Method for controlling lubricating oil of air conditioner compressor

Abstract

The lubricating oil control process in the lubricating oil control method of the present application includes a plurality of stages of two or more stages performed sequentially, in each of the stages, control is performed with a prescribed compressor upper limit frequency, a prescribed outdoor unit expansion valve lower limit opening degree, a prescribed maximum operation time of the lubricating oil control process, and a prescribed minimum operation time, and in the case where the discharge superheat in a certain stage after the discharge superheat in the stage satisfies a prescribed range, control in the stage is entered, and in each stage, the outdoor unit expansion valve lower limit opening degree is set in accordance with the outside air temperature, and the lower the outside air temperature, the larger the outdoor unit expansion valve lower limit opening degree. Thus, the oil separator can be eliminated to greatly reduce costs and the risk of breakage of the capillary oil return pipe is structurally avoided, and the amount of lubricating oil of the compressor is sufficiently ensured by the cooperation of a plurality of conditions.

Description

Technical Field

[0001] This invention relates to air conditioners, and more particularly to a method for controlling the lubricating oil of an air conditioner compressor. Background Technology

[0002] During the operation of an air conditioner compressor, lubricating oil will be discharged along with the miscible refrigerant. If the oil separation mechanism is not designed well, it will cause problems such as poor separation effect and poor oil return in the system.

[0003] With the development of multi-split air conditioning technology, in order to improve user comfort, the piping length of multi-split systems is getting longer and longer, and the number of indoor units is increasing. In order to ensure the amount of lubricating oil in the compressor and to ensure that the compressor can be fully lubricated and not dry-run, existing technologies generally set up an oil separator. When the air conditioner is running, lubricating oil and refrigerant are discharged from the compressor at the same time. After passing through the oil separator, the lubricating oil and refrigerant are separated, and the lubricating oil returns to the compressor.

[0004] For example, Figure 4 This illustrates the general structure of the refrigeration cycle in existing air conditioning technologies. For example... Figure 4 As shown, in the refrigeration cycle consisting of a compressor, condenser, expansion valve, and evaporator, an oil separator is connected to the compressor discharge side via a refrigerant pipe. The oil separator separates the oil from the refrigerant discharged from the compressor section, and the separated oil returns to the compressor section through the oil return pipe.

[0005] In addition, there are existing technologies that control the discharge of lubricating oil by suppressing the frequency of the compressor. Summary of the Invention

[0006] As mentioned above, existing technologies mostly control the discharge and separation of lubricating oil through oil separators and / or compressor frequency suppression. However, installing an oil separator significantly increases costs, and the oil separator cannot separate excessive amounts of lubricating oil in a timely manner. Moreover, the return oil pipe in the oil separator structure is generally an extremely thin capillary tube, which is structurally susceptible to breakage.

[0007] Furthermore, limiting lubricating oil discharge by controlling the frequency also fails to effectively suppress the discharge of lubricating oil from the compressor, resulting in problems such as incomplete control and poor performance.

[0008] In view of the above-mentioned problems, the present invention aims to provide a lubricating oil control method without using an oil separator, which ensures sufficient lubricating oil in the compressor by closely coordinating the expansion valve opening, compressor frequency, discharge of superheat and time.

[0009] The lubricating oil control method for an air conditioning compressor of the present invention is characterized in that: the lubricating oil control process in the above-mentioned lubricating oil control method includes multiple stages, two or more of which are executed sequentially. In each of the above-mentioned stages, control is performed with a specified upper limit frequency of the compressor, a specified lower limit opening of the outdoor unit expansion valve, a specified maximum operating time and a specified minimum operating time of the above-mentioned lubricating oil control process. The control of the above-mentioned stage is entered when the discharge overheating of the above-mentioned stage meets the range of the discharge overheating of a certain stage. The discharge overheating is the value obtained by subtracting the compressor high pressure temperature from the compressor discharge temperature. The range of the discharge overheating of the above-mentioned multiple stages gradually increases sequentially. The minimum operating time refers to the minimum operating time of the above-mentioned lubricating oil control process. If the minimum operating time is less than the minimum operating time, the control of the current stage continues even if the range of the discharge overheating of the next stage is met. The maximum operating time refers to the maximum operating time of the above-mentioned lubricating oil control process. If the maximum operating time is greater than the maximum operating time, the control of the next stage is entered even if the range of the discharge overheating of the next stage is not met. In each of the above-mentioned stages, the lower limit opening of the outdoor unit expansion valve is also set according to the external air temperature. The lower the external air temperature, the larger the lower limit opening of the outdoor unit expansion valve.

[0010] In the above-mentioned method for controlling the lubricating oil of the air conditioner compressor, it is also possible that, compared with the earlier stages of the above-mentioned multiple stages, the upper limit frequency of the compressor is equal to or increased, and the lower limit opening of the outdoor unit expansion valve is equal to or decreased.

[0011] In the above-mentioned method for controlling the lubricating oil of the air conditioning compressor, the above-mentioned lubricating oil control procedure may also be performed when the compressor is turned on, in heating mode and in normal operating mode.

[0012] In the above-mentioned method for controlling the lubricating oil of the air conditioner compressor, the lubricating oil control process may be performed after the initial expansion valve fixing process, which sets the outdoor unit expansion valve to its initial opening after the compressor starts.

[0013] In the above-mentioned method for controlling the lubricating oil of the air conditioning compressor, it is also possible that once the compressor stops and restarts, the above-mentioned lubricating oil control procedure needs to be re-executed from the initial stage.

[0014] In the aforementioned air conditioning compressor lubrication oil control method, the lubrication oil control process may also include five stages executed sequentially: a first stage, a second stage, a third stage, a fourth stage, and a fifth stage. In the first stage, the discharge overheat is defined as DSH, the range of discharge overheat is DSH < 3, the compressor upper limit frequency is 42Hz, the maximum running time is 5 minutes, the minimum running time is 30 seconds, and the lower limit opening of the outdoor unit expansion valve is 90 pulses when the external air temperature is greater than 10℃, and 120 pulses when the external air temperature is greater than 0℃ and less than or equal to 10℃. When the external air temperature is less than or equal to 0°C, the pulse rate is 140. In the second stage, the range of exhaust overheating is 3 ≤ DSH < 6, the compressor upper limit frequency is 42Hz, the maximum operating time is 5 minutes, the minimum operating time is 30 seconds, and the lower limit opening of the outdoor unit expansion valve is 80 pulses when the external air temperature is greater than 10°C, 110 pulses when the external air temperature is greater than 0°C and less than or equal to 10°C, and 130 pulses when the external air temperature is less than or equal to 0°C. In the third stage, the range of exhaust overheating is 6 ≤ DSH < 10, and the compressor upper limit frequency... The frequency is 48Hz, the maximum operating time is 3 minutes, the minimum operating time is 30 seconds, the lower limit opening of the outdoor unit expansion valve is 70 pulses when the external air temperature is greater than 10℃, 100 pulses when the external air temperature is greater than 0℃ and less than or equal to 10℃, and 120 pulses when the external air temperature is less than or equal to 0℃. In the fourth stage, the range of exhaust overheating is 10≤DSH<13, the upper limit frequency of the compressor is 54Hz, the maximum operating time is 3 minutes, the minimum operating time is 30 seconds, and the lower limit opening of the outdoor unit expansion valve is 70 pulses when the external air temperature is greater than 10℃, 100 pulses when the external air temperature is greater than 10℃, and 120 pulses when the external air temperature is less than or equal to 0℃. The number of pulses is 70 when the external air temperature is 10℃, 90 when the external air temperature is greater than 0℃ and less than or equal to 10℃, and 110 when the external air temperature is less than or equal to 0℃. In the fifth stage, the range of exhaust overheating is 13≤DSH, the upper limit frequency of the compressor is 58Hz, there is no maximum running time, the minimum running time is 2 minutes, and the lower limit opening of the outdoor unit expansion valve is 70 pulses when the external air temperature is greater than 10℃, 80 when the external air temperature is greater than 0℃ and less than or equal to 10℃, and 100 when the external air temperature is less than or equal to 0℃.

[0015] This invention can also be a multi-split air conditioning unit, which uses the above-mentioned air conditioning compressor lubrication oil control method to control the discharge of lubrication oil from the air conditioning compressor.

[0016] Invention Effects

[0017] This invention provides a lubricating oil control method without using an oil separator. It ensures sufficient lubricating oil in the compressor by closely coordinating the expansion valve opening, compressor frequency, discharge overheating, and time. This eliminates the need for an oil separator, significantly reducing costs and structurally avoiding the risk of capillary return pipe breakage. The combined effect of multiple conditions ensures adequate lubricating oil supply to the compressor. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the modules used in the lubricant control process of the present invention.

[0019] Figure 2 The execution conditions and parameters of the lubricating oil control process in the embodiments of the present invention are presented in tabular form.

[0020] Figure 3 illustrates the execution conditions and parameters of the lubricating oil control process in an embodiment of the present invention in the form of a flowchart. (A)(B)(C)(D)(E) are separated for ease of drawing and should be considered as one diagram.

[0021] Figure 4 This is a diagram showing the general structure of the refrigeration cycle in existing air conditioning technology. Detailed Implementation

[0022] The embodiments and examples of the present invention will now be described in detail with reference to the accompanying drawings, in which the same reference numerals denote the same elements or functional modules. The present invention is not limited to the specific embodiments and examples described below.

[0023] This embodiment omits a description of the structure of the air conditioner's refrigeration cycle; its general structure can be referenced from existing technologies. Figure 4 They simply removed the oil separator.

[0024] The activation of the air conditioning compressor lubrication oil control in this embodiment must meet the following conditions:

[0025] (1) The compressor starts.

[0026] (2) The air conditioner is in heating mode. This is because when in cooling mode, the compressor discharges less lubricating oil, and the existing control method for controlling the compressor frequency is sufficient to handle the situation.

[0027] (3) The air conditioner is in normal operating mode. That is, not in fixed mode, not in engineering inspection mode, etc.

[0028] (4) The lubricating oil control process of the present invention is performed after the initial expansion valve fixing process and before the SH control process begins. The initial expansion valve fixing process refers to setting the expansion valve to its initial opening degree after the compressor is started. The SH control process refers to superheat control, which is the process performed after the lubricating oil control process of the present invention.

[0029] (5) Meet the necessary DSH-related conditions. This will be described in detail later.

[0030] The lubricating oil control process of this invention uses the discharge superheated DSH (DSH = compressor discharge temperature TD - high pressure temperature HPT) as the pivot point. When DSH reaches a certain value or the running time meets the requirements, it will move to the next stage. During operation, the compressor's upper limit frequency gradually increases with DSH, aiming to increase the compressor discharge temperature more quickly to achieve better air conditioning performance. The lower limit opening of the outdoor unit expansion valve gradually decreases with DSH (there is a minimum opening after balancing oil level and air conditioning satisfaction). The following examples illustrate this process in detail.

[0031] Figure 1 This is a schematic diagram illustrating the modules used in the lubricant control process of the present invention.

[0032] like Figure 1 As shown, the modules used in the lubricating oil control process of the present invention include: DSH detection and judgment module 1, timing module 2, compressor upper limit frequency setting module 3, outdoor unit expansion valve lower limit opening setting module 4, and external air temperature detection module 5.

[0033] DSH detection and judgment module 1 detects the current DSH value and determines its range.

[0034] The timing module 2, or timer, measures the running time.

[0035] The compressor upper limit frequency 3 sets the upper limit frequency of the compressor.

[0036] The lower limit opening degree 4 of the outdoor unit expansion valve is set in accordance with the external air temperature detected by the external air temperature detection module 5.

[0037] It should be noted that the lubricating oil control process of this invention is a link in the air conditioning refrigeration cycle control. Each module can be shared with the modules used in other processes of air conditioning control, or it can be implemented by the control unit through software such as computer programs.

[0038] Figure 2 The execution conditions and parameters of the lubricating oil control process in the embodiments of the present invention are presented in tabular form.

[0039] Figure 3 illustrates the execution conditions and parameters of the lubricating oil control process in an embodiment of the present invention in the form of a flowchart.

[0040] As shown in Figure 3, after the initial expansion valve fixing process is completed, the process enters Stage 1 (first stage) of the lubricating oil control process in this embodiment.

[0041] In Stage 1, the compressor's upper limit frequency and the outdoor unit's expansion valve's lower limit opening are first set. In step S11, the compressor's upper limit frequency F1 is set, which is 42Hz in this embodiment. In step S12, the external air temperature T is determined. When the external air temperature T > 10℃, the outdoor unit's expansion valve's lower limit opening O11 is set, which is 90 in this embodiment; when the external air temperature 0 < T ≤ 10℃, the outdoor unit's expansion valve's lower limit opening O12 is set, which is 120 in this embodiment; when the external air temperature T ≤ 0℃, the outdoor unit's expansion valve's lower limit opening O13 is set, which is 140 in this embodiment. That is, the lower the external air temperature, the larger the outdoor unit's expansion valve's lower limit opening.

[0042] In this embodiment, the minimum running time of the lubricating oil control process in Stage 1 is set to 30 seconds, and the maximum running time of the lubricating oil control process is set to 5 minutes.

[0043] Therefore, in the next step S13, it is determined whether Stage1 has run for 30 seconds. If it has not run for 30 seconds ("No" in S13), it continues to run. If it has run for 30 seconds ("Yes" in S13), it proceeds to step S14 to detect and determine the current DSH value.

[0044] like Figure 2 As shown in Figure 3, in this embodiment, when DSH < 3, the system remains in Stage 1; when 3 ≤ DSH < 6, the system enters Stage 2; when 6 ≤ DSH < 10, the system enters Stage 3; when 10 ≤ DSH < 13, the system enters Stage 4; and when 13 ≤ DSH, the system enters Stage 5.

[0045] If DSH < 3, meaning the system remains in Stage 1, step S15 determines whether Stage 1 has already run for the maximum running time of 5 minutes. If it has not run for 5 minutes ("No" in S15), the system returns to step S14; if it has run for 5 minutes ("Yes" in S15), the system proceeds to the next stage, Stage 2, immediately following Stage 1. The purpose of setting a maximum running time is to prevent situations where, during actual operation, the DSH range for the next Stage may not be met even after a long period. Without limiting this time, the lubrication control process would run indefinitely, affecting subsequent compressor control processes, which would be counterproductive.

[0046] In Stage 2, the compressor's upper limit frequency and the outdoor unit's expansion valve's lower limit opening are first set. In step S21, the compressor's upper limit frequency F2 is set, which is 42Hz in this embodiment. In step S22, the outside air temperature T is determined. When the outside air temperature T > 10℃, the outdoor unit's expansion valve's lower limit opening O21 is set, which is 80 in this embodiment; when the outside air temperature 0 < T ≤ 10℃, the outdoor unit's expansion valve's lower limit opening O22 is set, which is 110 in this embodiment; when the outside air temperature T ≤ 0℃, the outdoor unit's expansion valve's lower limit opening O23 is set, which is 130 in this embodiment. That is, the lower the outside air temperature, the larger the outdoor unit's expansion valve's lower limit opening.

[0047] In this embodiment, the minimum running time of the lubricating oil control process in Stage 2 is set to 30 seconds, and the maximum running time of the lubricating oil control process is set to 5 minutes.

[0048] Therefore, in the next step S23, it is determined whether Stage2 has been running for 30 seconds. If it has not been running for 30 seconds ("No" in S23), it continues to run. If it has been running for 30 seconds ("Yes" in S23), it proceeds to step S24 to detect and determine the current DSH value.

[0049] As shown in Figure 3, in this embodiment, when DSH < 6, it remains in Stage 2 (because the transition of Stage cannot be reversed, so it is not necessary to determine whether the ≥3 condition in the original Stage 2 entry condition is met). When 6 ≤ DSH < 10, it enters Stage 3. When 10 ≤ DSH < 13, it enters Stage 4. When 13 ≤ DSH, it enters Stage 5.

[0050] If DSH < 6, meaning the program remains in Stage 2, step S25 determines whether Stage 2 has run for the maximum running time of 5 minutes. If it has not run for 5 minutes ("No" in S25), the program returns to step S24; if it has run for 5 minutes ("Yes" in S25), the program proceeds to the next stage, Stage 3, immediately following Stage 2.

[0051] In Stage 3, the compressor's upper limit frequency and the outdoor unit's expansion valve's lower limit opening are first set. In step S31, the compressor's upper limit frequency F3 is set, which is 48Hz in this embodiment. In step S32, the external air temperature T is determined. When the external air temperature T > 10℃, the outdoor unit's expansion valve's lower limit opening O31 is set, which is 70 in this embodiment; when the external air temperature 0 < T ≤ 10℃, the outdoor unit's expansion valve's lower limit opening O32 is set, which is 100 in this embodiment; when the external air temperature T ≤ 0℃, the outdoor unit's expansion valve's lower limit opening O33 is set, which is 120 in this embodiment. That is, the lower the external air temperature, the larger the outdoor unit's expansion valve's lower limit opening.

[0052] In this embodiment, the minimum running time of the lubricating oil control process in Stage 3 is set to 30 seconds, and the maximum running time of the lubricating oil control process is set to 3 minutes.

[0053] Therefore, in the next step S33, it is determined whether Stage3 has been running for 30 seconds. If it has not been running for 30 seconds ("No" in S33), it continues to run. If it has been running for 30 seconds ("Yes" in S33), it proceeds to step S34 to detect and determine the current DSH value.

[0054] As shown in Figure 3, in this embodiment, when DSH < 10, it remains in Stage 3 (because the transition of Stage cannot be reversed, so it is not necessary to determine whether the ≥6 condition in the original Stage 3 entry condition is met). When 10 ≤ DSH < 13, it enters Stage 4. When 13 ≤ DSH, it enters Stage 5.

[0055] If DSH < 10, meaning the stage remains in Stage 3, step S35 determines whether Stage 3 has already run for the maximum running time of 3 minutes. If it has not run for 3 minutes ("No" in S35), the process returns to step S34; if it has run for 3 minutes ("Yes" in S35), the process proceeds to the next stage, Stage 4, immediately following Stage 3.

[0056] In Stage 4, the compressor's upper limit frequency and the outdoor unit's expansion valve's lower limit opening are first set. In step S41, the compressor's upper limit frequency F4 is set, which is 54Hz in this embodiment. In step S42, the outside air temperature T is determined. When the outside air temperature T > 10℃, the outdoor unit's expansion valve's lower limit opening O41 is set, which is 70 in this embodiment; when the outside air temperature 0 < T ≤ 10℃, the outdoor unit's expansion valve's lower limit opening O42 is set, which is 90 (pulse) in this embodiment; when the outside air temperature T ≤ 0℃, the outdoor unit's expansion valve's lower limit opening O43 is set, which is 110 in this embodiment. That is, the lower the outside air temperature, the larger the outdoor unit's expansion valve's lower limit opening.

[0057] In this embodiment, the minimum running time of the lubricating oil control process in Stage 4 is set to 30 seconds, and the maximum running time of the lubricating oil control process is set to 3 minutes.

[0058] Therefore, in the next step S43, it is determined whether Stage4 has been running for 30 seconds. If it has not been running for 30 seconds ("No" in S43), it continues to run. If it has been running for 30 seconds ("Yes" in S43), it proceeds to step S44 to detect and determine the current DSH value.

[0059] As shown in Figure 3, in this embodiment, when DSH < 13, it remains in Stage 4 (because the transition of Stage cannot be reversed, so it is not necessary to determine whether the ≥10 condition in the original Stage 4 entry condition is met), and when 13 ≤ DSH, it enters Stage 5.

[0060] If DSH < 13, meaning the stage remains in Stage 4, step S45 determines whether Stage 4 has run for the maximum running time of 3 minutes. If it has not run for 3 minutes ("No" in S45), the process returns to step S44; if it has run for 3 minutes ("Yes" in S45), the process proceeds to the next stage, Stage 5, immediately following Stage 4.

[0061] In Stage 5, the compressor's upper limit frequency and the outdoor unit's expansion valve's lower limit opening are first set. In step S51, the compressor's upper limit frequency F4 is set, which is 54Hz in this embodiment. In step S52, the outside air temperature T is determined. When the outside air temperature T > 10℃, the outdoor unit's expansion valve's lower limit opening O51 is set, which is 70 in this embodiment; when the outside air temperature 0 < T ≤ 10℃, the outdoor unit's expansion valve's lower limit opening O52 is set, which is 80 in this embodiment; when the outside air temperature T ≤ 0℃, the outdoor unit's expansion valve's lower limit opening O53 is set, which is 100 in this embodiment. That is, the lower the outside air temperature, the larger the outdoor unit's expansion valve's lower limit opening.

[0062] In this embodiment, the minimum running time of the lubrication control process in Stage 5 is set to 2 minutes. Since Stage 5 is the last Stage, there is no maximum running time.

[0063] Therefore, in the next step S53, it is determined whether Stage 5 has been running for 2 minutes. If it has not been running for 2 minutes (S53 indicates "No"), it continues to run. If it has been running for 2 minutes (S53 indicates "Yes"), then Stage 5 ends, which means the lubricating oil control process ends. Then, it proceeds to the SH control process.

[0064] In Stages 1 through 5, the compressor's upper frequency limit satisfies the relationship F1 ≤ F2 ≤ F3 ≤ F4 ≤ F5, meaning the compressor's upper frequency limit gradually increases as DSH increases. The outdoor unit's expansion valve lower limit opening satisfies the relationships O11 ≥ O21 ≥ O31 ≥ O41 ≥ O51, O12 ≥ O22 ≥ O32 ≥ O42 ≥ O52, and O13 ≥ O23 ≥ O33 ≥ O43 ≥ O53, meaning that within the same external air temperature range, the outdoor unit's expansion valve lower limit opening gradually decreases as DSH increases. Furthermore, the Stage to enter is determined by judging the range of DSH values. The process proceeds sequentially from Stage 1 to Stage 5 and cannot be reversed; however, if the DSH value meets the conditions of a subsequent Stage, the intermediate Stage is skipped.

[0065] Furthermore, if the compressor is restarted after stopping, the above-mentioned lubrication control procedure needs to be repeated starting from Stage 1.

[0066] In this embodiment, precise control of the compressor lubricating oil is achieved through five stages. A minimum operating time is set to ensure necessary operation in each stage, while a maximum operating time is set to prevent a dead loop. The entire lubricating oil control process lasts from 4 to 18 minutes. Even under the worst-case scenario where DSH fails to reach the ideal range, it still achieves better control than existing technologies.

[0067] It should be noted that the values ​​in the above embodiments are merely examples and do not limit the present invention. Furthermore, the present invention is not limited to 5 stages; more than 2 stages can be set according to actual needs.

[0068] While the present invention has been specifically described above in conjunction with the accompanying drawings and embodiments, it is to be understood that the above description does not limit the invention in any way. Those skilled in the art can make modifications and variations to the present invention as needed without departing from its essential spirit and scope, and all such modifications and variations fall within the scope of the present invention.

[0069] Industrial availability

[0070] This invention ensures sufficient compressor lubricating oil quantity by closely coordinating the expansion valve opening, compressor frequency, discharge overheating, and time. This eliminates the need for an oil separator, significantly reducing costs and structurally avoiding the risk of capillary oil return pipe breakage. The combined effect of multiple conditions guarantees adequate compressor lubricating oil quantity. Therefore, it is highly useful for air conditioning control, especially for controlling the lubricating oil in multi-split air conditioning compressors.

Claims

1. A method for controlling the lubricating oil discharge of an air conditioning compressor, characterized in that: The lubricating oil control method comprises multiple stages, two or more, executed sequentially. In each stage, control is achieved using a specified upper limit compressor frequency, a specified lower limit opening of the outdoor unit expansion valve, a specified maximum operating time, and a specified minimum operating time. Control of a stage begins when the discharge overheating in that stage meets the discharge overheating range of a subsequent stage. The discharge overheat is the value obtained by subtracting the compressor high-pressure temperature from the compressor discharge temperature. The range of overheat discharge in the multiple stages increases sequentially and gradually. The minimum operating time refers to the minimum operating time of the lubricating oil control process. If the operating time is less than the minimum operating time, the control of this stage will continue even if the discharge overheating requirement is met. The maximum operating time refers to the maximum operating time of the lubricating oil control process. If the operating time is greater than the maximum operating time, the control of the next stage will proceed even if the discharge overheating requirement is not met. In each stage, the lower limit opening of the outdoor unit expansion valve is also set according to the outside air temperature; the lower the outside air temperature, the larger the lower limit opening of the outdoor unit expansion valve.

2. The lubricating oil control method for an air conditioning compressor as described in claim 1, characterized in that: Compared to the earlier stages, the later stages in the sequence of the multiple stages have the same or increased upper limit frequency of the compressor, and the same or decreased lower limit opening of the outdoor unit expansion valve.

3. The lubricating oil control method for an air conditioning compressor as described in claim 1 or 2, characterized in that: The lubricating oil control procedure is performed when the compressor is turned on, in heating mode, and in normal operating mode.

4. The lubricating oil control method for an air conditioning compressor as described in claim 1 or 2, characterized in that: The lubricating oil control process is executed after the initial expansion valve fixing process, which sets the outdoor unit expansion valve to its initial opening degree after the compressor starts.

5. The lubricating oil control method for an air conditioning compressor as described in claim 1 or 2, characterized in that: Once the compressor stops and restarts, the lubricating oil control process needs to be re-executed from the initial stage.

6. The lubricating oil control method for an air conditioning compressor as described in claim 1 or 2, characterized in that: The lubricating oil control process includes five stages executed sequentially: a first stage, a second stage, a third stage, a fourth stage, and a fifth stage. In the first stage, the discharge overheat is defined as DSH, the range of discharge overheat is DSH < 3, the upper limit frequency of the compressor is 42Hz, the maximum running time is 5 minutes, the minimum running time is 30 seconds, and the lower limit opening of the outdoor unit expansion valve is 90 pulses when the external air temperature is greater than 10℃, 120 pulses when the external air temperature is greater than 0℃ and less than or equal to 10℃, and 140 pulses when the external air temperature is less than or equal to 0℃. In the second stage, the range of overheat discharge is 3 ≤ DSH < 6, the upper limit frequency of the compressor is 42Hz, the maximum operating time is 5 minutes, the minimum operating time is 30 seconds, and the lower limit opening of the outdoor unit expansion valve is 80 pulses when the external air temperature is greater than 10℃, 110 pulses when the external air temperature is greater than 0℃ and less than or equal to 10℃, and 130 pulses when the external air temperature is less than or equal to 0℃. In the third stage, the range for discharging overheated air is 6 ≤ DSH < 10, the upper limit frequency of the compressor is 48 Hz, the maximum operating time is 3 minutes, the minimum operating time is 30 seconds, and the lower limit opening of the outdoor unit expansion valve is 70 pulses when the external air temperature is greater than 10°C, 100 pulses when the external air temperature is greater than 0°C and less than or equal to 10°C, and 120 pulses when the external air temperature is less than or equal to 0°C. In the fourth stage, the range for discharging overheat is 10 ≤ DSH < 13, the upper limit frequency of the compressor is 54 Hz, the maximum operating time is 3 minutes, the minimum operating time is 30 seconds, and the lower limit opening of the outdoor unit expansion valve is 70 pulses when the external air temperature is greater than 10°C, 90 pulses when the external air temperature is greater than 0°C and less than or equal to 10°C, and 110 pulses when the external air temperature is less than or equal to 0°C. In the fifth stage, the range of overheat discharge is 13≤DSH, the upper limit frequency of the compressor is 58Hz, there is no maximum running time, the minimum running time is 2 minutes, and the lower limit opening of the outdoor unit expansion valve is 70 pulses when the external air temperature is greater than 10℃, 80 pulses when the external air temperature is greater than 0℃ and less than or equal to 10℃, and 100 pulses when the external air temperature is less than or equal to 0℃.

7. A multi-split air conditioning unit, characterized in that: The lubricating oil discharge of the air conditioning compressor is controlled by the lubricating oil control method of any one of claims 1 to 6.

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