Gas compressor

Abstract

To know remaining life of an oil circulated in a gas compressor by inexpensive means.SOLUTION: A gas compressor includes: a compressing mechanism portion; a lubricant supplied to the compressing mechanism portion; a separator tank to which a mixture fluid of a working fluid and the lubricant discharged from the compressing mechanism portion is introduced to separate the lubricant; an oil cooler for cooling the lubricant from the separator tank; an oil circulation passage for supplying the cooled lubricant to the compressing mechanism portion; and a motor for driving the compressing mechanism portion and separating from the oil circulation passage. Further it comprises a suction temperature sensor for detecting a suction temperature of the working fluid; a discharge pressure sensor for detecting a discharge pressure of the compressed working fluid; a rotating speed sensor for detecting a rotating speed of the motor; and a lubricant state estimation portion for estimating a temperature of the lubricant on the basis of the detected suction temperature, the discharge pressure and the rotating speed of the motor. The lubricant state estimation portion estimates a deterioration state of the lubricant on the basis of the estimated lubricant temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas compressor for compressing air or other gases, and is particularly suitable as an oil-injected screw compressor. [Background technology]

[0002] Gas compressors (hereinafter simply referred to as compressors) are broadly classified into oil-lubricated compressors, in which lubricating oil is mixed with the gas (working fluid) during the compression process, and oil-free compressors, in which no lubricating oil is mixed with the working fluid. In oil-lubricated compressors, the lubricating oil lubricates and seals gaps between the components that form the compression chamber, for example, between the rotors and between the rotor and the casing in the case of an oil-lubricated screw compressor. The working fluid, which heats up during compression, can be cooled with lower-temperature lubricating oil, which has the advantage of reducing the power required for compression.

[0003] At this time, the lubricating oil is heated by the working fluid and reaches a high temperature, but the increase in oil temperature accelerates deterioration such as an increase in the total acid value, and if the deterioration progresses too much, it may cause the gas filter to clog or the compressor to malfunction due to an increase in viscosity. Therefore, in the past, the replacement period was determined according to the physical properties of the oil so that the oil deterioration would not progress beyond the allowable value even when the compressor was operated at maximum load for a certain period of time.

[0004] Furthermore, as a means of preventing oil deterioration due to high temperatures through operation control, for example, there is a technique described in Japanese Patent Application Laid-Open No. 2010-127218 (Patent Document 1). In the case of Patent Document 1, "inside the container, there is a compression element that compresses the refrigerant, a motor consisting of a stator and a rotor that drives the compression element, and lubricating oil with a kinematic viscosity at 40 degrees of 6 square millimeters per second or less is contained. The stator has windings and a protection device electrically connected to the windings. The efficiency of the motor has a motor efficiency of 82% or more under high load conditions, and the protection device operates by detecting the current flowing through the windings of the stator and the temperature of the container or inside the container or in the vicinity of the windings. A value obtained as a function of the current flowing through the windings and the temperature of the container or inside the container or in the vicinity of the windings is used as the operating value of the protection device. By detecting and operating when the winding temperature reaches 120 degrees or more, the actual kinematic viscosity of the lubricating oil under any load condition of the compressor can be limited to 1 square millimeter per second or more." A compressor is described in this way. It is described that this can prevent abnormal deterioration of the oil.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The actual load factor of the compressor varies greatly depending on the environment in which it is used. When the load factor is relatively small, even though the deterioration of the oil has not progressed much, there was no means to know the actual degree of deterioration in that individual device. Therefore, it was necessary to uniformly replace the oil at the above-described replacement time. As a result, although there was a margin in the remaining life of the oil, the oil had to be replaced, which could cause economic losses.

[0007] In addition, in an oil-fed compressor, by reducing the amount of oil supplied, the stirring loss of the oil can be reduced and the efficiency of the compressor can be improved. However, on the other hand, when the amount of oil in the compression chamber decreases, the oil is likely to become hot, and there is a problem that deterioration progresses easily.

[0008] Regarding this problem, if the remaining life of the oil in individual equipment can be known, when there is a margin in the remaining life, energy saving can be improved by reducing the amount of oil supplied while leaving the remaining power to the necessary extent. However, as described above, in the prior art, there was no means to know the remaining life of the oil, so it was not possible to operate a compressor that reduces the amount of oil supplied to improve energy saving.

[0009] In the case of the above Patent Document 1, it is possible to control the oil temperature so as not to exceed a certain upper limit value so that the deterioration of the oil does not progress rapidly according to the operating environment of individual equipment. However, when the oil temperature is operated below the upper limit value, it was not possible to know the remaining life itself, that is, how much margin there is until the deterioration of the oil exceeds the threshold value.

[0010] Also, in the case of the above Patent Document 1, although the oil temperature is limited by the winding temperature of the motor, the invention described in Patent Document 1 cannot be applied to a compressor having a structure in which the motor and the lubricating oil are separated so as not to contact each other.

[0011] There are sensors on the market that can measure the degree of deterioration of oil more directly, but such sensors are expensive and difficult to adopt from the perspective of cost when mounted on a compressor.

[0012] Therefore, if the deterioration state of the oil can be estimated using the pressure sensor and temperature sensor usually mounted on the compressor, the remaining life of the oil circulating in the gas compressor (inside the machine) can be known by an inexpensive means, and it becomes possible to reduce the amount of oil supplied and improve energy saving.

[0013] An object of the present invention is to obtain a gas compressor capable of knowing the remaining life of the oil circulating in the machine by an inexpensive means.

Means for Solving the Problems

[0014] In order to achieve the above object, the present invention employs, for example, the configurations described in the claims. the lubricating oil state estimating unit estimates the temperature of the lubricating oil based on the detected suction temperature, discharge pressure, and rotational speed of the motor, and the lubricating oil state estimating unit estimates the deterioration state of the lubricating oil based on the estimated temperature of the lubricating oil.

[0015] Another feature of the present invention is a gas compressor comprising: a compression mechanism that compresses a working fluid that is sucked in; a separator tank that receives lubricating oil to be supplied to the compression mechanism and a mixed fluid of the working fluid and lubricating oil discharged from the compression mechanism and separates the lubricating oil from the compressed working fluid; an oil cooler that receives the lubricating oil separated in the separator tank and cools it; an oil circulation path that supplies the lubricating oil cooled in the oil cooler to the compression mechanism; and a motor that drives the compression mechanism and is isolated from the oil circulation path, wherein the gas compressor comprises at least one of a suction temperature sensor that detects a suction temperature of the working fluid that is sucked into the compression mechanism, and a discharge pressure sensor that detects a discharge pressure of the working fluid compressed by the compression mechanism or a rotational speed sensor that detects a rotational speed of the motor. The lubricating oil condition estimation unit includes at least one of the following: a discharge pressure sensor or a rotational speed sensor that detects the discharge pressure or the rotational speed of the motor; a power sensor that detects the input power of the motor; the input power detected by the power sensor and the value of the discharge pressure or the rotational speed detected by the discharge pressure sensor or the rotational speed sensor that is provided are used to calculate the rotational speed or the discharge pressure that is not detected; and a lubricating oil condition estimation unit that estimates the temperature of the lubricating oil based on the detected suction temperature, the detected discharge pressure or the motor rotational speed, and the calculated motor rotational speed or the discharge pressure, and the lubricating oil condition estimation unit estimates the deterioration state of the lubricating oil based on the estimated lubricating oil temperature. [Effects of the Invention]

[0016] According to the present invention, it is possible to obtain a gas compressor that allows the remaining life of oil circulating inside the compressor to be known by inexpensive means. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a system diagram showing the equipment configuration of a gas compressor according to a first embodiment of the present invention. [Figure 2] 1 is a cross-sectional view perpendicular to the axis of a compression mechanism of a gas compressor according to a first embodiment of the present invention. [Figure 3]Flowchart showing the procedure for estimating the degree of oil deterioration in Example 1 of the present invention. [Figure 4] Graph showing an example of the acquired data of the operating state in Example 1 of the present invention. [Figure 5] System diagram showing the equipment configuration of the gas compressor in Example 2 of the present invention. [Figure 6] System diagram showing the equipment configuration of the gas compressor in Example 3 of the present invention. [Figure 7] System diagram showing the equipment configuration of the gas compressor in Example 4 of the present invention. [Figure 8] Flowchart showing the procedure for estimating the degree of oil deterioration in Example 4 of the present invention.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, specific embodiments of the gas compressor of the present invention will be described with reference to the drawings. In each figure, parts denoted by the same reference numerals indicate the same or corresponding parts. In each of the embodiments described below, the case where the compressor is an oil-injected screw compressor will be described. However, the scope of application of the present invention is not limited to oil-injected screw compressors, and it is also applicable to other types of compressors.

Examples

[0019] Example 1 of the present invention will be described with reference to FIGS. 1 to 4. First, the configuration of an oil-injected screw compressor, which is an example of the compressor of the present invention, will be described with reference to FIGS. 1 and 2. FIG. 1 is a system diagram showing the equipment configuration of the screw compressor in Example 1 of the present invention, and FIG. 2 is a cross-sectional view perpendicular to the axis of the compression mechanism part of the screw compressor in Example 1 of the present invention. In this example, the case where the working fluid is air will be described, but it is also applicable to compressors using gases other than air as the working fluid.

[0020] In FIG. 1, 1 is a power supply, 2 is an inverter electrically connected to the power supply 1, 3 is a motor electrically connected to the inverter 2, and 4 is a compression mechanism (compressor body) that incorporates a screw rotor that is rotationally driven by the motor 3.

[0021] As shown in Figure 2, the compression mechanism 4 is composed of a shaft 19, a male rotor 20, a female rotor 21, a casing 22, etc. The shaft 19 on the male rotor 20 side is adjacent to and integral with the male rotor 20 in the axial direction, and the shaft 19 on the female rotor 21 side is adjacent to and integral with the female rotor in the axial direction. The shaft 19 on the male rotor 20 side is mechanically coupled to the motor 3, so that the rotational torque of the motor 3 can be transmitted to the shaft 19 on the male rotor side. The motor 3 is configured to be isolated from the compression mechanism 4 so that fluids (compressed air and lubricating oil) inside the compression mechanism 4 do not flow into it.

[0022] The space surrounded by the male rotor 20, the female rotor 21, and the casing 22 is a compression chamber 23. The casing 22 is provided with an oil supply hole 24 that intermittently communicates with the compression chamber 23.

[0023] As shown in FIG. 1, a separator tank 5 is provided downstream of the compression mechanism 4, and the mixed fluid of compressed air and oil discharged from the compression mechanism 4 flows into the separator tank 5, where oil (lubricating oil) 6 is separated from the compressed air. The compressed air from which the oil has been separated in the separator tank 5 is sent to the demand side.

[0024] An intake air filter (hereinafter also referred to as an intake filter) 10 and an intake throttle valve 11 are provided in the intake line of external air to the compression mechanism 4. The intake filter 10 is disposed between a pipe (not shown) connected to the external air and the compression mechanism 4, and removes foreign matter such as dust from the intake air. The intake throttle valve 11 is disposed downstream of the intake filter 10, and adjusts the amount of intake air by controlling its opening. The downstream side of the intake throttle valve 11 is connected to the intake port of the compression mechanism 4, and the intake port is connected to the compression chamber 23.

[0025] The air flow and the like in the above-described oil-fed screw compressor will be described. Based on the electric power supplied from the power source 1, the inverter 2 controls the voltage waveform to control the rotational speed of the motor 3. The rotational torque of the motor 3 is transmitted via the shaft 19 to the male rotor 20 and the female rotor 21 that meshes with the male rotor 20, and these two rotors rotate in opposite directions to each other. As a result, the compression chamber 23 communicating with the suction port side expands its volume from 0, so that external air (outside air) is taken in through the suction filter 10 and the suction throttle valve 11 and flows into the compression chamber 23.

[0026] After that, as the rotors 20 and 21 further rotate, the compression chamber 23 reaches its maximum volume, and then the air is confined in the compression chamber 23 and its volume is reduced, compressing the air in the compression chamber 23 to a high temperature and high pressure state. During the compression stroke, lubricating oil 6 that is cooler than the compressed air is supplied (injected) into the compression chamber 23 from the oil supply hole 24, cooling the heated air, and the lubricating oil itself is heated. After that, the compression chamber 23 communicates with the discharge port and the discharge-side flow path at a predetermined rotor rotation angle, and the compressed air and the lubricating oil are discharged to the downstream side and flow into the separator tank 5.

[0027] The air and the lubricating oil that have flowed into the separator tank 5 are separated into compressed air and lubricating oil 6 by centrifugal force by being guided, for example, to form a swirling flow. The compressed air is further supplied to a pneumatic device (not shown) that requires downstream compressed air. On the other hand, the lubricating oil 6 is stored at the bottom of the separator tank 5.

[0028] The lubricating oil 6 separated in the separator tank 5 flows into an oil cooler 7, which is a heat exchanger provided on the downstream side of the separator tank 5 in a path (lubricating oil circulation path) different from the compressed air. In this oil cooler 7, it is cooled to a low temperature by the outside air blowing of the cooler fan 8. The lubricating oil that has exited the oil cooler 7 passes through an oil filter 9 provided downstream thereof, and after foreign substances in the lubricating oil 6 are removed, it is supplied again to the compression chamber 23 through the oil supply hole 24.

[0029] Next, a method for estimating the temperature of the compressed air and lubricating oil, and the deterioration state of the lubricating oil, will be described. To detect the state of the compressed air and lubricating oil, an intake temperature sensor 14 is provided somewhere upstream of the compression mechanism 4 (at the intake air filter 10 in FIG. 1) to measure the temperature of the intake air. Information on the measured intake air temperature is transferred as an electrical signal to the control device 12, and then sent to the arithmetic device 13. The arithmetic device 13 plays the role of a lubricating oil state estimation unit, which will be described later.

[0030] It is assumed that the computing device 13 may be located in a remote location via the Internet, etc., and so the control device 12 and computing device 13 are shown as being separate, but they do not necessarily need to be separate devices. The location where the suction temperature sensor 14 is provided does not necessarily need to be located on the piping inside the compressor device, and a sensor that measures the ambient temperature of the compressor (for example, an outside air temperature sensor) may be used instead.

[0031] A discharge pressure sensor 15 for measuring the pressure of the air is provided somewhere downstream of the compression mechanism 4. For example, the discharge pressure sensor 15 may be provided inside the separator tank 5, or may be provided in the piping before or after the separator tank 5. If there is a tank for storing compressed air downstream of the separator tank 5, the discharge pressure sensor 15 may be provided inside the tank, or before or after the tank. Pressure information measured by the discharge pressure sensor 15, like the intake air temperature information described above, is transferred as an electric signal to the control device 12 and then to the calculation device 13.

[0032] In addition, a rotation speed sensor 16 is provided to measure the rotation speed of the motor 3, and information about the rotation speed is also sent to the calculation device 13. The rotation speed may be detected by a command value from the inverter 2, or by a value estimated from the voltage or current, or the motion state of the motor may be measured by an optical or electromagnetic sensor.

[0033] The above-mentioned control device 12, computing device 13, suction temperature sensor 14, discharge pressure sensor 15, rotation speed sensor 16, etc. are normally provided in oil-lubricated screw compressors, and by using these sensors, etc. to estimate the temperature and degree of deterioration of the lubricating oil circulating inside the compressor, it is possible to know the remaining life of the lubricating oil in an inexpensive manner. In addition, knowing the remaining life of the lubricating oil can reduce the amount of oil to be used and improve energy conservation.

[0034] Next, a calculation flow for estimating the temperature and deterioration level of the lubricant oil from the information acquired as described above will be described with reference to Figures 3 and 4. Figure 3 is a flowchart showing the procedure for estimating the oil deterioration level in Example 1 of the present invention, and Figure 4 is a graph showing an example of acquired data of the operating state in Example 1 of the present invention. Note that, in this example, the calculation of each step shown in Figure 3 is performed by the calculation device 13, and therefore, in this example, the calculation device 13 constitutes a lubricant oil state estimation unit.

[0035] In the flowchart of Figure 3, the flow on the left side shows the flow of the entire calculation procedure, and the flow on the right side shows the details of the calculation procedure of step S2, which is part of the flow on the left side and is "updating the thermodynamic state of the compression chamber." When calculation starts, in step S1, the suction temperature Ts, discharge pressure Pd, and motor rotation speed N detected by the method described above are obtained. When air is drawn in from the outside, the suction pressure Ps is obtained assuming that the suction pressure is approximately atmospheric pressure. Note that if the drawn gas is not at atmospheric pressure, the suction pressure Ps can be easily obtained by providing a suction pressure sensor upstream of the compression mechanism 4.

[0036] Next, in step S2, based on these measured values, the thermodynamic state (pressure and temperature) of the compression chamber 23 is estimated. The time changes of the pressure and temperature of the compression chamber 23 that fluctuate during the compression stroke are respectively expressed as P (n) , T (n) (where n is the discretized time step), as shown in the flow on the right side of FIG. 3, the initial value of the compression chamber 23 (when n=0, in FIG. 3, when "Initial calculation?" in step S21 is Yes) is P (0) =Ps, T (0)is given as = Ts (step S22). When "Calculation Initial?" is No, this initialization operation is not performed and the process proceeds to step S23.

[0037] When the current time step is n (time t (n) ), the thermodynamic state of the compression chamber at the next time step n + 1 (time t (n+1) ) can be obtained, for example, as follows.

[0038] First, the volume of the compression chamber at time t (n+1) is determined by the specifications of the rotors 20, 21. By obtaining in advance the relationship between the geometrically calculable rotation angle and the volume of the compression chamber and incorporating this relationship into the arithmetic unit 13 in the form of a look-up table, the volume of the compression chamber corresponding to the rotation angle (crank angle) θ (= 2πNt (n+1) ) at time t (n+1) ) can be obtained. At this time, the information on the rotational speed N is used.

[0039] In addition, there are actually minute gaps between the male rotor 20, female rotor 21, and casing 22 that partition the compression chamber 23, which serve as leakage flow paths for air and lubricating oil. Although the cross-sectional shape of the leakage flow path of the gap changes with the rotation angle, based on geometric calculations based on the specifications of the rotors 20, 21, casing 22, etc., and estimated values of the gap amount based on prior performance tests, etc., by combining them and determining the relationship between the rotation angle and the cross-sectional area of the leakage flow path in the form of a look-up table, the cross-sectional area of each leakage flow path at the next calculation step time t (n+1) can be obtained (step S24).

[0040] In addition, another compression chamber adjacent to the compression chamber 23 to be calculated is a compression chamber that has advanced by a certain rotation angle α (has started compression earlier) or is delayed (starts compression later) with respect to the compression chamber 23 to be calculated. Therefore, the P (n) and T (n)If we refer to the value shifted backward in the past by the amount corresponding to the difference in the above-mentioned rotation angle α, when the iterative calculation of the suction, compression, and discharge processes has sufficiently converged, the pressures and temperatures in adjacent compression chambers can be approximately obtained. If the adjacent compression chamber is ahead, considering one cycle from suction to discharge, we can refer to the value of the corresponding rotation angle in the previous cycle. Once the pressures, temperatures, and the leakage flow path cross-sectional area between adjacent compression chambers are determined, the leakage flow rate can be obtained by using an empirical formula or a theoretical formula such as the nozzle formula.

[0041] Also, when oil is supplied to the compression chamber 23 at the time step to be calculated, since the flow rate is determined by the pressures before and after the oil supply hole 24 and the shape of the oil supply hole 24, for example, the oil supply amount when changing the discharge pressure, which is a high-pressure supply source, can be experimentally obtained, or the flow rate can be obtained analytically from the flow path shape of the oil supply path and the discharge pressure (or by using a theoretical formula for orifice flow, etc.), and thus the oil supply amount can be determined (step S25).

[0042] Furthermore, by multiplying the obtained leakage flow rate and oil supply amount by the time increment Δt = t (n+1) -t (n) we can also calculate the mass and energy of the air and lubricating oil flowing in and out of the compression chamber 23 between time t (n) and t (n+1) .

[0043] The lubricating oil supplied to the compression chamber 23 exchanges heat with the hotter air. Regarding the heat transfer amount, it can be calculated by experimentally obtaining the heat transfer amount in advance as a function of the rotation speed, suction temperature, and oil supply amount, or by performing an analysis of the gas-liquid two-phase flow in advance. Based on the obtained heat transfer amount, the energy exchange (heat transfer amount) between the air and lubricating oil in the compression chamber 23 can be calculated (step S26).

[0044] By calculating these together, the density and internal energy of the air and lubricating oil in the compression chamber 23 can be calculated (step S27). Once these are determined, the thermodynamic state is determined, and based on the state equation based on physical properties, or information that enables the calculation of pressure and temperature as functions (look-up tables) of density and internal energy derived from the state equation, the pressure P (n+1) and temperature T (n+1) at the next time step n + 1 can be obtained (step S28).

[0045] By repeating the above calculations, the thermodynamic state of the compression chamber 23 can be calculated sequentially (step S2). When the rotor rotation angle θ reaches the discharge start angle of the compression chamber 23 (step S3), using the discharge pressure Pd, the pressure P (n) of the compression chamber 23 and the relational expression (or look-up table) of pressure difference and flow rate that has been predetermined by experiment or theory and incorporated into the arithmetic unit 13 based on the shape data of a given discharge flow path, the discharge flow rate from the compression chamber 23 can be obtained (step S4), or assuming that the air adiabatically expands from the pressure P (n) to the discharge pressure Pd, the discharge temperature of the air can be obtained. Thereafter, heat exchange occurs between the air and the lubricating oil until they are separated from each other in the separator tank 5, and the amount of heat transfer can also be obtained by methods such as creating a look-up table based on the results obtained in advance by experiment or fluid analysis, etc., similar to the heat exchange in the compression chamber 23 above.

[0046] As described above, downstream of the separator tank 5, the lubricating oil 6 is cooled by the oil cooler 7 and further supplied to the oil supply hole 24 through pipes or the like. When the driving force of the lubricating oil 6 is a pressure difference, as already described, the relationship between the pressure difference and the flow rate in the oil circulation path can be obtained experimentally or analytically. Furthermore, by taking into account the cooling capacity of the oil cooler 7, the temperature and pressure changes of the lubricating oil 6 can be predicted (estimated). Also, by performing fluid analysis or the like in advance considering the shape of the flow path through which the lubricating oil flows, it is possible to estimate how long the lubricating oil stays at each location in the flow path. By taking the result into the arithmetic unit 13, it is possible to obtain the time history of the temperature and pressure changes in the circulation path of the lubricating oil (the flow path from when it is discharged from the compression chamber 23 until it is supplied again to the compression chamber 23 after passing through the separator tank 5, the oil cooler 7, etc.). This corresponds to step S5 "Calculation of oil temperature and pressure changes in the oil circulation path" in FIG. 3.

[0047] As described above, from the values detected by the suction temperature sensor 14, the discharge pressure sensor 15, and the rotation speed sensor 16, it is possible to estimate the time cycle of the temperature and pressure of the lubricating oil circulating in the compressor.

[0048] In the above description, the discharge pressure sensor 15 and the rotation speed sensor 16 are used to directly detect the discharge pressure and the motor rotation speed. However, instead, by using a power sensor that detects the input power of the motor, for example, a wattmeter or an ammeter, to detect the power (input power) of the motor, it is possible to detect the discharge pressure or the motor rotation speed without using either the discharge pressure sensor 15 or the rotation speed sensor 16.

[0049] That is, if the compressor efficiency and the volumetric efficiency are assumed in advance, the theoretical compression power can be obtained from the shaft power of the motor. This is because the theoretical adiabatic compression power is given as a function of the suction pressure, the suction temperature, the discharge pressure, and the rotation speed once the physical properties of the working fluid are determined. Therefore, instead of using either the discharge pressure sensor 15 or the rotation speed sensor 16, it is also possible to use means for detecting the power or current value of the motor.

[0050] Next, we will explain how to determine the degree of oil degradation and remaining life from the estimated temperature-pressure cycle of the obtained lubricant. For example, if we consider the total acid number as an indicator of oil degradation, by conducting material testing of the lubricant in a temperature- and pressure-controlled environment in advance, we can obtain the relationship of how quickly the total acid number increases when the target lubricant is exposed to a certain pressure or temperature. By incorporating these databases (approximation formulas) into the calculation device 13, we can estimate the increase in the total acid number using the above-mentioned temperature-pressure cycle of the lubricant as an input condition. In other words, we can estimate the degree of lubricant degradation. This corresponds to step S6 in Figure 3, "Predict the increase in the total acid number from the oil temperature-pressure time series."

[0051] Figure 4 is a graph showing an example of acquired data on operating conditions, showing examples of suction temperature, discharge pressure, and rotation speed acquired by an oil-lubricated screw compressor. When fluctuating operating history data like the graph in Figure 4 has been acquired over a long period of time, it is possible to predict the change in the degree of deterioration over the period for which the operating history data was acquired by predicting the total acid number increase value described above using this history data at each time point and integrating them.

[0052] By inputting the time when the lubricating oil was replaced with new oil into the calculation device 13 as information and recording all historical data of the suction temperature, discharge pressure, and rotation speed after the oil change (data shown as an example in Figure 4), it is possible to estimate the extent to which the deterioration has progressed (the increase in total acid number) from the state of the new lubricating oil. If lubricating oil quality standards (such as the allowable upper limit of total acid number) determined in advance at the time of product design are provided to the calculation device 13 (lubricant state estimation unit), it is possible to estimate how much time is left until the degree of deterioration of the lubricating oil reaches its upper limit based on the rate of progression of deterioration up to the present or a certain point in time, and this time can be used as the estimated remaining life of the lubricating oil.

[0053] In the above, the most desirable condition is that all historical data for suction temperature, discharge pressure, and rotational speed be recorded. However, if only the most recent data and the time interval between the most recent and previous data points can be obtained, the deterioration level during that time interval can be estimated using the above method. Therefore, by sequentially integrating only the deterioration level, it is not necessary to retain all historical data for temperature, pressure, etc. Furthermore, even if some data is missing, the remaining life of the lubricant can be estimated without any problems by excluding that data and performing the same calculation.

[0054] Furthermore, as shown in Figure 4, even if all operating history data from the last lubricant oil change is not acquired, but only operating history data for a certain period (period P2 in Figure 4) that is shorter than the entire operating period is retained, by acquiring the time that has elapsed since the last lubricant oil change (period P1 + P2 in Figure 4), it is possible to estimate the degree of deterioration of the oil over the period that has elapsed since the lubricant oil change from only the acquired operating history data. Therefore, by assuming that deterioration is progressing at a similar rate even for the period for which operating history data cannot be acquired (period P1 in Figure 4), it is possible to predict the degree of deterioration since the oil change, and the remaining life of the lubricant can be estimated in the same way as above.

[0055] In this case, the longer the period for which the operating history data is retained (period P2 in Figure 4), the higher the estimation accuracy. However, considering the shortest time cycle of environmental fluctuations in the compressor's operation (e.g., production activities using compressed air), it is preferable to retain operating history data for at least one day or to integrate instantaneous values for that period as the deterioration level, as described above. For example, if the compressor operates in the same pattern every day, the degree of oil deterioration can be estimated based on the operating history data for one day and then integrated over the compressor's operating period to predict the degree of oil deterioration to date and estimate the remaining life of the lubricating oil. Similarly, if the compressor operates in the same pattern periodically, such as every week or several months, the degree of oil deterioration (such as the total acid value) can be calculated based on the operating history data for that operating pattern and then integrated over the compressor's operating period to determine the remaining life.

[0056] According to the above-described embodiments, the remaining life of the lubricating oil of the compressor, that is, the remaining life of the lubricating oil of the compressor that varies depending on the operating environment and history, can be estimated by using the existing suction temperature sensor, discharge pressure sensor, motor rotation speed sensor, etc. that the gas compressor has. It is possible to obtain the effect of improving the economy by optimizing the oil change timing and further improving the energy saving by optimizing the oil supply amount. In the above description, the temperature and pressure changes of the lubricating oil are estimated to determine its deterioration state. However, it is also possible to estimate the deterioration state only from the estimation of the temperature change of the lubricating oil. In this case, the estimation accuracy of the oil deterioration state is slightly reduced compared to the case where the pressure change is also considered, but the oil deterioration state can be estimated more simply.

Embodiment

[0057] Embodiment 2 of the present invention will be described with reference to FIG. 5. FIG. 5 is a system diagram showing the equipment configuration of the screw compressor in Embodiment 2 of the present invention. In the description of this Embodiment 2, the description of the same configuration as that in Embodiment 1 shown in FIG. 1 will be omitted, and the description will be centered on the different parts.

[0058] The difference between this embodiment and Embodiment 1 is that a flow rate adjustment valve 17 is provided on the downstream side of the oil filter 9 in the circulation path of the lubricating oil 6. The flow rate adjustment valve 17 can freely change its opening degree according to a transmission signal from the control device 12 by using a solenoid valve or the like. Therefore, in this Embodiment 2, the flow rate (oil supply amount) of the lubricating oil 6 supplied to the compression chamber 23 can be made variable.

[0059] The lubricating oil 6 is agitated by the rotors 20 and 21 in the compression chamber 23, and the greater the oil supply amount, the greater the power loss due to agitation. Conversely, if the oil supply amount can be reduced, the agitation loss can be reduced and the efficiency of the compressor can be improved. However, when the oil supply amount is reduced, a smaller amount of oil is injected into the compression chamber 23, and it is necessary to cool the high-temperature air with a smaller amount of oil. For this reason, there is a problem that the lubricating oil becomes high temperature and deterioration progresses easily.

[0060] To address this issue, in the second embodiment, as shown in the first embodiment, the remaining life of the lubricating oil 6 is estimated. When the average load of the compressor is relatively low and the remaining life is longer than the standard replacement time, the opening of the flow control valve 17 is throttled by the command value from the control device 12, and the oil supply amount to the compression chamber 23 is decreased. At this time, if the relationship between the opening of the flow control valve 17, the pressure conditions, and the oil supply amount is obtained in advance through experiments or the like, the remaining life of the oil when the oil supply amount is decreased can be estimated in the same manner as the method shown in the first embodiment.

[0061] Therefore, according to this embodiment, the change in the remaining life of the lubricating oil due to the decrease in the oil supply amount can be estimated. When the load factor of the compressor is small and the remaining life is considerably long, the oil supply amount can be reduced while decreasing the remaining life to an acceptable level. Thereby, the reliability of the compressor can be ensured and its operating efficiency can be improved, and the electricity cost due to the compressor operation can be reduced by improving the energy-saving performance. Other configurations are the same as those in the first embodiment.

Embodiment

[0062] The third embodiment of the present invention will be described with reference to FIG. 6. FIG. 6 is a system diagram showing the equipment configuration of the screw compressor in the third embodiment of the present invention. In the description of the third embodiment, the description of the same configurations as those in the first embodiment shown in FIG. 1 and the second embodiment shown in FIG. 5 will be omitted, and the description will focus on the different parts.

[0063] Similar to the second embodiment, in the third embodiment, a flow control valve 17 is provided on the downstream side of the oil filter 9 in the circulation path of the lubricating oil 6. In this embodiment, the cooling capacity of the oil cooler 7 is varied in accordance with the oil supply amount determined by the opening of the flow rate adjustment valve 17. In this embodiment, a flow path switching valve 25 is provided upstream of the oil cooler 7, and is configured to select either a flow path for the lubricating oil 6 from the separator tank 5 to flow into the inlet end 7a of the heat exchanger of the oil cooler 7, or a flow path for the lubricating oil 6 to flow into the heat exchanger of the oil cooler 7 at a point 7b further downstream. The flow path switching valve 25, which switches the flow path, is controlled by the control device 12.

[0064] It is assumed that at a certain point in time, flow path switching valve 25 is in a state where lubricating oil 6 flows in from midway 7b of the heat exchange section of oil cooler 7. At this time, as described in the second embodiment, if the average load factor of the compressor is small and the remaining life of the oil is sufficient compared to the allowable lower limit, the amount of oil supplied can be reduced by flow control valve 17, thereby reducing the churning loss in compression chamber 23 (see FIG. 2).

[0065] However, when the amount of oil supplied is reduced, the flow rate of lubricating oil 6 passing through oil cooler 7 is reduced, and the cooling capacity of oil cooler 7 is reduced. In order to cool the compressed air to the same degree while reducing the amount of oil supplied, the temperature of the lubricating oil supplied from oil supply port 24 to compression chamber 23 must be lower than before the amount of oil supplied was reduced. However, because the cooling capacity of oil cooler 7 is reduced, the lubricating oil cannot be cooled to a necessary and sufficient temperature, and the ability to cool the compressed air in the compression chamber is reduced compared to before the amount of oil supplied was reduced. As a result, hotter air is compressed, requiring extra power, which poses a problem of reduced compressor efficiency.

[0066] In contrast to this, in the third embodiment, the flow path switching valve 25 is switched at the same time as the amount of oil supplied is reduced, so that the lubricating oil 6 flows into the inlet end 7a of the oil cooler 7. This increases the heat transfer area of the heat exchange section of the oil cooler 7, making it possible to suppress a decrease in cooling capacity due to a decrease in the amount of oil supplied. In other words, the compressed air can be cooled with lubricating oil at a lower temperature, thereby improving the efficiency of the compressor.

[0067] Although the remaining life of the lubricating oil 6 varies due to the improvement of the cooling capacity, as explained in the first embodiment, in the present invention, the temperature cycle of the lubricating oil 6 due to the cooling capacity of the oil cooler 7 is estimated, so that the cooling capacity can be controlled after predicting the remaining life of the lubricating oil 6 when the flow path of the oil cooler 7 is switched. Therefore, it is possible to improve energy saving while maintaining the reliability of the compressor.

[0068] Furthermore, the means for varying the cooling capacity of the oil cooler 7 is not necessarily limited to the above, and may be configured to switch the heat transfer area by branching the flow path on the outlet side of the oil cooler 7. Alternatively, when the opening of the flow rate control valve 17 is narrowed, the rotation speed of the cooler fan 8 that sends cooling air to the oil cooler 7 may be increased to prevent a decrease in the cooling capacity of the oil cooler 7. In other words, if the cooling capacity of the oil cooler 7 is controlled to increase when the opening of the flow rate control valve 17 is narrowed, the same effect as that of the third embodiment described above can be obtained. [Example]

[0069] A fourth embodiment of the present invention will be described with reference to Figures 7 and 8. Figure 7 is a system diagram showing the equipment configuration of a screw compressor in the fourth embodiment of the present invention, and Figure 8 is a flowchart showing the procedure for estimating the degree of oil deterioration in the fourth embodiment. In the description of the fourth embodiment, the description of the same configuration as in the first embodiment shown in Figures 1 to 4 will be omitted, and the description will focus on the different parts.

[0070] In this fourth embodiment, as shown in FIG. 7, a humidity sensor 18 is provided in the intake side flow path upstream of the compression mechanism 4 to detect the humidity of the air (working fluid) drawn into the compression mechanism 4 through the intake air filter 10.

[0071] According to the fourth embodiment shown in Fig. 7, the humidity of the intake air drawn into the compression mechanism 4 is detected, so that the amount of moisture contained in the intake air can be estimated. In the fourth embodiment, too, the amount of moisture contained in the air that condenses when the compressed air is cooled can be calculated by supplying low-temperature lubricating oil to the compression chamber 23 in a procedure almost similar to that of the first embodiment described in Fig. 3.

[0072] Specifically, for example, the relationship between the amount of condensed water generated and the operating conditions may be obtained in advance by an experiment in which air with different humidity levels is compressed, and the relationship may be incorporated as a look-up table into the computing device 13. Alternatively, the rate at which condensation occurs may be calculated by assuming a flow field in which lubricating oil is dispersed within the compression chamber 23 and using a known correlation equation for the mass transfer coefficient, or by determining the mass transfer coefficient through fluid analysis, and using the relationship, based on mass transfer theory, that the amount of condensation per unit time is proportional to the product of the difference in moisture concentration in the air and the mass transfer coefficient.

[0073] The procedure corresponds to the "humid air-oil heat transfer calculation" in step S26a and the "moisture condensation amount calculation" in step S26b in the flow on the right side of Fig. 8. In the "moisture condensation amount calculation" in step S26b, the above-mentioned calculation is performed, and in the "humid air-oil heat transfer calculation" in step S26a, calculations can be performed in the same manner as in the first embodiment, including the effect of latent heat due to moisture condensation.

[0074] Furthermore, for the moisture condensing or evaporating from the air in the separator tank 5 or in the piping before and after it, the evaporation or condensation rate can be similarly obtained in advance by experimental or numerical analysis methods in association with the operating conditions (corresponding to "Calculation of the amount of moisture moving in the oil circulation path" in step S5a of Figure 8).

[0075] According to the above method, in Example 4 of the present invention, not only the temperature-pressure cycle of the lubricating oil but also the change in the amount of moisture mixed into the lubricating oil can be predicted. Further, as described in Example 1, in addition to obtaining in advance by experiments or the like the amount of change in the degree of deterioration (for example, total acid value) with respect to temperature and pressure, if the amount of change in the degree of deterioration due to the amount of moisture is also obtained, the remaining life of the lubricating oil can be calculated with higher accuracy. Therefore, it becomes possible to further optimize the oil change timing. Also, as in Example 2 described above, by using the flow rate adjustment valve 17, it becomes easy to reduce the oil supply amount based on the remaining life of the lubricating oil, so that further high efficiency of the compressor can be achieved.

[0076] In this example, the humidity sensor 18 is provided to detect the humidity of the suction air. However, instead of providing the humidity sensor 18, information on the installation area of the compressor may be obtained, and the humidity of the suction air may be estimated using weather data provided separately from relevant institutions. In this case, although there is a high possibility that the estimation accuracy of the amount of moisture in the air will decrease compared to the case of using the humidity sensor 18, as described in Example 4 of the present invention, the effect of being able to estimate the remaining life of the lubricating oil considering the amount of moisture can be obtained.

[0077] Note that the present invention is not limited to the above-described examples and includes various modifications. Also, it is possible to replace a part of the configuration of one example with the configuration of another example, and it is also possible to add the configuration of another example to the configuration of one example. Furthermore, the above-described examples have been described in detail for the purpose of explaining the present invention clearly, and are not necessarily limited to those having all the configurations described.

Explanation of Reference Numerals

[0078] 1: Power supply, 2: Inverter, 3: Motor, 4: Compression mechanism section, 5: Separator tank, 6: Lubricating oil, 7: Oil cooler, 7a: Inlet end, 7b: Middle of heat exchange section, 8: Cooler fan, 9: Oil filter, 10: Suction air filter (suction filter), 11: Suction throttle valve, 12: control device, 13: arithmetic device, 14: suction temperature sensor, 15: discharge pressure sensor, 16: rotation speed sensor, 17: flow control valve, 18: humidity sensor, 19: shaft, 20: male rotor, 21: female rotor, 22: casing, 23: compression chamber, 24: oil supply port, 25: flow path switching valve.

Claims

1. A gas compressor comprising: a compression mechanism unit that compresses an inhaled working fluid; lubricating oil supplied to the compression mechanism unit; a separator tank that introduces a mixed fluid of the working fluid and the lubricating oil discharged from the compression mechanism unit and separates the lubricating oil from the compressed working fluid; an oil cooler that introduces and cools the lubricating oil separated by the separator tank; an oil circulation path that supplies the lubricating oil cooled by the oil cooler to the compression mechanism unit; and a motor that drives the compression mechanism unit and is isolated from the oil circulation path, a suction temperature sensor that detects the suction temperature of the working fluid inhaled into the compression mechanism unit; a discharge pressure sensor that detects the discharge pressure of the working fluid compressed by the compression mechanism unit; a rotational speed sensor that detects the rotational speed of the motor; a lubricating oil state estimation unit that estimates the temperature of the lubricating oil based on the detected suction temperature, discharge pressure, and rotational speed of the motor, wherein the lubricating oil state estimation unit estimates the deterioration state of the lubricating oil based on the estimated temperature of the lubricating oil.

2. A gas compressor comprising: a compression mechanism unit that compresses an inhaled working fluid; lubricating oil supplied to the compression mechanism unit; a separator tank that introduces a mixed fluid of the working fluid and the lubricating oil discharged from the compression mechanism unit and separates the lubricating oil from the compressed working fluid; an oil cooler that introduces and cools the lubricating oil separated by the separator tank; an oil circulation path that supplies the lubricating oil cooled by the oil cooler to the compression mechanism unit; and a motor that drives the compression mechanism unit and is isolated from the oil circulation path, a suction temperature sensor that detects the suction temperature of the working fluid inhaled into the compression mechanism unit; at least one of a discharge pressure sensor that detects the discharge pressure of the working fluid compressed by the compression mechanism unit or a rotational speed sensor that detects the rotational speed of the motor, and the discharge pressure or the rotational speed of the motor is detected by the provided discharge pressure sensor or rotational speed sensor, further comprising a power sensor that detects the input power of the motor, using the input power detected by the power sensor and the value of the discharge pressure or rotational speed detected by the provided discharge pressure sensor or rotational speed sensor to calculate the rotational speed or discharge pressure that has not been detected. A lubricating oil state estimation unit that estimates the temperature of the lubricating oil based on the detected suction temperature, the detected discharge pressure or the rotational speed of the motor, and the calculated rotational speed or discharge pressure of the motor is provided. The gas compressor is characterized in that the lubricating oil state estimation unit estimates the deterioration state of the lubricating oil based on the estimated temperature of the lubricating oil.

3. The gas compressor according to claim 1 or 2, The lubricating oil state estimation unit also estimates the pressure of the lubricating oil together with the temperature of the lubricating oil, and estimates the deterioration state of the lubricating oil based on the temperature and pressure of the lubricating oil. The gas compressor is characterized by this.

4. The gas compressor according to claim 1 or 2, The lubricating oil state estimation unit obtains the values of the suction temperature, the discharge pressure, and the rotational speed of the motor in a certain period shorter than the entire operation period, and obtains the elapsed time since the last lubricating oil change. Based on these, the gas compressor is characterized in that the deterioration state of the lubricating oil is estimated.

5. The gas compressor according to claim 4, The lubricating oil state estimation unit estimates the deterioration state of the lubricating oil based on the values of the suction temperature, the discharge pressure, and the rotational speed of the motor obtained in a period of at least one day or more. The gas compressor is characterized by this.

6. The gas compressor according to claim 4, The certain period is the shortest time cycle of environmental fluctuations during which the compressor is operated. Based on the values of the suction temperature, the discharge pressure, and the rotational speed of the motor obtained in this shortest time cycle, the deterioration state of the lubricating oil during that period is estimated, and this is integrated over the operation period of the compressor. The gas compressor is characterized by predicting the progress of oil deterioration and estimating the remaining life of the lubricating oil.

7. The gas compressor according to claim 4, The lubricating oil state estimation unit is given an allowable upper limit value of the total acid value of the lubricating oil, and the remaining life of the lubricating oil is estimated based on this allowable upper limit value of the total acid value and the estimated deterioration state of the lubricating oil. The gas compressor is characterized by this.

8. The gas compressor according to claim 1 or 2, A flow rate adjustment valve is provided in the oil circulation path that supplies lubricating oil to the compression mechanism unit, Based on the deterioration state of the lubricating oil estimated by the lubricating oil state estimation unit, the flow rate adjustment valve is controlled to adjust the flow rate of the lubricating oil supplied to the compression mechanism unit. The gas compressor is characterized by this.

9. The gas compressor according to claim 8, wherein the oil cooler is provided with a cooler fan for generating cooling air for cooling the lubricating oil, and when reducing the opening degree of the flow rate adjustment valve, the rotational speed of the cooler fan is increased. The gas compressor is characterized by this.

10. The gas compressor according to claim 8, wherein the oil cooler is provided with a flow path switching valve for switching the heat transfer area of the heat exchange section through which the lubricating oil flows, and when reducing the opening degree of the flow rate adjustment valve, the flow path switching valve is controlled so that the heat transfer area of the heat exchange section of the oil cooler increases. The gas compressor is characterized by this.

11. The gas compressor according to claim 1 or 2, wherein the lubricating oil state estimation unit estimates the amount of moisture accumulated by mixing a part of the moisture contained in the working fluid into the lubricating oil based on the suction humidity of the working fluid sucked into the compression mechanism unit, and based on the estimated temperature of the lubricating oil and the amount of moisture contained in the lubricating oil, estimates the deterioration state of the lubricating oil. The gas compressor is characterized by this.

12. The gas compressor according to claim 11, wherein a humidity sensor for detecting the suction humidity of the working fluid sucked into the compression mechanism unit is provided, and the lubricating oil state estimation unit estimates the amount of moisture contained in the lubricating oil based on the humidity detected by the humidity sensor. The gas compressor is characterized by this.

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