Oil feed type air compressor

Abstract

Provided is an oil feed type air compressor capable of detecting the amount of drained liquid without separating drained liquid and oil.　The oil feed type air compressor comprises: a compressor body 2 for compressing air while injecting oil into an operation chamber; a separator 5 for separating oil from the compressed air discharged from the compressor body 2; an oil cooler 10 for cooling the oil separated in the separator 5 and supplying the oil to the operation chamber of the compressor body 2; a temperature sensor 14 for detecting the temperature of the oil separated in the separator 5; and a control device 9 for calculating the amount of drain mixed in the oil. The control device 9 calculates the increase amount of the temperature of the oil, on the basis of a detection result of the temperature sensor 14, when a predetermined time has elapsed after the compressor body 2 activates, and calculates the amount of the drain on the basis of the increase amount of the temperature of the oil.

Description

Oil-lubricated air compressor

[0001] The present invention relates to an oil-lubricated air compressor.

[0002] An oil-lubricated air compressor includes a compressor body that compresses air while injecting oil into the working chamber, a separator that separates the oil from the compressed air discharged from the compressor body, and an oil cooler that cools the oil separated by the separator and supplies it to the working chamber of the compressor body. Injecting oil into the working chamber of the compressor body allows for cooling of the heat of compression. However, depending on the operating conditions, moisture in the air can condense, generating drainage that becomes mixed with the oil. Because drainage accelerates oil deterioration, it is necessary to monitor the amount of drainage generated.

[0003] A known method for detecting the amount of drainage is to use a float with a specific gravity intermediate between that of drainage and oil (see, for example, Patent Document 1). In this method, drainage and oil are separated in the tank due to the difference in specific gravity (more specifically, drainage moves to the bottom and oil to the top), and the float moves according to the position of the interface between the drainage and oil. The amount of drainage can be detected based on the position of this float.

[0004] Japanese Patent Application Publication No. 03-164584

[0005] However, the above-mentioned method cannot detect the amount of drain unless the drain and oil are separated. One of the objects of the present invention is to detect the amount of drain even if the drain and oil are not separated.

[0006] In order to solve the above problem, the present invention provides the following configuration. The present invention includes a plurality of means for solving the above problem, and one example thereof is an oil-injected air compressor including a compressor main body that compresses air while injecting oil into a working chamber, a separator that separates oil from compressed air discharged from the compressor main body, and an oil cooler that cools the oil separated in the separator and supplies the oil to the working chamber of the compressor main body, the oil compressor further including a first temperature sensor that detects the temperature of the oil separated in the separator, and a control device that calculates an amount of drain mixed in the oil, the control device calculating an amount of drain mixed in the oil based on a detection result of the first temperature sensor, the amount of rise in temperature of the oil when a predetermined time has elapsed since the compressor main body started up or since the compressor main body was switched from unloaded operation to loaded operation, and the amount of drain based on the amount of rise in temperature of the oil.

[0007] According to the present invention, the amount of drain can be detected even if the drain and the oil do not separate.

[0008] Problems, configurations, and effects other than those described above will become clear from the following description.

[0009] 1 is a block diagram showing the configuration of an oil-lubricated air compressor according to an embodiment of the present invention; FIG. 2 is a block diagram showing the functional configuration of a control device according to an embodiment of the present invention;

[0010] An embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a diagram showing the configuration of an oil-lubricated air compressor in this embodiment.

[0011] The oil-lubricated air compressor of this embodiment includes an electric motor 1, a compressor main body 2 that is driven by the electric motor 1 and compresses air while injecting oil into a working chamber, an air filter 3 that is provided on the suction side of the compressor main body 2 and removes foreign matter from the air, a suction throttle valve 4 that is arranged between the compressor main body 2 and the air filter 3, a separator 5 that separates oil from the compressed air discharged from the compressor main body 2, an oil piping 6 that supplies the oil separated in the separator 5 to the working chamber of the compressor main body 2, a compressed air piping 7 that supplies the compressed air separated in the separator 5 to equipment (not shown) that consumes the compressed air, a user interface 8, and a control device 9.

[0012] The compressor body 2 has, for example, a pair of intermeshing male and female screw rotors and a casing that houses the screw rotors, with multiple working chambers formed in the tooth grooves of the screw rotors. Each working chamber moves axially as the rotor rotates, and sequentially performs an intake process to draw in air, a compression process to compress the air, and a discharge process to discharge the compressed air. The compressor body 2 is designed to inject oil into the working chambers for the purposes of cooling the heat of compression, sealing the working chambers, and lubricating the rotors.

[0013] The separator 5 has, for example, a swirl flow path that swirls the compressed air, separates oil from the compressed air by centrifugal separation, and stores the separated oil. However, if moisture in the air condenses and generates drainage, the drainage will be mixed with the oil. The oil piping 6 is provided with an oil cooler 10 that cools the oil separated in the separator 5, an oil filter 11 that removes foreign matter from the oil, and the like. The compressed air piping 7 is provided with an aftercooler 12 that cools the compressed air separated in the separator 5, and a pressure sensor 13 that detects the pressure of the compressed air.

[0014] The user interface 8 includes, for example, an operation switch and a stop switch that are operated by the user, and a monitor that is visually recognized by the user. The control device 9 includes a processor that executes processing according to a program, and a memory that stores the program and data.

[0015] In response to operation of the operation switch, the control device 9 drives the electric motor 1 and controls the suction throttle valve 4 to an open state, thereby performing load operation of the compressor main body 2. In response to operation of the stop switch, the control device 9 stops the electric motor 1 and controls the suction throttle valve 4 to a closed state, thereby stopping the compressor main body 2.

[0016] When the pressure detected by the pressure sensor 13 rises to a predetermined upper limit value Pu during the load operation of the compressor body 2, the control device 9 switches the suction throttle valve 4 to a closed state, thereby switching the operation of the compressor body 2 to unload operation. When the pressure detected by the pressure sensor 13 falls to a predetermined lower limit value Pd (where Pd<Pu) during the unload operation of the compressor body 2, the control device 9 switches the suction throttle valve 4 to an open state, thereby switching the operation of the compressor body 2 to load operation.

[0017] When the electric motor 1 starts and the compressor body 2 starts up, heat is generated due to friction between the components that make up the compressor body 2 and the compression of the air, and the generated heat increases the temperatures of the compressor body 2, the compressed air, and the oil. The amount of increase in temperature of the compressor body 2, the compressed air, and the oil varies depending on the amount of drainage generated. The following equation 1 holds due to the relationship between the heat balance of the compressor body 2, the compressed air, the oil, and the drainage.

[0018]

[0019] In the formula, ΔTc1, ΔTa1, and ΔTo1 are the amounts of temperature rise of the compressor body 2, the amount of temperature rise of the compressed air, and the amount of temperature rise of the oil when no drain is generated. ΔTc2, ΔTa2, ΔTo2, and ΔTw are the amounts of temperature rise of the compressor body 2, the amount of temperature rise of the compressed air, the amount of temperature rise of the oil, and the amount of temperature rise of the drain when drain is generated and mixed with the oil (where ΔTo2 = ΔTw). In the formula, Mc, Ma, Mo, and Mw are the quantity (mass) of the compressor body 2, the flow rate (mass flow rate) of the compressed air, the amount (mass) of the oil, and the amount (mass) of the drain. In the formula, Cc, Ca, Co, and Cw are the specific heats of the compressor body 2, the specific heat of the compressed air, the specific heat of the oil, and the specific heat of the drain. By modifying the above formula 1, the following formula 2 can be derived.

[0020]

[0021] The oil-lubricated air compressor of this embodiment is configured to calculate the amount of drain mixed in the oil using the above-mentioned Equation 2. More specifically, the oil-lubricated air compressor of this embodiment is equipped with a temperature sensor 14 (first temperature sensor) that detects the temperature of the oil separated in the separator 5 (more specifically, the oil in the separator 5), a temperature sensor 15 (third temperature sensor) that detects the temperature of the compressed air (more specifically, the compressed air upstream of the aftercooler 12 in the compressed air piping 7), and a temperature sensor 16 (third temperature sensor) that detects the temperature of the compressor main body 2 (e.g., the discharge side portion). As shown in Fig. 2, the control device 9 has, as functional components related to the calculation of the amount of drain, an oil temperature rise amount calculation unit 17, a compressed air temperature rise amount calculation unit 18, a compressor main body temperature rise amount calculation unit 19, and a drain amount calculation unit 20.

[0022] The control device 9 uses a timer to determine whether a predetermined time (e.g., one minute) has elapsed since the compressor main body 2 was started. The oil temperature rise calculation unit 17 calculates the amount of rise ΔTo2 in oil temperature when the predetermined time has elapsed since the compressor main body 2 was started, based on the detection result of the temperature sensor 14. The compressed air temperature rise calculation unit 18 calculates the amount of rise ΔTa2 in compressed air temperature when the predetermined time has elapsed since the compressor main body 2 was started, based on the detection result of the temperature sensor 15. The compressor main body temperature rise calculation unit 19 calculates the amount of rise ΔTc2 in temperature of the compressor main body 2 when the predetermined time has elapsed since the compressor main body 2 was started, based on the detection result of the temperature sensor 16.

[0023] The drain amount calculation unit 20 calculates the amount of drain Mw by substituting the above-mentioned oil temperature increase amount ΔTo2, compressed air temperature increase amount ΔTa2, and compressor body 2 temperature increase amount ΔTc2 into Equation 2. Note that ΔTo1, ΔTc1, and ΔTa1 in the equation are obtained in advance by testing or simulation, or are measured when the compressor is operated for the first time or immediately after oil change, and are stored in the control device 9. Mo, Mc, Ma, Mw, Co, Cc, Ca, and Cw in the equation are stored in the control device 9.

[0024] The control device 9, for example, displays the calculated amount of drain on a monitor, or displays a warning message on the monitor when the calculated amount of drain is equal to or greater than a predetermined value, thereby urging the user to change the oil, etc.

[0025] As described above, in this embodiment, the amount of drainage can be detected even if the drainage and oil do not separate. This makes it possible to deal with cases where it is difficult to separate the drainage and oil or where it takes a long time to separate the drainage and oil, and also improves the accuracy of estimating the amount of drainage.

[0026] In the above embodiment, the temperature sensor 14 detects the temperature of the oil in the separator 5, but this is not limiting and, for example, the temperature sensor 14 may detect the temperature of the oil upstream of the oil cooler 10 in the oil pipe 6. In the above embodiment, the temperature sensor 15 detects the temperature of the compressed air upstream of the aftercooler 12 in the compressed air pipe 7, but this is not limiting and, for example, the temperature sensor 15 may detect the temperature of the compressed air in the separator 5.

[0027] In the above embodiment, the control device 9 calculates the amount of drainage based on the amounts of increase in oil temperature, the amount of increase in compressed air temperature, and the amount of increase in temperature of the compressor body 2 after a predetermined time has elapsed since the compressor body 2 was started, but this is not limiting. The control device 9 may also calculate the amount of drainage based on the amounts of increase in oil temperature, the amount of increase in compressed air temperature, and the amount of increase in temperature of the compressor body 2 after a predetermined time has elapsed since the compressor body 2 was switched from unloaded operation to loaded operation.

[0028] In the above embodiment, the control device 9 calculates the amount of drain using Equation 2, i.e., based on the amount of oil temperature increase, the amount of compressed air temperature increase, and the amount of compressor body 2 temperature increase. However, this is not limited to this. Of the amount of oil temperature increase, the amount of compressed air temperature increase, and the amount of compressor body 2 temperature increase, the amount of oil temperature increase varies most significantly depending on the amount of drain generated. This is because, since drain is mixed in the oil, the oil exchanges heat directly with the drain, whereas the compressed air and the compressor body 2 exchange heat with the drain via the oil. Therefore, since the first and second terms on the right side of Equation 2 are much smaller than the third term, at least one of them may be ignored. A modification based on this perspective will now be described.

[0029] The oil-lubricated air compressor according to the first modification of the present invention is equipped with temperature sensors 14, 15 but does not have temperature sensor 16. Based on the detection results of temperature sensors 14, 15, control device 9 calculates the amount of increase in oil temperature and the amount of increase in compressed air temperature when a predetermined time has elapsed since compressor main body 2 started up or since compressor main body 2 was switched from unloaded operation to loaded operation. Then, the amount of drain is calculated by the sum of the second and third terms on the right side of Equation 2.

[0030] The oil-lubricated air compressor according to the second modification of the present invention is equipped with temperature sensors 14, 16 but does not have temperature sensor 15. Based on the detection results of temperature sensors 14, 16, control device 9 calculates the amount of rise in oil temperature and the amount of rise in temperature of compressor body 2 when a predetermined time has elapsed since compressor body 2 was started or since compressor body 2 was switched from unloaded operation to loaded operation. Then, the amount of drain is calculated by the sum of the first and third terms on the right side of Equation 2.

[0031] The oil-lubricated air compressor according to the third modification of the present invention includes temperature sensor 14 but does not include temperature sensors 15 and 16. Based on the detection result of temperature sensor 14, control device 9 calculates the amount of oil temperature rise when a predetermined time has elapsed since compressor main body 2 started up or since compressor main body 2 was switched from unloaded operation to loaded operation. Then, the amount of drain is calculated using only the third term on the right side of Equation 2.

[0032] In the above embodiment and modified examples, the control device 9 calculates the amount of drain using a formula, but this is not limited to this. An oil-lubricated air compressor according to a fourth modified example of the present invention includes a temperature sensor 14 but does not include temperature sensors 15 and 16. Based on the detection result of the temperature sensor 14, the control device 9 calculates the amount of oil temperature rise a predetermined time after the compressor main body 2 starts up or after the compressor main body 2 switches from unloaded operation to loaded operation. The control device 9 then calculates the amount of drain by referencing a table containing multiple combinations of the amount of oil temperature rise and the amount of drain. The table was created based on the results of a test in which the amount of drain was changed and the amount of oil temperature rise was measured, and is stored in the control device 9.

[0033] 2...Compressor body, 5...Separator, 9...Control device, 10...Oil cooler, 14...Temperature sensor (first temperature sensor), 15...Temperature sensor (second temperature sensor), 16...Temperature sensor (third temperature sensor)

Claims

1. An oil-lubricated air compressor comprising: a compressor main body that compresses air while injecting oil into a working chamber; a separator that separates oil from the compressed air discharged from the compressor main body; and an oil cooler that cools the oil separated by the separator and supplies the oil to the working chamber of the compressor main body, the oil compressor further comprising: a first temperature sensor that detects the temperature of the oil separated by the separator; and a control device that calculates the amount of drain mixed in with the oil, the control device calculating, based on the detection result of the first temperature sensor, the amount of rise in temperature of the oil when a predetermined time has elapsed since the compressor main body started up or since the compressor main body was switched from unloaded operation to loaded operation, and calculating the amount of drain based on the amount of rise in temperature of the oil.

2. An oil-lubricated air compressor as claimed in claim 1, further comprising a second temperature sensor for detecting the temperature of the compressed air, wherein the control device calculates, based on the detection result of the second temperature sensor, the amount of rise in temperature of the compressed air when the specified time has elapsed since the compressor main body was started or since the compressor main body was switched from unloaded operation to loaded operation, and calculates the amount of drain based on the amount of rise in temperature of the oil and the amount of rise in temperature of the compressed air.

3. An oil-lubricated air compressor as claimed in claim 1, further comprising a third temperature sensor for detecting the temperature of the compressor body, wherein the control device calculates, based on the detection result of the third temperature sensor, the amount of temperature rise of the compressor body when the specified time has elapsed since the compressor body was started or since the compressor body was switched from unloaded operation to loaded operation, and calculates the amount of drain based on the amount of temperature rise of the oil and the amount of temperature rise of the compressor body.

4. An oil-lubricated air compressor as claimed in claim 2, further comprising a third temperature sensor for detecting the temperature of the compressor body, wherein the control device calculates, based on the detection result of the third temperature sensor, the amount of temperature rise of the compressor body when the specified time has elapsed since the compressor body was started or since the compressor body was switched from unloaded operation to loaded operation, and calculates the amount of drain based on the amount of temperature rise of the oil, the amount of temperature rise of the compressed air, and the amount of temperature rise of the compressor body.

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