface temperature T _{surface of} the evaporator (28) if icing of the evaporator (28) is imminent. Method according to Claim 1 , characterized in that in step c. is determined based on a difference between the surface temperature T _{surface of} the evaporator (28) and the dew point temperature τ of the ambient _air , whether icing of the evaporator (28) threatens. Method according to one of the preceding claims, characterized in that the actual dew point temperature τ is modified with an offset, before it is determined whether an icing of the evaporator (28) threatens. Method according to one of the preceding claims, characterized in that the surface temperature of the evaporator T _{surface is determined} from a pressure p of the refrigerant in the refrigerant _circuit . Method according to one of the preceding claims, characterized in that a mass air flow (17) via the evaporator (28) is increased as the primary measure for increasing the surface temperature T _{surface of} the evaporator (28). Method according to one of the preceding claims, characterized in that to increase the surface temperature T _{Oberfl of} the evaporator (28) of the refrigerant _{mass flow} through the evaporator (28) is reduced. Method according to one of the preceding claims, characterized in that for increasing the surface temperature T _{Oberfl of} the evaporator (28) a portion of the refrigerant _{mass flow} through a second evaporator (40), which does not interact with the ambient _air (17) is passed. Method according to Claim 9 , characterized in that the second evaporator (40) is part of a circuit for cooling traction components of the vehicle. Method according to one of the preceding claims, characterized in that a temperature gradient of the coolant is monitored in the circuit for cooling traction components, and that, as soon as this temperature gradient is negative, a target Ausaustemperatures is lowered until again a positive temperature gradient is measured. An air conditioning device (2) for a motor vehicle with a heat pump unit having a refrigerant refrigerant circuit, the refrigerant circuit at least one of ambient air overflowed evaporator (28), an expansion valve (12, 22, 24), a compressor (4), and a Fan, characterized by a control unit, which is adapted for performing a method according to any one of the preceding claims.

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