JP7836734B2 - Oil-free compressor - Google Patents

Description

This invention relates to an oil-free compressor.

Oil-free compressors that do not require the supply of oil or water to the compression chamber (operating space) are known. For example, a screw compressor is known that has a pair of male and female screw rotors that can rotate non-contact and without lubrication, and compresses gases such as air using these rotors. Oil-free compressors generally have a lubrication system that circulates lubricating oil to lubricate and cool the rotor bearings, gears, and compressor body.

The amount of lubricating oil required to lubricate and cool the bearings of a rotor, which is a rotating compression body, is defined, for example, by a constant specified by the bearing specifications, the target bearing temperature, the rotor's rotational speed, the compressed gas discharge pressure, and the load from the gears. During operation, the compressor's rotational speed or discharge pressure becomes a variable, and the amount of lubricating oil supplied changes depending on either of these. As the operating conditions change, the relationship between the rotor's rotational speed and the compressed gas discharge pressure changes, and the required amount of lubricating oil to be supplied to the bearings also changes.

Patent Document 1 discloses a gas compressor equipped with a control device that reduces the amount of lubricating oil supplied during low-pressure increased-airflow operation compared to rated operation. The control device described in Patent Document 1 calculates the required amount of lubricating oil to the bearings from the bearing load corresponding to the discharge pressure of the compressor body detected by a pressure sensor and the rotor rotation speed corresponding to the rotation frequency output by the inverter, and controls the flow rate of the lubricating oil based on the required supply amount. If the flow rate of lubricating oil from the oil pump corresponding to the inverter output frequency exceeds the required supply amount, the control device described in Patent Document 1 opens the oil discharge solenoid valve to limit the flow rate of lubricating oil supplied to the bearings.

WO2015/198647A1

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, indicating room for improvement in terms of responsiveness.

The present invention aims to provide an oil-free compressor capable of supplying the necessary lubricating oil flow rate to the bearings with good responsiveness when the operating conditions change.

An oil-free compressor according to one aspect of the present invention comprises a compressor body having a rotor and bearings , a discharge temperature sensor for detecting 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 bearings, a pressure sensor for detecting the pressure of the lubricating oil supplied to the bearings , and a control device, wherein the control device switches between a first control and a second control based on the discharge temperature detected by the discharge temperature sensor, the first control is a control that maintains the flow rate of lubricating oil supplied to the bearings by the flow rate control device at a predetermined flow rate, and the second control is a control that adjusts the flow rate of lubricating oil supplied to the bearings by the flow rate control device based on the pressure of the lubricating oil detected by the pressure sensor.

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

Figure 1 is an overall diagram of the oil-free compressor. Figure 2 shows the lubrication system of the compressor. 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 is a flowchart showing an example of the process flow for valve control performed by the control device. Figure 5 is a flowchart illustrating an example of the flag setting process.

The following describes one embodiment of the present invention 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.

As shown in Figure 1, the compressor 100 according to this embodiment is a two-stage screw compressor, comprising 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 the compressor body 1 below. The compressor body 1 includes 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 and discharge sides of the compressor body 1.

The compressor 100 comprises 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 includes 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 mutually meshing bull gear 7 and pinion gear 8. 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, air taken in from the intake of the compressor body 1 is compressed within the working space formed by the rotor 3 and the rotor casing 4, and discharged from the discharge of the compressor body 1.

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 14b (14bL, 14bH) for compressed air are tube-type or plate-type heat exchangers. The heat exchangers 14b receive a supply of a cooling liquid (water or coolant) (not shown) and cool the compressed air to a desired temperature through heat exchange with the cooling liquid.

The compressor 100 comprises 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.

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 capable of executing various calculations, set values, thresholds, etc. In other words, the non-volatile memory 43 is a storage medium (device) from which programs realizing the functions of this embodiment can be read. The volatile memory 42 is a storage medium (device) that temporarily stores the calculation results from the arithmetic unit 41 and input signals. The arithmetic unit 41 is a processing unit that loads the programs stored in the non-volatile memory 43 into the volatile memory 42 and performs calculation processing. According to the program, it performs predetermined calculation processing on data acquired from various sensors, the non-volatile memory 43, and the volatile memory 42.

The control device 40, through the cooperation of software and the arithmetic unit 41, realizes multiple functions and performs input and output of control signals to various parts 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 exterior of the housing 50 and is operated by the user. When the user operates the input device, an operation signal corresponding to the user's operation is output from the input device to the control device 40. The control device 40 performs various operations such as changing setting values and registering new setting values in response to the operation signal from the input device. The control device 40 can also be connected to control equipment (notebook PC, tablet PC, server, etc.) via a network, and stores setting values in the non-volatile memory 43 in response to signals from the control equipment.

Various sensors and devices are connected to the control device 40. For example, a discharge pressure sensor 18 is connected to the control device 40 to detect the discharge pressure of compressed air supplied from the compressor 100 to the user. Additionally, a lubricating oil pressure sensor 21 is connected to the control device 40 to detect the pressure of the lubricating oil system 60.

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

The housing 50, which houses each device, is provided with an air intake port 51 for drawing in outside air from outside the housing 50, and an exhaust port 52 for discharging air from inside the housing 50 to the outside. The air intake port 51 is located opposite the motor 2, which is situated upstream of the airflow inside the housing. A cooling fan 20 is provided near the exhaust port 52 inside the housing 50. As the cooling fan 20 rotates, air is drawn into the housing 50 from the air intake port 51. The air drawn into the housing 50 flows as cooling air, mainly through the motor 2, the compressor body 1, and the heat exchangers 14a and 14b, before being discharged outside the housing 50 through the exhaust port 52. The rotation speed of the cooling fan 20 is controlled by a control device 40. The control device 40 controls the rotation speed of the cooling fan 20 to maintain the temperature inside the housing 50 within a certain range, based on the discharge pressure of compressed air detected by a discharge pressure sensor 18 and the temperature of the motor 2 detected by a motor temperature sensor (not shown).

Motor 2 receives power of any frequency from inverter 19 via control device 40, enabling it to rotate at a variable speed.

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.

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 towards the aftercooler 14bH, and prohibits air from flowing from the aftercooler 14bH towards the high-pressure stage compressor body 1H. An air release path 26 is connected upstream of the check valve 29 in the second discharge pipe 25H. Downstream of the air release path 26 is an air release valve 27, which is a solenoid valve capable of opening and closing the air release path 26.

The control device 40 performs load operation (normal operation) of the compressor body 1 when the discharge pressure Pa of compressed air detected by the discharge pressure sensor 18 is less than the set pressure Pa0, and performs no-load operation 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.

During load operation, the control device 40 outputs a close signal to the air release valve 27, completely closing the air release valve 27. Therefore, during load operation, compressed air discharged from the high-pressure stage compressor body 1H flows through the check valve 29 to the aftercooler 14bH. During no-load operation, the control device 40 outputs an open signal to the air release valve 27, completely opening the air release valve 27. Therefore, when the user's compressed air consumption 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, resulting in lower power consumption compared to load operation. Note that during no-load operation, the control device 40 may reduce the rotational speed of the motor 2 compared to load operation.

The lubrication system 60 of the compressor 100 will be described in detail with reference to Figures 1 and 2. Figure 2 shows 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. The power of 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, the lubricating oil circulates within the lubrication system 60. The oil pump 10 in this embodiment is a fixed-displacement pump with a constant displacement volume.

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 drawing in and discharging the lubricating oil stored in the storage section 12, a lubricating oil heat exchanger 14a for cooling the lubricating oil, an oil filter 15 for capturing dust and debris within the lubricating system 60, and lubricating oil piping (13a, 13b, 13c) for connecting the various devices installed in the lubricating system 60.

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 within the gear case 11 connected to the rotor casings 4 of the low-pressure stage compressor body 1L and the high-pressure stage compressor body 1H.

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 below 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 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 capable of detecting 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.

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.

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

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 supplied from the oil pump 10 to the bearing 6 decreases. Thus, 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 ensure the necessary supply amount of lubricating oil to the bearing 6, and returns excess lubricating oil to the storage unit 12 through the return pipe 13c.

The configuration of the flow control device for controlling the supply amount of lubricating oil is not limited to the oil drain control valve 17. For example, the compressor 100 may be equipped with an autonomous engine (such as an electric motor) that drives the oil pump 10 as the 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 and adjusting the rotational speed of the oil pump 10. The compressor 100 may also be equipped with both the oil drain control valve 17 and the engine as the flow control device. Furthermore, the oil drain control valve 17 may be a solenoid proportional valve whose opening degree can be continuously adjusted according to the control current from the control device 40, or it may be a solenoid 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 a solenoid valve whose opening degree can be adjusted in multiple stages will be described.

The non-volatile memory 43 of the control device 40 stores target pressures for multiple operating states in advance. 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 through experiments, etc. The required amount is the amount of oil sufficient to 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) reaches the set target pressure.

The control device 40 sets target pressure Pots 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 when the compressor 100 is in a load operation state and the required amount of lubricating oil is supplied to the bearing 6 in the experiment. 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 when the compressor 100 is in an unload operation state and the required amount of lubricating oil is supplied to the bearing 6 in the experiment. In an unload operation state, the load acting on the compressor body 1 is smaller than in a load operation state. Therefore, under no-load conditions, the required amount of lubricating oil supplied to the bearing 6 is smaller than under load conditions. Consequently, the second target pressure Pot2 is lower than the first target pressure Pot1 (Pot2 < Pot1).

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) pre-stored in the non-volatile memory 43, the control device 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 lubricating oil pressure supplied to the bearing 6 and the target pressure, with the target opening degree of the oil drain control valve 17. This information is predetermined through experiments or other means.

Figure 3 shows an example of a control table that defines the relationship between the pressure difference between the lubricating oil pressure (detected pressure) supplied to the bearing 6 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 configured such that the larger the pressure difference ΔPo, the larger the target opening degree Vot of the oil drain control valve 17 becomes.

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 closest to the calculated value ΔPoc. For example, if the stored value ΔPom 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 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).

The control device 40 controls the oil drain control valve 17 so that its opening degree reaches the 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%, decreasing 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%, 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.

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.

Therefore, the control device 40 according to this embodiment determines whether the invalidation condition described later is met. 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 instead 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.

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 reference value ΔTb (temperature Ti of the air drawn into the compressor body 1) 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 pre-stored in the non-volatile memory 43.

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

In the initial settings (not shown), the control device 40 sets a reference value (also referred to as the reference temperature difference) ΔTb for the temperature difference between the air temperature To discharged from the compressor body 1 and the air temperature Ti drawn into the compressor body 1. Since the compressor 100 in this embodiment is configured for 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.

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.

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.

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.

Once the initial setup is complete, the process proceeds to step S110, as shown in Figure 4. In step S110, the control device 40 executes the flag setting process. Figure 5 is a flowchart showing an example of the flag setting process flow. 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 31-34 and proceeds to step S116.

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.

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 complete, the process proceeds to step S119.

In step S119, the control device 40 determines whether 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, the control device 40 determines that the invalidation condition is met and proceeds to step S122.

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.

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.

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.

In step S140, the control device 40 outputs a closing 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 invalid flag is set to ON. If it is determined in step S143 that the invalid flag is set to OFF, the process proceeds to step S147. If it is determined in step S143 that the invalid flag is set to ON, the process proceeds to step S180.

In step S147, the control device 40 sets the target pressure Pot1 of the lubricating oil to Pot (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.

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.

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.

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 completely closes the oil drain control valve 17. Once the control of the oil drain control valve 17 is completed through any of the processes in steps S158, S178, or S180, the process shown in the flowchart of Figure 4 for this control cycle is completed.

In this embodiment, a lower target pressure is set during no-load operation than during load operation, and the opening 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 of the oil drain control valve 17 increases. This reduces the flow rate of lubricating oil supplied to the bearing 6. 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 of the oil drain control valve 17 decreases. This increases the flow rate of lubricating oil supplied to the bearing 6.

In this way, the opening 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.

According to the above-described embodiment, the following effects and advantages are achieved.

(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 includes 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) that stores 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.

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, a compressor 100 is provided that can supply the necessary lubricating oil flow rate to the bearing 6 with good responsiveness when the operating conditions change.

(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 unit 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. This configuration allows for a reduction in the cost of the compressor 100 compared to a configuration where 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.

(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, which is 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.

According to 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. This allows the detected pressure Poa to quickly approach the target pressure Pot, while simultaneously suppressing the amount of overshoot where the detected pressure Poa exceeds the target pressure Pot.

(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, the flow rate of lubricating oil supplied to the bearing 6 is reduced, thereby reducing stirring losses and power consumption. Furthermore, it is possible to prevent damage to the bearing 6 (smearing) caused by excessive lubricating oil supply to the bearing 6.

(5) The control device 40 determines whether the invalidation 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 invalidation 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 invalidation 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, regardless of the pressure difference between the detected pressure and the target pressure, the oil discharge control valve 17 is completely closed, thereby supplying the entire amount of lubricating oil discharged from the oil pump 10 to the bearing 6 of the compressor body 1.

For example, when the operating state switches from a loaded operation state to an unloaded operation 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). Furthermore, for example, if the invalidation condition is met while the operating state is an unloaded operation state, 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.

This configuration ensures a sufficient flow rate of lubricating oil supplied to the bearing 6 even if a deactivation condition is met for any reason. As a result, the temperature of the bearing 6 can be maintained within the operating temperature range, preventing damage to the bearing 6. Furthermore, if an engine capable of adjusting the rotational speed of the oil pump 10 is provided as the 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 within the rotational speed range when a deactivation condition is not met.

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.

<Variation 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.

<Modified Example 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 to this. The control device 40 may also control the oil drain control valve 17 using different control tables in the load operation state and the no-load operation state.

<Example 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.

<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.

<Example 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.

<Modification 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:
Modification 1 of the invalid condition: 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. Note that the reference value in Modification 1 of the invalid condition may be the value at the time the compressor 100 is started (start of operation), or it may be a predetermined fixed value.
Modification 2 of the invalid condition: The temperature of the air discharged from the compressor body 1 is greater than the upper limit. Note that the upper limit in Modification 2 of the invalid condition is a predetermined fixed value.

<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.

Although embodiments of the present invention have been described above, these embodiments represent only a portion of the applications 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.

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...Lubricating oil 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 (stored value), ΔTa...Current temperature difference, ΔTa1...Current value of the first temperature difference, ΔTa2...Current value of the second temperature difference, ΔTb...Reference temperature difference (reference value of the 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 (6)

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. 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. 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. The oil-free compressor according to claim 3, characterized in that the target pressure during load operation is higher than the target pressure during unload operation. 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.
The oil-free compressor according to claim 2, characterized in that the control adjusts the oil drain control valve so that the opening degree of the oil drain control valve becomes the target opening degree. 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.