Method for operating a drive device and corresponding drive device

Abstract

Method for operating a drive unit (1) for a motor vehicle, wherein the drive unit (1) has at least one drive unit (2) and a coolant circuit (3) for temperature control of the at least one drive unit (2), wherein a coolant circulated in the coolant circuit (3) is supplied at least temporarily to a coolant cooler (4), wherein a cooling fluid different from the coolant is stored in a pressure accumulator (5) and is supplied at least temporarily to the coolant cooler (4) for cooling the coolant by expansion of the cooling fluid, wherein the cooling fluid is supplied to the pressure accumulator (5) at least temporarily via a compressor (7), wherein the cooling fluid is compressed from a lower first pressure to a higher second pressure, characterized in that the cooling fluid is supplied downstream of the coolant cooler (4) in a closed circuit to an expansion tank (11) and via this to the compressor (7).

Description

[0001] The invention relates to a method for operating a drive device for a motor vehicle, wherein the drive device has at least one drive unit and a coolant circuit for controlling the temperature of the at least one drive unit. A coolant circulated in the coolant circuit is at least temporarily supplied to a coolant cooler. A cooling fluid different from the coolant is stored in a pressure accumulator and is at least temporarily supplied to the coolant cooler for cooling the coolant while expanding the cooling fluid. The invention further relates to a drive device for a motor vehicle.

[0002] For example, the prior art document DE 10 2008 004 161 A1 is known. This describes a method for operating an internal combustion engine with a coolant-carrying cooling circuit having a first thermostat, wherein the first thermostat opens at a first threshold temperature. It is provided that a second thermostat is assigned to the coolant circuit, which opens at a second threshold temperature, wherein the two threshold temperatures are different, so that in full-load operation, the internal combustion engine receives the coolant at a first temperature via the first thermostat and in partial-load operation, the coolant at a second temperature via the second thermostat.

[0003] The document DE 10 2013 019 493 A1 relates to a cooling device for a drive unit, in particular an internal combustion engine, of a motor vehicle, with at least one liquid source for providing a liquid and with at least one dispensing element fluidically connected to the liquid source for ejecting the liquid conducted from the liquid source to the dispensing element, wherein a compressed gas source is provided for providing a gas, wherein the dispensing element is fluidically connected to the compressed gas source and is designed as a two-substance dispensing element for ejecting a mixture comprising the liquid and the gas conducted from the compressed gas source to the dispensing element.

[0004] The prior art also includes document US 9,359,936 B2.

[0005] The object of the invention is to propose a method for operating a drive device for a motor vehicle, which has advantages over the known prior art, in particular increases a cooling capacity of a coolant circuit of the drive device and thus enables more efficient operation of the drive device.

[0006] This is achieved according to the invention with a method for operating a drive device for a motor vehicle having the features of the new claim 1. It is provided that the cooling fluid is fed downstream of the coolant cooler in a closed circuit to an expansion tank and via this to the compressor.

[0007] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0008] The drive device preferably serves to drive the motor vehicle, thus providing a drive torque directed towards driving the motor vehicle. To provide the drive torque, the drive device has at least one drive unit, which can be in the form of an internal combustion engine, an electric machine, or the like. During operation of the drive unit to provide the drive torque, heat is generated on and / or in the drive unit. The heat should be dissipated at least temporarily to enable reliable and continuous operation of the drive unit. For this purpose, the coolant circuit is provided, which serves to regulate the temperature, namely in particular to cool, the at least one drive unit.

[0009] In the coolant circuit, the coolant is circulated at least temporarily for temperature control. The term "temperature control" expresses that a temperature of the drive unit is set to a specific temperature, in particular an operating temperature of the drive unit, preferably in a controlled and / or regulated manner. For this purpose, the coolant is supplied to the at least one drive unit, whereby heat is transferred between the drive unit and the coolant, so that heat is transferred from the at least one drive unit to the coolant, and the coolant temperature of the coolant rises accordingly.

[0010] To cool the heated coolant, it is fed to the coolant cooler. The coolant is cooled in the coolant cooler, thus at least partially removing the heat previously supplied to it. The coolant is then preferably fed back to the at least one drive unit, thus creating a closed coolant circuit. The coolant cooler is preferably connected to the at least one drive unit via the coolant circuit, both thermally and fluidically. Of course, the coolant cooler can also be connected to the at least one drive unit only thermally, for example, via a heat exchanger.

[0011] In principle, it can be provided that the coolant cooler is supplied with cooling air to cool the coolant. This air is taken, for example, from the outside environment of the motor vehicle and flows through the coolant cooler. However, the cooling capacity of the coolant cooler is limited by the ambient temperature of the outside environment. This is particularly the case at comparatively high ambient temperatures, where the maximum available drive power of the drive device is correspondingly reduced due to the reduced cooling capacity.

[0012] The invention therefore provides for the cooling fluid to be supplied to the radiator at least temporarily to cool the coolant. The cooling fluid is different from the coolant and is stored in the pressure accumulator, which is preferably a component of the motor vehicle. Thus, the cooling fluid supplied to the radiator is at least partially carried by the motor vehicle. The pressure accumulator contains a quantity of cooling fluid from which the cooling fluid supplied to the radiator is withdrawn at least temporarily.

[0013] The cooling fluid is preferably a substance that is largely gaseous, in particular completely gaseous, at an ambient pressure prevailing in the external environment, in particular at a pressure prevailing in the coolant cooler, and / or at an ambient temperature prevailing in the external environment, in particular at a temperature prevailing in the coolant cooler. The ambient pressure and the ambient temperature comprise pressures and temperatures that occur during intended operation of the drive device or the motor vehicle under normal ambient conditions. In particular, the cooling fluid is largely or—preferably—completely gaseous under normal conditions.In particular, the cooling fluid is selected such that it is largely or entirely gaseous at a pressure prevailing in the coolant cooler during intended operation of the drive device and / or at a temperature prevailing in the coolant cooler under these conditions. The cooling fluid is preferably air, for example, compressed air, or a component of air, for example, nitrogen. In any case, the cooling fluid is a fluid that cools upon expansion, i.e., has a positive Joule-Thomson coefficient.

[0014] The cooling fluid is present in the pressure accumulator at a storage pressure that is greater than the ambient pressure in the outside environment. The cooling fluid supplied to the coolant cooler is removed from the pressure accumulator by being forced out of the pressure accumulator by the storage pressure. This causes the cooling fluid to expand, whereby its pressure decreases, in particular towards the ambient pressure or down to the ambient pressure or a pressure present in the coolant cooler. The cooling fluid is supplied to the coolant cooler during or after the expansion, in particular the cooling fluid flows through the coolant cooler. This causes heat to be transferred between the coolant and the cooling fluid, whereby the coolant temperature is reduced. The heat temporarily stored in the coolant is thus at least partially released to the cooling fluid.

[0015] The expansion of the cooling fluid is associated with a cooling of the cooling fluid, so that a cooling fluid temperature of the cooling fluid decreases during the expansion, starting from a storage temperature present in the pressure accumulator. Thus, the cooling fluid temperature drops during the expansion to a temperature that is lower than the storage temperature present in the pressure accumulator. Particularly preferably, the cooling fluid temperature drops during the expansion to a temperature that is lower than an ambient temperature of the external environment of the motor vehicle. This increases the cooling capacity of the coolant cooler and thus improves the efficiency of the drive device. In particular, the maximum available drive power of the drive device at high ambient temperatures can be increased, at least temporarily.

[0016] The invention provides that the cooling fluid is supplied to the pressure accumulator at least temporarily via a compressor, wherein the cooling fluid is compressed from a lower first pressure to a higher second pressure. The compressor is preferably a component of the motor vehicle and is present, for example, as an electrically driven compressor. Preferably, the cooling fluid is simultaneously compressed to the higher second pressure and supplied to the pressure accumulator. For example, the cooling fluid is initially at the first pressure and is compressed to the second pressure via the compressor. Preferably, the first pressure corresponds to the ambient pressure and the second pressure to the accumulator pressure. One pressure side of the compressor is fluidly connected to the pressure accumulator and the cooling fluid is supplied to the pressure accumulator at least temporarily at the accumulator pressure.

[0017] Particularly preferably, the cooling fluid is supplied to the pressure accumulator as a function of the amount of cooling fluid present in the pressure accumulator. For example, cooling fluid is supplied to the pressure accumulator when the accumulator pressure falls below a lower pressure threshold. The lower pressure threshold preferably corresponds to a minimum cooling fluid quantity. In this respect, cooling fluid is supplied to the pressure accumulator as soon as the cooling fluid quantity reaches or falls below the minimum cooling fluid quantity. In addition, it can be provided that the cooling fluid is supplied until the accumulator pressure reaches or exceeds an upper pressure threshold. The upper pressure threshold is greater than the lower pressure threshold. The upper pressure threshold preferably corresponds to a maximum cooling fluid quantity. In this respect, cooling fluid is supplied to the pressure accumulator until the cooling fluid quantity reaches the maximum cooling fluid quantity.This ensures that there is always a sufficient amount of cooling fluid in the accumulator and that the maximum cooling fluid quantity is not exceeded. This enables reliable and safe operation of the drive system.

[0018] The invention does not provide for the coolant cooler to be at least temporarily exposed to the cooling fluid and a cooling air flow supplied from the external environment of the drive device. The coolant cooler is at least temporarily exposed to cooling air taken from the external environment of the motor vehicle. The cooling air flows through the coolant cooler in the form of a cooling air flow. Heat transfer occurs between the coolant and the cooling air flow. Downstream of the coolant cooler, the cooling air is discharged to the external environment.

[0019] The cooling fluid is preferably mixed with the cooling air flow, in particular, the cooling fluid and the cooling air flow together through the coolant cooler. The cooling air flow supplied to the coolant cooler thus consists, on the one hand, of cooling air taken directly from the outside environment and, on the other hand, of cooling fluid taken from the pressure accumulator. In this case, the cooling fluid is preferably also ambient air. By mixing the cooling fluid with the cooling air flow, the temperature of the cooling air flow is reduced, thus increasing the cooling capacity of the coolant circuit.

[0020] Alternatively, it can be provided that in addition to the coolant cooler, there is another coolant cooler in the coolant circuit, which is supplied with the cooling air flow supplied from the outside environment. In this case, there are two coolant coolers, namely the coolant cooler supplied with the cooling fluid on the one hand, and the further coolant cooler supplied with the cooling air flow on the other. The further coolant cooler is preferably arranged upstream of the coolant cooler in the coolant circuit, so that the coolant downstream of the at least one drive unit is first supplied to the further coolant cooler and then to the coolant cooler. As a result, the coolant is first cooled by the cooling air flow and then cooled by means of the cooling fluid. This creates a particularly efficient coolant circuit.

[0021] The invention does not provide for ambient air to be used as the cooling fluid, which is supplied to the compressor in an open circuit, at least temporarily, from the outside environment. The use of ambient air as the cooling fluid has already been mentioned. The ambient air is supplied to the compressor from the outside environment. For this purpose, a suction side of the compressor is fluidly connected to the outside environment. The cooling fluid is discharged to the outside environment downstream of the coolant cooler, thus forming an open circuit. The use of the open circuit enables particularly flexible operation of the drive device.

[0022] The cooling fluid is supplied to the compressor at a temperature corresponding to the ambient temperature in the outside environment. The compressor compresses the cooling fluid to the accumulator pressure and feeds it into the pressure accumulator. This causes the cooling fluid to heat up accordingly, meaning that the cooling fluid downstream of the compressor is at a temperature greater than the ambient temperature. This leads to a corresponding increase in the storage temperature in the pressure accumulator. To achieve particularly efficient cooling of the coolant, it is advantageous to cool the cooling fluid after compression. For example, it is provided to cool an outer wall of the pressure accumulator with ambient air. This further improves the efficiency of the coolant circuit.

[0023] A further development of the invention provides that the pressure accumulator is at least temporarily filled with the cooling fluid by means of an external pressure supply device, wherein the external pressure supply device provides the cooling fluid at the second pressure. The external pressure supply device is preferably provided in addition to the compressor already explained above. The external pressure supply device is designed to provide the cooling fluid at the second pressure. The second pressure preferably corresponds to the accumulator pressure or is greater than it. The external pressure supply device can provide the cooling fluid, in particular, with a higher cooling fluid mass flow than the compressor; in this respect, a particularly rapid filling of the pressure accumulator is possible by means of the external pressure supply device.

[0024] Furthermore, it can be provided that a substance other than ambient air is provided as a cooling fluid by means of the external pressure supply device. The substance is preferably a non-toxic substance, for example nitrogen. By means of the external pressure supply device, the pressure accumulator can be filled with the cooling fluid in addition to or alternatively to the compressor. For example, it can be provided that the pressure accumulator is at least temporarily filled with ambient air via the compressor. In addition, the pressure accumulator can be at least temporarily filled with cooling fluid via the external pressure supply device, with nitrogen, for example, being used as the cooling fluid. In this case, the cooling fluid subsequently stored in the pressure accumulator consists of a mixture of ambient air and nitrogen. This enables particularly flexible operation of the drive device.

[0025] The invention provides that the cooling fluid is fed downstream of the coolant cooler in a closed circuit to an expansion tank and, via this, to the compressor. Thus, the cooling fluid is not discharged to the outside environment downstream of the coolant cooler, as is the case in the previously explained open circuit. Instead, after flowing through the coolant cooler, the cooling fluid is fed back to the compressor and, via this, to the pressure accumulator.

[0026] In terms of fluid dynamics, the expansion tank is located between the coolant cooler and the compressor. The cooling fluid initially flows from the coolant cooler into the expansion tank. The expansion tank serves to equalize pressure in the closed circuit, particularly due to temperature fluctuations. The initial pressure is present in the expansion tank. Since the circuit is closed, the initial pressure can be greater or lesser than the ambient pressure. In particular, the cooling fluid can be expanded to a pressure that is lower than the ambient air pressure during expansion. This enables particularly efficient operation of the drive system.

[0027] A further development of the invention provides that the cooling fluid is fluidly fed to a cooling fluid cooler between the compressor and the pressure accumulator. As already explained above, the cooling fluid is heated during compression by the compressor. In order to achieve a particularly low cooling fluid temperature during the subsequent expansion of the cooling fluid, it is advantageous to cool the cooling fluid downstream of the compressor. For this purpose, the cooling fluid cooler is provided, through which the cooling fluid is fed to the pressure accumulator.

[0028] The cooling fluid, compressed to the second pressure by the compressor, flows into the pressure accumulator via the cooling fluid cooler. The cooling fluid cooler is configured, for example, with surface-enlarging elements and arranged in a flow path around the motor vehicle. As a result, ambient air flows around the cooling fluid cooler while the motor vehicle is traveling. Additionally or alternatively, an air conveying device can be provided that at least temporarily supplies the cooling fluid cooler with ambient air. This approach further improves the cooling performance of the coolant circuit.

[0029] A further development of the invention provides that the cooling fluid in the cooling fluid cooler and / or in the external pressure supply device becomes liquid at least temporarily. For example, the cooling fluid is in gaseous form at the first pressure. The gaseous cooling fluid is compressed to the second pressure by means of the compressor. The cooling fluid is then fed to the cooling fluid cooler, where the temperature of the cooling fluid is lowered such that the cooling fluid in the pressure accumulator is at least partially in liquid form.

[0030] Additionally or alternatively, the cooling fluid is already provided in liquid form by the external pressure supply device. Thus, the cooling fluid provided by the external pressure supply device is already at least partially liquefied at the second pressure. By liquefying the cooling fluid, a larger amount of cooling fluid can be stored in the pressure accumulator.

[0031] A further development of the invention provides that a component of the ambient air, in particular nitrogen, is used as the cooling fluid in the closed circuit. Since the cooling fluid is not discharged to the outside environment in the closed circuit, a component of the ambient air can be used as the cooling fluid instead of ambient air. The component of the ambient air is preferably a non-toxic and / or non-flammable substance, preferably nitrogen. This enables efficient operation of the drive device on the one hand, and on the other hand, prevents any hazard or contamination of the outside environment from any escaping cooling fluid.

[0032] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the embodiments in the context of this description, wherein the drive device has at least one drive unit and a coolant circuit for controlling the temperature of the at least one drive unit, wherein a coolant circulated in the coolant circuit is at least temporarily supplied to a coolant cooler. It is provided that the drive device is provided and designed to store a cooling fluid different from the coolant in a pressure accumulator and to supply it at least temporarily to the coolant cooler for cooling the coolant while expanding the cooling fluid, wherein a cooling fluid different from the coolant is stored in a pressure accumulator and is at least temporarily supplied to the coolant cooler for cooling the coolant while expanding the cooling fluid.The drive device is further provided and designed to supply the cooling fluid downstream of the coolant cooler in a closed circuit to an expansion tank and via this to the compressor.

[0033] The advantages of such a procedure or such a design of the drive device have already been pointed out. Both the drive device and the method for its operation can be further developed according to the explanations in this description, so reference is made to these in this regard.

[0034] The features and feature combinations described in the description, particularly the features and feature combinations described in the following description of the figures and / or shown in the figures, can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also considered to be encompassed by the invention that are not explicitly shown and explained in the description and / or the figures, but which follow from or can be derived from the explained embodiments.

[0035] The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings, without limiting the invention. In the drawings: Fig. 1 is a schematic representation of a drive device for a motor vehicle in an embodiment not according to the invention, and Fig. 2 a schematic representation of a drive device for a motor vehicle in an embodiment according to the invention.

[0036] The Fig. 1 shows a drive device 1 for a motor vehicle (not shown in detail) in an exemplary embodiment not according to the invention. The drive device 1 has at least one drive unit 2, which is designed, for example, in the form of an internal combustion engine. To control the temperature of the drive unit 2, the drive device 1 has a coolant circuit 3 in which a coolant is circulated and at least temporarily fed to a coolant cooler 4.

[0037] A cooling fluid that is different from the coolant is stored in a pressure accumulator 5 of the drive device 1. The cooling fluid is present in the pressure accumulator 5 at a storage pressure. The cooling fluid is at least temporarily supplied to the coolant cooler 4 while expanding. For this purpose, the pressure accumulator 5 is fluidly connected to the coolant cooler 4, for example, via a throttle device 6. The cooling fluid is forced towards the coolant cooler 4 by the storage pressure present in the pressure accumulator 5. As the cooling fluid expands, its temperature decreases, thereby at least temporarily increasing the cooling capacity of the coolant cooler 4.

[0038] A compressor 7 is connected to the pressure accumulator 5. The cooling fluid is supplied to the pressure accumulator 5 at least temporarily via the compressor 7, wherein the cooling fluid is compressed from a lower first pressure to a higher second pressure. The cooling fluid is supplied to the compressor 7 from an external environment of the drive device 1. The cooling fluid is preferably supplied to the coolant cooler 4 at least temporarily together with a cooling air stream 8 supplied from the external environment. In this case, the cooling fluid is mixed with the cooling air stream 8; in particular, the cooling fluid and the cooling air stream 8 flow through the coolant cooler 4 together.

[0039] In addition to the coolant cooler 4, a further coolant cooler 9 can be provided, which is supplied with a cooling air flow 8 supplied from the outside environment. For example, the further coolant cooler 9 is a main water cooler of the drive device 1, which is supplied with the cooling air flow 8, while the coolant cooler 4 is present as an additional cooler, which is at least temporarily supplied with the cooling fluid. The further coolant cooler 9 is preferably arranged upstream of the coolant cooler 4 in the coolant circuit 3, so that the coolant downstream of the drive unit 2 first flows through the further coolant cooler 9 and then through the coolant cooler 4.

[0040] Downstream of the coolant cooler 4, the cooling fluid is discharged to the outside environment. This creates an open circuit. In addition to or as an alternative to the compressor 7, an external pressure supply device 10 can be provided. The external pressure supply device 10 serves to fill the pressure accumulator 5 and provides the cooling fluid at the second pressure. By means of the external pressure supply device 10, the cooling fluid can be provided, in particular, at least partially liquefied. In this respect, the cooling fluid is stored in the pressure accumulator 5 in at least partially liquefied form.

[0041] The Fig.Figure 2 shows a drive device 1 in an embodiment according to the invention. The above explanations regarding the first embodiment also apply to the second embodiment, so that only the differences between the two embodiments will be discussed here. According to the second embodiment, the cooling fluid downstream of the coolant cooler 4 is not discharged to the outside environment, but rather is fed back to the pressure accumulator 5 in a closed circuit via the compressor 7.

[0042] For this purpose, an expansion tank 11 is arranged fluidically between the coolant cooler 4 and the compressor 7. The cooling fluid is supplied to the compressor 7 via the expansion tank 11. In the expansion tank 11, the cooling fluid is at the first pressure. Since this is a closed circuit, the first pressure can be lower than the ambient pressure of the outside environment. As a result, the cooling fluid can reach a lower temperature by expanding to the first pressure than is the case in the open circuit. Furthermore, a component of the ambient air, in particular nitrogen, can be used as the cooling fluid in the closed circuit.

[0043] A cooling fluid cooler 12 is arranged fluidically between the compressor 7 and the pressure accumulator 5. The cooling fluid cooler 12 serves to cool the cooling fluid. The cooling fluid cooler 12 is supplied with a cooling air stream taken from the outside environment, for example. Additionally or alternatively, the cooling fluid cooler 12 can be actively cooled by means of an air conveying device. The cooling fluid cooler 12 can, in particular, be designed to at least partially liquefy the cooling fluid compressed to the second pressure by the compressor 7. LIST OF REFERENCE SYMBOLS: 1 drive device 2 drive unit 3 Coolant circuit 4 coolant coolers 5 pressure accumulators 6 Throttle device 7 compressors 8 Cooling air flow 9 additional coolant coolers 10 external print provision device 11 Expansion tank 12 cooling fluid coolers

Claims

[1] Method for operating a drive device (1) for a motor vehicle, wherein the drive device (1) has at least one drive unit (2) and a coolant circuit (3) for controlling the temperature of the at least one drive unit (2), wherein a coolant circulated in the coolant circuit (3) is at least temporarily supplied to a coolant cooler (4), wherein a cooling fluid different from the coolant is stored in a pressure accumulator (5) and is at least temporarily supplied to the coolant cooler (4) for cooling the coolant while expanding the cooling fluid, wherein the cooling fluid is at least temporarily supplied to the pressure accumulator (5) via a compressor (7), wherein the cooling fluid is compressed from a lower first pressure to a higher second pressure, characterized by that the cooling fluid is fed downstream of the coolant cooler (4) in a closed circuit to an expansion tank (11) and via this to the compressor (7). [2] Method according to claim 1, characterized by that the pressure accumulator (5) is at least temporarily filled with the cooling fluid by means of an external pressure supply device (10), wherein the external pressure supply device (10) provides the second pressure. [3] Method according to one of the preceding claims, characterized by that the cooling fluid is flow-wise fed to a cooling fluid cooler (12) between the compressor (7) and the pressure accumulator (5). [4] Method according to claim 3, characterized by that the cooling fluid is at least temporarily liquefied in the cooling fluid cooler (12) and / or in the external pressure supply device (10). [5] Method according to one of the preceding claims, characterized by that a component of the ambient air, in particular nitrogen, is used as a cooling fluid in the closed circuit. [6] Drive device (1) for a motor vehicle for carrying out the method according to one or more of the preceding claims, wherein the drive device (1) has at least one drive unit (2) and a coolant circuit (3) for controlling the temperature of the at least one drive unit (2), wherein a coolant circulated in the coolant circuit (3) is at least temporarily supplied to a coolant cooler (4), wherein the drive device (1) is provided and designed to store a cooling fluid different from the coolant in a pressure accumulator (5) and to supply it at least temporarily to the coolant cooler (4) for cooling the coolant while expanding the cooling fluid, wherein the cooling fluid is supplied to the pressure accumulator (5) at least temporarily via a compressor (7), wherein the cooling fluid is compressed from a lower first pressure to a higher second pressure, characterized bythat the drive device (1) is further provided and designed to supply the cooling fluid downstream of the coolant cooler (4) in a closed circuit to an expansion tank (11) and via this to the compressor (7).

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