Method for operating a refrigeration system for a vehicle and a corresponding refrigeration system

Abstract

A method for operating a refrigeration system for a vehicle with a refrigerant circuit including a heat exchanger. A controllable environmental air flow (L) is flowed through the heat exchanger and the heat exchanger can be operated as a refrigerant condenser or a gas cooler for a refrigeration system operation.

Claims

1. A method for operating a refrigeration system for a vehicle with a refrigerant circuit comprising: flowing a controllable environmental air flow (L) through a heat exchanger, wherein the heat exchanger can be operated as a refrigerant condenser or a gas cooler for a refrigeration system operation, for setting a predetermined pressure ratio between the high pressure and the low pressure of the refrigerant circuit, wherein the amount of air of the environmental air flow (L) flowing through the heat exchanger is controlled by a device as a function of a temperature limit value of the environmental temperature of the vehicle, wherein above the temperature limit value, the amount of air flowing through the heat exchanger is increased by the device, and at an environmental temperature corresponding at most to the temperature limit value, decreasing the amount of air flowing through the heat exchanger by controlling the device.

2. The method according to claim 1, wherein the device is designed as a controllable air supply device.

3. The method according to claim 2, wherein the air supply device is formed with a plurality of pivotable air flaps which can be pivoted individually, jointly or in groups between an open position and a closed position.

4. The method according to claim 3, wherein a cooling air flow (L1) from the environmental air flow (L) is set by means of the device with a cross section which corresponds to the maximum cooling surface of the heat exchanger.

5. The method according to claim 3, wherein the device is formed with at least two partial devices, wherein the partial devices correspond to disjoint cooling surfaces of the heat exchanger, in such a manner that the partial cooling air flow generated by a partial device from the environmental air flow (L) impinges on the cooling surface of the heat exchanger.

6. The method according to claim 2, wherein a cooling air flow (L1) from the environmental air flow (L) is set by means of the device with a cross section which corresponds to the maximum cooling surface of the heat exchanger.

7. The method according to claim 2, wherein the device is formed with at least two partial devices, wherein the partial devices correspond to disjoint cooling surfaces of the heat exchanger, in such a manner that the partial cooling air flow generated by a partial device from the environmental air flow (L) impinges on the cooling surface of the heat exchanger.

8. The method according to claim 1, wherein a cooling air flow (L1) from the environmental air flow (L) is set by means of the device with a cross section which corresponds to the maximum cooling surface of the heat exchanger.

9. The method according to claim 8, wherein the device is formed with at least two partial devices, wherein the partial devices correspond to disjoint cooling surfaces of the heat exchanger, in such a manner that the partial cooling air flow generated by a partial device from the environmental air flow (L) impinges on the cooling surface of the heat exchanger.

10. The method according to claim 1, wherein the device is formed with at least two partial devices, wherein the partial devices correspond to disjoint cooling surfaces of the heat exchanger, in such a manner that the partial cooling air flow generated by a partial device from the environmental air flow (L) impinges on the cooling surface of the heat exchanger.

Description

(1) Additional advantages, features and details of the invention result from the following description of preferred embodiments and from the drawings. The figures show:

(2) FIG. 1 a circuit diagram of an embodiment example of a refrigeration system according to the invention with a heat exchanger and a device for generating a cooling air flow flowing through the heat exchanger, and

(3) FIG. 2 a detailed representation of a heat exchanger with an alternative embodiment of the device for generating a cooling air flow flowing through the heat exchanger.

(4) For explaining the method according to the invention, to begin with the refrigeration system 10 for a vehicle used therefor and represented in FIG. 1 is first explained.

(5) The refrigeration system 10 represented in FIG. 1 consists of a refrigerant circuit 1 with carbon dioxide (R744) as refrigerant or with another suitable refrigerant. This refrigerant circuit 1 is operated in a refrigeration system operation, hereafter referred to as AC operation, wherein this refrigerant circuit 1 for a heat pump operation for conditioning a supply air flow to be supplied to the vehicle interior of the vehicle can be supplemented with the components known to a person skilled in the art.

(6) The refrigerant circuit 1 according to FIG. 1 comprises a heat exchanger 2 which is operated as gas cooler or as condenser for the AC operation.

(7) Furthermore, in addition to the heat exchanger 2, the refrigerant circuit 1 according to FIG. 1 comprises, a refrigerant compressor 3, an evaporator 4 which is preceded by an associated expansion device 4.0, a refrigerant collector 5, and an inner heat exchanger 6. These components are flowed through in a known manner in flow direction S by the refrigerant of the refrigerant circuit 1.

(8) During the AC operation of the refrigerant circuit 1, the refrigerant compressed by means of the refrigerant compressor 3 flows in flow direction S into the heat exchanger 2, in which, as a function of the amount of air of an environmental air flow L1, the refrigerant is cooled, or cooled and condensed, and condensation heat is released to the vehicle environment.

(9) After the refrigerant has left the heat exchanger 2, its pressure it is expanded via the high pressure section of the inner heat exchanger 6 by means of the expansion device 4.0 into the evaporator 4, in order to receive heat from the cabin supply flow. Subsequently, the refrigerant is returned via the refrigerant collector 5 and the low pressure section of the inner heat exchanger 6 to the refrigerant compressor 3.

(10) The inclusion of the sensors (pressure, temperature, pressure temperature sensor) necessary for the proper operation of the system is dispensed with in the drawing since said sensors are known to the person skilled in the art.

(11) A device 7 designed as an air supply device 7.0 is associated with the heat exchanger 2, by means of which an environmental air flow L is converted into a cooling air flow L1 and thus the heat exchanger 2 is impinged on for cooling the refrigerant in the area of same.

(12) This air supply device 7.0 is implemented as a closable cooling air louver with pivotable air flaps 7.01 (also known as lamellas) which can be pivoted jointly between an open position, in which the entire cooling surface of the heat exchanger 2 is impinged on by the entire environmental air flow L as cooling air flow L1, and a closed position, in which the air flaps 7.01 are closed so that the cooling surface of the heat exchanger 2 is not impinged on by cooling air. Moreover, every intermediate position is possible, in which the amount of air of the supply flow L1 guided via the air flaps 7.01 is reduced to varying degrees in comparison to the amount of air of the entire environmental air flow L.

(13) The cross section of the cooling air flow L1 generated by the air supply device 7.0 corresponds in the vehicle vertical direction (z direction) to at most the entire effective cooling surface of the heat exchanger 2, also in a vehicle vertical direction.

(14) Due to the different design of the cooling air channels, but also due to the different positioning possibilities of the air supply device 7 in x direction, the exposed surface thereof can vary up to values which correspond to the entire effective cooling surface of the heat exchanger 2. The heat exchanger 2, as part of a unit cooler pack which can comprise additional components such as high and/or low temperature coolers, can itself also be oriented in different inclination positions.

(15) The control of the air flaps 7.01 of the air supply device 7.0 occurs by means of a control unit 8 as a function of parameters such as, for example, the pressure levels, i.e., the pressure difference in the refrigerant circuit 1. The resting pressure level of the refrigerant circuit 1 is already reached at the low pressure level that is expedient for a system operation, so that a more stable continuous operation is not achieved, i.e., due to the low environmental temperature, the high pressure in the system is lowered to the extent that the refrigerant compressor 3 is not able to ensure a stable pressure difference between low pressure and high pressure side and, in the process, the high pressure comes very close to the low pressure. This means that the resulting high pressure level is sufficiently low so that no pronounced pressure ratio between the low pressure side and the high pressure side of the refrigeration system 10 is reached, i.e., the high pressure almost reaches the value of the low pressure, which in turn is equivalent to a pressure ratio of slightly more than 1. The reason for this is that the cooling effect achieved via the heat exchanger 2 is excessively dominant, whereby a strong cooling of the refrigerant results and, in the end, a low condensation pressure level is set.

(16) During an AC operation, the air flaps 7.01, as a function of, for example, a detected environmental temperature or a determined pressure difference are steered into a predetermined pivoted position which corresponds to the open or closed position or to an intermediate position between the open and closed position.

(17) For the AC operation, as a function of the environmental temperature of the vehicle, the air flaps 7.01, starting from a current position, are pivoted by means of the control unit 8 as a function of the environmental temperature of the vehicle. The environmental temperature is detected by means of a suitable temperature sensor and supplied to the control unit 8 for evaluation, wherein, in the control unit 8, for this purpose, a temperature limit value is stored.

(18) If an environmental temperature which is higher than the temperature limit value is detected, the air supply device 7.0 is controlled by the control unit 8 in such a manner that the air flaps 7.01 are pivoted in the direction of their open position, whereby the amount of air of the cooling air flow L1 is increased by a predetermined amount. Thus, a maximum heat exchange occurs by means of the cooling air flow with the maximum amount of air supplied to the heat exchanger 2.

(19) On the other hand, if the environmental temperature reaches the temperature limit value or if the environmental temperature drops below this temperature limit value, the air supply device 7.0 is controlled by the control unit 8 in such a manner that the air flaps 7.01 are pivoted in the direction of their closed position, so that the amount of air of the cooling air flow L1 is reduced by a predetermined amount.

(20) Thus, for the heat exchange of the heat exchanger 2 with the environmental air of the vehicle, a smaller amount of air is available, whereby the condensation capacity in a heat exchanger 2 operated as refrigerant condenser or the cooling capacity in a heat exchanger 2 operated as gas cooler is also reduced in comparison to a flow through the heat exchanger 2 with the complete environmental air flow L. Thereby, during a startup of the refrigeration system 10 at low outside temperatures, an increase of the high pressure of the refrigerant circuit for achieving a sufficient pressure ratio between the low pressure and high pressure side of the refrigerant circuit 1 for ensuring a stable continuous operation is achieved, or it is achieved that during the operation of the refrigeration system a sufficient high pressure for ensuring a stable continuous operation is generated.

(21) The temperature limit value can be set, for example, at 6° C. in order to reduce the amount of air of the cooling air flow L1 and at 8° C. in order to increase the amount of air of the cooling air flow L1, since, in this range, it can already be assumed that, on the system side, i.e., by the refrigerant circuit 1, only small capacities are implemented, and thus only smaller amounts of heat have to be dissipated on the heat exchanger 2.

(22) Alternatively or additionally to the temperature limit value, in the control device 8, a pressure difference limit value can be stored. For this purpose, the value of the high pressure value detected by a pressure (temperature) sensor is used. If, in the case of a chemical refrigerant, for example, a high pressure of more than 1 bar relative to the low pressure is reached, then the amount of air of the cooling air flow L1 flowing through the heat exchanger 2 is increased, otherwise or below this value, a reduction of the amount of air of the cooling air flow L1 flowing through the heat exchanger 2 occurs. In the case of the refrigerant R744, for example, a value of 5 bar can be used as limit value for a pressure difference between the high pressure and the low pressure of the refrigerant circuit 1.

(23) If a pressure difference which is greater than the pressure difference threshold value is detected, the air supply device 7.0 is controlled by the control unit 8 in such a manner that the air flaps 7.01 are pivoted in the direction of their open position, so that the amount of air of the cooling air flow L1 is increased by a predetermined amount. Thus, a maximum heat exchange occurs by means of the cooling air flow with a maximum amount of air supplied to the heat exchanger 2.

(24) On the other hand, if the pressure difference reaches the pressure difference limit value or if the pressure difference falls below this pressure difference value, the air supply device 7.0 is controlled by the control unit 8 in such a manner that the air flaps 7.01 are pivoted in the direction of their closed position, so that the amount of air of the cooling air flow L1 is reduced by a predetermined amount.

(25) Thus, for the heat exchange of the heat exchanger 2 with the environmental air of the vehicle, a smaller amount of air is available, whereby the condensation capacity in the case of a heat exchanger 2 operated as refrigerant condenser or the cooling capacity in the case of a heat exchanger 2 operated as gas cooler is also reduced in comparison to a throughflow with the complete environmental air flow L. Thereby, during a start up of the refrigeration system 10 at low outside temperatures, an increase of the high pressure of the refrigerant circuit is reached for achieving a sufficient pressure ratio between the low pressure and high pressure side of the refrigerant circuit 1 for ensuring a stable continuous operation, or it is achieved that during the operation of the refrigeration system a sufficient high pressure for ensuring a stable continuous operation is generated.

(26) In contrast to the joint control of the air flaps 7.01, it is also possible, alternatively, to enable each individual air flap 7.01 to be actuated individually by the control unit 8. Thereby, it is possible that individual flows of the heat exchanger 2 can be separated completely from the air flow, as needed, especially also in the case of heat exchangers 2 functioning as condensers or gas coolers, with flows selectively impinged on by refrigerant. The impinging of air on heat exchangers upstream and/or downstream of the heat exchanger 2 functioning as a condenser or gas cooler represents an additional criterion. Said heat exchangers in this manner are not completely cut off from the air flow and, instead, are locally flowed through by a partial air flow in order to implement a required cooling capacity in this manner.

(27) The air supply device 7.0 can also be implemented so that the air flaps 7.01 are combined in groups, and each group of such air flaps 7.01 in each case is jointly controlled by the control unit 8 and thus pivoted independently of the other group of air flaps. Each of this group of air flaps generates a partial air flow of the environmental air flow, of which the amount of air is generated independently of the amount of air of the other partial air flow.

(28) An equivalent embodiment of the device 7 implemented as air supply device 7.0 consists in subdividing said device into at least two partial devices 7.1 and 7.2, as represented diagrammatically in FIG. 2. Each of these partial devices 7.1 and 7.2 is designed as air supply device 7.10 and 7.20 with air flaps 7.11 and 7.21. An environmental air flow L impinging on such a device 7 is divided by the two partial devices 7.1 and 7.2 into two partial cooling air flows L11 and L12 which in turn impinge on two disjoint cooling surfaces A1 and A2 of the heat exchanger 2.

(29) In such an air supply device 7 subdivided into two partial devices 7.1 and 7.2, a heat exchanger 2 can be used which is implemented with two flows, a first flow 2.1 and a second flow 2.2. The first flow 2.1 is arranged in the vehicle vertical direction (z direction) below the second flow 2.2 and thus corresponds to the cooling surface A1, while the second flow 2.2 corresponds to the cooling surface A2.

(30) A two-flow flow through the heat exchanger 2 then occurs if the environmental temperature of the vehicle is higher than the temperature limit value or if the pressure difference between the high pressure and the low pressure of the refrigerant circuit 1 is greater than the pressure difference threshold. In this case, the two air supply devices 7.10 and 7.20 are actuated simultaneously by a control unit 8, in that their air flaps 7.11 and 7.21 are pivoted from a predetermined position in the direction of its open position by a predetermined amount, whereby the amount of air of each of the two partial cooling air flows L11 and L12 is increased.

(31) A single-flow flow through the heat exchanger 2, namely through the first flow 2.1, occurs if the environmental temperature of the vehicle is equal to or less than the temperature limit value or if the pressure difference between the high pressure and the low pressure of the refrigerant circuit 1 is equal to or less than the pressure difference threshold value. In this heat exchanger 2 of which a partial surface is impinged on by refrigerant, the lower air supply device 7.20 is closed, that is to say its air flaps 7.21 are closed, or the amount of air of the partial cooling air flow generated by this air supply device 7.20 is controlled by the control unit 8 to a predetermined value in the direction of its closed position. In this case, the partial cooling air flow L11 of the upper air flow device 7.10 impinges on the cooling surface A1 of the second flow 2.2 of the heat exchanger 2, through which no refrigerant flows. If the heat exchanger 2 is arranged in a cooler pack with at least one cooler or a water cooling circuit for cooling a combustion engine, this cooler can be impinged on by the partial cooling air flow L11 or the amount of air thereof can be controlled.

(32) However, for aerodynamic reasons it is reasonable to move the device 7 as close as possible in the direction of the cooling air inlet of the vehicle, i.e., to the area of the vehicle outer shell of the vehicle, which however has the consequence that, with the movement of the air flap 7.01, the entire cooler pack is affected in the same manner by a reduction of the total air flow L1 and not only individual sectors of the cooler pack, as allowed by the implementation according to FIG. 2.

(33) The method carried out by such a refrigeration system according to FIGS. 1 and 2 for conditioning the supply flow into the vehicle interior, in particular for cooling and/or dehumidifying this supply flow at an environmental temperature around the freezing point or slightly higher, ensures a stable refrigeration system operation.