Method for Controlling or Regulating a Coolant Circuit of a Motor Vehicle Air Conditioning System

Abstract

A method and a correspondingly designed device are provided for controlling or regulating a coolant circuit of an air conditioning system, which includes at least one compressor, at least one condenser or gas cooler, and at least one evaporator. A controllable coolant expansion device is connected to the coolant inlet of the evaporator. It is detected when the coolant circuit is under filled with a coolant and, when an under filling of the coolant is detected, the control strategy of the expansion device is changed.

Claims

1. A method for controlling or regulating a coolant circuit of a motor vehicle air conditioning system having a compressor, a condenser or gas cooler, and an evaporator, as well as a controllable coolant expansion device connected to a coolant inlet of the evaporator, the method comprising the acts of: detecting an underfilling of coolant in the coolant circuit; and when an undesirable underfilling of the coolant is detected in the coolant circuit, changing a control strategy of the controllable coolant expansion device.

2. The method according to claim 1, wherein when the undesirable underfilling of the coolant is detected, the changing of the control strategy is carried out by deviating from a standard control strategy of the controllable coolant expansion device in order to set an optimum high pressure of the coolant.

3. The method according to claim 1, wherein when the undesirable underfilling of the coolant is detected, the changing of the control strategy is carried out such that the expansion device is adjusted to an underfilling dependent desired high pressure of the coolant that is lower than a predetermined optimum high pressure when the coolant circuit is not underfilled.

4. The method according to claim 1, wherein the undesirable underfilling of the coolant is detected when: (i) initial effects of the underfilling of the coolant on air conditioning comfort or power are detected, or (ii) critical states of air conditioning system components are detected.

5. The method according to claim 1, wherein when an underfilling of the coolant is detected, the control strategy of the controllable coolant expansion device is changed in favor of an increase in flow of the coolant through the expansion device.

6. The method according to claim 1, wherein the underfilling of the coolant in the coolant circuit is detected by detecting overheating of the coolant downstream of the evaporator.

7. The method according to claim 1, wherein the underfilling of the coolant in the coolant circuit is detected via a filling level measurement of the coolant in a collector of the air conditioning system.

8. A device for controlling or regulating a coolant circuit of a motor vehicle air conditioning system equipped with a compressor, a condenser or gas cooler, and an evaporator as well as a controllable coolant expansion device connected to an input of the evaporator, the device comprising: an air conditioning control unit including a processor executing instructions to: detect an underfilling of the coolant in the coolant circuit; and when an undesirable underfilling of the coolant is detected, change a control strategy of the controllable coolant expansion device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a schematic, simplified construction of a coolant circuit of a motor vehicle air conditioning system (not illustrated specifically).

[0021] FIG. 2 is a simplified diagram for illustrating a possibility of refining the exemplary method according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0022] The coolant circuit KK, illustrated in FIG. 1, of a motor vehicle air conditioning system includes a compressor K for compressing the coolant KM, downstream of which on the high pressure side is a condenser or gas cooler GK. An externally adjustable or controllable coolant expansion device EXV, which is followed by an evaporator V, is connected downstream of said condenser or gas cooler GK. A collector S can also be provided downstream of the evaporator V or downstream of the condenser/gas cooler GK. As a rule, “R744 coolant circuits” generally also contain an internal heat exchanger, which is omitted on the illustration here. For the precise configuration of such coolant circuits, reference is made to the known prior art.

[0023] An air conditioning control unit SG controls the operation of the air conditioning system in a conventional manner depending on the activation signal directly or indirectly (by control or regulation of the evaporator temperature) to the coolant flow or coolant differential pressure realized between the high pressure part and low pressure part of the coolant circuit KK. Furthermore, a first and second sensor S1 and S2 are provided, wherein the first sensor S1 here detects the temperature s1 of the coolant KM downstream of the evaporator V, and the second sensor S2 detects the pressure s2 of the coolant KM downstream of the evaporator V. The two signals s1 and s2 are transmitted to the air conditioning system control unit SG. Alternatively, the air-side temperature difference downstream of the evaporator is also determined, and this is used as a measure of the underfilling. Similarly, the coolant-side temperature difference can also be determined and used as a measure of the underfilling.

[0024] FIG. 2 now shows an advantageous configuration of the method according to the invention with reference to a simplified flow diagram. The diagram starts at step 20, wherein here first of all a standard regulation of the coolant circuit is undertaken or is maintained. The externally controllable expansion device EXV is set or adjusted here in accordance with a predefined control strategy, for example for setting an optimum high pressure.

[0025] In the next step 30, the two supplied signals s1 and s2 are evaluated in order to detect overheating. If overheating of the coolant downstream of the evaporator is determined, first of all, in the next step 40, the degree of opening of the expansion device EXV is checked. If the expansion device EXV is not yet completely open, the expansion device EXV is activated in step 60 in such a manner that the coolant flow is increased. If, however, it is determined in step 40 that the expansion device is already open to a maximally permitted opening, a transition is made to step 50 and, in order to avoid damage, the coolant circuit is deactivated and a warning output to the driver. Further opening of the expansion device can also be achieved by the control variable, i.e., for example, the desired pressure of the coolant being changed in such a manner that, by controlling or regulating the expansion device, the flow of coolant is increased.

[0026] Alternatively to the embodiment illustrated here, the checking for overheating can also be undertaken immediately at the beginning of the method and, depending on the result, either the standard regulation can be started or the expansion device can be opened further. A parallel procedure (standard regulation and parallel checking for overheating of the coolant) would likewise be possible. Depending on the overheating value or extent, a different target value for the optimum high pressure regulation can then be determined, and therefore there can be a response to the underfilling within the standard regulation. If the overheating is excessive and the expansion member has already been opened to the defined maximally permitted opening, then the overheating cannot be compensated for further.

[0027] By means of this method, when an underfilling of the coolant is detected, the operation of the coolant circuit can be further maintained at least initially. This results in an extension of the operating period of the coolant circuit despite the reduced quantity of coolant. Customer satisfaction can therefore also be increased since, because of the error detection and initiating of appropriate countermeasures, first of all the period before the required maintenance is extended, and also prompt maintenance and topping up of the coolant can then be carried out.

[0028] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.