Oil-free compressor

Abstract

To provide a non-oil supply type compressor capable of supplying a necessary flow rate of lubrication oil to a bearing with good responsiveness when an operation condition changes.SOLUTION: A non-oil supply type compressor comprises a compressor body 1 that has a rotor 3 for compressing a gas and a bearing 6 rotatably supporting the rotor 3, a lubrication oil system 60 for supplying lubrication oil to the bearing 6, and a control device 40. The lubrication oil system 60 has a storage unit 12 for storing lubrication oil, an oil pump 10 for discharging the lubrication oil stored in the storage unit 12, a flow control device 17 for controlling a flow rate of the lubrication oil supplied from the oil pump 10 to the bearings 6, and a pressure sensor 21 for detecting a pressure of the lubrication oil supplied to the bearing 6. The control device 40 has a storage unit 43 that stores a target pressure for each of a plurality of operation states, reads out the target pressure according to the operation state from the storage unit 43 and sets it, and controls the flow control device 17 so that a pressure detected by the pressure sensor 21 becomes the set target pressure.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] An oil-free compressor that does not require the supply of oil or water to a compression working chamber (working space) is known. As an oil-free compressor, for example, a screw compressor having a pair of male and female screw rotors that are non-contact and oil-free and rotatable, and compressing a gas such as air by these rotors is known. An oil-free compressor generally includes a lubricating oil system that circulates lubricating oil for lubricating and cooling a rotor bearing, a gear, and a compressor body.

[0003] The supply amount of lubricating oil required for lubricating and cooling a bearing of a rotor, which is a compression rotating body, is defined by, for example, a constant according to the bearing specifications, a target temperature of the bearing, a rotational speed of the rotor, a discharge pressure of the compressed gas, and a load by a gear. During operation, the compressor has a variable rotational speed or discharge pressure, and either one of them changes the supply amount of lubricating oil. When the relationship between the rotational speed of the rotor and the discharge pressure of the compressed gas changes due to a change in the operating state, the required supply amount of lubricating oil to the bearing also changes.

[0004] Patent Document 1 discloses a gas compressor provided with a control device that reduces the supply amount of lubricating oil during low-pressure boost operation compared to rated operation. The control device described in Patent Document 1 calculates the required supply amount of lubricating oil to a bearing from the load of the bearing corresponding to the discharge pressure of the compressor body detected by a pressure sensor and the rotational speed of the rotor corresponding to the rotational frequency output by an inverter, and performs flow control of the lubricating oil based on the required supply amount. When the flow rate of lubricating oil from an oil pump corresponding to the output frequency of the inverter exceeds the required supply amount, the control device described in Patent Document 1 opens an oil drain solenoid valve to limit the flow rate of lubricating oil supplied to the bearing.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] WO2015 / 198647A1 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the gas compressor described in Patent Document 1, the required supply amount is calculated based on multiple parameters (discharge pressure, rotational frequency), and the opening and closing of the oil discharge solenoid valve is controlled so that the actual amount of lubricating oil supplied matches the required amount. Therefore, when the operating conditions change, it may take time to adjust the amount of lubricating oil supplied to the bearings to the required amount, and there was room for improvement in terms of responsiveness.

[0007] The present invention aims to provide an oil-free compressor that can supply the necessary flow rate of lubricating oil to the bearings with good responsiveness when the operating conditions change. [Means for solving the problem]

[0008] An oil-free compressor according to one aspect of the present invention is ,B ta and bearing The compressor body and A discharge temperature sensor detects the discharge temperature, which is the temperature of the gas discharged from the compressor body, A storage section for storing lubricating oil, an oil pump for discharging the lubricating oil stored in the storage section, a flow rate control device for controlling the flow rate of lubricating oil supplied from the oil pump to the bearing, and a pressure sensor for detecting the pressure of the lubricating oil supplied to the bearing. An oil-free compressor comprising a control device, The control device is Based on the discharge temperature detected by the discharge temperature sensor, the system switches between a first control and a second control. The first control maintains the flow rate of lubricating oil supplied to the bearing by the flow rate control device at a predetermined flow rate, while the second control adjusts the flow rate of lubricating oil supplied to the bearing by the flow rate control device based on the pressure of the lubricating oil detected by the pressure sensor. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an oil-free compressor that can responsively supply the necessary flow rate of lubricating oil to the bearings when the operating conditions change. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is an overall diagram of the oil-free compressor. [Figure 2]Figure 2 shows the lubrication system of the compressor. [Figure 3] Figure 3 shows an example of a control table that defines the relationship between the pressure difference between the pressure of the lubricating oil supplied to the bearing (detected pressure) and the target pressure, and the target opening degree of the oil drain control valve. [Figure 4] Figure 4 is a flowchart illustrating an example of the process flow for valve control performed by the control device. [Figure 5] Figure 5 is a flowchart illustrating an example of the flag setting process. [Modes for carrying out the invention]

[0011] One embodiment of the present invention will be described below with reference to the drawings. Figure 1 is an overall configuration diagram of an oil-free compressor (hereinafter also simply referred to as "compressor") 100 according to one embodiment of the present invention.

[0012] As shown in Figure 1, the compressor 100 according to this embodiment is a two-stage screw compressor and comprises a low-pressure stage compressor body 1L and a high-pressure stage compressor body 1H that further compresses the air compressed by the low-pressure stage compressor body 1L. Since the low-pressure stage compressor body 1L and the high-pressure stage compressor body 1H have similar configurations, they will collectively be referred to as compressor body 1 below. Compressor body 1 has a pair of male and female screw rotors (rotors) 3 that can rotate non-contact and without lubrication by timing gears, a rotor casing 4 that houses the rotors 3, and bearings 6 that rotatably support the rotors 3. The bearings 6 support the shaft ends of the rotors 3 on the intake side and discharge side of compressor body 1.

[0013] The compressor 100 includes a motor 2 that drives the compressor body 1, and a power transmission mechanism that transmits the power of the motor 2 to the rotor 3 of the compressor body 1. This power transmission mechanism has a bull gear 7 provided on the output shaft of the motor 2 and a pinion gear 8 provided on the shaft end of the rotor 3 of the compressor body 1. The power of the motor 2 is transmitted to the rotor 3 of the compressor body 1 via the bull gear 7 and pinion gear 8, which mesh with each other. The bull gear 7 and pinion gear 8 are housed in a gear case 11. The gear case 11 is connected to the rotor casing 4. As the rotor 3 rotates due to the motor 2, the air taken in from the intake of the compressor body 1 is compressed in the working space formed by the rotor 3 and the rotor casing 4, and discharged from the discharge of the compressor body 1.

[0014] The compressor 100 includes an intercooler 14bL, which is a heat exchanger for compressed air that cools the compressed air discharged from the low-pressure stage compressor body 1L, and an aftercooler 14bH, which is a heat exchanger for compressed air that cools the compressed air discharged from the high-pressure stage compressor body 1H. The heat exchangers for compressed air 14b (14bL, 14bH) are tube-type or plate-type heat exchangers. The heat exchanger for compressed air 14b receives a supply of a coolant (water or coolant) not shown and cools the compressed air to a desired temperature through heat exchange with the coolant.

[0015] The compressor 100 includes a lubrication system 60 that supplies lubricating oil to the bearings 6 of the compressor body 1, and a control device 40 that controls the operation of the compressor 100. The lubricating oil is used for lubricating and cooling the bearings 6, as well as for lubricating the gears in the gear case 11 and cooling the compressor body 1. Details of the lubrication system 60 will be described later.

[0016] The control device 40 is a programmable computer including an arithmetic unit 41, a volatile memory 42, and a non-volatile memory 43. The non-volatile memory 43 stores programs, set values, threshold values, etc. that can execute various operations. That is, the non-volatile memory 43 is a storage medium (storage device) that can read a program for realizing the functions of the present embodiment. The volatile memory 42 is a storage medium (storage device) that temporarily stores the operation results by the arithmetic unit 41 and the input signals. The arithmetic unit 41 is a processing device that develops the program stored in the non-volatile memory 43 in the volatile memory 42 and performs arithmetic processing, and performs predetermined arithmetic processing on the data taken in from various sensors, the non-volatile memory 43, and the volatile memory 42 according to the program.

[0017] The control device 40 realizes a plurality of functions through the cooperation of software and the arithmetic unit 41, and performs input and output of control signals with each part of the compressor 100. An input device (not shown) is connected to the control device 40. The input device is, for example, an input panel installed on the outer shell of the housing 50 and is operated by a user. When the input device is operated by the user, an operation signal corresponding to the user's operation is output from the input device to the control device 40. The control device 40 changes various set values, newly registers set values, etc. according to the operation signal from the input device. Note that the control device 40 can be connected to control devices (notebook PCs, tablet PCs, servers, etc.) via a network, and stores the set values in the non-volatile memory 43 according to the signals from the control devices.

[0018] Various sensors and devices are connected to the control device 40. For example, a discharge pressure sensor 18 for detecting the discharge pressure of the compressed air supplied from the compressor 100 to the user side is connected to the control device 40. Also, a lubricating oil pressure sensor 21 for detecting the pressure of the lubricating oil system 60 is connected to the control device 40.

[0019] Furthermore, the control device 40 is connected to a first intake temperature sensor 31 that detects the temperature of the air (first intake temperature) Ti1 sucked into the low-pressure stage compressor body 1L, a first discharge temperature sensor 32 that detects the temperature of the compressed air (first discharge temperature) To1 discharged from the low-pressure stage compressor body 1L, a second intake temperature sensor 33 that detects the temperature of the air (second intake temperature) Ti2 sucked into the high-pressure stage compressor body 1H, and a second discharge temperature sensor 34 that detects the temperature of the compressed air (second discharge temperature) To2 discharged from the high-pressure stage compressor body 1H.

[0020] The housing 50 that houses each device is provided with an intake port 51 that takes in air (outside air) from outside the housing 50 into the housing 50, and an exhaust port 52 that discharges the air inside the housing 50 to the outside of the housing 50. The intake port 51 is provided at a position facing the motor 2 located on the upstream side of the airflow inside the housing. A cooling fan 20 is provided near the exhaust port 52 inside the housing 50. When the cooling fan 20 rotates, air is taken into the housing 50 from the intake port 51, and the air taken into the housing 50 flows as cooling air mainly in the order of the motor 2, the compressor body 1, and the heat exchangers 14a and 14b, and is discharged from the exhaust port 52 to the outside of the housing 50. The rotational speed of the cooling fan 20 is controlled by the control device 40. The control device 40 controls the rotational speed of the cooling fan 20 so as to maintain the temperature inside the housing 50 within a certain range based on the discharge pressure of the compressed air detected by the discharge pressure sensor 18 and the temperature of the motor 2 detected by a motor temperature sensor (not shown).

[0021] The motor 2 receives electric power of an arbitrary frequency from the inverter 19 via the control device 40 and can rotate at a variable speed.

[0022] The compressor body 1 draws in air from the intake section by the rotation of the rotor 3, compresses the drawn-in air, and discharges it. The compressed air generated by the compressor body 1 is discharged into the discharge pipe 25. In this embodiment, the compressor 100 performs two-stage compression as described above. The low-pressure stage compressor body 1L compresses the air (outside air) drawn in through the air filter 5 and discharges the compressed air into the first discharge pipe 25L. The compressed air discharged into the first discharge pipe 25L is guided through the intercooler 14bL to the intake section of the high-pressure stage compressor body 1H. The high-pressure stage compressor body 1H further compresses the compressed air discharged from the low-pressure stage compressor body 1L and discharges the compressed air into the second discharge pipe 25H.

[0023] The second discharge pipe 25H is equipped with a check valve 29 that allows air to flow from the high-pressure stage compressor body 1H toward the aftercooler 14bH, and prohibits air from flowing from the aftercooler 14bH toward the high-pressure stage compressor body 1H. An air discharge path 26 is connected upstream of the check valve 29 of the second discharge pipe 25H. Downstream of the air discharge path 26 is an air discharge valve 27, which is a solenoid valve capable of opening and closing the air discharge path 26.

[0024] The control device 40 operates the compressor body 1 under load (normal operation) when the discharge pressure Pa of compressed air detected by the discharge pressure sensor 18 is less than the set pressure Pa0, and operates it without load when the discharge pressure Pa of compressed air detected by the discharge pressure sensor 18 is equal to or greater than the set pressure Pa0.

[0025] During load operation, the control device 40 outputs a close signal to the air release valve 27, causing the air release valve 27 to close completely. Therefore, during load operation, compressed air discharged from the high-pressure stage compressor body 1H flows to the aftercooler 14bH through the check valve 29. During no-load operation, the control device 40 outputs an open signal to the air release valve 27, causing the air release valve 27 to open completely. Therefore, when the amount of compressed air consumed by the user decreases and the discharge pressure Pa detected by the discharge pressure sensor 18 becomes equal to or greater than the set pressure Pa0, the air release valve 27 opens, and compressed air is released into the atmosphere through the air release path 26 and the air release silencer 28. During no-load operation, the load on the compressor body 1 is reduced, so power consumption is reduced compared to load operation. In addition, during no-load operation, the control device 40 may reduce the rotational speed of the motor 2 compared to load operation.

[0026] The lubrication system 60 of the compressor 100 will be described in detail with reference to Figures 1 and 2. Figure 2 is a diagram showing the lubrication system 60 of the compressor 100. As shown in Figure 1, a pump drive gear 9 is provided at the end of the output shaft of the motor 2. The pump drive gear 9 meshes with a driven gear (not shown) connected to the oil pump 10. Power from the motor 2 is transmitted to the oil pump 10 via the pump drive gear 9 and the driven gear. As the oil pump 10 rotates due to the motor 2, lubricating oil circulates within the lubrication system 60. The oil pump 10 according to this embodiment is a fixed-displacement pump having a constant displacement volume.

[0027] As shown in Figures 1 and 2, the lubrication system 60 comprises a gear case 11 having a storage section 12 for storing lubricating oil, an oil pump 10 for sucking in and discharging the lubricating oil stored in the storage section 12, a heat exchanger 14a for cooling the lubricating oil, an oil filter 15 for capturing dust and debris in the lubrication system 60, and lubricating oil piping (13a, 13b, 13c) for connecting the various devices installed in the lubrication system 60.

[0028] The lubrication oil piping includes, for example, a main pipe 13a that guides the lubricating oil discharged from the oil pump 10 to the bearing 6, a bypass pipe 13b that branches off from the main pipe 13a and bypasses the lubricating oil heat exchanger 14a, and a return pipe 13c that branches off from the main pipe 13a and returns a portion of the lubricating oil discharged from the oil pump 10 to the storage section 12 of the gear case 11 without guiding it to the bearing 6. Downstream of the oil filter 15, the main pipe 13a branches into a first branch pipe 13a1 connected to the rotor casing 4 of the low-pressure stage compressor body 1L, and a second branch pipe 13a2 connected to the rotor casing 4 of the high-pressure stage compressor body 1H. The lubricating oil supplied to the bearing 6 of the low-pressure stage compressor body 1L and the lubricating oil supplied to the bearing 6 of the high-pressure stage compressor body 1H merge in the gear case 11 connected to the rotor casing 4 of the low-pressure stage compressor body 1L and the high-pressure stage compressor body 1H.

[0029] The oil pump 10 pumps the lubricating oil stored in the storage section 12 of the gear case 11 to the lubricating oil heat exchanger 14a via the main piping 13a. The lubricating oil, cooled to a predetermined temperature or lower in the lubricating oil heat exchanger 14a, is guided through the oil filter 15 to the bearings 6 of the high-pressure stage compressor body 1H and the bearings 6 of the low-pressure stage compressor body 1L, and is recovered in the gear case 11. In this embodiment, a lubricating oil pressure sensor 21 is attached to the second branch pipe 13a2. The lubricating oil pressure sensor 21 only needs to be able to detect the pressure of the lubricating oil supplied to the bearings 6, and its mounting location is not limited. For example, the lubricating oil pressure sensor 21 may be attached to the first branch pipe 13a1 or to the rotor casing 4.

[0030] In this embodiment, the oil pump 10 and the compressor body 1 are driven by a single motor 2 (see Figure 1). Therefore, as the rotational speed of the rotor 3 of the compressor body 1 increases, the amount of lubricating oil discharged from the oil pump 10 increases.

[0031] The return pipe 13c is equipped with a solenoid valve (hereinafter also referred to as an oil drain control valve) 17, which serves as a flow control device to control the flow rate of lubricating oil returned from the oil pump 10 to the storage unit 12.

[0032] The control device 40 adjusts the opening degree of the oil drain control valve 17. The larger the opening degree of the oil drain control valve 17, the greater the flow rate of lubricating oil returning from the oil pump 10 to the storage unit 12 through the oil drain control valve 17. As a result, the flow rate of lubricating oil guided from the oil pump 10 to the bearing 6 decreases. In this way, the control device 40 according to this embodiment controls the flow rate (hereinafter also referred to as the supply amount) of lubricating oil supplied from the oil pump 10 to the bearing 6 by controlling the opening degree of the oil drain control valve 17. Based on the target pressure set according to the operating state, the control device 40 adjusts the opening degree of the oil drain control valve 17 to secure the amount of lubricating oil required for the bearing 6 and returns the excess lubricating oil to the storage unit 12 through the return pipe 13c.

[0033] The configuration of the flow control device for controlling the amount of lubricating oil supplied is not limited to the oil drain control valve 17. For example, the compressor 100 may be equipped with an autonomous engine (electric motor, etc.) that drives the oil pump 10 as a flow control device instead of the oil drain control valve 17. In this case, the control device 40 controls the flow rate of lubricating oil supplied from the oil pump 10 to the bearing 6 by controlling the engine to adjust the rotational speed of the oil pump 10. The compressor 100 may be equipped with both the oil drain control valve 17 and the engine as flow control devices. Furthermore, the oil drain control valve 17 may be an electromagnetic proportional valve whose opening degree can be continuously adjusted according to the control current from the control device 40, or it may be an electromagnetic switching valve that can be switched between two positions, "open" and "closed". In this embodiment, an example in which the oil drain control valve 17 is an electromagnetic valve whose opening degree can be adjusted in multiple stages will be described.

[0034] The non-volatile memory 43 of the control device 40 stores in advance target pressures for multiple operating states. The target pressure for each operating state is determined based on measured values ​​of the lubricating oil pressure when the required amount of lubricating oil flows to the bearing 6, as determined by experiments, etc. The required amount is the amount of oil that can properly lubricate and cool the bearing 6. The control device 40 reads and sets the target pressure corresponding to the current operating state from the non-volatile memory 43. The control device 40 controls the oil drain control valve 17 so that the pressure detected by the lubricating oil pressure sensor 21 (hereinafter also referred to as the detected pressure) becomes the set target pressure.

[0035] The control device 40 sets target pressure Pot for each operating state of the lubricating oil pressure sensor 21. When the operating state is a load operation state, the control device 40 sets the target pressure Pot to the first target pressure Pot1 (Pot=Pot1). The first target pressure Pot1 can be the pressure detected by the lubricating oil pressure sensor 21 in the experiment when the compressor 100 is in a load operation state and the required amount of lubricating oil is supplied to the bearing 6. When the operating state is an unload operation state, the control device 40 sets the target pressure Pot to the second target pressure Pot2 (Pot=Pot2). The second target pressure Pot2 can be the pressure detected by the lubricating oil pressure sensor 21 in the experiment when the compressor 100 is in an unload operation state and the required amount of lubricating oil is supplied to the bearing 6. In an unload operation state, the load acting on the compressor body 1 is smaller than in a load operation state. Therefore, in an unload operation state, the required amount of lubricating oil supplied to the bearing 6 can be smaller than in a load operation state. Therefore, the second target pressure Pot2 is lower than the first target pressure Pot1 (Pot2 <Pot1)。

[0036] The control device 40 calculates the pressure difference ΔPo between the actual pressure (detected pressure) Poa detected by the lubricating oil pressure sensor 21 and the set target pressure Pot. Based on the calculated pressure difference ΔPo and the control table (see Figure 3) stored in the non-volatile memory 43, the control device 40 determines the target opening degree Vot of the oil drain control valve 17. The control table is opening degree information that links the pressure difference between the pressure of the lubricating oil supplied to the bearing 6 and the target pressure with the target opening degree of the oil drain control valve 17, and is predetermined through experiments or other means.

[0037] Figure 3 shows an example of a control table that defines the relationship between the pressure difference between the pressure of the lubricating oil supplied to the bearing 6 (detected pressure) and the target pressure, and the target opening degree of the oil drain control valve 17. The relationship between the pressure differences ΔPa, ΔPb, ΔPc, ΔPd, and ΔPe in the control table is ΔPa < ΔPb < ΔPc < ΔPd < ΔPe, for example, ΔPc is 0, ΔPa and ΔPb are negative values, and ΔPd and ΔPe are positive values. The control table is defined such that the larger the pressure difference ΔPo, the larger the target opening degree Vot of the oil drain control valve 17 becomes.

[0038] The control device 40 sets the target opening degree Vot of the oil drain control valve 17 based on the calculated pressure difference ΔPo and the control table stored in the non-volatile memory 43. The control device 40 compares the calculated pressure difference ΔPo (hereinafter also referred to as the calculated value ΔPoc) with the pressure difference ΔPo stored in the control table (hereinafter also referred to as the stored value ΔPom), and sets the target opening degree Vot corresponding to the stored value ΔPom that is closest to the calculated value ΔPoc. For example, if the stored value ΔPom that is closest to the calculated value ΔPoc is ΔPa, the control device 40 sets the target opening degree Vot of the oil drain control valve 17 to 0% (i.e., fully closed). Also, if the stored value ΔPom that is closest to the calculated value ΔPoc is ΔPe, the control device 40 sets the target opening degree Vot of the oil drain control valve to 100% (i.e., fully open).

[0039] The control device 40 controls the oil drain control valve 17 so that its opening degree becomes a set target opening degree Vot, thereby bringing the detected pressure Poa closer to the target pressure Pot. If the target pressure Pot is higher than the detected pressure Poa, the control device 40 reduces the target opening degree Vot to less than 50%, thereby reducing the flow rate of lubricating oil returned to the reservoir 12 through the oil drain control valve 17. This increases the flow rate of lubricating oil directed to the bearing 6, causing the detected pressure Poa to increase closer to the target pressure Pot. If the target pressure Pot is lower than the detected pressure Poa, the control device 40 increases the target opening degree Vot to more than 50%, thereby increasing the flow rate of lubricating oil returned to the reservoir 12 through the oil drain control valve 17. This reduces the flow rate of lubricating oil directed to the bearing 6, causing the detected pressure Poa to decrease closer to the target pressure Pot.

[0040] Thus, the control device 40 controls the opening degree of the oil drain control valve 17 based on the pressure difference ΔPo between the detected pressure Poa and the target pressure Pot, thereby bringing the detected pressure Poa closer to the target pressure Pot. However, if the temperature of the compressed air discharged from the compressor 100 becomes high due to some abnormality, the temperature of the bearing 6 will also rise. Therefore, it is preferable to disable the control of the opening degree of the oil drain control valve 17 according to the pressure difference ΔPo and keep the oil drain control valve 17 fully closed at all times.

[0041] Therefore, the control device 40 according to this embodiment determines whether the invalidation condition described later is met, and if the invalidation condition is met, it does not perform opening control of the oil drain control valve 17 according to the pressure difference ΔPo, and forcibly closes the oil drain control valve 17 completely. As a result, the entire flow rate of lubricating oil discharged from the oil pump 10 is distributed to the low-pressure stage compressor body 1L and the high-pressure stage compressor body 1H.

[0042] The invalidation condition is met when the difference ΔTd between the current temperature difference ΔTa (temperature To of the air discharged from the compressor body 1 and the temperature Ti of the air drawn into the compressor body 1) and the reference value ΔTb is greater than a predetermined value (hereinafter also referred to as the temperature difference threshold) ΔTt. The invalidation condition is not met if the difference ΔTd is less than or equal to the temperature difference threshold ΔTt. The temperature difference threshold ΔTt is a threshold used to determine if the temperature of the air discharged from the compressor body 1 is abnormally high, and is stored in advance in the non-volatile memory 43.

[0043] Figure 4 is a flowchart showing an example of the valve control process performed by the control device 40. The flowchart shown in Figure 4 starts, for example, when the start switch of the input device is turned on and the compressor 100 is started. After initial settings (not shown) are performed, the process from step S110 onwards is repeatedly executed at a predetermined control cycle.

[0044] In the initial settings (not shown), the control device 40 sets a reference value (also referred to as the reference temperature difference) ΔTb of the temperature difference between the temperature To of the air discharged from the compressor body 1 and the temperature Ti of the air drawn into the compressor body 1. Since the compressor 100 according to this embodiment is configured to perform two-stage compression, the control device 40 determines the first reference temperature difference ΔTb1 for the low-pressure stage compressor body 1L and the second reference temperature difference ΔTb2 for the high-pressure stage compressor body 1H as follows.

[0045] The control device 40 calculates the temperature difference between the first discharge temperature To1 and the first intake temperature Ti1 (hereinafter also referred to as the first temperature difference) by subtracting the first intake temperature Ti1 detected by the first intake temperature sensor 31 at the time of compressor 100 startup (start of operation) from the first discharge temperature To1 detected by the first discharge temperature sensor 32 at the time of compressor 100 startup (start of operation). The control device 40 stores the first temperature difference calculated at the start of operation as the first reference temperature difference ΔTb1 in the non-volatile memory 43.

[0046] The control device 40 calculates the temperature difference between the second discharge temperature To2 and the first intake temperature Ti1 (hereinafter also referred to as the second temperature difference) by subtracting the first intake temperature Ti1 detected by the first intake temperature sensor 31 at the time of compressor 100 startup (start of operation) from the second discharge temperature To2 detected by the second discharge temperature sensor 34 at the time of compressor 100 startup (start of operation). The control device 40 stores the second temperature difference calculated at the start of operation as the second reference temperature difference ΔTb2 in the non-volatile memory 43.

[0047] The method for determining the reference temperature difference ΔTb(ΔTb1, ΔTb2) is not limited to this. For example, the reference temperature difference ΔTb may be determined based on the detection results of each temperature sensor detected after a predetermined time has elapsed since the compressor 100 was started. Alternatively, the reference temperature difference ΔTb may be determined based on the average value of the detection results of each temperature sensor detected within a predetermined period after the compressor 100 was started.

[0048] Once the initial setup is complete, the process proceeds to step S110 shown in Figure 4. In step S110, the control device 40 executes a flag setting process. Figure 5 is a flowchart showing an example of the flow of the flag setting process. As shown in Figure 5, once the flag setting process begins, in step S113, the control device 40 acquires temperature information (detection results) from each temperature sensor 31 to 34 and proceeds to step S116.

[0049] In step S116, the control device 40 calculates the current value of the first temperature difference ΔTa1 by subtracting the first intake air temperature Ti1 obtained in step S113 from the first discharge temperature To1 obtained in step S113. Also in step S116, the control device 40 calculates the current value of the second temperature difference ΔTa2 by subtracting the first intake air temperature Ti1 obtained in step S113 from the second discharge temperature To2 obtained in step S113.

[0050] Furthermore, the control device 40 calculates the difference ΔTd1 between the current value ΔTa1 of the first temperature difference and the reference value by subtracting the reference value ΔTb1 of the first temperature difference stored in the non-volatile memory 43 from the current value ΔTa1 of the first temperature difference calculated in this step. The control device 40 also calculates the difference ΔTd2 between the current value ΔTa2 of the second temperature difference and the reference value by subtracting the reference value ΔTb2 of the second temperature difference stored in the non-volatile memory 43 from the current value ΔTa2 of the second temperature difference calculated in this step. Once the temperature difference calculation process in step S116 is completed, the process proceeds to step S119.

[0051] In step S119, the control device 40 determines whether the invalidation condition is met. The control device 40 determines that the invalidation condition is met if the difference ΔTd1 between the current value ΔTa1 of the first temperature difference calculated in step S116 and the reference value ΔTb1 is greater than the first temperature difference threshold ΔTt1, or if the difference ΔTd2 between the current value ΔTa2 of the second temperature difference calculated in step S116 and the reference value ΔTb2 is greater than the second temperature difference threshold ΔTt2, and proceeds to step S122.

[0052] In step S119, the control device 40 determines that the invalidation condition is not met if the difference ΔTd1 between the current value ΔTa1 of the first temperature difference calculated in step S116 and the reference value Tb1 is less than or equal to the first temperature difference threshold ΔTt1, and the difference ΔTd2 between the current value ΔTa2 of the second temperature difference calculated in step S116 and the reference value Tb2 is less than or equal to the second temperature difference threshold ΔTt2, and proceeds to step S125.

[0053] In step S122, the control device 40 sets the invalid flag to ON and proceeds to step S130 in Figure 4. In step S125, the control device 40 sets the invalid flag to OFF and proceeds to step S130 in Figure 4.

[0054] As shown in Figure 4, in step S130, the control device 40 acquires pressure information (detection results) from the pressure sensors 18 and 21 and proceeds to step S135. In step S135, the control device 40 determines whether the discharge pressure Pa of the compressor 100 acquired in step S130 is less than the set pressure Pa0. If it is determined in step S135 that the discharge pressure Pa is less than the set pressure Pa0, the process proceeds to step S140. If it is determined in step S135 that the discharge pressure Pa is equal to or greater than the set pressure Pa0, the process proceeds to step S160.

[0055] In step S140, the control device 40 outputs a closed signal to the air release valve 27, starts load operation control, and proceeds to step S143. In step S143, the control device 40 determines whether the disabled flag is set to ON or OFF. If it is determined in step S143 that the disabled flag is set to OFF, the process proceeds to step S147. If it is determined in step S143 that the disabled flag is set to ON, the process proceeds to step S180.

[0056] In step S147, the control device 40 sets the target pressure Pot of the lubricating oil to a first target pressure Pot1 (Pot=Pot1) and proceeds to step S150. In step S150, the control device 40 calculates the pressure difference ΔPo by subtracting the first target pressure Pot1 set in step S147 from the detected pressure Poa of the lubricating oil pressure sensor 21 acquired in step S130. In the next step S155, the control device 40 refers to the control table (see Figure 3) and determines the target opening degree Vot of the oil drain control valve 17 based on the pressure difference ΔPo calculated in step S150, and proceeds to step S158. In step S158, the control device 40 outputs a control signal to the oil drain control valve 17 and adjusts the opening degree of the oil drain control valve 17 to the target opening degree Vot determined in step S155.

[0057] In step S160, the control device 40 outputs an open signal to the air release valve 27, starts no-load operation control, and proceeds to step S163. In step S163, the control device 40 determines whether the invalid flag is set to ON. If it is determined in step S163 that the invalid flag is set to OFF, the process proceeds to step S167. If it is determined in step S163 that the invalid flag is set to ON, the process proceeds to step S180.

[0058] In step S167, the control device 40 sets the second target pressure Pot2 to the target lubricating oil pressure Pot (Pot = Pot2), and proceeds to step S170. In step S170, the control device 40 calculates the pressure difference ΔPo by subtracting the second target pressure Pot2 set in step S167 from the detected pressure Poa of the lubricating oil pressure sensor 21 acquired in step S130. In the next step S175, the control device 40 refers to the control table (see Figure 3) and determines the target opening degree Vot of the oil drain control valve 17 based on the pressure difference ΔPo calculated in step S170, and proceeds to step S178. In step S178, the control device 40 outputs a control signal to the oil drain control valve 17 and adjusts the opening degree of the oil drain control valve 17 to the target opening degree Vot determined in step S175.

[0059] In step S180, the control device 40 outputs a control signal to the oil drain control valve 17 regardless of the pressure difference ΔPo, and closes the oil drain control valve 17 completely. When the control of the oil drain control valve 17 is completed by any of the processes in steps S158, S178, or S180, the processes shown in the flowchart of Figure 4 for this control cycle are completed.

[0060] As described above, in this embodiment, a lower target pressure is set during no-load operation than during load operation, and the opening degree of the oil drain control valve 17 is controlled according to the pressure difference between the target pressure and the pressure detected by the lubricating oil pressure sensor 21 (detected pressure). When switching from load operation to no-load operation, the target pressure switches to the second target pressure (< first target pressure), so the opening degree of the oil drain control valve 17 increases. As a result, the flow rate of lubricating oil supplied to the bearing 6 decreases. On the other hand, when switching from no-load operation to load operation, the target pressure switches to the first target pressure (> second target pressure), so the opening degree of the oil drain control valve 17 decreases. As a result, the flow rate of lubricating oil supplied to the bearing 6 increases.

[0061] In this way, the opening degree of the oil drain control valve 17 is adjusted according to the pressure difference between the target pressure and the detected pressure set for each operating state, so that the actual pressure of the lubricating oil in the rotor casing 4 can be quickly brought closer to the target pressure. In other words, the flow rate of lubricating oil supplied to the bearing 6 can be quickly brought closer to the required supply amount in response to changes in the operating state.

[0062] According to the above-described embodiment, the following effects are achieved.

[0063] (1) The compressor 100 is an oil-free compressor comprising a compressor body 1 having a rotor 3 for compressing air (gas) and a bearing 6 that rotatably supports the rotor 3, a lubrication system 60 for supplying lubricating oil to the bearing 6, and a control device 40. The lubrication system 60 has a storage section 12 for storing lubricating oil, an oil pump 10 for discharging the lubricating oil stored in the storage section 12, an oil discharge control valve (flow rate control device) 17 for controlling the flow rate of lubricating oil supplied from the oil pump 10 to the bearing 6, and a lubricating oil pressure sensor (pressure sensor) 21 for detecting the pressure of the lubricating oil supplied to the bearing 6. The control device 40 has a non-volatile memory 43 (storage device) for storing target pressure Pots for multiple operating states. The control device 40 reads and sets the target pressure from the non-volatile memory 43 according to the operating state, and controls the oil discharge control valve 17 so that the pressure detected by the lubricating oil pressure sensor 21 (detected pressure) becomes the set target pressure Pot.

[0064] In this configuration, the target pressure is immediately set according to the operating conditions, and the oil drain control valve 17 is controlled according to the target pressure and the detected pressure. Therefore, according to this embodiment, it is possible to provide a compressor 100 that can supply the necessary lubricating oil flow rate to the bearing 6 with good responsiveness when the operating conditions change.

[0065] (2) The lubrication system 60 includes a main pipe 13a that guides the lubricating oil discharged from the oil pump 10 to the bearing 6, a return pipe 13c that returns a portion of the lubricating oil discharged from the oil pump 10 to the storage section 12 without guiding it to the bearing 6, and an oil discharge control valve 17 provided in the return pipe 13c as a flow rate control device. Thus, the compressor 100 according to this embodiment is configured to control the flow rate of lubricating oil supplied to the bearing 6 by controlling the oil discharge control valve 17. With this configuration, the cost of the compressor 100 can be reduced compared to a configuration in which the flow rate of lubricating oil supplied to the bearing 6 is controlled by controlling the rotational speed of the oil pump 10 with an engine.

[0066] (3) The non-volatile memory 43 stores a control table (see Figure 3) as opening degree information, which links the pressure difference between the pressure of the lubricating oil supplied to the bearing 6 and the target pressure, with the target opening degree Vot of the oil drain control valve 17. The control device 40 calculates the pressure difference ΔPo between the pressure (detected pressure) Poa detected by the lubricating oil pressure sensor 21 and the target pressure Pot set according to the operating state. Based on the calculated pressure difference ΔPo and the control table (see Figure 3), the control device 40 determines the target opening degree Vot of the oil drain control valve 17. The control device 40 controls the oil drain control valve 17 so that its opening degree becomes the determined target opening degree Vot, thereby bringing the pressure (detected pressure) Poa detected by the lubricating oil pressure sensor 21 closer to the target pressure Pot.

[0067] With this configuration, the opening degree of the oil drain control valve 17 is appropriately controlled according to the pressure difference ΔPo between the detected pressure Poa and the target pressure Pot, allowing the detected pressure Poa to quickly approach the target pressure Pot, while keeping the amount of overshoot where the detected pressure Poa exceeds the target pressure Pot low.

[0068] (4) When the operating state is no-load operation, the control device 40 sets a lower target pressure Pot than when the operating state is under load. With this configuration, when the operating state is no-load operation, the flow rate of lubricating oil supplied to the bearing 6 is reduced, thereby reducing stirring loss and power consumption. Furthermore, it is possible to prevent damage to the bearing 6 (smearing) caused by excessive supply of lubricating oil to the bearing 6.

[0069] (5) The control device 40 determines whether the invalid condition is met based on the temperature of the air discharged from the compressor body 1. In this embodiment, the control device 40 determines that the invalid condition is met if the difference (e.g., ΔTd1) between the current value (e.g., ΔTa1) and the reference value (e.g., ΔTb1) of the temperature difference (e.g., first temperature difference) between the temperature of the air discharged from the compressor body 1 (e.g., first discharge temperature To1) and the temperature of the air drawn into the compressor body 1 (e.g., first intake temperature Ti1) is greater than the temperature difference threshold (e.g., predetermined value ΔTt1). If the invalid condition is met, the control device 40 does not control the opening degree of the oil discharge control valve 17 based on the detected pressure and target pressure. That is, the control device 40 does not control the flow rate of lubricating oil supplied from the oil pump 10 to the bearing 6 based on the detected pressure and target pressure. In this embodiment, if the invalidation condition is met, the oil discharge control valve 17 is completely closed, regardless of the pressure difference between the detected pressure and the target pressure, thereby supplying the entire amount of lubricating oil discharged from the oil pump 10 to the bearing 6 of the compressor body 1.

[0070] For example, when the operating state switches from a loaded operating state to an unloaded operating state and the invalidation condition is not met, the control device 40 controls the opening of the oil drain control valve 17 to the open side, thereby reducing the flow rate of lubricating oil supplied from the oil pump 10 to the bearing 6, and bringing the pressure detected by the lubricating oil pressure sensor 21 closer to the set target pressure Pot (=Pot2). Also, for example, when the operating state is an unloaded operating state and the invalidation condition is met, the control device 40 controls the opening of the oil drain control valve 17 to the closed side, regardless of the set target pressure Pot (=Pot2), thereby increasing the flow rate of lubricating oil supplied from the oil pump 10 to the bearing 6.

[0071] With this configuration, if a deactivation condition is met for any reason, a sufficient flow rate of lubricating oil supplied to the bearing 6 can be ensured. As a result, the temperature of the bearing 6 can be maintained within the operating temperature range, and damage to the bearing 6 can be prevented. In addition, if an engine capable of adjusting the rotational speed of the oil pump 10 is provided as a flow rate control device instead of the oil drain control valve 17, the control device 40 sets the rotational speed of the engine to a predetermined value regardless of the pressure difference between the detected pressure and the target pressure when a deactivation condition is met. Here, the predetermined value is, for example, the maximum value in the rotational speed range when a deactivation condition is not met.

[0072] The following modifications are also within the scope of the present invention, and it is possible to combine the configurations shown in the modifications with the configurations described in the embodiments described above, or to combine the configurations described in the following different modifications.

[0073] <Example 1> In the above embodiment, an example was described in which an oil drain control valve 17 capable of adjusting the opening degree in five ways is used as a flow rate control device. However, an oil drain control valve 17 capable of adjusting the opening degree in six or more ways, or four or fewer ways, may also be used as a flow rate control device.

[0074] <Modification 2> In the above embodiment, an example was described in which the control device 40 controls the oil drain control valve 17 using the same control table (Figure 3) in both the load operation state and the no-load operation state, but the present invention is not limited thereto. The control device 40 may control the oil drain control valve 17 using different control tables in the load operation state and the no-load operation state.

[0075] <Variation 3> In the above embodiment, a loaded operating state and an unloaded operating state were described as examples of operating states, but the present invention is not limited thereto. The loaded operating state may be further subdivided, and a target pressure may be set for each subdivided operating state. By setting a target pressure for each of the multiple operating states, the target pressure can be switched in accordance with changes in the operating state, allowing the amount of supply required for the bearing 6 of the compressor body 1 to be adjusted moment by moment in real time.

[0076] <Modification 4> In the above embodiment, an example of performing the invalid flag setting process was described, but the invalid flag setting process does not have to be performed. In this case, it is preferable to warn the user using a display device or sound output device when the invalid condition is met.

[0077] <Modification 5> In the above embodiment, an example was described in which the temperature difference between the discharge temperature and the intake air temperature at the start of the compressor 100 is stored in the non-volatile memory 43 as a reference temperature difference, but the present invention is not limited thereto. The reference temperature difference may be a fixed value stored in the non-volatile memory 43 at the time of product shipment, etc.

[0078] <Variation 6> The invalidation conditions are not limited to the examples described in the embodiments above. For example, the invalidation conditions may be defined as follows: Modified example of invalid condition 1: The difference between the current temperature of the air discharged from the compressor body 1 and the reference value is greater than a predetermined value. In addition, the reference value in the modified example 1 of the invalidation condition may be the value at the time of starting the compressor 100 (start of operation), or it may be a predetermined fixed value. Modification of invalid condition 2: The temperature of the air discharged from the compressor body 1 is greater than the upper limit. Note that the upper limit in the modified example 2 of the invalidation conditions is a predetermined fixed value.

[0079] <Example 7> In the above embodiment, an example was described in which the compressor 100 is a two-stage compressor, but it may also be a multi-stage compressor with three or more stages, or a single-stage compressor. Furthermore, although a twin-rotor type screw rotor compressor was described as an example, the present invention can also be applied to screw compressors other than the twin-rotor type, such as single-rotor type or triple-rotor type. In addition, the present invention can be applied to various oil-free compressors that supply lubricating oil to the bearing 6 of the rotor 3, which is the compressive rotating body. Moreover, the gas compressed by the rotor 3 of the compressor body 1 is not limited to air.

[0080] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of Symbols]

[0081] 1... Compressor body, 1H... High-pressure stage compressor body, 1L... Low-pressure stage compressor body, 2... Motor, 3... Rotor, 4... Rotor casing, 6... Bearing, 10... Oil pump, 11... Gear case, 12... Storage section, 13a... Main piping, lubricating oil piping, 13a1... First branch pipe, 13a2... Second branch pipe, 13b... Bypass piping, lubricating oil piping, 13c... Return piping, lubricating oil piping, 14a... Heat exchanger for lubricating oil, 14b... Heat exchanger for compressed air, 14bH... Aftercooler, 14bL... Intercooler, 17... Oil drain control valve (flow rate) Control device), 18…Discharge pressure sensor (pressure sensor), 19…Inverter, 20…Cooling fan, 21…Lubricating oil pressure sensor (pressure sensor), 25…Discharge piping, 25H…Second discharge piping, 25L…First discharge piping, 26…Ventilation path, 27…Ventilation valve, 29…Check valve, 31…First intake air temperature sensor, 32…First discharge temperature sensor, 33…Second intake air temperature sensor, 34…Second discharge temperature sensor, 40…Control device, 41…Calculation unit, 42…Volatile memory (storage device), 43…Non-volatile memory (storage device), 60…Moisture Lubrication system, 100... Compressor (oil-free compressor), Pa... Discharge pressure, Pa0... Set pressure, Poa... Detected pressure, Pot... Target pressure, Pot1... First target pressure, Pot2... Second target pressure, Tb1... Reference value for first temperature difference, Tb2... Reference value for second temperature difference, Ti... Temperature of gas drawn into the compressor body, Ti1... First intake temperature, To... Temperature of gas discharged from the compressor body, To1... First discharge temperature, To2... Second discharge temperature, Vot... Target opening, ΔPo... Pressure difference, ΔPoc... Calculated value of pressure difference, ΔPom ...Pressure difference memory value, ΔTa...Current temperature difference value, ΔTa1...Current value of the first temperature difference, ΔTa2...Current value of the second temperature difference, ΔTb...Reference temperature difference (reference value of temperature difference), ΔTb1...First reference temperature difference (reference value of the first temperature difference), ΔTb2...Second reference temperature difference (reference value of the second temperature difference), ΔTd...Difference between the current temperature difference and the reference value, ΔTd1...Difference between the current temperature difference and the reference value of the first temperature difference, ΔTd2...Difference between the current temperature difference and the reference value of the second temperature difference, ΔTt...Temperature difference threshold (predetermined value), ΔTt1...First temperature difference threshold, ΔTt2...Second temperature difference threshold

Claims

1. A compressor body having a rotor and bearings, A discharge temperature sensor detects the discharge temperature, which is the temperature of the gas discharged from the compressor body, A storage section for storing lubricating oil, An oil pump for discharging the lubricating oil stored in the aforementioned storage section, A flow control device that controls the flow rate of lubricating oil supplied from the oil pump to the bearing, A pressure sensor for detecting the pressure of the lubricating oil supplied to the bearing, An oil-free compressor comprising a control device, The control device is Based on the discharge temperature detected by the discharge temperature sensor, the first control and the second control are switched. The first control, when the discharge temperature detected by the discharge temperature sensor is greater than a threshold, controls the flow rate control device to maintain the flow rate of lubricating oil supplied to the bearing at a predetermined flow rate. The second control is an oil-free compressor that controls the flow rate control device to adjust the flow rate of lubricating oil supplied to the bearing based on the pressure of the lubricating oil detected by the pressure sensor when the discharge temperature detected by the discharge temperature sensor is less than a threshold.

2. The control device is It has a memory device that stores the target pressure, The second control is, The flow rate control device is controlled so that the pressure of the lubricating oil detected by the pressure sensor becomes the target pressure. The oil-free compressor according to feature 1.

3. The aforementioned target pressure is stored for each operating state of the oil-free compressor. The second control is, The flow control device is controlled so that the pressure of the lubricating oil detected by the pressure sensor becomes the target pressure corresponding to the current operating state. The oil-free compressor according to feature 2.

4. The target pressure during load operation is higher than the target pressure during unload operation. The oil-free compressor according to feature 3.

5. The aforementioned oil-free compressor is The flow rate control device has an oil drain control valve, The aforementioned storage device is The system stores opening degree information that links the pressure of the lubricating oil supplied to the bearing with the pressure difference between that pressure and the target pressure, and the opening degree of the oil drain control valve. The second control is, The pressure difference between the pressure of the lubricating oil detected by the pressure sensor and the target pressure is calculated. Based on the pressure difference calculated by the calculation and the opening degree information, the target opening degree of the oil drain control valve is determined. This control adjusts the oil drain control valve so that its opening degree becomes the target opening degree. The oil-free compressor according to feature 2.

6. The aforementioned oil-free compressor is The compressor body is equipped with an intake air temperature sensor that detects the intake air temperature, which is the temperature of the gas drawn into the compressor. Based on the intake air temperature detected by the intake air temperature sensor and the discharge temperature detected by the discharge air temperature sensor, the first control and the second control are switched. The first control described above is The temperature difference between the intake air temperature detected by the intake air temperature sensor and the discharge air temperature detected by the discharge air temperature sensor is calculated. If the difference between the calculated temperature difference and the reference value is greater than the threshold, the flow rate control device is controlled to maintain the flow rate of lubricating oil supplied to the bearing at a predetermined flow rate. The oil-free compressor according to feature 1.

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