Methods for operating heat pumps for motor vehicles and heat pumps

Abstract

A method (100) for operating a heat pump for a motor vehicle is proposed, wherein the heat pump includes a refrigerant circuit having a refrigerant, an ambient heat exchanger, a compressor, a heating heat exchanger, and a throttle valve. The method (100) includes determining (101) an expected start time for the charging process of the motor vehicle's battery and determining (103) the maximum dew point drop and / or maximum frost mass. The method (100) further includes operating (107) the heat pump such that the maximum dew point drop and / or maximum frost mass are reached within a predetermined time period prior to the expected start time.

Description

Technical Field

[0001] The present invention relates to a method for operating a heat pump for a motor vehicle, and a heat pump for a motor vehicle. Background Technology

[0002] In principle, heat pumps are known from existing technology for heating the interior space of motor vehicles, especially electric vehicles. The heat required for heating is typically drawn from the vehicle's ambient air, i.e., from outside air. For this purpose, the ambient heat exchanger of the heat pump must be cooled below ambient temperature. However, if the ambient air is below its dew point, frost or ice forms on the surface of the ambient heat exchanger, thereby impeding airflow, and the heat pump will no longer be able to operate effectively.

[0003] Therefore, a defrosting cycle is necessary to melt frost or ice and thus ensure airflow through the heat exchanger. For the heat pump to operate particularly efficiently, the defrosting process should be carried out as efficiently as possible. Summary of the Invention

[0004] The object of the present invention is to improve a method for operating a heat pump for a motor vehicle, and a heat pump in such a way as to increase the efficiency of the heat pump.

[0005] The aforementioned objective is achieved by a method for operating a heat pump for motor vehicles, particularly electric or hybrid vehicles, wherein the heat pump includes a refrigerant circuit with a refrigerant. The heat pump also includes an ambient heat exchanger, a compressor, a heating heat exchanger, and a throttling valve. These are integrated into the refrigerant circuit. The method includes determining an expected start time for the charging process of the vehicle's battery, wherein the method further includes determining the maximum dew point drop and / or the maximum frost mass. The maximum frost mass describes the maximum mass of frost or ice that the ambient heat exchanger can absorb. This maximum frost mass may occur at the point of maximum temperature drop. The heat pump is then operated such that the maximum dew point drop and / or the maximum frost mass are reached within a predetermined time period prior to the determined start time.

[0006] Furthermore, the method includes initiating the defrosting process when the maximum dew point drop is reached and / or when the maximum frost mass is reached and / or during the charging process of the start-up battery. The maximum frost mass is reached when it forms on the ambient heat exchanger. The maximum temperature drop refers to the temperature of the refrigerant in the ambient heat exchanger.

[0007] Since defrosting cannot always occur while the vehicle is in motion, it is preferable to schedule it for a period of time when the vehicle is stationary due to charging. Defrosting during charging offers the advantages of allowing for precise estimation of the charging start time and thus enabling optimized operation of the heat pump in advance, whether in heating or icing mode. This allows for targeted frosting of the heat pump's ambient heat exchanger and schedules defrosting initiation at a well-predictable and known time when the vehicle is not running and is charging.

[0008] When charging a vehicle in ambient temperatures below 0°C, it is advantageous to defrost for at least 10 minutes beyond the point at which the heat exchanger is free of frost and ice. In particular, the defrosting process should be extended to ensure the surface temperature of the heat exchanger is above 0°C, thereby guaranteeing water drainage during charging. This reduces the amount of meltwater by allowing the heat exchanger surface to refreeze and extends the subsequent heating process of the heat pump.

[0009] This method enables highly efficient heat pump operation because the ambient heat exchanger is blocked for as short a time as possible before the start of the charging process, or the absorption of heat from the ambient air by the ambient heat exchanger is significantly reduced. Thus, the maximum possible heat can be absorbed from the environment during heating operation.

[0010] The minimum suction pressure of the refrigerant in the refrigerant loop can be determined based on the maximum dew point drop and / or maximum frost mass, as the suction pressure is directly related to the temperature in the ambient heat exchanger. Determining the suction pressure is particularly advantageous because the refrigerant can also experience localized overheating. The suction pressure and dew point drop or frost mass serve as measures of icing in the ambient heat exchanger. If the suction pressure falls below the previously determined minimum suction pressure used as a limit, this is an indication of maximum icing, i.e., reaching the maximum dew point drop and / or maximum frost mass. This method may include measuring the suction pressure using a pressure sensor. Alternatively, the method may include monitoring the suction pressure.

[0011] Operating the heat pump in this way allows for the achievement of maximum dew point drop and / or maximum frost quality within a predetermined time period prior to the expected start time, through control, particularly the regulation of the compressor and / or throttle valve. This is achieved during the heating operation of the heat pump. Preferably, a reduction in the heat power to be generated by the heat pump can be made. The missing heat power of the heat pump can be generated via an additional heat source (e.g., an electric heater), thereby avoiding any adverse effects on the vehicle occupants. For example, the ratio between the heat power to be provided by the heat pump and the heat power to be provided by other heat sources can be determined. For example, the heat pump can cover 2 / 3 of the required heat power for a predetermined time period until the charging time, with the remainder provided by an additional heat source. Furthermore, an additional heat source for the heat pump can be used to increase the suction pressure to the required level until the heat exchanger reaches the calculated maximum frost quality at the expected start time of the charging process.

[0012] For example, the predefined time period could be half an hour, preferably fifteen minutes. The degree of icing can be monitored, for example, by means of suction pressure. Based on the change in the degree of icing over time, it is possible to estimate when the maximum degree of icing and / or preferably the maximum dew point drop will be achieved. For example, if this time point is after the expected start time of the next charging process, the time point for faster icing of the ambient heat exchanger and thus the maximum dew point drop can be pushed forward by controlling or adjusting the compressor and / or throttle valve. In particular, the throttle valve regulates the efficiency of the icing process.

[0013] Once heat transfer efficiency is significantly reduced, then the defrosting process can be initiated, as effective heat absorption from the environment becomes virtually impossible. For example, when the degree of icing on the ambient heat exchanger exceeds a certain threshold, especially when there is a maximum frost mass, the defrosting process can be started, which can be determined by calculation or with the aid of sensors.

[0014] In an ambient heat exchanger, heat is transferred between the refrigerant and the environment (i.e., ambient air), while in a heating heat exchanger, heat is transferred between the refrigerant and the air inside the vehicle's interior. During heating operation, the ambient heat exchanger functions as an evaporator, and the heating heat exchanger functions as a condenser. During the defrosting process—in other words, during defrosting operation—the refrigerant's "path" is particularly reversed compared to the heating process. The ambient heat exchanger functions as an evaporator during heating operation and as a condenser during defrosting operation. The same applies to the heating heat exchanger, which functions as an evaporator during defrosting operation and as a condenser in heating mode.

[0015] Therefore, the defrosting process specifically involves compressing the refrigerant to high pressure using a compressor, transferring heat from the refrigerant to an ambient heat exchanger, which is particularly prone to frosting or freezing, and then depressurizing the refrigerant to low pressure using a throttling valve and reabsorbing heat. Specifically, the refrigerant is further heated during compression, and then guided to the ambient heat exchanger, where it releases heat. This causes the ambient heat exchanger to defrost or freeze. In this sense, heat is transferred to the ambient heat exchanger by means of the refrigerant. Therefore, the defrosting process is carried out by reversing the process. Especially in heat pump operation, the heating and defrosting processes alternate in a cycle.

[0016] Determining the expected start time of the charging process takes into account, in particular, the state of charge of the vehicle's battery and / or the vehicle's travel range and / or the expected duration of vehicle operation. The expected duration of vehicle operation can be determined, for example, from user data (e.g., data from a navigation system, such as destination input).

[0017] To determine the maximum dew point drop, the air mass flow rate through the ambient heat exchanger is first determined. For this, the refrigeration fan speed of the vehicle's refrigeration unit and / or the vehicle's speed and / or wind speed can be considered. These can be measured using appropriate sensors. Furthermore, to determine the maximum dew point drop, the partial pressure difference between the air (in other words, ambient air) and the surface of the ambient heat exchanger can be determined. The maximum frost mass can also be determined in this way. For example, the water mass flow rate can be calculated as follows: .

[0018] Here, It is density, and This refers to the mass fraction of water vapor in the humid airflow at the inlet of the ambient heat exchanger. The mass fraction of water vapor in a saturated state near the wall of the ambient heat exchanger is... The heat transfer surface through which the flow passes is given by A, and the mass transfer coefficient due to convection is given by... Provided.

[0019] If the water vapor sublimates, frost will form on the ambient heat exchanger. The frost mass is the integral of time from the start of the frosting or icing cycle.

[0020] This method may include dynamically adapting the maximum dew point drop and / or maximum frost mass. For example, if outside air is not used as a heat source for heating operations because, for example, other heat sources are used, such as the traction components of a motor vehicle, the values ​​of the dew point drop and / or maximum frost mass can be dynamically adapted. The same applies when outside air is used and other heat sources, such as the traction components of a motor vehicle, are employed. In other words, a higher dew point drop and / or a greater frost mass can be allowed due to the different use of different heat sources. Therefore, the previously determined maximum dew point drop and / or maximum frost mass can thus be adapted or corrected for current conditions.

[0021] During the charging process, the vehicle's radiator fan can operate continuously when the outside temperature is above 0°C. The radiator fan can also continue operating after the charging process is complete, especially when the outside temperature is below 0°C. This helps ensure the heat pump operates for as long as possible at the start of driving, as the continuous operation of the radiator fan allows water to evaporate from the ambient heat exchanger after ice or frost sublimates. Otherwise, water or ice residue would result in a smaller plate cross-section, causing the ambient heat exchanger to clog more early. The radiator fan speed can be adapted to the charging duration. For example, the charging duration can be derived from the battery's state of charge.

[0022] In another aspect, the present invention relates to a heat pump comprising an ambient heat exchanger, a compressor, a heating heat exchanger, and a throttling valve, and configured to perform the method described above. For this purpose, the heat pump may particularly include an evaluation unit for performing the aforementioned steps of the method and a control unit for transmitting corresponding control signals to operate the heat pump. Attached Figure Description

[0023] Figure 1 A schematic diagram illustrating the method according to the present invention is provided. Detailed Implementation

[0024] Figure 1 A method diagram of method 100 according to the present invention is shown, which includes determining 101 an expected start time point for the charging process of a vehicle's battery. Furthermore, determining 103 the maximum dew point drop and / or maximum frost mass. The method also includes operating 107 a heat pump such that the maximum dew point drop and / or maximum frost mass are reached within a predetermined time period prior to the expected start time point.

[0025] To determine the expected start time of the charging process, 102 the charging state and / or travel range and / or expected vehicle operating duration can be considered. To determine the maximum dew point drop and / or maximum frost mass, 104 the partial pressure difference between the air and the surface of the ambient heat exchanger and the air mass flow rate through the ambient heat exchanger can be determined. For this purpose, 105 the cooler fan speed and / or the vehicle's travel speed and / or wind speed can be considered.

[0026] Based on the determined maximum dew point drop and / or maximum frost mass, the minimum suction pressure of the refrigerant in the 106 refrigerant circuit can be determined.

[0027] To operate the heat pump, the compressor (108) and / or throttling valve can be controlled accordingly. Depending on specific conditions, such as using a heat source other than outside air when operating in heating mode, the maximum dew point drop (109) and / or maximum frost quality (109) can be dynamically adapted.

[0028] Method 100 includes initiating a defrosting process 110 when the maximum dew point drop and / or maximum frost mass is reached and / or during the charging process of the start-up battery. A cooler fan 111 operates continuously during the charging process.

[0029] List of reference numerals 100 methods 101. Determine the expected start time of the charging process for the vehicle's battery. 102. Consider the state of charge and / or range and / or expected vehicle operating duration. 103 Determine the maximum dew point drop and / or maximum frost mass. 104. Determine the partial pressure difference between the surfaces of the air and the ambient heat exchanger, and the air mass flow rate through the ambient heat exchanger. 105. Consider the cooler fan speed and / or the vehicle's speed and / or wind speed. 106. Determine the minimum suction pressure of refrigerant in the refrigerant circuit based on the maximum dew point drop and / or maximum frost mass. 107 includes operating the heat pump in such a way that maximum dew point drop and / or maximum frost quality are achieved within a predefined time period prior to the expected start time. 108 Control compressor and / or throttle valve 109 Dynamically adapts to maximum dew point drop and / or maximum cream quality 110. The defrosting process is initiated when the maximum dew point drop is reached and / or when the maximum frost mass is reached and / or during the battery charging process. 111 The cooler fan runs continuously.

Claims

1. A method (100) for operating a heat pump for a motor vehicle, in, A heat pump includes a refrigerant circuit containing refrigerant. A heat pump includes an ambient heat exchanger, a compressor, a heating heat exchanger, and a throttling valve. Its features are, The method (100) includes determining (101) the expected start time of the charging process of the vehicle's battery and determining (103) the maximum dew point drop and / or maximum frost mass. The method (100) further includes operating (107) the heat pump such that the maximum dew point drop and / or the maximum frost mass are reached within a predetermined time period prior to the expected start time. The method (100) includes initiating a defrosting process (110) when the maximum dew point drop is reached and / or when the maximum frost mass is reached and when the charging process of the battery is initiated. Determining the expected start time of the charging process (101) includes considering the state of charge of the battery (102) and / or the travel range of the motor vehicle and / or the expected duration of vehicle operation, and Among them, the dynamic adaptation (109) refers to the maximum dew point decrease and / or the maximum frost quality.

2. The method (100) according to claim 1, Its features are, The method (100) includes determining (106) the minimum suction pressure of the refrigerant in the refrigerant circuit based on the maximum dew point drop and / or the maximum frost mass.

3. The method (100) according to any one of the preceding claims, Its features are, Operating the heat pump (107) includes controlling (108) the compressor and / or the throttle valve.

4. The method (100) according to claim 1 or 2, Its features are, In order to determine the maximum dew point drop and / or maximum frost mass (103), the air mass flow rate through the ambient heat exchanger and the partial pressure difference between the air and the surface of the ambient heat exchanger are determined (104).

5. The method (100) according to claim 4, Its features are, To determine the air mass flow rate, (105) cooler fan speed and / or the vehicle's speed and / or wind speed are taken into account.

6. The method (100) according to claim 1 or 2, Its features are, During the charging process when the external temperature is greater than 0°C or after the charging process is completed, the cooler fan of the motor vehicle is continuously operated (111).

7. A heat pump for motor vehicles, in, The heat pump includes an ambient heat exchanger, a compressor, a heating heat exchanger, and a throttling valve, and wherein the heat pump is configured to perform the method (100) according to any one of claims 1 to 6.

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