DE102020103862A1 - Method for regulating a heat pump for a motor vehicle, in particular a hybrid electric motor vehicle or electric vehicle, and a heat pump for a motor vehicle - Google Patents

Abstract

In order to provide a method for regulating a heat pump for a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, which enables efficient operation of the heat pump and also does not require excessive technical complexity on the part of the heat pump, a method (100) for regulating a heat pump (13) for a motor vehicle (10), in particular a hybrid electric vehicle or electric vehicle (12), is proposed, the heat pump (13) having an evaporator (14) designed as a heat exchanger (18), a compressor (15), a condenser (15) and a throttle (17) ) comprises, comprising the steps of determining the value of a pressure parameter of the heat pump (13), comparing the determined value of the pressure parameter with a lower limit value and / or an upper limit value, and if the determined value of the pressure parameter is less than or equal to the lower limit value and / or if the determined value of the print parameter is greater than or equal to the o The upper limit value is: - Carrying out a defrosting process for the evaporator (14), or, if the determined value of the pressure parameter is greater than the lower limit value and / or if the determined value of the pressure parameter is less than the upper limit value: - Repeat the process starting with the first process step.

Description

The present invention relates to a method for regulating a heat pump for a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, the heat pump comprising an evaporator designed as a heat exchanger, a compressor, a condenser and a throttle. The present invention also relates to a heat pump for a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, and a motor vehicle, in particular a hybrid electric vehicle or electric vehicle.

Technological background

Heat pumps are used, among other things, to heat passenger compartments in motor vehicles. The motor vehicles can in particular be hybrid electric vehicles or electric vehicles. The heat required to heat the vehicle interior is taken from the outside air by means of a heat exchanger designed as an evaporator. To do this, the heat exchanger must be cooled below the ambient temperature. If the ambient or outside air falls below its dew point, frost forms on the surface of the heat exchanger, which prevents the air from flowing through the heat exchanger. The efficiency of the heat pump decreases.

the DE 37 06 152 A1 discloses a method for controlling an automotive air conditioning system. The motor vehicle air conditioning system comprises a refrigeration circuit with a refrigerant compressor, a condenser, an evaporator and a throttle device arranged upstream of the evaporator. The compressor output, the condenser output and the evaporator output are recorded directly or indirectly by sensor means, and depending on at least two of these output values and the inclusion of the parameters for the cooling output requirement, the evaporator icing, the compression end temperature and the liquid deflection, output signals are used to influence the compressor output, the condenser output and / or the evaporator output generated. The suction pressure can be measured using a pressure sensor as a measure of evaporator icing.

the DE 101 55 457 A1 discloses an air conditioning system with a variable-stroke compressor, the stroke of the compressor being controlled by the inflow of the refrigerant from the outlet pressure chamber into the drive chamber and / or by the outflow of the refrigerant from the drive chamber into the suction pressure chamber, with two valves that can be operated independently of one another being connected to a control device, with a valve is arranged in the engine compartment inlet and a valve in the engine compartment outlet. In the case of the air conditioning system, the outlet pressure or the suction pressure can be used as a control variable, depending on whether the system is operated as a heat pump or as a refrigeration system. Furthermore, by opening both valves at the same time, the refrigerant flow moving through the vehicle-side components can be minimized in order to prevent the evaporator from icing up if the system is not supposed to provide any refrigeration capacity.

In order to counteract icing of the heat exchanger, time-controlled defrosting cycles are known in the prior art, in which the heat exchanger is heated up cyclically. The ice on the heat exchanger melts due to the heating, and the ambient air can flow through the heat exchanger again. Time-controlled defrost cycles are very inefficient and significantly influence the performance of the heat pump.

In the as yet unpublished German patent application “Method for operating an air conditioning system for a vehicle” by the applicant, a method for operating an air conditioning system for a vehicle is described, it being provided that overall energy efficiencies are determined for a group of operating strategies for the air conditioning system and an operating strategy is selected with the greatest overall efficiency that covers a determined heating power requirement.

Presentation of the invention: task, solution, advantages

The present invention is based on the object of providing a method for regulating a heat pump for a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, which enables efficient operation of the heat pump and also does not require excessive technical complexity on the part of the heat pump. A further object of the present invention is to provide a heat pump for a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, and a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, with which the aforementioned advantages are achieved.

• - Ermittlung des Wertes eines Druckparameters der Wärmepumpe,
• - Vergleichen des ermittelten Wertes des Druckparameters mit einem unteren Grenzwert und/oder einem oberen Grenzwert, und wenn der ermittelte Wert des Druckparameters kleiner oder gleich dem unteren Grenzwert und/oder wenn der ermittelte Wert des Druckparameters größer oder gleich dem oberen Grenzwert ist:
• - Durchführen eines Enteisungsverfahrens für den Verdampfer, oder wenn der ermittelte Wert des Druckparameters größer als der untere Grenzwert und/oder wenn der ermittelte Wert des Druckparameters kleiner als der obere Grenzwert ist:
• - Wiederholen des Verfahrens beginnend mit dem ersten Verfahrensschritt.

To solve the problem on which the invention is based, a method for regulating a heat pump for a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, is proposed, the heat pump comprising an evaporator designed as a heat exchanger, a compressor, a condenser and a throttle, comprising the steps

• - Determination of the value of a pressure parameter of the heat pump,
• - Comparing the determined value of the print parameter with a lower limit value and / or an upper limit value, and if the determined value of the print parameter is less than or equal to the lower limit value and / or if the determined value of the print parameter is greater than or equal to the upper limit value:
• - Carrying out a defrosting procedure for the evaporator, or if the determined value of the pressure parameter is greater than the lower limit value and / or if the determined value of the pressure parameter is less than the upper limit value:
• - Repeat the process starting with the first process step.

The evaporator is a heat exchanger. In the following, these terms can be used synonymously.

By carrying out a de-icing process according to the invention depending on whether a determined value of a pressure parameter of the heat pump is less than or equal to a lower limit value and / or greater than or equal to an upper limit value, a method for regulating a heat pump and in particular a de-icing control of a heat pump is provided, according to which, depending on the situation, defrosting is only carried out if the evaporator of the heat pump is actually iced up. Since in particular no time-controlled defrosting cycles are carried out, the efficiency of the heat pump is improved. Since it is also known in the prior art to record pressure parameters for reasons of protecting the heat pump, in particular the compressor, no additional sensor system is required for a heat pump to carry out the method. The method can preferably be used with little effort by adapting an existing control device even with known heat pump concepts.

The method for regulating a heat pump for a motor vehicle can also be referred to as defrosting regulation.

It can preferably be provided that the pressure parameter is a suction pressure and that the suction pressure is compared with the lower limit value, the lower limit value being a suction pressure limit value, and / or that the pressure parameter is a suction pressure change rate and that the suction pressure change rate is compared with the upper limit value, wherein the upper limit is a suction pressure change rate limit.

If the pressure parameter is the rate of change in suction pressure, then the amount of the rate of change in suction pressure is preferably used as the value of the pressure parameter. The pressure parameter is particularly preferably the amount of the suction pressure change rate, and the amount of the suction pressure change rate is compared with the upper limit value, the upper limit value being a suction pressure change rate limit value.

Thus, on the one hand, the suction pressure can be used as a pressure parameter and the prerequisite for the de-icing process to be carried out is that the determined value of the suction pressure reaches or falls below a, in particular, predetermined, suction pressure limit value.

Alternatively or at the same time, the suction pressure change rate, in particular the amount of the suction pressure change rate, can also be used as the pressure parameter and the prerequisite that the de-icing process is carried out is that the determined value of the suction pressure change rate, in particular that the amount of the suction pressure change rate, is a, in particular, predetermined, suction pressure change rate limit value reached or exceeded.

To determine the suction pressure, a sensor for determining the suction pressure, in particular a suction pressure sensor, can be provided in the heat pump, in particular in the refrigerant circuit on the suction side of the compressor.

The suction pressure sensor determines, preferably cyclically, the suction pressure in the refrigerant circuit and can transmit the determined value of the suction pressure, or a corresponding electrical signal, to a control device.

It can preferably be provided that the control device compares the determined value of the suction pressure with a predetermined suction pressure limit value, and / or that the control device compares the determined value of the suction pressure change rate with a predetermined suction pressure change rate limit value.

If the pressure parameter is the rate of change in suction pressure, the regulating device can furthermore be designed to determine a rate of change in suction pressure from at least two values of the suction pressure determined at a time interval. The rate of change in suction pressure can also be referred to as a gradient, a temporal gradient or a derivative of the suction pressure over time.

The design of the method using the suction pressure or the suction pressure change rate as a pressure parameter is based on the knowledge that the change in the suction pressure under known operating conditions of the heat pump, for example the ambient temperature, the humidity, the speed of a fan of the compressor and / or the one designed as a heat exchanger The amount of air flowing through the compressor indicates the efficiency of the heat pump.

The thermal insulation effect of the frost deposited on the evaporator designed as a heat exchanger in the event of icing and the resulting reduced air flow through the evaporator designed as a heat exchanger due to the blockage lead to a lower temperature of the refrigerant of the heat pump and thus also a lower suction pressure Achieving the required heating power is necessary.

If the suction pressure of the, preferably power-regulated, heat pump falls below a predetermined suction pressure limit value, this can be interpreted as an indication of icing or the precipitation of frost on the evaporator. Since the suction pressure initially only changes slowly at the start of icing and drops faster and faster in the course of icing, the rate of change in suction pressure is a good indicator for detecting icing of the evaporator.

If the heat pump includes, for example, R-744 as the refrigerant, it can be provided that if the suction pressure falls below, for example, 15 bar, a de-icing process is carried out for the heat pump's evaporator, which is designed as a heat exchanger.

It can preferably be provided that the defrosting process includes heating up the evaporator, which is designed as a heat exchanger.

To heat the evaporator, the heat pump can be operated in reverse mode, so that heat is given off via the evaporator. Furthermore, it can be provided that the evaporator designed as a heat exchanger comprises an electric heater which is activated to carry out the defrosting process. It is also possible that engine waste heat is passed through the evaporator in order to defrost the evaporator.

It can preferably be provided that the suction pressure limit value and / or the suction pressure change rate limit value are determined as a function of environmental parameters and / or operating parameters of the heat pump.

Since the suction pressure during operation and when the heat exchanger is not iced up depends on the ambient parameters and / or operating parameters, a fixed suction pressure limit value or a fixed suction pressure change rate limit value can lead to defrosts that are too early or too late.

It is therefore of particular advantage if the suction pressure limit value or the suction pressure change rate limit value is determined as a function of the ambient parameters and / or the operating parameters of the heat pump. The determination of the suction pressure limit value and / or the suction pressure change rate limit value is preferably carried out at regular time intervals so that the suction pressure limit value and / or the suction pressure change rate limit value correlates as optimally as possible with the currently available environmental parameters or operating parameters.

The determination of the suction pressure limit value or the suction pressure change rate limit value is particularly preferably carried out as the first step of the method, particularly preferably immediately before the determination of the value of the pressure parameter of the heat pump.

It can preferably be provided that the environmental parameters and / or the operating parameters include at least one of the parameters from the group comprising an ambient temperature, an amount of air flowing through the evaporator designed as a heat exchanger and an amount of heat extracted from the evaporator and / or the condenser, an air humidity and a compressor speed .

Furthermore, it is possible that the environmental parameters and / or the operating parameters also include other parameters.

The amount of heat removed from the evaporator preferably corresponds to the amount of heat absorbed from the environment by the evaporator.

At very low ambient temperatures, small amounts of air flowing through the evaporator, which is designed as a heat exchanger, and / or large amounts of heat extracted from the evaporator, defrosting processes that are carried out too early can occur if a solid Suction pressure limit value or a fixed suction pressure change rate limit value is assumed. Accordingly, at high ambient temperatures, high amounts of air flowing through the evaporator designed as a heat exchanger and / or small amounts of heat withdrawn from the evaporator, defrosting processes that are carried out too late can occur if a fixed suction pressure limit value or a fixed suction pressure change rate limit value is assumed.

It is therefore particularly advantageous if the suction pressure limit value and / or the suction pressure change rate limit value is determined or determined as a function of the ambient temperature, an amount of air flowing through the evaporator designed as a heat exchanger, and an amount of heat taken from the evaporator and / or the condenser. The suction pressure limit value and / or the suction pressure change rate limit value can be determined or established in any combination as a function of one or more of these parameters.

Thus, it can preferably be provided that the suction pressure limit value is increased when the ambient temperature increases.

The suction pressure limit value is thus adapted as a function of the ambient temperature, specifically in such a way that the suction pressure limit value is lowered at low ambient temperatures and the suction pressure limit value is increased at higher ambient temperatures. For example, it can be provided that the suction pressure limit value is 25 bar at an ambient temperature of 0 ° C and that the suction pressure limit value is 15 bar at an ambient temperature of -10 ° C.

It can preferably be provided that the amount of air flowing through the evaporator designed as a heat exchanger is estimated using at least one of the parameters speed of a fan, an opening degree of a radiator blind or a radiator blind or the driving speed of a motor vehicle, and / or that the amount of air flowing through the evaporator designed as a heat exchanger Air volume is measured.

It can preferably be provided that the suction pressure limit value is increased when the amount of air flowing through the evaporator, which is designed as a heat exchanger, becomes greater. A large amount of air flowing through the evaporator designed as a heat exchanger thus leads to an increase in the suction pressure limit value, and a small amount of air flowing through the evaporator designed as a heat exchanger leads to a reduction in the suction pressure limit value.

For example, it can be provided that with an air quantity of 0.2 kg / s flowing through the evaporator designed as a heat exchanger, the suction pressure limit value is set at 15 bar, while with an air quantity flowing through the evaporator designed as a heat exchanger, the suction pressure limit value is set at 0.8 kg / s 30 bar is set.

Furthermore, it can preferably be provided that the amount of heat withdrawn from the evaporator and / or the condenser is estimated taking into account the operating parameters of the heat pump, and / or that the amount of heat withdrawn from the evaporator and / or the condenser is measured.

The method and procedure for estimating the amount of heat withdrawn from the evaporator and / or the condenser on the basis of the operating parameters of the heat pump are known to those skilled in the art. An estimate is preferred because the corresponding measurement technology required to measure the amount of heat withdrawn from the evaporator is expensive and complex. In principle, however, it is also possible to measure the amount of heat taken from the evaporator directly.

Furthermore, it can be provided that the suction pressure limit value is increased when the amount of heat withdrawn from the evaporator and / or the condenser increases.

In the case of large amounts of heat withdrawn from the evaporator, the suction pressure limit is thus increased, and in the case of small amounts of heat withdrawn from the evaporator, the suction pressure limit is lowered.

Particularly preferably, the suction pressure limit value can be determined from a combination of the parameters of the ambient temperature, the amount of air flowing through the evaporator designed as a heat exchanger and the amount of heat withdrawn from the evaporator and / or the condenser.

In a further embodiment it can also be provided that the suction pressure change rate limit value is also determined as a function of the ambient temperature, the amount of air flowing through the evaporator designed as a heat exchanger or the amount of heat withdrawn from the heat exchanger.

The adaptations of the suction pressure change rate limit value can be made in accordance with the adaptations of the suction pressure limit value, which means that the suction pressure change rate limit value is also increased when the ambient temperature increases and / or the amount of air flowing through the heat exchanger increases and / or when the amount of heat withdrawn from the heat exchanger increases.

It is also possible for the suction pressure change rate limit value to be adapted in the opposite direction so that, for example, when the Ambient temperature, and / or when the amount of air flowing through the evaporator designed as a heat exchanger is reduced and / or when the amount of heat removed from the evaporator designed as a heat exchanger is reduced, the suction pressure change rate limit value is increased.

Preferably, however, the suction pressure change rate limit value is at least not dependent on the amount of air flowing through the evaporator designed as a heat exchanger, since the suction pressure change rate is preferably an indicator of the air amount flowing through the evaporator designed as a heat exchanger.

Another solution to the problem on which the invention is based is to provide a heat pump for a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, comprising an evaporator designed as a heat exchanger, a compressor, a condenser and a throttle, the heat pump also having a sensor for measuring a suction pressure , and wherein the heat pump has a control device, wherein the control device is designed to receive signals from the sensor, wherein the control device is designed to carry out a method described above.

The method step of carrying out a defrosting method for the evaporator designed as a heat exchanger can be implemented in that the regulating device sends a control or regulating signal to a defrosting device.

The sensor for determining the suction pressure is preferably arranged on the suction pressure side of the compressor in the refrigerant circuit.

In addition, further sensors can also be provided.

Another solution to the problem on which the invention is based is to provide a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, comprising a heat pump as described above.

Yet another solution to the problem on which the invention is based is to provide an air conditioning system comprising a previously described heat pump and to provide a motor vehicle, in particular a hybrid electric vehicle or electric vehicle, including such an air conditioning system.

Figure list

The invention is explained in more detail below with reference to the accompanying figures.

• 1 ein Kraftfahrzeug mit einer Wärmepumpe,
• 2 ein Ablaufdiagramm eines Verfahrens zur Regelung einer Wärmepumpe,
• 3 ein Ablaufdiagramm eines weiteren Verfahrens zur Regelung einer Wärmepumpe, und
• 4 einen Graphen mit dem zeitlichen Verlauf eines Saugdrucks und einer einen Wärmeübertrager durchströmenden Luftmenge.

Show it

• 1 a motor vehicle with a heat pump,
• 2 a flow chart of a method for regulating a heat pump,
• 3 a flow chart of a further method for regulating a heat pump, and
• 4th a graph with the temporal course of a suction pressure and an amount of air flowing through a heat exchanger.

Detailed description of the figures

1 shows a motor vehicle 10 with a heat pump 13th comprehensive air conditioning 11 . The heat pump 13th is for performing a flow chart in 2 procedure shown 100 for controlling a heat pump 13th for a motor vehicle 10 educated. This in 1 shown motor vehicle 10 can be used as hybrid electric car or electric vehicle 12th be trained. The heat pump 13th includes an evaporator 14th , a compressor 15th , a capacitor 16 and a throttle 17th . The evaporator 14th is used to absorb ambient heat as a heat exchanger 18th educated. In the refrigerant circuit 19th the heat pump 13th is a sensor 20th arranged to measure the suction pressure. The heat pump 13th also includes a control device 21 , which is formed, signals from the sensor 20th to receive and a procedure described below 100 perform.

According to 2 is in a first step S1 of the method, a value of a pressure parameter of the heat pump 13th determined. The pressure parameter can be the suction pressure or the suction pressure change rate. In a second process step S2 the determined value of the print parameter is compared with a lower limit value and / or an upper limit value. In the case of the suction pressure as the pressure parameter, this is compared with a lower limit value, the lower limit value being a suction pressure limit value. If, on the other hand, the pressure parameter is a suction pressure change rate, the suction pressure change rate, preferably the amount of the suction pressure change rate, is compared with an upper limit value, the upper limit value being a suction pressure change rate limit value.

If the determined value of the suction pressure falls below the suction pressure limit value and / or if the determined value exceeds the suction pressure change rate, in particular the determined value of the The amount of the suction pressure change rate, the suction pressure change rate limit value, is then used in a next method step S3 a de-icing process for the as a heat exchanger 18th trained evaporator 14th carried out. After performing the de-icing procedure, the procedure is 100 for controlling a heat pump 13th starting again with the first process step S1 carried out.

If, on the other hand, the determined value of the suction pressure is greater than the suction pressure limit value or if the determined value of the suction pressure change rate, in particular the determined value of the amount of the suction pressure change rate, is less than the suction pressure change rate limit value, the method becomes 100 according to step S4 starting again with the first process step S1 run through.

3 shows an expanded embodiment of the method according to the invention 100 .

The procedure 100 starts in a first step S0 so that depending on environmental parameters and / or operating parameters of the heat pump 13th a suction pressure limit value and / or a suction pressure change rate limit value is calculated. The ambient parameters or the operating parameters can in particular be an ambient temperature, which is used as a heat exchanger 18th trained evaporator 14th Amount of air flowing through or an evaporator 14th include the amount of heat withdrawn. In a next process step S1 of the procedure 100 a value of the suction pressure or the suction pressure change rate is determined.

In a subsequent process step S2 the determined value of the suction pressure is compared with a suction pressure limit value and / or the suction pressure change rate, preferably the amount of the suction pressure change rate, is compared with a suction pressure change rate limit value. If the determined value of the suction pressure falls below the suction pressure limit value and / or if the determined value of the suction pressure change rate, in particular the determined value of the amount of the suction pressure change rate, exceeds the suction pressure change rate limit value, then in a next method step S3 a de-icing procedure for the heat exchanger 18th carried out. After performing the de-icing procedure, the procedure is 100 for controlling a heat pump 13th starting again with the first process step S0 carried out. If, on the other hand, the determined value of the suction pressure is greater than the suction pressure limit value or if the determined value of the suction pressure change rate, in particular the determined value of the amount of the suction pressure change rate, is less than the suction pressure change rate limit value, the method becomes 100 after step S2 according to step S4 starting again with the first process step S0 run through.

4th shows the change in suction pressure when the heat exchanger freezes over time 18th the heat pump 13th . The time t is plotted on the x-axis of the coordinate system. The first graph 22nd shows the course of the suction pressure over time when the heat exchanger is iced up over time 18th . The second graph 23 shows the time course of the air-side pressure loss at the heat exchanger 18th . When the heat exchanger begins to ice up 18th the suction pressure is high and the air-side pressure loss is low. With increasing icing, the suction pressure decreases, while at the same time the pressure loss on the air side at the heat exchanger 18th increases. In particular the first graph 22nd for suction pressure shows that the decrease in suction pressure is an indicator of icing of the heat exchanger 18th is. As with increasing icing of the heat exchanger 18th the amount of the change rate of the suction pressure, that is to say the amount of the suction pressure change rate, increases, the suction pressure change rate is also an indicator of icing of the heat exchanger 18th .

List of reference symbols

100

procedure

50

Process step

51

Process step

S2

Process step

S3

Process step

S4

Process step

10

Motor vehicle

11

air conditioning

12th

Electric vehicle

13th

Heat pump

14th

Evaporator

15th

compressor

16

capacitor

17th

throttle

18th

Heat exchanger

19th

Refrigerant circulation

20th

sensor

21

Control device

22nd

First graph

23

Second graph

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 3706152 A1 [0003]
• DE 10155457 A1 [0004]

Claims (12)

Method (100) for regulating a heat pump (13) for a motor vehicle (10), in particular a hybrid electric vehicle or electric vehicle (12), the heat pump (13) having an evaporator (14) designed as a heat exchanger (18), a compressor (15), a capacitor (15) and an inductor (17) comprising the steps - Determination of the value of a pressure parameter of the heat pump (13), - comparing the determined value of the print parameter with a lower limit value and / or an upper limit value, and, if the determined value of the print parameter is less than or equal to the lower limit value and / or if the determined value of the print parameter is greater than or equal to the upper limit value: - Carrying out a defrosting procedure for the evaporator (14), or, if the determined value of the print parameter is greater than the lower limit value and / or if the determined value of the print parameter is less than the upper limit value: - Repeat the process starting with the first process step. Method (100) according to Claim 1 , characterized in that the pressure parameter is a suction pressure and that the suction pressure is compared with the lower limit value, the lower limit value being a suction pressure limit value, and / or that the pressure parameter is a suction pressure change rate and that the suction pressure change rate is compared with the upper limit value, wherein the upper limit is a suction pressure change rate limit. Method (100) according to Claim 1 or 2 , wherein the de-icing process comprises heating up the evaporator (14) designed as a heat exchanger (18). Method (100) according to Claim 2 or 3 , the suction pressure limit value and / or the suction pressure change rate limit value being determined as a function of environmental parameters and / or operating parameters of the heat pump (13). Method (100) according to Claim 4 , wherein the environmental parameters and / or operating parameters include at least one of the parameters from the group comprising an ambient temperature, an amount of air flowing through the evaporator (14) designed as a heat exchanger (18) and an amount of heat removed from the evaporator (14) and / or the condenser (15) include. Method (100) according to Claim 5 , whereby the suction pressure limit is increased as the ambient temperature increases. Method (100) according to one of the Claims 5 or 6th , the amount of air flowing through the evaporator (14) designed as a heat exchanger (18) being estimated using at least one of the parameters speed of a fan, an opening degree of a radiator roller blind or a radiator blind or the driving speed of a motor vehicle (10), and / or wherein the The amount of air flowing through the evaporator (14) designed as a heat exchanger (18) is measured. Method (100) according to one of the Claims 5 until 7th , wherein the suction pressure limit value is increased when the amount of air flowing through the evaporator (14) designed as a heat exchanger (18) becomes greater. Method (100) according to one of the Claims 5 until 8th , wherein the amount of heat removed from the evaporator (14) and / or the condenser (15) is estimated taking into account the operating parameters of the heat pump (13), and / or wherein the amount of heat removed from the evaporator (14) and / or the condenser (15) is measured. Method (100) according to one of the Claims 5 until 9 , wherein the suction pressure limit value is increased when the amount of heat removed from the evaporator (14) and / or the condenser (15) increases. Heat pump (13) for a motor vehicle (10), in particular a hybrid electric vehicle or electric vehicle (12), comprising an evaporator (14) designed as a heat exchanger (18), a compressor (15), a condenser (15) and a throttle (17), further comprising a sensor (20) for measuring a suction pressure, and a control device (21), wherein the control device (21) is designed to receive signals from the sensor (20), characterized in that the control device (21) is designed, to carry out a method (100) according to one of the preceding claims. Motor vehicle (10), in particular hybrid electric vehicle or electric vehicle (12), comprising a heat pump (13) Claim 11 .

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