Method to detect low charge levels in a refrigeration circuit

Abstract

A method to detect the charge level of a refrigerant within a refrigeration circuit, where the refrigeration circuit has a compressor, a sensor to detect a pressure, and a sensor to detect a temperature. The method has a key cycle that has a first part and a second part.

Claims

1. A method to detect a charge level of a refrigerant within a refrigeration circuit, the method comprising: providing a compressor to compress a refrigerant; providing a sensor to detect a pressure; providing a sensor to detect a temperature; and performing a key cycle that has a first part and a second part, wherein the first part comprises: detecting a pressure in the refrigeration circuit; detecting an ambient temperature; comparing the ambient temperature with a given threshold temperature; comparing the pressure to a given threshold pressure; counting up a first counter C.sub.1 each time the pressure is compared to the threshold pressure, the first part being started over if the pressure is below the threshold pressure and/or if the ambient temperature is below the threshold temperature, with the second part being started if the pressure is above the threshold pressure, and wherein the second part comprises: detecting the pressure; detecting the ambient temperature; comparing the pressure against a predetermined pass/fail pressure; counting up a second counter C.sub.2 each time the pressure is compared against the pass/fail pressure p.sub.t2; counting up a third counter C.sub.3 each time the pressure is below the pass/fail pressure, the second part being started over after the comparison between the pressure and the pass/fail pressure, and wherein the values of the counters C.sub.1, C.sub.2 and C.sub.3 are combined to an overall value after an end of the key cycle and are compared to a threshold value, which represents a predetermined low charge level of the refrigerant within the refrigeration circuit.

2. The method as claimed in claim 1, wherein the compressor is disengaged within the first part and is engaged within the second part.

3. The method as claimed in claim 1, wherein the values of the counter C.sub.1 and/or C.sub.2 and/or C.sub.3 are weighted by a given mathematical function or by using a table of predetermined values before they are combined to an overall value.

4. The method as claimed in claim 1, wherein the values of the counter C.sub.1 and/or C.sub.2 and/or C.sub.3 are weighted and are totaled up to an overall value by using a function: value of C.sub.1+(value of C.sub.3/value of C.sub.2).

5. The method as claimed in claim 1, wherein the value of counter C.sub.1 and/or C.sub.2 and/or C.sub.3 is weighted in dependency to the detected ambient temperature, and wherein higher temperatures lead to higher weightings.

6. The method as claimed in claim 1, wherein the pass/fail pressure is set in dependency of a detected ambient temperature.

7. The method as claimed in claim 1, wherein the threshold pressure is set in dependency of a detected ambient temperature.

8. The method as claimed in claim 1, wherein the key cycle is defined by a predetermined time after which the method is started over again.

9. The method as claimed in claim 1, wherein the respective overall values of more than one of the previous key cycles are stored and compared individually to the threshold value.

10. The method as claimed in claim 1, wherein the method is only used if the vehicle speed is above idle for a predetermined time and/or if a gradient of the ambient temperature slips below a predetermined limit.

11. The method as claimed in claim 1, wherein the compressor will be disengaged if the ambient temperature is below the threshold temperature.

12. The method as claimed in claim 1, wherein the compressor will be engaged if the ambient temperature is above the threshold temperature and the pressure is above the threshold pressure.

13. The method as claimed in claim 1, wherein the compressor is disengaged if the comparison between the overall value and the threshold value shows a trend for low charge levels of the refrigerant within the refrigeration circuit.

14. The method as claimed in claim 1, wherein the key cycle is only started when operation of the compressor is requested.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 shows a flow chart of the method, which is used to detect a low charge level of the refrigerant within the refrigeration circuit;

(3) FIG. 2 shows a diagram with two graphs, where each graph represents a conversion line that can be used to correlate an ambient temperature t.sub.a to either a threshold pressure p.sub.t1 or a pass/fail pressure p.sub.t2;

(4) FIG. 3 shows a diagram with one graph, with the graph representing a conversion line, which represents the weighting factor that can be used for weighting the values of counter C.sub.3 either with regard to the respective ambient temperature t.sub.a or with regard to another relevant reference figure; and

(5) FIG. 4 shows a diagram with one graph, with the graph representing a conversion line, which represents the weighting factor that can be used for weighting the values of counter C.sub.1 either with regard to the detected ambient temperature t.sub.a or with regard to another relevant reference figure.

DETAILED DESCRIPTION

(6) FIG. 1 shows a flow diagram of the method used to detect a low refrigerant level within a refrigeration circuit. The method comprises a key cycle 1 that has two parts, with one being the first part 2 and the other being the second part 3.

(7) The method is started in box 4 where a key cycle 1 is started. The key cycle 1 can last a predetermined amount of time or an otherwise limited time period. In a preferable embodiment a key cycle is characterized by a time span that is long enough to allow the pressure p.sub.s within the refrigeration circuit to raise enough to safely engage the compressor of the refrigeration circuit. The method is usually started when a request for the engagement of the compressor has been issued by either an occupant of the vehicle or by any other regulating components of the vehicle, which is capable of requesting the engagement.

(8) After the start of the key cycle 1 in box 4 a pressure p.sub.s is detected in box 5. The detection is preferably done by a sensor capable of either detecting a pressure directly or indirectly through other means. The pressure p.sub.s can be the pressure of the refrigerant itself in the refrigeration circuit or other pressures, which allow a conclusion of the pressure of the refrigerant. In box 6 the ambient temperature t.sub.a is detected. Therefore a temperature sensor can be used. The ambient temperature t.sub.a can also be acquired by using data of sensors that typically are not related to the refrigeration circuit itself, e.g. the sensor for the temperature display in a vehicle.

(9) The boxes 5 and 6 can be arranged in virtually any order. The ambient temperature t.sub.a and the pressure p.sub.s can be detected simultaneously or in sequence.

(10) In box 7 a first check is conducted, where the detected ambient temperature t.sub.a is compared to a defined threshold temperature t.sub.min. The threshold temperature t.sub.min can be fixed for all key cycles or can be adjusted with respect to the detected ambient temperature t.sub.a or other relevant reference figures. If the ambient temperature t.sub.a is below the threshold temperature t.sub.min, the process leads on to box 8 where the signal is issued that the compressor should be disengaged. If the compressor was actually not engaged at the moment of the check 7, the signal is issued to ensure that the compressor stays disengaged. The process starts over at box 5 with the detection of pressure p.sub.s.

(11) If the ambient temperature t.sub.a is above the threshold temperature t.sub.min in box 7, the process goes on to box 9, where the detected pressure p.sub.s is checked against a threshold pressure p.sub.t1, which reflects a minimum pressure in the refrigeration circuit that is required to safely engage the compressor. If the pressure p.sub.s is below the threshold pressure p.sub.t1, the process goes on to box 10, which represents a first counter C.sub.1. The counter C.sub.1 counts up every time the check at box 9 is performed and failed. The process then starts over again at box 5 with the detection of pressure p.sub.s. The threshold pressure p.sub.t1 is set in dependency from the ambient temperature t.sub.a. It can either be set fixed for one defined key cycle 1 or can be periodically adjusted with each detection of the ambient temperature t.sub.a.

(12) If the pressure p.sub.s is above the threshold pressure p.sub.t1, the process slips over into the second part 3.

(13) The second part 3 starts at box 11 where the compressor is engaged when the pressure p.sub.s and the ambient temperature t.sub.a, which have been detected in the first part 2, are above the respective limits so that the compressor can be safely engaged.

(14) Following box 11 is box 12, where the pressure p.sub.s is detected again. Afterwards the ambient temperature t.sub.a is detected at box 13 again. As in the first part 2 the detection of the pressure p.sub.s and the ambient temperature t.sub.a can be made in different order or simultaneously. The boxes 12 and 13 might be repeated for a predetermined period of time, either fixed or event driven and/or either averaged or maximum values are used.

(15) Following box 13 in the process is box 14, which represents a second counter C.sub.2, which counts up every time the check in the following box 15 is conducted or in other words every time the second part 3 is passed through.

(16) In the following box 15 the detected pressure p.sub.s is compared to a pass/fail pressure p.sub.t2, which is dependent from the ambient temperature t.sub.a or another relevant reference figure. Preferably the pass/fail pressure p.sub.t2 and the threshold pressure p.sub.t1 from the first part 2 are both set in dependency from the respectively detected ambient temperature t.sub.a. The pass/fail pressure p.sub.t2 can either be set to a fixed value for a key cycle 1 or adjusted with every detection of the ambient temperature t.sub.a.

(17) If the pressure p.sub.s is above the pass/fail pressure p.sub.t2, the process jumps back to box 11, where the compressor is still engaged. The process then runs again through the boxes 12, 13 and 14. This goes on as long as the pressure p.sub.s is above the pass/fail pressure p.sub.t2. If the key cycle 1 only lasts a predetermined time, the method can end with the end of the time span of the key cycle 1.

(18) If the pressure p.sub.s is however below the pass/fail pressure p.sub.t2, the process goes on to box 16, which represents a third counter C.sub.3. The counter C.sub.3 counts up every time the check at box 15 is failed and the pressure p.sub.s is below the pass/fail pressure p.sub.t2. From the counter C.sub.3 in box 16 the process is directed back to box 11 and the second part 3 is started all over again.

(19) After the end of the key cycle all values of the three counters C.sub.1, C.sub.2 and C.sub.3 are cumulated together to an overall value. This is represented by the box 20, to which the values of the counters C.sub.1, C.sub.2 and C.sub.3 are channeled along the dotted arrows 17, 18 and 19. This overall value is then compared to a predefined threshold value V.sub.LC, which represents a low charge level within the refrigeration circuit. The low charge level can be set with respect to experience values or to absolute limits, which result from the technical design of the refrigeration circuit.

(20) The values of the counter C.sub.1, C.sub.2 and C.sub.3 can be cumulated by using a preset mathematical function. Preferably the values are cumulated by using a function where the value of C.sub.1 is added to the relation between the value of C.sub.3 and the value of C.sub.2 (value of C.sub.1+(value of C.sub.3/value of C.sub.2)). The overall value thus reflects the amount of failed checks in box 9 and the ratio of failed checks in box 15 to all conducted checks in box 15.

(21) All values of the counters C.sub.1, C.sub.2 and C.sub.3 can be used as they are or they can be weighted to achieve better results. In case of weighting the values can either be weighted after each individual count of the respective counter C.sub.1, C.sub.2 and C.sub.3, after a certain number of counts of the counters or after the end of one key cycle 1.

(22) The weighting factors are preferably dependent from either the ambient temperature t.sub.a or other relevant reference figures. In an embodiment the counts obtained at high ambient temperatures t.sub.a are weighted higher that the counts obtained at low ambient temperatures t.sub.a, as higher ambient temperatures mean less cycling and more repeatable pressures, which leads to a better prediction quality for the charge level in the refrigeration circuit. Higher weighting for the counts at higher ambient temperatures reflect this.

(23) The weighting can either be done by using graphs, which give certain weighting factors for different ambient temperatures t.sub.a, or by using tables, which are filled with predetermined values.

(24) FIG. 2 shows a diagram 30 with a first graph 31 and a second graph 32. The first graph 31 is a conversion line that allows determining the threshold pressure p.sub.t1, which is used in the first part 2, with regard to the ambient temperature t.sub.a. The second graph 32 is a conversion line that allows determining the pass/fail pressure p.sub.t2, which is used in the second part 3, with regard to the detected ambient temperature t.sub.a. The ambient temperature t.sub.a is plotted along the y-axis 33, whereas the pressure is plotted along the x-axis 34.

(25) Furthermore the vertical chain dotted line 35 represents the minimum pressure that can be used for either threshold pressure p.sub.t1 or pass/fail pressure p.sub.t2. The horizontal chain dotted line 36 represents the threshold temperature t.sub.min, which needs to be exceeded to allow the operation of the compressor.

(26) For a given ambient temperature t.sub.a, which is represented through the horizontal dotted line 37, a value for the threshold pressure p.sub.t1 can be obtained from the conversion line 31 by going vertically down to the x-axis 34 from the point of intersection between the ambient temperature t.sub.a 37 and the first conversion line 31.

(27) In a similar method the pass/fail pressure p.sub.t2 can be obtained by going vertically down from the point of intersection between the ambient temperature t.sub.a 37 and the second conversion line 32.

(28) Both conversion lines 31, 32 are generic and only reflect the main characteristics of an exemplary embodiment. As can be seen in FIG. 2 it is preferred, when the respective pressures p.sub.t1 and p.sub.t2 grow very slowly at first with respect to a growing ambient temperature t.sub.a. That is represented through the very low gradient of the conversion lines 31 and 32 starting from the chain dotted line 35 of the minimal pressure.

(29) Both conversion lines 31 and 32 are showing strongly increasing gradients that lead to strong growing pressures by even modest rises of the ambient temperature t.sub.a. Both conversion lines 31 and 32 then go back to lower gradients, which result in slower growing pressures with a rising ambient temperature t.sub.a.

(30) In alternative embodiments the conversion lines could be vastly different. The conversion line is preferably oriented at the technical design of the refrigeration circuit and especially the compressor. Especially the minimum pressure, which is needed to safely engage the compressor (threshold pressure p.sub.t1) or to keep the compressor safely engaged (pass/fail pressure p.sub.t2), is important to form the conversion line in a way that leads to reasonable pressure values at all expectable ambient temperatures t.sub.a. Generally the trend, in which higher ambient temperatures t.sub.a lead to higher pressures p.sub.t1 and p.sub.t2, should be incorporated in the chosen conversion lines.

(31) FIG. 3 shows a diagram 40. The y-axis 41 shows the ambient temperature t.sub.a, whereas the x-axis 42 shows a weighting factor for the values of counter C.sub.3. The graph 43 shows a conversion line that allows determining a weighting factor for a given ambient temperature t.sub.a. The conversion line 43 can be incorporated into the method to allow an instantaneous weighting of the values of counter C.sub.3 at the instance they are counted. The values of the counter C.sub.3 can either be weighted directly with every count of the counter with respect to the particular ambient temperature t.sub.a or after the end of a key cycle. The weighting of each value at the instance of the individual count gives a more precise picture, which is preferably.

(32) For a given ambient temperature t.sub.a 44 a weighting factor can be obtained by going vertically downwards from the point of intersection between the ambient temperature t.sub.a 44 and the conversion line 43.

(33) The conversion line 43 of FIG. 3 is just a generic sketch and only represents the basic characteristics of a preferred conversion line.

(34) FIG. 4 shows a diagram 50 that shows a conversion line 51. The y-axis 52 shows the counted value of the first counter C.sub.1, whereas the x-axis 53 shows the weighting factor for the values of counter C.sub.1. From a certain value of C.sub.1 54 a corresponding weighting factor can be obtained by vertically going down from the point of intersection from the value of C.sub.1 54 to the x-axis 53 showing the weighting factors for the values of C.sub.1.

(35) By using a conversion line 51, which in case of FIG. 4 is just a generic sketch, the values of the counter C.sub.1 can be weighted to increase the precision of the method to detect a low charge level of the refrigerant.

(36) The foregoing discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the present invention.

(37) Especially the conversion lines shown in FIGS. 2, 3 and 4 are only generic lines. They indicate the most characteristic qualities of the conversion lines preferably used for the present invention. Changes to the conversion lines can easily be made. In alternative embodiments tables can be used instead of conversion lines within the method without interfering with the scope of the invention.

(38) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.