Method for initiating a defrost process in a heat exchanger of a heat pump of a motor vehicle

Abstract

In order to provide a method for introducing a defrost process of a heat exchanger of a heat pump of a motor vehicle which is insensitive to external influences and can also be used in combination with other methods, a method (100) is proposed for introducing a defrost process of a heat exchanger (10) of a heat pump (11) of a motor vehicle (200), the motor vehicle being in particular an electric vehicle or a battery-electric vehicle (12) or a hybrid electric vehicle, wherein the heat exchanger (10) and a coolant heat exchanger (13) of a cooling circuit (14) of the motor vehicle (200) are arranged in a common air path (15), wherein the coolant outlet temperature of the coolant coming out of the coolant heat exchanger (13) is determined, wherein the icing state of the heat exchanger (10) is determined using the coolant outlet temperature, and wherein the defrost process of the heat exchanger (10) is introduced when icing of the heat exchanger (10) is determined.

Description

Technical Field

[0001] The invention relates to a method for introducing a defrost process into a heat exchanger of a heat pump of a motor vehicle, in particular an electric vehicle, a battery-electric vehicle or a hybrid-electric vehicle, wherein the heat exchanger and a coolant heat exchanger of a cooling circuit of the motor vehicle are arranged in a common air path.

[0002] Furthermore, the present invention relates to a motor vehicle having a device for defrosting a heat exchanger of a heat pump of the motor vehicle, wherein the device has a computing unit. Background Art

[0003] Heat pumps are used in electric vehicles to heat the vehicle interior. The heat required for heating is drawn from the outside air. To do this, the heat pump's heat exchanger (also known as the ambient heat exchanger) must be cooled below the ambient temperature. If the outside air falls below its dew point, frost forms on the heat exchanger surface, hindering air flow through the heat exchanger. This no longer ensures efficient operation of the heat pump.

[0004] In order to allow outside air to flow through the heat exchanger, a defrost cycle is required in which the heat exchanger is heated. During the defrost cycle, the ice melts and outside air can flow through the heat exchanger again.

[0005] In order to initiate a defrost process, methods are known in the prior art in which a reduction in the suction pressure of the heat pump is monitored.

[0006] Furthermore, methods are known in which additional sensor systems are used with which the thickness of the layer of ice or frost formed on the heat exchanger is measured.

[0007] DE 10 2009 052 409 B4 discloses an air / water heat pump with an evaporator, wherein the evaporator is associated with a ventilator and a ventilator control unit. The ventilator control unit detects the current and / or speed of the ventilator and, based on the detected current and / or speed, determines the ventilator's operating point. The ventilator control unit is designed to monitor the ventilator's operating point and, if it falls below or exceeds a threshold value, transmits a defrost initiation signal to a controller.

[0008] EP 0 563 724 B1 discloses a method for determining ice formation on the evaporator of a cooling device, wherein the cooling device has a ventilator driven by an electric motor for flowing air through the evaporator. In the method, the change in an operating parameter of the motor operating the ventilator is measured.

[0009] A disadvantage of the known methods for monitoring the suction pressure of a heat pump of a motor vehicle is that the suction pressure can also temporarily drop during the starting process of the motor vehicle, so that unnecessary defrosting processes can be initiated.

[0010] Furthermore, in known methods for determining the icing state of a heat exchanger, it can happen that changes in external influences lead to the detection of icing despite the absence of an ice layer on the heat exchanger. Summary of the Invention

[0011] The object of the present invention is to provide a method for initiating a defrost process of a heat exchanger of a heat pump of a motor vehicle which is insensitive to external influences and which can also be used in combination with other methods.

[0012] To achieve the object underlying the present invention, a method is proposed for initiating a defrost process of a heat exchanger of a heat pump of a motor vehicle, in particular an electric vehicle or a battery-electric vehicle or a hybrid electric vehicle, wherein the heat exchanger and a coolant heat exchanger of a cooling circuit of the motor vehicle are arranged in a common air path, wherein the coolant outlet temperature of the coolant exiting the coolant heat exchanger is determined, wherein it is further provided that the icing state of the heat exchanger is determined using the coolant outlet temperature, and wherein a defrost process of the heat exchanger is initiated when icing of the heat exchanger is determined.

[0013] The heat exchanger of the heat pump can also be referred to as ambient heat exchanger.The heat pump is preferably used for heating the passenger compartment of a motor vehicle.

[0014] The cooling circuit of a motor vehicle, in particular an electric vehicle or a battery electric vehicle or a hybrid electric vehicle, may be a circuit for cooling an electric drive motor and / or a battery of the motor vehicle.

[0015] The heat exchanger (or ambient heat exchanger) and the coolant heat exchanger are arranged in a common air path, ie the ambient air flowing through the heat exchanger on the air side also flows through the coolant heat exchanger.

[0016] According to the invention, it is provided that a coolant outlet temperature of the coolant exiting the coolant heat exchanger is determined, wherein an icing state of the heat exchanger is determined using the coolant outlet temperature, and wherein a defrosting process of the heat exchanger is initiated when icing of the heat exchanger is detected.

[0017] If the heat pump's heat exchanger (or the ambient heat exchanger) is icing, this results in a reduction in the air mass flow in the air path. If the air mass flow in the air path is reduced, the air mass flow through the coolant heat exchanger is also reduced. This can cause the coolant outlet temperature of the coolant at the coolant heat exchanger to change. The coolant outlet temperature can therefore be an indicator of the icing status of the heat pump's heat exchanger.

[0018] The icing state can be an uniced state, a slightly iced state or a heavily iced state. If icing, in particular a slightly iced or heavily iced state, occurs on the heat exchanger, a defrosting process known per se to a person skilled in the art for heat pumps is initiated.

[0019] By using the coolant outlet temperature of the coolant heat exchanger to determine the icing state of the heat exchanger of the heat pump, the determination of the icing state of the heat exchanger is made insensitive to external influences. Furthermore, the method according to the invention can be used in combination with other methods for determining the icing state of heat exchangers of heat pumps, such as those known from the prior art.

[0020] Preferably, the coolant heat exchanger is arranged after the heat exchanger in the air path in the flow direction of the air.

[0021] Furthermore, it is preferably provided that the icing state of the heat exchanger, in particular the icing, is determined from a change in the coolant outlet temperature, in particular from an increase in the coolant outlet temperature.

[0022] If the air mass flow in the air path is reduced due to icing of the heat exchanger, the cooling capacity of the coolant heat exchanger, which is typically used for the cooling circuit of the drive motor or battery of a motor vehicle, is reduced. Consequently, the coolant outlet temperature from the coolant heat exchanger may increase. If a change, in particular an increase, in the coolant outlet temperature is detected, the icing state of the heat exchanger can be determined from the change in the coolant outlet temperature.

[0023] Furthermore, it can preferably be provided that the coolant inlet temperature of the coolant entering the coolant heat exchanger is measured, the coolant temperature difference is determined from the coolant inlet temperature and the coolant outlet temperature, and the icing state of the heat exchanger, in particular icing, is determined from a change, in particular a decrease, in the coolant temperature difference.

[0024] In addition to a change, particularly an increase, in the coolant outlet temperature, the coolant temperature difference can also be used as an alternative or parallel tool to determine the icing state of the heat exchanger. If the coolant outlet temperature increases due to icing of the heat exchanger, the temperature difference decreases even if the coolant inlet temperature remains unchanged, so that the coolant temperature difference also provides an indication of icing of the heat exchanger of the heat pump. In principle, it is also possible that, in the event of icing of the heat exchanger of the heat pump, the coolant outlet temperature remains constant, while the coolant inlet temperature decreases due to the current demand characteristics. A reduced coolant temperature difference, while simultaneously keeping the coolant outlet temperature approximately constant, can thus also be an indicator of icing of the heat exchanger.

[0025] Furthermore, it can be advantageously provided that the coolant volume flow and / or the power of a coolant pump of the cooling circuit is determined and used to determine the icing state of the heat exchanger.

[0026] The coolant volume flow and / or power of the coolant pump can be considered to determine whether a change, in particular an increase, in the coolant outlet temperature and / or a change, in particular a decrease, in the coolant temperature difference is due to icing of the heat exchanger of the heat pump. The coolant volume flow and / or power of the coolant pump influence the cooling power of the coolant heat exchanger. With a lower coolant volume flow or power of the coolant pump, a lower cooling power and, therefore, a lower coolant temperature difference are generally expected, which therefore does not necessarily indicate icing of the heat exchanger. However, if a change, in particular a decrease, in the coolant temperature difference or a change, in particular an increase, in the coolant outlet temperature occurs with a higher coolant volume flow or higher power of the coolant pump, this indicates icing of the heat exchanger of the heat pump.

[0027] It is further preferably provided that the cooling circuit is operated preferably cyclically for determining the icing state, wherein the cooling circuit is operated for determining the icing state preferably for a specific time period, further preferably for a time period of less than 30 seconds, particularly preferably less than 20 seconds.

[0028] In motor vehicles, in particular electric vehicles, battery-electric vehicles, or hybrid-electric vehicles, the cooling circuit is not necessarily operated continuously to cool the electric drive or battery. In order to be able to infer icing of the heat exchanger of the heat pump from the coolant outlet temperature or the coolant temperature difference, it can be advantageous to operate the cooling circuit at least briefly even when the cooling capacity of the cooling circuit is not required for cooling the electric drive and / or battery. The cooling circuit can thus be operated at irregular intervals or at regular, in particular periodic, intervals.

[0029] Advantageously, provision can be made for the coolant temperature, in particular the coolant inlet temperature, to be increased or decreased when the coolant temperature, in particular the coolant inlet temperature, corresponds approximately to the ambient temperature.

[0030] If the coolant temperature of the coolant in the cooling circuit, for example the coolant inlet temperature, is approximately at the ambient temperature, heat exchange cannot take place. To determine the freezing state of the heat exchanger of a heat pump, it is therefore advantageous to increase or decrease the coolant temperature. The coolant temperature can be increased, for example, via a PTC heating element (positive temperature coefficient) or via a refrigerator, in particular a refrigerator of a heat pump. Cooling the coolant can also be achieved via a refrigerator.

[0031] Furthermore, it can be advantageously provided that a parameter is taken into account for determining the icing state, wherein the parameter is an indicator for the current relative air speed of the surrounding air relative to the motor vehicle.

[0032] External influences that affect the relative air velocity of the ambient air relative to the vehicle also influence the air mass flow through the heat exchanger and through the coolant heat exchanger arranged in the same air path. This change in the air mass flow through the coolant heat exchanger can influence the coolant outlet temperature or the coolant temperature difference. By taking into account a parameter relating to the current relative air velocity of the ambient air relative to the vehicle, this influence can be incorporated into the determination of the icing state of the heat exchanger.

[0033] It can further advantageously be provided that the parameter is the current driving speed of the motor vehicle and / or the parameter is the wind speed and / or wind direction.

[0034] If the motor vehicle moves at a higher driving speed, the relative air speed of the ambient air relative to the motor vehicle increases. Thus, the coolant outlet temperature can remain constant despite the increased icing of the heat exchanger of the heat pump.

[0035] Accordingly, the wind speed or wind direction can also have an impact on the coolant outlet temperature or the coolant temperature difference. For this reason, it is advantageous to use the wind speed and / or wind direction for determining the icing state.

[0036] It can further advantageously be provided that the parameter is a distance signal, preferably a distance value, of the motor vehicle relative to the vehicle traveling ahead and / or the parameter is the vehicle position, wherein the vehicle position is preferably the position of the motor vehicle in a road tunnel, in a valley or in a street canyon.

[0037] Modern vehicles often have so-called distance sensors, which can be used to determine whether a motor vehicle is behind a preceding vehicle. Some of these systems also measure a distance value, for example, in meters. The obstruction caused by the preceding vehicle can alter, or in particular reduce, the air mass flow through the heat exchanger and the coolant heat exchanger. Therefore, it is advantageous to use the distance signal, in particular the distance value, to determine the icing state of the heat exchanger of the heat pump from the coolant outlet temperature or the coolant temperature difference of the coolant heat exchanger.

[0038] Even if the vehicle is in a highway tunnel, in a valley, or in a street canyon, the air mass flow through the heat exchanger and the coolant heat exchanger can change. Therefore, it can also be advantageous to take the vehicle's position into account when determining the icing state of the heat exchanger of the heat pump. The vehicle's position can be determined, for example, using the vehicle's navigation system.

[0039] Furthermore, it can preferably be provided that the dew point temperature of the air at the heat exchanger is determined and / or that the defrosting process is initiated only when the temperature of the air at the heat exchanger is below the dew point temperature.

[0040] Taking the dew point temperature and / or the temperature into account can avoid initiating a defrost process even though no ice has formed on the heat exchanger.

[0041] Furthermore, it can be advantageously provided that the air density and / or the outside air temperature and / or the outside air humidity are taken into account for determining the icing state of the heat exchanger.

[0042] It can further advantageously be provided that the parameter is the degree of opening of radiator shutters.

[0043] In a motor vehicle, radiator shutters, preferably arranged upstream of a heat exchanger in the flow direction, influence the air mass flow through the heat exchanger and the air mass flow through a coolant heat exchanger, preferably arranged downstream of the heat exchanger, depending on their degree of opening. Therefore, it is advantageous to take the degree of opening of the radiator shutters into account for determining the icing state of the heat exchanger.

[0044] Another solution to the object of the present invention is to provide a motor vehicle, in particular an electric vehicle, a battery-electric vehicle or a hybrid-electric vehicle, having a device for defrosting a heat exchanger of a heat pump of the motor vehicle, wherein the device has a computing unit that is designed to execute the above-described method.

[0045] The motor vehicle preferably has sensors for determining the coolant outlet temperature and, if appropriate, the coolant inlet temperature, the coolant volume flow and / or the power of a coolant pump of the cooling circuit.

[0046] Furthermore, the motor vehicle may have a distance sensor system, a sensor for determining wind speed and / or wind direction, and / or a navigation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The invention is explained below with reference to the accompanying drawings.

[0048] Figure 1 A schematic diagram of a motor vehicle is shown with a heat exchanger of a heat pump and a coolant heat exchanger of a cooling circuit. DETAILED DESCRIPTION

[0049] in accordance with Figure 1 A method 100 for initiating a defrost process of a heat exchanger 10 of a heat pump 11 of a motor vehicle 200, shown only schematically, is described. Motor vehicle 200 is configured as a battery-electric vehicle 12. Heat pump 11 of motor vehicle 200 is used to heat the passenger compartment of motor vehicle 200. A coolant heat exchanger 13 of a cooling circuit 14 for the electric drive and battery of motor vehicle 200 is arranged together with heat exchanger 10 of heat pump 11 in the same air path 15. A first temperature sensor 16 is provided in cooling circuit 14 at the outlet of coolant heat exchanger 13, which measures the coolant outlet temperature of the coolant exiting coolant heat exchanger 13. Furthermore, a second temperature sensor 17 is provided in cooling circuit 14 at the inlet of coolant heat exchanger 13 for measuring the coolant inlet temperature into coolant heat exchanger 13. The sensor data of the first temperature sensor 16 and the second temperature sensor 17 are transmitted to a computer 18 of the motor vehicle 200. The computer 18 calculates a coolant temperature difference from the coolant inlet temperature and the coolant outlet temperature and uses the coolant temperature difference and / or the coolant outlet temperature to determine the icing state of the heat exchanger 10 of the heat pump 11. If icing of the heat exchanger 10 is present, a defrosting process of the heat exchanger 10 is initiated. For this purpose, methods known from the prior art, such as, for example, the use of a heating element 19, can be used.

[0050] In addition, the power of the coolant pump 20 and the coolant volume flow in the cooling circuit 14 are determined by means of further sensors 21, 22 and transmitted to the computing device 18. The computing device 18 uses the determined power of the coolant pump 20 and the determined coolant volume flow in addition to the coolant temperature difference and / or the coolant outlet temperature to infer the icing state of the heat exchanger 10.

[0051] Since cooling circuit 14 is usually operated discontinuously for cooling the electric drive or battery of motor vehicle 200, computing device 18 is further configured to operate cooling circuit 14 at periodic intervals, for example, for a period of approximately 30 seconds, for determining the icing state of heat exchanger 10 of heat pump 11. If the coolant temperature in cooling circuit 14 substantially corresponds to the ambient temperature, so that no heat exchange is possible, the coolant temperature, in particular the coolant inlet temperature, can be increased by means of PTC heating element 23.

[0052] In addition to the aforementioned parameters, computing unit 18 can also use further parameters to determine the icing state of heat exchanger 10 of heat pump 11. Thus, a distance signal from distance sensor 24 can be used to determine the distance between motor vehicle 200 and a preceding vehicle and / or a measured value from sensor 25 can be used to determine the wind speed. Furthermore, if motor vehicle 200 includes a navigation system 26, information from the navigation system regarding the position of motor vehicle 200 can also be used to determine the icing state of heat exchanger 10.

[0053] Reference Signs List

[0054] 100 methods

[0055] 200 motor vehicles

[0056] 10. Heat exchanger

[0057] 11. Heat Pump

[0058] 12 Battery Electric Vehicles

[0059] 13 Coolant heat exchanger

[0060] 14 Cooling circuit

[0061] 15 Air Path

[0062] 16 First temperature sensor

[0063] 17 Second temperature sensor

[0064] 18 computing units

[0065] 19 Heating element

[0066] 20 Coolant pump

[0067] 21 Sensors

[0068] 22 sensors

[0069] 23 PTC heating element

[0070] 24 spacing sensing mechanism

[0071] 25 Sensing mechanism

[0072] 26 Navigation system.

Claims

1. A method (100) for initiating a defrosting process of a heat exchanger (10) of a heat pump (11) of a motor vehicle (200), wherein: The heat exchanger (10) and the coolant heat exchanger (13) of the cooling circuit (14) of the motor vehicle (200) are arranged in a common air path (15), wherein the coolant outlet temperature of the coolant coming out of the coolant heat exchanger (13) is determined, wherein the icing state of the heat exchanger (10) is determined using the coolant outlet temperature, and wherein when icing of the heat exchanger (10) is determined, a defrosting process of the heat exchanger (10) is initiated.

2. The method (100) according to claim 1, characterized in that The icing state of the heat exchanger (10) is determined from the change in the coolant outlet temperature.

3. The method (100) according to claim 1 or 2, characterized in that The coolant inlet temperature of the coolant entering the coolant heat exchanger (13) is measured, the coolant temperature difference is measured from the coolant inlet temperature and the coolant outlet temperature, and the icing state of the heat exchanger (10) is measured from the change in the coolant temperature difference.

4. The method (100) according to claim 1 or 2, characterized in that The coolant volume flow and / or the power of the coolant pump (20) of the cooling circuit (14) is determined and used to determine the icing state of the heat exchanger (10).

5. The method (100) according to claim 1 or 2, characterized in that The cooling circuit (14) is operated cyclically to determine the icing state, wherein the cooling circuit (14) is operated to determine the icing state over a period of less than 30 seconds.

6. The method (100) according to claim 1 or 2, characterized in that The coolant temperature is increased or decreased when the coolant temperature corresponds approximately to the ambient temperature.

7. The method (100) according to claim 1 or 2, characterized in that A parameter is used to determine the icing state, wherein the parameter is an indicator of a current relative air speed of the ambient air relative to the motor vehicle (200).

8. The method (100) according to claim 7, characterized in that The parameter is the current driving speed of the motor vehicle (200) and / or the parameter is the wind speed and / or wind direction.

9. The method (100) according to claim 7, characterized in that The parameter is a distance signal of the motor vehicle (200) relative to a preceding vehicle and / or the parameter is a vehicle position, wherein the vehicle position is the position of the motor vehicle (200) in a road tunnel, in a valley or in a street canyon.

10. The method (100) according to claim 1 or 2, characterized in that The cooling circuit (14) is operated cyclically to determine the icing state, wherein the cooling circuit (14) is operated to determine the icing state over a period of less than 20 seconds.

11. A motor vehicle (200) having a device for defrosting a heat exchanger (10) of a heat pump (11) of the motor vehicle (200), wherein: The device (20) has a computing unit (19) which is designed to carry out a method (100) according to any one of the preceding claims.

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