Gas compressor

Abstract

The purpose of the present invention is to optimize the cleaning and replacement frequency of a compressed air pre-filter and a cooling air pre-filter.　To achieve said purpose, this gas compressor comprises: an intake filter in which a compressed air pre-filter that primarily removes dust is disposed in an intake port for compressed air in a housing, and that further secondarily removes dust; at least one compressor main body that suctions air through the intake filter and an intake passage and compresses the air; a motor that drives the compressor main body; an air cooler that cools the compressed air; a cooling fan that passes cooling air to the air cooler; a cooling air intake port that suctions from outside air with the cooling fan; a cooling air pre-filter provided to the cooling air intake port; and a control device that controls the operation of the compressor. The control device determines the cleaning and replacement frequency of the compressed air pre-filter and the cooling air pre-filter on the basis of a load factor serving as an indicator of an operating state.

Description

[Technical Field]

[0001] The present invention relates to a gas compressor. [Background technology]

[0002] Among gas compressors, for example, compressors that suck in and compress gaseous air are equipped with one or more intake filters for filtering the air flowing into a compressor body that has a reciprocating or rotating body inside. The compressor body is installed in a housing that provides soundproofing and weather resistance, and an outside air filter may be further provided at the intake port of the housing to remove some dust and other particles from the outside air. A technique is known in which clean air is sucked into the compressor body using multiple stages of filters. For example, Patent Document 1 discloses this type of prior art.

[0003] Patent document 1 discloses a system for predicting the deterioration rate of turbomachinery components using condition-based monitoring, which predicts the compressor deterioration rate for a compressor using a compressor deterioration prediction model that provides a function of compressor performance based on sensor data, one or more filter deterioration rates, or some combination thereof, and performs one or more preventive actions based on the compressor deterioration rate prediction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-44546 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, regarding a filter deterioration prediction model that calculates the filter deterioration rate, it can be predicted that the amount of intake air passing through the filter and the load operating time of the compressor also have a significant impact on the prediction model, but no specific mention is made of the relationship between the compressor drive method, which is related to the air amount, the ratio between the open time and operating time of the suction valve provided in the compressor, or the load factor, which is an indicator of the operating state of the compressor, which is determined by parameters such as the rotational speed of the motor or prime mover that drives the compressor body.

[0006] Furthermore, Patent Document 1 does not specifically mention measures for determining when to clean or replace a pre-filter that primarily removes dust from the air, when the pre-filter is located further upstream of the filter house.

[0007] Furthermore, the filter in Patent Document 1 filters the air drawn into the turbo compressor body. However, in the case of a compressor equipped with an air-cooled cooler for cooling the compressed air, a cooling fan is provided, and a cooler pre-filter for the primary removal of dust may be provided at the intake port of the cooling fan, and no study equivalent to a filter deterioration prediction model for the cooler pre-filter is mentioned.

[0008] In view of the above problems, an object of the present invention is to optimize the frequency of cleaning or replacing a compressed air pre-filter and a cooling air pre-filter. [Means for solving the problem]

[0009] One example of the present invention is a gas compressor comprising: a compressed air prefilter disposed in a compressed air intake port of a housing for primary removal of dust; an intake filter for secondary removal of dust; at least one compressor body that draws in and compresses air through the intake filter and an intake passage; a motor that drives the compressor body; an air cooler that cools the compressed air; a cooling fan that passes cooling air to the air cooler; a cooling air intake port through which outside air is drawn in by the cooling fan; a cooling air prefilter disposed in the cooling air intake port; and a control device that controls operation of the compressor, wherein the control device determines the frequency of cleaning or replacement of the compressed air prefilter and the cooling air prefilter from the load factor that is an indicator of the operating state. [Effects of the Invention]

[0010] According to the present invention, the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter can be optimized. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a system diagram showing components of a gas compressor in a first embodiment. FIG. [Figure 2] 4 is a process flowchart for determining the timing of cleaning or replacing pre-filters for compressed air and cooling air in the first embodiment. [Figure 3] 10 is a process flowchart for determining the timing of cleaning or replacing a pre-filter in the second embodiment. [Figure 4] FIG. 10 is a system diagram showing components of a gas compressor according to a third embodiment. [Figure 5] FIG. 10 is a diagram showing the relationship between the output frequency of the cooling fan inverter and the inverter input current in the fourth embodiment. [Figure 6] 10 is a process flowchart for determining the timing of cleaning or replacing a pre-filter in the fourth embodiment. [Figure 7] FIG. 10 is a system diagram showing components of a gas compressor in a fifth embodiment. [Figure 8] FIG. 10 is a system diagram showing components of a gas compressor in a sixth embodiment. [Figure 9] 13 is a process flowchart for determining the timing of cleaning or replacing a pre-filter in a seventh embodiment. [Figure 10] FIG. 10 is a diagram showing a pressure loss curve and a cumulative pressure loss curve in Example 7. [Figure 11] FIG. 10 is a graph showing pressure loss versus operation time in Example 7. [Figure 12] FIG. 11 is a graph showing cumulative pressure loss versus operation time in Example 7. [Figure 13] FIG. 10 is a graph showing the slope of the cumulative pressure loss curve with respect to the operation time in Example 7. [Figure 14] 13 is a process flowchart for determining the timing of cleaning or replacing a pre-filter in the eighth embodiment. [Figure 15] 13 is a process flowchart for determining the timing of cleaning or replacing a pre-filter in a ninth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described below with reference to the drawings. [Example]

[0013] In this embodiment, an air-cooled, oil-free, two-stage screw air compressor will be described as an example of the gas compressor.

[0014] Figure 1 is a system diagram showing the components of a gas compressor in this embodiment. In Figure 1, gas compressor 1 is configured to compress air in two stages, and by driving low-pressure stage compressor main body 101 and high-pressure stage compressor main body 102, air is sucked in, compressed, and discharged.

[0015] 1 , a low-pressure stage compressor body 101, a high-pressure stage compressor body 102, a motor 103, and an oil pump 105 are fixed to a speed increaser case 104. A low-pressure stage pinion 107 is attached to the tip of the drive shaft of the low-pressure stage compressor body 101, and a high-pressure stage pinion 108 is attached to the tip of the drive shaft of the high-pressure stage compressor body 102. A bull gear 106 and an oil pump pinion 109 are fitted to the drive shaft of the motor 103 from the base side of the drive shaft. The bull gear 106 meshes with the low-pressure stage pinion 107 and the high-pressure stage pinion 108, and the oil pump pinion 109 meshes with an oil pump gear 110. When the motor 103 is driven and the bull gear 106 rotates, the low-pressure stage compressor body 101, the high-pressure stage compressor body 102, and the oil pump 105 are driven.

[0016] At the start of operation, motor 103 drives low-pressure stage compressor main body 101 and high-pressure stage compressor main body 102, and suction valve 301 is opened, so that air is sucked in from the atmosphere through compressed air prefilter 600a provided at intake port 2a of the housing of gas compressor 1, dust is primarily separated from the sucked air, the air passes through intake duct 2b, and dust is further secondarily separated by intake filter 601, and highly clean air flows into low-pressure stage compressor main body 101 via intake air path 401, which is an intake passage, and suction valve 301.

[0017] The low-pressure stage compressor main body 101 compresses air to a predetermined pressure, and the compressed air flows into the intercooler 201 through a low-pressure stage discharge air path 402. The intercooler 201 is an air-cooled heat exchanger, i.e., an air cooler, and cools the high-temperature compressed air by passing cooling air generated by a cooling fan 204 through it. The compressed air cooled by the intercooler 201 flows through a high-pressure stage suction air path 403 and into the high-pressure stage compressor main body 102, where it is compressed to a higher pressure. The high-pressure compressed air discharged from the high-pressure stage compressor main body 102 flows through a high-pressure stage discharge air path 404 and into the aftercooler 202. The aftercooler 202 is also an air-cooled heat exchanger, i.e., an air cooler, like the intercooler 201, and cools the compressed air using cooling air from the cooling fan 204. The compressed air cooled by the aftercooler 202 passes through a discharge air path 405 and is supplied to a compressed air consumer.

[0018] The compressed air prefilter 600a generally has a lower filtering accuracy than the intake air filter 601 and is intended to primarily remove relatively large foreign objects and dust, thereby delaying clogging of the intake air filter 601. Similarly, attaching the cooling air prefilter 600b to the cooling air intake port 3a similarly removes relatively large foreign objects and dust, so that the air drawn in by the cooling fan 204 through the cooling air intake port 3a and the cooling air duct 3b is purified to a certain extent, reducing dust clogging of the cooling fins of the air-cooled intercooler 201, aftercooler 202, and oil cooler 203. After passing through the intercooler 201, aftercooler 202, and oil cooler 203 and exchanging heat with the high-temperature compressed air and lubricating oil, the cooling air passes through the fan duct 4b and is discharged to the atmosphere through the exhaust port 4a.

[0019] The low-pressure stage compressor body 101, the high-pressure stage compressor body 102, the speed increaser case 104, and the oil pump 105 each have built-in bearings that support internal rotating bodies (not shown), and since the bull gear 106, the low-pressure stage pinion 107, the high-pressure stage pinion 108, the oil pump pinion 109, and the oil pump gear 110 rotate while meshing with each other, these mechanical parts generally require lubricant, and in this embodiment, lubricating oil is stored in the lower part of the speed increaser case 104.

[0020] When the oil pump 105 is driven by the motor 103, lubricating oil is sucked from the bottom of the speed increaser case 104, passes through the suction oil piping 411, flows into the oil pump 105, and is discharged. The lubricating oil discharged from the oil pump 105 passes through a discharge oil path 412, is cooled by an oil cooler 203, which is an air-cooled heat exchanger, and is then sent to a main oil supply path 413. An oil filter 603 is installed midway along the main oil supply path 413. The main oil supply path 413 also branches into a low-pressure stage oil supply path 414, a high-pressure stage oil supply path 415, and a speed increaser oil supply path 416, and supplies lubricating oil to the low-pressure stage compressor body 101, the high-pressure stage compressor body 102, and the speed increaser case 104.

[0021] On the compressed air path, there is an air release device for releasing compressed air remaining in the compressed air path to the outside when the gas compressor is operating without load or when operation is stopped, and air release valve 302 and air release valve 303 release compressed air on the air path from the discharge side of high-pressure stage compressor main body 102 to check valve 304 to the outside.

[0022] Various detectors are installed at various locations inside gas compressor 1 so that control device 703 can determine whether the gas compressor is operating normally and control the operation of the gas compressor. For example, a suction pressure sensor 501 is provided on suction air path 401, a low-pressure stage discharge air temperature sensor 505 is provided on low-pressure stage discharge air path 402, a high-pressure stage suction air pressure sensor 502 and a high-pressure stage suction air temperature sensor 506 are provided on high-pressure stage suction air path 403, a high-pressure stage discharge air temperature sensor 507 is provided on high-pressure stage discharge air path 404, and a discharge air pressure sensor 503 is provided on discharge air path 405. In addition, an oil pressure sensor 504 and an oil temperature sensor 508 are provided on low-pressure stage oil supply path 414.

[0023] The operation of gas compressor 1 is input to display and input device 701, and based on the input values, control device 703 controls and outputs all of the electric and electronic devices of gas compressor 1. Control device 703 also receives inputs from various detectors inside the gas compressor, and monitors, judges, and controls the operating state of the gas compressor based on a program previously set in storage device 702.

[0024] The antenna 704 is a wireless transceiver device for transmitting and receiving values ​​detected by various detection devices built into the gas compressor 1 and information stored in the memory device 702 to and from an external server 802 via the communication network 801.

[0025] A viewer in a remote location (not shown) can view the information about the gas compressor stored in the external server 802 via various information terminals.

[0026] Fig. 2 is a process flowchart for determining the timing of cleaning or replacing pre-filters for compressed air and cooling air, performed by the gas compressor 1 of Fig. 1 in this embodiment. Note that the low-pressure stage compressor body 101 and the high-pressure stage compressor body 102 in this embodiment are fixed-speed machines in which the motor 103 is driven at a constant speed based on the power supply frequency, and the cooling fan 204 is also under fixed-speed control in which it is operated at a constant rotational speed based on the power supply frequency.

[0027] When the operator of gas compressor 1 performs an operation to start operation using display and input device 701, motor 103 starts, driving low-pressure stage compressor main body 101 and high-pressure stage compressor main body 102, and suction valve 301 opens. Air drawn in from the atmosphere passes through compressed air pre-filter 600a and intake filter 601, with most of the dust removed, and then flows into low-pressure stage compressor main body 101, where it is compressed in the first stage. Thereafter, the air flows in the direction of flow in the system diagram of FIG. 1, and finally, the compressed air that has reached a predetermined pressure is supplied from discharge air path 405 to a compressed air demand destination.

[0028] At the same time as the motor 103 starts, the cooling fan 204 also starts, and the outside air is passed through the cooling air pre-filter 600b to remove most of the dust, and then passes through the intercooler 201, the aftercooler 202, and the oil cooler 203 to exchange heat with the high-temperature fluid, before being exhausted from the exhaust port 4a.

[0029] 2, when motor 103 starts, suction valve 301 opens, and air begins to be sucked in. If suction pressure Ps (a negative value because it is a gauge pressure) detected by suction pressure sensor 501 is greater than Ps0 relative to a preset suction pressure warning value Ps0, the process proceeds to step S103. If Ps≦Ps0, this indicates that the intake filter is clogged. This increases the pressure ratio inside the compressor body, potentially causing the discharge air temperature to become abnormally high, which could lead to a malfunction. To prevent this, the process proceeds to step S102, where an alarm is quickly displayed on display / input device 701 and external server 802 via communication network 801, or on an information terminal (not shown) remotely monitoring the system via server 802. The process then ends.

[0030] In step S103, if the cumulative operating time Hc from the last cleaning instruction to the present is an integral multiple of the predetermined determination cycle H, the process proceeds to step S104, and if not, the process ends.

[0031] Next, in step S104 and subsequent steps, the frequency of cleaning or replacing the prefilter is determined. However, cleaning or replacing both prefilters simultaneously, regardless of whether they are cooling air prefilters or compressed air prefilters, is preferable to maintain the performance and reliability of the gas compressor. Therefore, the average load factor R of the gas compressor and the average load factor Rf of the cooling fan may be compared, and the greater load factor may be used to determine the frequency of cleaning or replacing the prefilter. Alternatively, in the case of fixed-speed control in which cooling fan 204 is always operated at a constant rotational speed regardless of the operating state of gas compressor 1, the frequency of cleaning or replacing the prefilter may be determined based solely on the average load factor R of the gas compressor. Therefore, although the following processing will be described using the average load factor R of the gas compressor, if the average load factor Rf of the cooling fan is used, R is replaced with Rf.

[0032] In step S104, if the average load factor R of the gas compressor satisfies R≦RM with respect to the medium load factor determination value RM, the process proceeds to step S106, and if not, the process proceeds to step S105.

[0033] Here, the average load factor R is defined as follows. That is, in the case where the rotation speed of the motor 103 is fixed, for example, if a cycle in which one load operation and one no-load operation are performed is defined as an operation cycle time T3, the current load factor Rc [%] is calculated as follows: current load factor Rc [%] = loaded operation time T2 ÷ operation cycle time T3. Here, operation cycle time T3 = no-load operation time T1 + loaded operation time T2. Note that T1, T2, and T3 refer to the respective times in the operation cycle immediately preceding the operation cycle in which the gas compressor is currently operating. The current load factor Rc is summed up for the number of loads (= number of operation cycles) N from the last load factor determination to the present, and this is divided by N to obtain the average load factor R. In other words, the average load factor R can be expressed as average load factor R = ΣRc / N.

[0034] If it is determined in step S104 that R>RM and the process proceeds to step S105, a predetermined high frequency cleaning cycle HH, for example, 100 hours, is substituted into the pre-filter determination cycle H, and the process proceeds to step S109.

[0035] If it is determined in step S104 that R≦RM and the process proceeds to step S106, and if the average load factor R satisfies R≦RL with respect to the low load factor determination value RL, the process proceeds to step S108. If this is not satisfied, the process proceeds to step S107.

[0036] In step S107, the normal cleaning cycle HM, for example, 200 hours, is substituted for the pre-filter determination cycle H, and the process proceeds to step S109. If it is determined in step S106 that R≦RL and the process proceeds to step S108, the low frequency cleaning cycle HL, for example, 400 hours, is substituted for the pre-filter determination cycle H, and the process proceeds to step S109.

[0037] In step S109, the difference H-Hc between the cumulative operating time Hc from the last cleaning instruction to the present and the pre-filter judgment cycle H assigned in the steps before step S109 is calculated, and if H-Hc≦0 is satisfied, that is, the cumulative operating time Hc from the last cleaning instruction to the present exceeds the cycle (judgment cycle H) for cleaning the pre-filter, it is determined that it is time to clean the pre-filter, and the process proceeds to step S110, where a message recommending cleaning or replacement of the pre-filter is displayed on display / input device 701, and data recommending cleaning or replacement of the pre-filter is transmitted to server 802 via communication network 801. Thereafter, the process proceeds to step S111, where the cumulative operating time Hc from the last cleaning instruction to the present is initialized to 0, and this flowchart ends.

[0038] If H-Hc≦0 is not satisfied in step S109, that is, if the cumulative operating time Hc from the last cleaning instruction to the present has not reached the determination period H, this flowchart ends.

[0039] According to the flowchart in Figure 2, the load rate of the gas compressor is related to the amount of air passing through the intake compressed air prefilter 600a. If the average load rate R is higher than the medium load rate judgment value RM, the amount of air passing through the compressed air prefilter 600a increases, and the amount of dust captured by the compressed air prefilter 600a also increases proportionally. In this case, the high-frequency cleaning cycle HH is selected as the recommended cleaning cycle, and it is determined that it is desirable to clean or replace the prefilter more frequently than usual.

[0040] On the other hand, when the average load rate R is lower than the low load rate judgment value RL, the amount of dust captured by the compressed air prefilter 600a is also reduced, so the cleaning frequency is reduced. Therefore, the low frequency cleaning cycle HL is selected, the prefilter cleaning cycle is extended, and the user can reduce the number of times the prefilter needs to be cleaned.

[0041] As described above, according to this embodiment, it is possible to optimize the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter depending on the type and load factor of the gas compressor. [Example]

[0042] In this embodiment, an example will be described in which a command to clean or replace a pre-filter is given in consideration of a change in input current to a cooling fan.

[0043] The system diagram showing the components of the gas compressor in this embodiment differs from the configuration in FIG. 1 in that it is equipped with an ammeter for measuring the input current of the cooling fan 204, and the system diagram is omitted here.

[0044] Figure 3 is a process flowchart for determining when to clean or replace the pre-filter in this embodiment. In Figure 3, the same process steps as in Figure 2 are given the same reference numerals, and their explanations will be omitted. Figure 3 differs from Figure 2 in that step S201 has been added.

[0045] In the case of fixed-speed control in which the cooling fan 204 is constantly operated at a constant speed based on the power supply frequency, as the cooling air prefilter 600b becomes increasingly clogged, the amount of air drawn in through the cooling air intake port 3a decreases. When the amount of drawn air decreases, the power consumption of the cooling fan decreases compared to when the cooling air prefilter 600b is less clogged, and the input current value also decreases. Therefore, in step S201, a predetermined threshold value Ith is set for the input current If of the cooling fan 204. If the cooling fan input current If is smaller than the predetermined threshold value Ith, it is determined that the cooling air prefilter 600b has become significantly clogged, and an instruction to clean or replace the cooling air prefilter 600b, or both the cooling air prefilter 600b and the compressed air prefilter 600a, is displayed on the display / input device 701 to prompt the user to take appropriate action.

[0046] As described above, according to this embodiment, in addition to the effect of the first embodiment, there is an effect that clogging of the cooling air pre-filter 600b can be determined in advance. [Example]

[0047] In this embodiment, a case will be described in which the cooling fan is inverter-driven and the rotational speed is variably controlled.

[0048] Figure 4 is a system diagram showing the components of the gas compressor in this embodiment. In Figure 4, the same components as in Figure 1 are assigned the same reference numerals, and their explanation will be omitted. Figure 4 differs from Figure 1 in that control device 703 is equipped with a cooling fan inverter 703a, which is a variable speed control device for the cooling fan.

[0049] The processing flowchart of Fig. 4 for determining the timing of cleaning or replacing the compressed air and cooling air pre-filters performed by gas compressor 1 in this embodiment is the same as Fig. 2, but in the case of a cooling fan that is inverter-driven and has variable speed control, the method of calculating the average load factor differs from that in the case of a fixed speed. For example, in the case of an inverter-driven cooling fan, the current load factor Rfc of the cooling fan is calculated as (load time T2 · fan inverter current frequency ffc [Hz]) ÷ (operation cycle time T3 · fan inverter rated frequency ffr [Hz]), and this is averaged over the N load counts from the last load factor determination to the last operation cycle to obtain the cooling fan average load factor Rf [%] = ΣRfc / N.

[0050] As described above, according to this embodiment, similar to the first embodiment, it is possible to optimize the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter depending on the type and load factor of the gas compressor. [Example]

[0051] In the second embodiment, an example was described in which a command to clean or replace a pre-filter is given in consideration of changes in the input current to the cooling fan. However, in the second embodiment, while cooling fan 204 is controlled at a fixed speed, if the cooling fan is controlled at a variable speed, for example, if the rotation speed of cooling fan 204 is controlled to be lower during no-load operation than during loaded operation, the input current to cooling fan 204 also decreases due to the decrease in rotation speed, and therefore simply determining the clogged state of the pre-filter based only on the threshold value of the input current does not necessarily result in an accurate determination.

[0052] Therefore, in this embodiment, an example will be described in which clogging of the cooling air pre-filter 600b can be determined in advance when the cooling fan is inverter-driven and the rotation speed is variably controlled.

[0053] The system diagram showing the components of the gas compressor in this embodiment is configured to include an ammeter that measures the input current of the cooling fan inverter 703a, as compared to the configuration in Figure 4, but the other configurations are the same, so the description thereof will be omitted.

[0054] Fig. 5 shows the relationship between the output frequency of the cooling fan inverter and the inverter input current value in this embodiment. In Fig. 5, the relationship between the output frequency ffc of the cooling fan inverter and the input current Iif of the cooling fan inverter is such that when the pre-filter is clogged, the input current Iif drops compared to when the pre-filter is normal, for the same output frequency ffc.

[0055] Fig. 6 is a process flowchart for determining when to clean or replace the pre-filter in this embodiment. In Fig. 6, the same process steps as in Fig. 3 are given the same reference numerals, and their explanations will be omitted. Fig. 6 differs from Fig. 3 in that step S201 is replaced with step S301.

[0056] In step S301 of Fig. 6, the characteristics of the cooling fan inverter output frequency ffc and the cooling fan inverter input current Iif, as assumed in advance, are grasped as shown in Fig. 5, and if the actually measured cooling fan inverter input current Iif is, for example, 60% or less of the predicted inverter input current Io at a predetermined output frequency, it is determined that the cooling air pre-filter 600b is clogged, and instructions for cleaning or replacement are displayed on the display / input device 701 to prompt the user to take caution and take action. Note that the value of 60% or the like is related to the frequency of pre-filter clogging, so it is desirable to make it a parameter that can be adjusted by the user depending on the actual installation environment of the gas compressor 1.

[0057] As described above, according to this embodiment, in addition to the effect of the third embodiment, there is an effect that clogging of the cooling air pre-filter 600b can be determined in advance. [Example]

[0058] In this embodiment, the gas compressor is a variable speed machine in which the rotation speed of the motor can be controlled by a motor inverter, which is a frequency conversion device, and the cooling fan is inverter-driven and its rotation speed is variably controlled.

[0059] Figure 7 is a system diagram showing the components of the gas compressor in this embodiment. In Figure 7, the same components as in Figure 4 are assigned the same reference numerals, and their explanation will be omitted. Figure 4 differs from Figure 4 in that a motor inverter 703b, which is a variable speed control device, is provided inside the control device 703.

[0060] The process flowchart of FIG. 7 for determining when to clean or replace the compressed air and cooling air prefilters performed by the gas compressor 1 in this embodiment is the same as that shown in FIG. 2. However, in the case of a variable-speed compressor in which the motor rotation speed can be controlled by the motor inverter 703b, the method for calculating the average load factor differs from that of a fixed-speed compressor. For example, the rotation speed of the motor 103 is changed by varying the inverter output frequency so that the discharge air pressure remains constant during load operation. The current load factor Rc can be expressed as Rc [%] = (load time T2 · current frequency fc [Hz]) ÷ (operation cycle time T3 · rated frequency fr [Hz]). Therefore, the average load factor R [%] of the variable-speed compressor during the prefilter cleaning determination cycle can be calculated as ΣRc / (load count N [times]).

[0061] As described above, according to this embodiment, similar to the first and third embodiments, it is possible to optimize the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter depending on the type and load factor of the gas compressor. [Example]

[0062] In the fifth embodiment, the intake port 2a for compressed air and the intake port 3a for cooling air are separate and independent from each other. However, in this embodiment, it is possible to use an intake port 3a for cooling air that also serves the function of the intake port 2a for compressed air.

[0063] Figure 8 is a system diagram showing the components of a gas compressor in this embodiment. In Figure 8, the same components as in Figure 7 are assigned the same reference numerals, and their description will be omitted. Figure 8 differs from Figure 7 in that there is no compressed air intake port 2a, and the cooling air intake port 3a also functions as the compressed air intake port 2a. There is also no compressed air prefilter 600a, and the cooling air prefilter 600b also functions as the compressed air prefilter 600a.

[0064] Thus, in this embodiment, even in a configuration in which the cooling air intake port 3a also serves as the compressed air intake port 2a, it is possible to optimize the frequency of cleaning or replacing the pre-filter that serves both the compressed air and the cooling air depending on the type and load factor of the gas compressor, just as in the fifth embodiment.

[0065] The configuration in which cooling air intake 3a also serves as compressed air intake 2a can be applied to each combination of fixed speed or variable speed gas compressors, or fixed speed or variable speed control cooling fans, as shown in Examples 1 to 3. [Example]

[0066] In this embodiment, in contrast to the first embodiment, the suction pressure Ps is considered to be a pressure loss (pressure drop) relative to atmospheric pressure, and the absolute value of the suction pressure (a negative value with atmospheric pressure as the zero reference) is taken as the pressure loss δp. This is then accumulated over the operating time to determine the cumulative pressure loss S. The method of estimating the degree of clogging of the prefilter and increasing or decreasing the determination cycle will be described below.

[0067] Fig. 9 is a process flowchart for determining the timing of cleaning or replacing the pre-filters for compressed air and cooling air, which is performed by the gas compressor 1 of Fig. 1 in this embodiment. In Fig. 9, instead of steps S104 to S109 in Fig. 2, step S113 is performed to determine whether the relationship (ΔSn-1 / Hn-1)<(ΔSn / Hn) holds between the slope ΔSn / Hn of the cumulative pressure loss curve at the time of the current determination and the slope ΔSn-1 / Hn-1 of the cumulative pressure loss curve at the time of the previous determination, and step S113 is performed to determine whether the relationship (ΔSn / Hn)<(ΔSn-1 / Hn-1) holds when step S113 does not hold. Step S115 determines whether the gradient ΔS1 / H1 of the cumulative pressure loss between the first and second pre-filter cleaning instructions and the gradient ΔSn / Hn of the current cumulative pressure loss satisfies (ΔS1 / H1)<(ΔSn / Hn), if the result of step S115 is not satisfied. Step S119 determines whether the gradient ΔS1 / H1 of the cumulative pressure loss between the first and second pre-filter cleaning instructions and the gradient ΔSn / Hn of the current cumulative pressure loss satisfies (ΔS1 / H1)<(ΔSn / Hn), steps S114 and S118 determine whether the relationship of average load rate R≦medium load rate judgment value RM satisfies (ΔS1 / H1)<(ΔSn / Hn), and steps S116 and S118 determine whether the relationship of average load rate R≦low load rate judgment value RL satisfies (ΔS1 / H1)<(ΔSn / Hn). Steps S116 and S120, steps S123 and S122, in which the judgment period Hn is multiplied by a decrease coefficient α1 or α2 (where α2<α1<1) for shortening the judgment period, and a new judgment period Hn is assigned as the result; steps S117, S124, and S126, in which the current judgment period Hn is maintained; and steps S117, S124, and S126, in which the judgment period Hn is multiplied by an increase coefficient β1 or β2 (where 1<β1<β2) for extending the judgment period, and a new judgment period Hn is assigned as the result. In place of S125 and S121 and step S109 in FIG. 2, the following steps have been newly added: step S127 for determining whether the judgment period Hn is equal to or less than the lower limit judgment period HLL; step S128 for substituting the lower limit judgment period HLL for the judgment period Hn if step S127 is satisfied; step S129 for determining whether the judgment period Hn is equal to or greater than the upper limit judgment period HHH; and step S130 for substituting the upper limit judgment period HHH for the judgment period Hn if step S129 is satisfied.

[0068] FIG. 10 shows the pressure loss curve and cumulative pressure loss curve for this embodiment, with the horizontal axis representing operating time, the left vertical axis representing pressure loss δp, and the right vertical axis representing cumulative pressure loss S. In FIG. 10, for example, when a compressor is equipped with only an intake filter and no pre-filter, and the compressor load factor is always constant, the pressure loss curve 900 is a stepped graph (due to digital values). The pressure loss δp begins to rise at approximately 80% of the operating time (the right end of the graph), which is the point at which an intake filter clogging alarm is issued. Thereafter, the pressure loss increases rapidly over a short period of time, triggering the intake filter clogging alarm. On the other hand, when a pre-filter is used, the pressure loss curve 910 shows that the pressure loss δp rises within a short period of time as the pre-filter becomes clogged, then drops when the pre-filter is cleaned or replaced, indicating a peak in pressure loss due to pre-filter clogging and cleaning. However, in addition to pre-filter and intake filter clogs, the pressure loss δp also changes depending on the compressor load factor, and the compressor load factor changes more rapidly and dramatically than the progression of filter clogs. Therefore, it is difficult to use the instantaneous value of pressure loss δp to determine pre-filter clogs. Therefore, a cumulative pressure loss curve is calculated, which is a function of the operating time t and accumulates the measured pressure loss δp.

[0069] In FIG. 10, compared to cumulative pressure loss curve 950 without a prefilter, cumulative pressure loss curve 960 with a prefilter has a further increase in cumulative pressure loss due to the addition of pressure loss caused by clogging of the prefilter, and the cumulative pressure loss is greater in cumulative pressure loss curve 960 with a prefilter than in cumulative pressure loss curve 950 without a prefilter.

[0070] FIG. 11 is a graph showing pressure loss Δp versus operating time t in this embodiment. The cumulative pressure loss Sn = Σ(Δpn) from operating time 0 to operating time tn for the nth determination. Here, the difference between operating time tn-1 for the (n-1)th determination and operating time tn for the nth determination is the determination cycle Hn, and the increment of cumulative pressure loss Sn over the determination cycle Hn is ΔSn. In FIG. 11, the increment ΔSn of cumulative pressure loss from the (n-1)th determination to the nth determination is equal to the area surrounded by the operating time tn, operating time tn-1, and the curve for pressure loss Δp.

[0071] Fig. 12 is a graph showing the cumulative pressure loss S versus operating time t in this embodiment, with the horizontal axis representing operating time, corresponding to Fig. 11. In Fig. 12, the cumulative pressure loss curve 970 always increases upward to the right, but the magnitude of the slope varies depending on the degree of clogging of the prefilter and the load factor of the compressor. Here, the increment ΔSn (=Sn - (Sn-1)) in the cumulative pressure loss per determination cycle Hn is expressed as the slope of the cumulative pressure loss ΔSn / Hn, and the slope of the cumulative pressure loss at the immediately previous determination, i.e., the (n-1)th determination cycle Hn-1, is similarly expressed as (ΔSn-1 / Hn-1). In Figure 11, the lengths of the judgment cycle Hn-2 (= (tn-2) - (tn-3)) and the judgment cycle Hn-1 (= (tn-1) - (tn-2)) are assumed to be equal, and the pressure loss Δp during this period is constant, so the curve of the cumulative pressure loss S in Figure 12 has the same slopes (ΔSn-2 / Hn-2) and (ΔSn-1 / Hn-1) for the judgment cycle Hn-2 and the judgment cycle Hn-1. On the other hand, the pressure loss Δp increases during the judgment cycle Hn-1 (=(tn-1)-(tn-2)) and judgment cycle Hn (=(tn)-(tn-1)) in Figure 11, and at this time, the increment in cumulative pressure loss ΔSn is larger than ΔSn-1 and ΔSn-2, so the slope ΔSn / Hn is larger than (ΔSn-2 / Hn-2) and (ΔSn-1 / Hn-1).

[0072] FIG. 13 compares the slopes ΔS / H980 and ΔS' / H990 of the cumulative pressure loss curves without and with a prefilter, respectively, for the cumulative pressure loss curve 950 without a prefilter and the cumulative pressure loss curve 960 with a prefilter in FIG. 10 . It can be seen that the slope ΔS / H980 of the cumulative pressure loss curve without a prefilter rapidly increases over the course of operation, as clogging of the intake filter 601 progresses rapidly from the middle of the operation. Meanwhile, the slope ΔS' / H990 of the cumulative pressure loss curve with a prefilter also fluctuates and peaks as the prefilter becomes clogged and the clogging is removed by cleaning. Calculating the slope of the cumulative pressure loss in this way makes it easier to determine the state of prefilter clogging.

[0073] Furthermore, as shown in Figure 9, by combining this with the average load rate R of the compressor, for example, when the load rate is high, it is possible to separate the increase in cumulative pressure loss caused by a large amount of air passing through the filter from the increase in cumulative pressure loss caused by the progression of clogging of the pre-filter.This makes it possible to change the pre-filter cleaning determination cycle H depending on the degree of filter clogging.

[0074] For example, in FIG. 9, at step S113, if (ΔSn-1 / Hn-1) < (ΔSn / Hn) holds, the process proceeds to step S114. This means that the pressure loss has increased compared to the previous determination. At step S114, if R ≦ RM does not hold, it is determined as a high load factor, and the process proceeds to step S117. Since it is estimated that the pressure loss is large at a high load factor, the determination period H is maintained at the current determination period. On the other hand, if R ≦ RM holds at step S114, the process proceeds to step S116. Here, if R ≦ RL holds, it is determined as a low load factor, and the process proceeds to step S122. At this time, although the load factor is low, since the pressure loss is large, it is determined that the clogging of the pre-filter has progressed considerably, and it is updated to a shorter determination period Hn × α2 obtained by multiplying the current determination period Hn by the reduction coefficient α2. On the other hand, if R ≦ RL does not hold at step S116, that is, it is determined as a medium load factor in the range of RL < R ≦ RM, at the next step S123, it is updated to a shorter determination period Hn × α1 obtained by multiplying the current determination period Hn by the reduction coefficient α1. Here, the reduction coefficients have the relationship of α2 < α1 < 1, and as a result, the determination period H is shortened as the load factor becomes smaller and the pressure loss becomes larger.

[0075] On the other hand, if (ΔSn-1 / Hn) < (ΔSn / Hn) does not hold in step S113, the process proceeds to step S115. In step S115, it is further determined whether (ΔSn / Hn) < (ΔSn-1 / Hn-1) holds. If it holds, the process proceeds to step S118. If it does not hold, that is, (ΔSn / Hn) = (ΔSn-1 / Hn-1), which means there is no change in the pressure loss in the previous and current determination periods, the process proceeds to step S119. In step S118, if R ≤ RM holds, the process proceeds to the next step S120. If R ≤ RL holds in step S120, it is determined as a low load factor, and the process proceeds to step S124. At this time, it is determined that the pressure loss is small at a low load factor, and the determination period Hn is maintained as the current determination period. On the other hand, if R ≤ RM does not hold in step S118, it is determined as a high load factor, and the process proceeds to step S121. Since it is estimated that the pressure loss is small at a high load factor, it can be judged that the progress of the pre-filter clogging is slow, so it is updated to a longer determination period Hn × β2, which is the current determination period Hn multiplied by the increase factor β2. If R ≤ RL does not hold in step S120, that is, it is determined as a medium load factor in the range of RL < R ≤ RM, and in the next step S125, it is updated to a long determination period Hn × β1, which is the current determination period Hn multiplied by the increase factor β1. Here, the increase factor has the relationship of 1 < β1 < β2, and as a result, the larger the load factor is in the state where the pressure loss is small, the longer the determination period Hn is extended.

[0076] If the step S115 is not satisfied, the process proceeds to step S119. In step S119, the initial cumulative pressure loss slope ΔS1 / H1 obtained from the increase in the cumulative pressure loss ΔS1 during the determination period H1 hours between the first pre-filter determination after the compressor starts operating and the second pre-filter determination is compared with the cumulative pressure loss slope ΔSn / Hn at the current determination. If (ΔS1 / H1) < (ΔSn / Hn) holds, the process proceeds to step S126, and the current determination period Hn is substituted into Hn to maintain the length of the determination period. If it does not hold, the process merges into the load factor determination flow of step S118. As an effect of step S119, even if the slopes of the pressure losses in the previous and current determination periods are the same and have not changed, if the clogging of the pre-filter progresses and the absolute value of the slope is large, it is preferable not to extend the determination period Hn. Therefore, as one of the evaluation criteria for the slope of the cumulative pressure loss, the initial cumulative pressure loss slope ΔS1 / H1 and the cumulative pressure loss slope ΔSn / Hn at the current determination are compared. When (ΔS1 / H1) < (ΔSn / Hn) holds, the length of the determination period is maintained. The initial cumulative pressure loss slope ΔS1 / H1 is assumed to have a small degree of clogging of the intake filter 601, and it is expected that the influence of the slope of the cumulative pressure loss due to the clogging of the pre-filter is likely to appear. By using the slope ΔS1 / H1 of the cumulative pressure loss at this time as an evaluation criterion, the validity of the cumulative pressure loss slope ΔSn / Hn at the current determination is improved.

[0077] The judgment period Hn varies depending on the magnitude of the slope of the cumulative pressure loss and the magnitude of the average load factor, but to prevent the judgment period updated in steps S121, S122, S123, and S125 from continually shortening due to the decrease coefficient α or continually lengthening due to the increase coefficient β under certain conditions, an upper limit judgment period HHH and a lower limit judgment period HLL are predetermined to prevent the judgment period H from changing beyond these upper and lower limit periods. After steps S122 and S123 have been completed, the process proceeds to step S127, where if Hn≦HLL is satisfied, HLL is substituted for the judgment period Hn, and the process proceeds to step S110. Similarly, after steps S121 and S125 have been completed, the process proceeds to step S129, where if HHH≦Hn is satisfied, HHH is substituted for the judgment period Hn, and the process proceeds to step S110. If the process has passed through steps S117, S124, and S126, the determination cycle Hn remains the same as that at the time of the previous determination, and the process proceeds to step S110.

[0078] As described above, according to this embodiment, the combination of the slope ΔS of the cumulative pressure loss curve and the average load factor R makes it easy to determine the clogged state of the prefilter. As in the first embodiment, it becomes possible to optimize the frequency of cleaning or replacing the compressed air prefilter and the cooling air prefilter depending on the type and load factor of the gas compressor. [Example]

[0079] In this embodiment, as compared with the seventh embodiment, an example will be described in which, similar to the second embodiment, an instruction to clean or replace a pre-filter is given in consideration of a change in input current to a cooling fan.

[0080] Figure 14 is a process flowchart for determining when to clean or replace the pre-filter in this embodiment. In Figure 14, the same process steps as in Figure 9 are given the same reference numerals, and their explanations will be omitted. Figure 14 differs from Figure 9 in that step S201 has been added. In FIG. 14, as explained in FIG. 3, in step S201, a predetermined threshold value Ith is set for the input current If of the cooling fan 204, and if the cooling fan input current If is smaller than the predetermined threshold value Ith, it is determined that the cooling air pre-filter is considerably clogged, and the process proceeds to step S102, where an alarm is displayed.

[0081] As described above, according to this embodiment, in addition to the effect of the seventh embodiment, there is an effect that clogging of the cooling air pre-filter can be determined in advance. [Example]

[0082] In contrast to the eighth embodiment, the present embodiment will describe an example in which clogging of the cooling air pre-filter 600b can be determined in advance when the cooling fan is inverter-driven and the rotation speed is variably controlled, similar to the fourth embodiment.

[0083] Figure 15 is a process flowchart for determining when to clean or replace the pre-filter in this embodiment. In Figure 15, the same process steps as in Figure 14 are given the same reference numerals, and their explanations will be omitted. Figure 15 differs from Figure 14 in that step S201 is replaced with step S301.

[0084] In FIG. 15, as explained in FIG. 6, if the actually measured inverter input current Iif for the cooling fan is, for example, 60% or less of the predicted value Io of the inverter input current at a predetermined output frequency, it is determined that the cooling air pre-filter is clogged, and the process proceeds to step S102, where an alarm is displayed.

[0085] As described above, according to this embodiment, as in the eighth embodiment, there is an effect that clogging of the cooling air pre-filter can be determined in advance.

[0086] Although the embodiments have been described above, the present invention is not limited to the above-described embodiments and includes various modifications. For example, the gas compressor described in the above-described embodiments is an oil-free two-stage screw air compressor, but is not limited to this type of fluid machine. For example, the present invention may be applied to a single-stage compressor having only one compressor body, or to an oil-injected compressor in which lubricating oil is injected into the compression chamber inside the compressor body for the purposes of cooling and sealing the compressed air and lubricating the sliding surfaces of a pair of male and female screw rotors (not shown).

[0087] Furthermore, although the gas compressors of the above-described first to ninth embodiments are air-cooled, even water-cooled compressors have an intake port 2a for compressed air, and furthermore, when a small cooling fan is provided for ventilation inside the housing or when a self-cooling fan is provided on the anti-load side of the motor 103, an intake port 3a for cooling air is often provided regardless of size, so the above-described embodiments can also be applied to water-cooled compressors.

[0088] Similarly, the compression method is not limited to the twin-screw type incorporating a pair of male and female screw rotors as in the above-described embodiment, but can also be applied to single-screw types consisting of one screw rotor and multiple gate rotors, tooth types, reciprocating types, and any other positive displacement compressor, as well as centrifugal and axial flow turbo compressors.

[0089] Furthermore, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0090] 1: gas compressor, 2a: intake port, 2b: intake duct, 3a: cooling air intake port, 3b: cooling air duct, 101: low-pressure stage compressor body, 102: high-pressure stage compressor body, 103: motor, 201: intercooler, 202: aftercooler, 204: cooling fan, 600a: compressed air prefilter, 600b: cooling air prefilter, 601: intake filter, 701: display and input device, 702: storage device, 703: control device, 703a: cooling fan inverter, 703b: motor inverter, 900, 910 : Pressure loss curve, 950, 960, 970: Cumulative pressure loss curve, 980, 990: Slope of cumulative pressure loss curve, Ps: Suction pressure, Ps0: Suction pressure alarm set value, R: Average load factor of gas compressor, Rc: Current load factor of gas compressor, Rf: Average load factor of cooling fan, Rfc: Current load factor of cooling fan, RH: High load factor judgment value, RM: Medium load factor judgment value, RL: Low load factor judgment value, HH: High frequency cleaning cycle, HM: Normal cleaning cycle, HL: Low frequency cleaning cycle, Hc: Cumulative operating time from the last cleaning instruction to the present, H: Judgment cycle

Claims

1. a compressed air pre-filter disposed in a compressed air intake port of a housing for primary removal of dust, an intake filter for secondary removal of dust, at least one compressor body that draws in and compresses air through said intake filter and an intake passage, a motor that drives said compressor body, an air cooler that cools the compressed air, a cooling fan that passes cooling air to said air cooler, a cooling air intake port that draws in outside air by said cooling fan, a cooling air pre-filter provided in said cooling air intake port, and a control device that controls operation of the compressor, the control device determines the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter based on a load factor that is an index of an operating state; The compressor body is a fixed speed machine, Assuming that the operation cycle time for performing one load operation and one no-load operation of the compressor main body is T3, the no-load operation time is T1, the load operation time is T2, the number of operation cycles is N, T3 = T1 + T2, the current load factor Rc = T2 ÷ T3, and the average load factor R = ΣRc / N, The control device calculates the average load rate R as the load rate, and compares the average load rate R with a load rate judgment value to determine the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter. A gas compressor characterized by:

2. 2. The gas compressor according to claim 1, The cooling fan is fixed speed controlled, The control device calculates an average load factor Rf of the cooling fan, compares the average load factor R of the compressor body with the average load factor Rf of the cooling fan, and uses the larger load factor value to determine the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter. A gas compressor characterized by:

3. 2. The gas compressor according to claim 1, The cooling fan is fixed speed controlled, an ammeter for measuring an input current of the cooling fan; a display device; When the input current to the cooling fan is smaller than a predetermined threshold, the control device displays an instruction to clean or replace the cooling air pre-filter, or the compressed air pre-filter and the cooling air pre-filter, on the display device. A gas compressor characterized by:

4. 2. The gas compressor according to claim 1, The cooling fan is variable speed controlled, a variable speed control device that controls the speed of the cooling fan; When the operation cycle time for performing one load operation and one no-load operation of the cooling fan is T3, the no-load operation time is T1, the load operation time is T2, T3=T1+T2, the current frequency of the variable speed control device is ffc, the rated frequency of the variable speed control device is ffr, the number of operation cycles is N, and the current load factor of the cooling fan Rfc=(T2·ffc)÷(T3·ffr), the control device calculates an average load factor Rf of the cooling fan as Rf=ΣRfc / N; The average load factor R of the compressor body is compared with the average load factor Rf of the cooling fan, and the larger of the two load factors is compared with a load factor judgment value to determine the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter. A gas compressor characterized by:

5. a compressed air pre-filter disposed in a compressed air intake port of a housing for primary removal of dust, an intake filter for secondary removal of dust, at least one compressor body that draws in and compresses air through said intake filter and an intake passage, a motor that drives said compressor body, an air cooler that cools the compressed air, a cooling fan that passes cooling air to said air cooler, a cooling air intake port that draws in outside air by said cooling fan, a cooling air pre-filter provided in said cooling air intake port, and a control device that controls operation of the compressor, the control device determines the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter based on a load factor that is an index of an operating state; The compressor body is a variable speed compressor, a variable speed control device that controls the variable speed of the compressor body; When the operation cycle time for performing one load operation and one no-load operation of the compressor main body is T3, the no-load operation time is T1, the load operation time is T2, T3=T1+T2, the current frequency of the variable speed control device is fc [Hz], the rated frequency of the variable speed control device is fr [Hz], the number of operation cycles is N, the current load factor Rc=(T2·fc) / (T3·fr), and the average load factor R=ΣRc / N, The control device calculates the average load rate R as the load rate, and compares the average load rate R with a load rate judgment value to determine the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter. A gas compressor characterized by:

6. The gas compressor according to any one of claims 1, 4 and 5, The cooling air intake port and the cooling air pre-filter serve the functions of the compressed air intake port and the compressed air pre-filter. A gas compressor characterized by:

7. a compressed air pre-filter disposed in a compressed air intake port of a housing for primary removal of dust, an intake filter for secondary removal of dust, at least one compressor body that draws in and compresses air through said intake filter and an intake passage, a motor that drives said compressor body, an air cooler that cools the compressed air, a cooling fan that passes cooling air to said air cooler, a cooling air intake port that draws in outside air by said cooling fan, a cooling air pre-filter provided in said cooling air intake port, an intake pressure sensor, and a control device that controls operation of the compressor, the control device determines the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter based on a load factor that is an index of an operating state; The compressor body is a fixed speed machine, Assuming that the operation cycle time for performing one load operation and one no-load operation of the compressor main body is T3, the no-load operation time is T1, the load operation time is T2, the number of operation cycles is N, T3 = T1 + T2, the current load factor Rc = T2 ÷ T3, and the average load factor R = ΣRc / N, The control device calculates an accumulated pressure loss, which is an accumulated value of the suction pressure detected by the suction pressure sensor over the operation time, and determines the frequency of cleaning or replacing the compressed air pre-filter and the cooling air pre-filter based on the amount of change in the accumulated pressure loss per predetermined time and the average load factor R. A gas compressor characterized by:

8. 8. The gas compressor according to claim 7, The cooling fan is fixed speed controlled, an ammeter for measuring an input current of the cooling fan; a display device; When the input current to the cooling fan is smaller than a predetermined threshold, the control device displays an instruction to clean or replace the cooling air pre-filter, or the compressed air pre-filter and the cooling air pre-filter, on the display device. A gas compressor characterized by:

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