Air compressor

Abstract

The invention provides a technology capable of recovering oil stored in a gearbox without using a pump. A compressor (100) is provided with: a rotor (9) that compresses air; an electric motor (42) for driving the rotor (9); a gear for transmitting the drive of the electric motor (42) to the rotor (9); a gear box (22) for receiving the gear; an oil tank (11) for storing oil separated from the compressed air; an oil supply flow path (25) communicating from the oil tank (11) to the gear box (22); an oil recovery flow path (26) communicating from the gearbox (22) to the compressor suction part (20); and an oil pressurization flow path (27) communicating from the discharge port (14b) to the gear case (22), oil is supplied from the oil tank (11) to the gear case (22) via the oil supply flow path (25) by the discharge pressure of the compressor (100), the gear case (22) is pressurized by the discharge pressure via the oil pressurization flow path (27), and the oil of the gear case (22) is recovered to the compressor suction part (20) via the oil recovery flow path (26).

Description

Technical Field

[0001] The present invention relates to an air compressor. Background Art

[0002] Air compressors are known that compress air by rotating a pair of male and female rotors arranged inside a housing. Among these air compressors, there is a rotary screw compressor, in which a male rotor is rotated by a drive source such as a motor, and a female rotor is rotated by the male rotor via a timing gear or a spiral groove.

[0003] The transmission path between the motor and the male rotor can be a direct connection or a configuration that uses gears to adjust the speed. The gears consist of a main gear connected to the drive source and a pinion gear connected to the rotor. The compression chamber formed by the grooves of the male and female rotors and the housing creates a negative pressure in the housing's intake section, as the volume decreases due to rotation, increasing the pressure from atmospheric pressure to the desired pressure at the end of use.

[0004] A known structure involves a gearbox housing the gears adjacent to the housing's intake port, where oil for lubricating and cooling the gears is stored within the gearbox. This stored oil is used to cool and lubricate the rotor's compression chamber. Therefore, a connecting hole is provided between the gearbox and the housing, allowing the negative pressure in the housing's intake port to be used to recover the oil from the gearbox back to the intake port.

[0005] On the other hand, there are cases where the negative pressure in the casing's intake port cannot be used to recover the oil inside the gearbox as described above. For example, in a two-stage rotary screw compressor with two pairs of male and female rotors arranged one above the other, the increased number of pinions connected to the male rotor increases the volume of the gearbox housing the main gear and pinions, increasing the amount of oil accumulated within the gearbox. Consequently, there is a concern that relying solely on the negative pressure in the casing's intake port may not allow for timely oil recovery, leading to gears being immersed in oil, increasing stirring resistance, and potentially leaking oil into the drive source.

[0006] Patent Document 1 describes the use of an oil pump to pressure-feed lubricating oil stored in a gearbox via lubricating oil piping to a lubricating oil heat exchanger. The lubricating oil, cooled to a temperature below a specified temperature in the lubricating oil heat exchanger, is then fed through the lubricating oil piping and oil filter to the compressor bearings on both the discharge and supply sides, and then recovered in the gearbox.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: International Publication No. 2015 / 198647 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] The technology in Patent Document 1 uses a pump to recover oil from the gearbox. However, the rotor and / or the motor driving the pump typically rotate at a constant speed, maintaining the same rotational speed even during no-load operation as during loaded operation. Furthermore, the amount of oil supplied to the gears is determined by the discharge pressure acting on the oil. Therefore, less oil remains in the gearbox during no-load operation than during loaded operation.

[0012] Therefore, during no-load operation, the pump's suction volume is large relative to the amount of oil recovered by the pump, causing the oil to contain air, which can increase pump vibration. This can also cause damage to the piping connected to the pump due to the vibration being transmitted to the pump.

[0013] Therefore, an object of the present invention is to provide a technology capable of recovering oil stored in a gear box without using a pump.

[0014] Technical solutions to problems

[0015] In order to solve the above-mentioned problems, one of the representative air compressors of the present invention is an air compressor that compresses air sucked in by an intake part and discharges it from a discharge port, and the air compressor includes: a compressor for compressing air; a driving source for driving the compressor; a gear for transmitting the drive of the driving source to the compressor; a gear box for storing the gear; an oil tank for storing oil separated from the compressed air; an oil supply flow path connected from the oil tank to the gear box; an oil recovery flow path connected from the gear box to the intake part; and a pressurizing flow path connected from the discharge port to the gear box, wherein the discharge pressure of the air compressor is used to supply oil from the oil tank to the gear box via the oil supply flow path, and the gear box is pressurized via the pressurizing flow path using the discharge pressure to recover the oil in the gear box to the intake part via the oil recovery flow path.

[0016] Effects of the Invention

[0017] According to the present invention, the oil stored in the gear box can be recovered without using a pump.

[0018] Other problems, structures, and effects than those described above will become apparent from the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a diagram showing an example of the structure of the air compressor of Example 1.

[0020] Figure 2 This is a diagram showing an example of the internal structure of the compressor body of the first embodiment.

[0021] Figure 3 This is a diagram showing an example of the internal structure of the compressor body of the second embodiment.

[0022] Figure 4This is a diagram showing an example of the internal structure of the compressor body of the third embodiment. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present invention will be described in detail using the accompanying drawings.

[0024] Example 1

[0025] Figure 1 1 is a diagram showing an example of the structure of an air compressor 100 (hereinafter referred to as “compressor 100 ”) according to the first embodiment.

[0026] Figure 2 This is a diagram showing an example of the internal structure of the compressor body 2 according to the first embodiment.

[0027] In this embodiment, air is used as the compressed gas, but this is not limiting and other gases may also be used. Compressor 100 is a liquid-feed positive displacement compressor that supplies liquid (e.g., oil) to the compression chamber. In this embodiment, an oil-feed screw compressor is used. However, the present invention is not limited to this and a turbine type may also be used.

[0028] Compressor 100 includes an enclosure 1, a compressor body 2 disposed within the enclosure 1, and an electric motor 42 that drives the compressor body 2. The compressor body 2 is connected to the electric motor 42 via a main gear (bull gear) 3, a primary gear 4, and a secondary gear 5. The main gear 3 rotates as the motor 42 rotates, transmitting the rotation of the main gear 3 to the primary gear 4 and secondary gear 5. The primary rotor 6 and secondary rotor 7 then draw in and compress the external atmosphere from the compressor intake 20 of the compressor body 2.

[0029] Sometimes, the outside air is taken in from outside the air compressor 100 using the compressor intake flow path 8b communicating with the outside of the air compressor 100, and sometimes, the air inside the air compressor 100 is taken in without providing the compressor intake flow path 8b.

[0030] Figure 1 、 Figure 2 The male and female rotor groups in the rotor 9 shown are arranged up and down, and are arranged from the front side toward the back side of the figure, with the male rotor on the front side and the female rotor on the back side.

[0031] In addition, the figure of this embodiment shows an oil-cooled two-stage compressor, but it is not limited to this. It can also be a single-stage liquid-cooled air compressor. In the two-stage compressor, the yin and yang rotors arranged at the upper part are called a first-stage compressor, and the yin and yang rotors arranged at the lower part are called a second-stage compressor. It is expected that both the first-stage compressor and the second-stage compressor compress at the same compression ratio. For example, when compressing air from atmospheric pressure to 0.75 MPa, the first-stage compressor is used to compress from atmospheric pressure to 0.18 MPa, and the second-stage compressor is used to compress to 0.75 MPa. In order to suppress the temperature rise accompanying compression, oil is supplied while compression is carried out during the compression process.

[0032] The supplied oil is transported to the oil separation unit 10 along with the compressed air and separated (this is called secondary separation). Furthermore, before reaching the oil separation unit 10, the oil is swirled and separated by the skirt 12 disposed inside the oil tank 11 and the cylindrical area formed by the inner circumference of the oil tank 11 (this is called primary separation).

[0033] The oil after primary separation is stored in the oil tank 11. Meanwhile, the compressed air after secondary separation is discharged from the compressed air outlet 17 to the outside of the air compressor 100 via the pressure regulating check valve 43 and the aftercooler 13, and is supplied to the user end.

[0034] A pressure lower than the pressure of the discharge port 14b of the compressor body 2 and higher than the pressure of the compressed air supplied to the user end (for example, 0.7 MPa) acts in the oil tank 11. As a result, the oil stored in the oil tank 11 is transported from the oil tank 11 to the oil cooler 15 via the oil flow path 14a connected to the oil cooler 15. The oil transported to the oil cooler 15 undergoes heat exchange with the cooling water 16 inside the oil cooler 15. In order to cool the compressor body 2 and the gears (main gear 3, primary gear 4, secondary gear 5), the oil after heat exchange passes through the oil filter 18 and is then supplied from the oil filter 18 to the compressor body 2 via the oil supply flow path 25 connected to the compressor body 2.

[0035] The compressor 100 of this embodiment is equipped with a temperature control valve 19 at the outlet of the oil cooler 15. When the temperature of the oil reaching the oil cooler 15 falls below a predetermined temperature, the temperature control valve 19 is switched to supply oil to the compressor body 2 without heat exchange in the oil cooler 15. This prevents the formation of condensed water by controlling the lower limit temperature of the compressed air.

[0036] Furthermore, the secondary separated oil is stored inside the oil separation member 10. The oil separation member 10 has an oil recovery flow path 2 (8a) that communicates with the compressor intake 20 of the compressor body 2. During operation of the compressor 100, the pressure inside the oil separation member 10 is often higher than the pressure in the compressor intake 20. Therefore, the secondary separated oil is recovered to the compressor intake 20 by utilizing this pressure difference.

[0037] A suction throttle valve 21 is provided in the compressor intake portion 20 of the compressor body 2. The suction throttle valve 21 is opened and closed by pressurization and depressurization of a pipe (not shown) connected from the oil separation component 10 to a pressurization chamber of the suction throttle valve 21, thereby switching between loaded and no-load operation.

[0038] Figure 2 This is a diagram showing the state in which the motor 42, the gearbox 22, and the compressor body 2 are connected. Only the flange portion connecting the motor 42 to the gearbox 22 is shown. A main gear 3 is provided at the end of the shaft 23 connected to the motor 42. The main gear 3 is engaged with the primary gear 4 connected to the male rotor of the primary rotor 6 and the secondary gear 5 connected to the female rotor of the secondary rotor 7. Although not shown in the figure, the respective male and female rotors of the primary rotor 6 and the secondary rotor 7 are engaged. By the rotation of the motor 42, the male rotor rotates from the main gear 3 via the primary gear 4 and the secondary gear 5. By the rotation of the male rotor, the female rotor engaged with the male rotor rotates. By the rotation of both the male and female rotors, a compression volume is formed between the housing 24 that houses the rotors, and the air is compressed due to the change in the compression volume caused by the rotation of the male and female rotors.

[0039] Meanwhile, the temperatures of the main gear 3, primary gear 4, and secondary gear 5 increase due to friction between the gears during rotation. Therefore, oil must be applied to the gears for cooling and lubrication. Therefore, it is best to regularly supply oil to the gears. In this embodiment, the gears are arranged within the gear case 22 to prevent contaminants from adhering to the gears and / or to prevent the accumulation of oil supplied to the gears.

[0040] As a method of supplying oil to the gears, oil that has passed through the oil filter 18 is supplied to the interior of the gear box 22 via an oil supply flow path 25 connected to the gear box 22. Furthermore, the oil stored in the gear box 22 is recovered to the compressor intake 20 via an oil recovery flow path 26 that communicates from the gear box 22 to the compressor intake 20.

[0041] However, the connection portion of the oil recovery flow path 26 with the compressor intake portion 20 is located higher than the connection portion with the gear box 22 . Therefore, it is difficult to recover the oil from the gear box 22 simply by providing the oil recovery flow path 26 .

[0042] Therefore, an oil pressurization flow path 27 is provided, connecting the discharge port 14b of the secondary rotor 7 to the interior of the gearbox 22. The discharge pressure of the compressor 100 is used to pressurize the interior of the gearbox 22 through the oil pressurization flow path 27. As a result, the oil accumulated in the gearbox 22 is recovered to the compressor intake port 20 through the oil recovery flow path 26.

[0043] At this time, in order to increase the pressure inside the gear box 22, the following structure is adopted: sealing mechanisms 1 (30), 2 (31), and 3 (32) such as mechanical seals or oil seals are provided in the portions through which the shafts (shafts 23, 28, and 29) of the gear box 22 pass, thereby sealing the interior of the gear box 22.

[0044] In order to cool the gears, seal mechanism 1 ( 30 ), seal mechanism 2 ( 31 ), and seal mechanism 3 ( 32 ) inside the gear box 22 , oil is supplied from the oil tank 11 through the oil cooler 15 and the oil filter 18 to the gear box 22 .

[0045] Here, the pressure of the compressor intake portion 20 is P1, the discharge pressure of the compressor 100 is P2, the pressure inside the gear box 22 is P3, and the pressure of the oil supplied from the oil tank 11 to the gear box 22 is P4.

[0046] When the pressure P3 inside the gear box 22 becomes greater than the pressure P4 of the oil supplied from the oil tank 11 to the gear box 22, the oil flowing from the oil tank 11 to the gear box 22 flows backwards, and the oil does not flow into the gear box 22. Therefore, P3 needs to be lower than P4.

[0047] Therefore, a pressure reducing valve 33 is provided in the oil pressurizing flow path 27 , and the set pressure of the pressure reducing valve 33 is adjusted so that P3 < P4 .

[0048] During full-load operation, when the amount of compressed air used at the end of the operation decreases, the pressure on the compressed air outlet 17 side increases. When the detection value of the pressure sensor 2 (39) arranged at the outlet of the aftercooler 13 exceeds a certain threshold, pressure is supplied from the oil tank 11 to the pressurizing chamber (not shown) of the suction throttle valve 21, and no-load operation with the suction throttle valve 21 closed begins.

[0049] During no-load operation, the pressure P1 of the compressor suction section 20 becomes close to vacuum pressure. Therefore, even when the inside of the gear box 22 is not pressurized, that is, when P3 is at atmospheric pressure, the relationship P1>P3 can be maintained, and thus, oil can be recovered from the inside of the gear box 22 through the oil recovery flow path 26.

[0050] During no-load operation, no external air is drawn in, so discharge pressure P2 is at or below atmospheric pressure. However, since suction throttle valve 21 is not completely closed, discharge pressure P2 is higher than atmospheric pressure (e.g., 0.15 MPa). At this point, pressure P4 is, for example, 0.03 MPa, lower than during full-load operation (0.75 MPa), but maintained above atmospheric pressure (0 MPa in gauge pressure). Therefore, oil can be supplied from oil tank 11 to the interior of gearbox 22.

[0051] As a flow path connected to the interior of the gear box 22, there are: an oil supply flow path 25 that supplies oil from the oil tank 11 to the interior of the gear box 22; an oil recovery flow path 26 that recovers the oil inside the gear box 22 to the compressor intake part 20; and an oil pressurizing flow path 27 that uses the discharge pressure of the compressor 100 to pressurize the interior of the gear box 22.

[0052] During no-load operation, the compressor intake 20 reaches a near-vacuum pressure, allowing oil to be recovered from the gearbox 22. Furthermore, the pressure P3 is lowered below atmospheric pressure by the negative pressure of the intake throttle valve 21. This maintains P4 > P3, preventing backflow of oil in the oil supply passage 25.

[0053] Meanwhile, the oil pressurization passage 27 connects the discharge port 14b to the interior of the gearbox 22. When the pressure at the discharge port 14b flows through the oil pressurization passage 27 and pressurizes the interior of the gearbox 22, the pressure P3 increases, reaching P4 < P3. This could cause a reverse flow of oil from the oil tank 11 to the gearbox 22. To prevent this, a solenoid valve 35 with an on / off function is provided in the oil pressurization passage 27. During no-load operation, the solenoid valve 35 is closed, preventing compressed air from the discharge port 14b from flowing into the gearbox 22.

[0054] As a method for closing the solenoid valve 35 during no-load operation, for example, to control the opening and closing of the suction throttle valve 21, a solenoid valve (not shown) provided in the operating chamber pressurizing flow path (not shown) connecting the oil tank 11 to the pressurizing chamber of the suction throttle valve 21 is actuated at the same timing. This solenoid valve (not shown) is connected to a control board (not shown) via wiring, and is operated based on a no-load determination flag detected by the control board (not shown).

[0055] According to Example 1, an oil pressurizing flow path 27 is provided that communicates with the interior of the gear box 22 from the discharge port 14b of the secondary rotor 7. The discharge pressure of the compressor 100 is utilized to pressurize the interior of the gear box 22 through the oil pressurizing flow path 27. Therefore, the oil stored in the gear box can be recovered without using a pump.

[0056] This prevents vibrations caused by the pump sucking air during no-load operation, thus preventing damage to the piping caused by pump vibrations. Furthermore, the power required to drive the pump is no longer required, reducing power consumption.

[0057] Example 2

[0058] The second embodiment considers that the pressure values ​​of P2 and P4 fluctuate according to the usage status of the compressor 100 during load operation.

[0059] The discharge pressure of the compressor 100 fluctuates depending on the usage of the compressed air at the user end. The discharge pressure of the compressor 100 is determined by the amount of air flowing through the discharge flow path (not shown) at the outlet of the aftercooler 13 and the flow path diameter of the discharge flow path (not shown) at the outlet of the aftercooler 13. When the air is used at the user end, the diameter of the discharge flow path (not shown) at the outlet of the aftercooler 13 increases, and the discharge pressure decreases. On the other hand, when the air is no longer used at the user end, the diameter of the discharge flow path (not shown) at the outlet of the aftercooler 13 decreases, or the discharge flow path (not shown) at the outlet of the aftercooler 13 is blocked, the discharge pressure increases.

[0060] An induction motor driven at a constant rotational speed and / or a variable-speed motor controlled by an inverter is used as the motor 42 used in the compressor 100. In a variable-speed motor, the rotational speed of the rotor 9 is changed according to the amount of compressed air used at the end (load factor). In a screw compressor, the higher the discharge pressure, the higher the rotational speed of the rotor 9, and the higher the output of the motor 42.

[0061] Therefore, in a variable-speed screw compressor, when the pressure exceeds a certain rated point (rotor speed, discharge pressure) based on a certain rated point, the rotation speed of the rotor 9 is reduced to suppress the increase in the output of the motor 42. In addition, in a variable-speed screw compressor, when the pressure falls below the rated point, the rotation speed of the rotor 9 is increased within the range of the output that the motor 42 can tolerate.

[0062] When operating a fixed-speed or variable-speed compressor in this manner, if the pressure at P2 falls below its rated value, the pressure at P4 will also drop. For example, if the rated value of P2 is 0.75 MPa, the pressure at P4 is 0.3 MPa, and the set pressure of the pressure reducing valve 33 is 0.2 MPa, that is, P3 is 0.2 MPa, then when P2 drops to 0.45 MPa, the pressure at P4 falls below the set pressure of the pressure reducing valve 33 by 0.2 MPa, resulting in a relationship of P4 < P3. Consequently, the oil flow from the oil filter 18 to the gearbox 22 may be reversed, preventing oil supply.

[0063] In order to eliminate such a hidden danger, the setting pressure of the pressure reducing valve 33 is made variable according to the pressure of P4.

[0064] Figure 3 This is a diagram showing an example of the internal structure of the compressor body 2 according to the second embodiment.

[0065] Relative to Figure 2 structure, Figure 3 The compressor body 2 is provided with a control substrate 37, a pressure sensor 3 (38) and a pressure sensor 2 (39).

[0066] Pressure sensor 2 (39) and Figure 1 The pressure sensor 2 (39) is the same as that of the compressor 100 and is arranged at the outlet of the aftercooler 13 to detect the discharge pressure of the compressor 100.

[0067] The pressure sensor 3 ( 38 ) is disposed at the discharge port 14 b and detects the discharge pressure P2 of the compressor 100 .

[0068] The set pressure of the pressure reducing valve 33 is changed according to the value of the pressure sensor 2 (39). Alternatively, the set pressure of the pressure reducing valve 33 is changed according to the value of the pressure sensor 3 (38) provided at the discharge port 14b.

[0069] The pressure sensor 2 (39) or the pressure sensor 3 (38) is connected to the control board 37. The control board 37 determines the set pressure of the pressure reducing valve 33 using a pre-prepared table (not shown) based on the value of the pressure sensor 2 (39) or the pressure sensor 3 (38).

[0070] When the set pressure of the pressure reducing valve 33 is determined by the control substrate 37, the value is converted into a voltage, for example, and a command to change the set pressure is given to the pressure reducing valve 33. The pressure reducing valve 33 may also be a mechanism that uses a solenoid (not shown) to adjust the flow path diameter of the oil pressurizing flow path 27, or a mechanism (not shown) that automatically switches the adjustment handle of a diaphragm-type pressure reducing valve.

[0071] The set pressure of the pressure reducing valve 33 changes according to the pressure of P4. For example, if P2 is reduced from 0.75 MPa to 0.45 MPa, and P4 is reduced to 0.15 MPa, the set pressure of the pressure reducing valve 33 is set to a value lower than P4. This maintains the relationship P4 > P3, preventing backflow of oil from the oil filter 18 to the gearbox 22.

[0072] The value of P4 can also be read by, for example, the pressure sensor 1 (40) disposed in the oil supply flow path 25. In addition, the relationship between the pressure of P2 and the pressure of P4 can be known in advance without using the pressure sensor 1 (40), and the pressure of P4 can be predicted based on the actual measured value of the pressure of P2 read by the pressure sensor 3 (38).

[0073] According to Example 2, the control substrate 37 determines the set pressure of the pressure reducing valve 33 based on the value of the pressure sensor 2 (39) or the pressure sensor 3 (38), thereby being able to maintain the relationship P4>P3 and prevent the oil from flowing back from the oil filter 18 to the gear box 22.

[0074] Example 3

[0075] Figure 4 This is a diagram showing an example of the internal structure of the compressor body 2 according to the third embodiment.

[0076] Relative to Figure 2 structure, Figure 4 The compressor body 2 has a pressure reducing valve 2 ( 41 ) added to the oil supply passage 25 from the oil filter 18 to the gear box 22 .

[0077] As in the second embodiment, the discharge pressure P2 of the compressor 100 is assumed to vary depending on the usage of the compressed air at the user end, and a structure is adopted in which the relationship P4>P3 is maintained even if P2 varies. This is an alternative embodiment to the second embodiment.

[0078] In this embodiment, the set pressures of the pressure reducing valve 33 and the pressure reducing valve 2 (41) are set so that the set pressure of the pressure reducing valve 33 is lower than the set pressure of the pressure reducing valve 2 (41). As a result, even if the pressure of P2 fluctuates, the relationship of P4>P3 can be maintained, without adding a function of automatically changing the set pressure of the pressure reducing valve 33 based on the value of the pressure sensor 2 (39) or the pressure sensor 3 (38) as in the second embodiment.

[0079] According to Example 3, the set pressures of the pressure reducing valve 33 and the pressure reducing valve 2 (41) are set in such a way that the set pressure of the pressure reducing valve 33 is lower than the set pressure of the pressure reducing valve 2 (41). Therefore, even if the pressure of P2 fluctuates, the relationship of P4>P3 can be maintained.

[0080] Description of Reference Numerals

[0081] 1…Package, 2…Compressor body, 3…Main gear, 4…First stage gear, 5…Second stage gear, 6…First stage rotor, 7…Second stage rotor, 8a…Oil recovery flow path 2, 8b…Compressor intake flow path, 9…Rotor, 10…Oil separation component, 11…Oil tank, 12…Apron, 13…Aftercooler, 14a…Oil flow path, 15…Oil cooler, 16…Cooling water, 17…Compressed air discharge port, 18…Oil filter, 19…Thermostatic control valve, 20…Compressor intake, 2… 1...Suction throttle valve, 22...Gearbox, 23...Shaft, 24...Casing, 25...Oil supply path, 26...Oil recovery path, 27...Oil pressurization path, 28...Shaft, 29...Shaft, 30...Seal mechanism 1, 31...Seal mechanism 2, 32...Seal mechanism 3, 33...Pressure reducing valve, 35...Solenoid valve, 37...Control board, 38...Pressure sensor 3, 39...Pressure sensor 2, 40...Pressure sensor 1, 41...Pressure reducing valve 2, 42...Motor, 43...Pressure regulating check valve.

Claims

1. An air compressor that compresses air sucked in by an air intake portion and discharges the air from a discharge port, the air compressor comprising: a compressor for compressing the air; a driving source for driving the compressor; a gear for transmitting the drive of the drive source to the compressor; a gear box for accommodating the gear; an oil tank for storing oil separated from the compressed air; an oil supply passage communicating from the oil tank to the gear box; an oil recovery flow path communicating from the gear box to the air intake portion; and a pressurized flow path communicating from the discharge port to the gear box, The oil is supplied from the oil tank to the gear box via the oil supply passage using the discharge pressure of the air compressor. The gear box is pressurized via the pressurizing flow path by utilizing the discharge pressure, and the oil in the gear box is recovered to the intake portion via the oil recovery flow path.

2. The air compressor according to claim 1, wherein: The gear includes a drive shaft connected to the drive source and a compressor shaft connected to the compressor. The gear box includes a sealing mechanism that seals a portion through which the drive shaft and the compressor shaft pass.

3. The air compressor according to claim 2, wherein: The pressurized flow path includes a pressure reducing valve capable of adjusting the pressure of the gear box so that the pressure of the gear box is lower than the pressure of the oil supply flow path.

4. The air compressor according to claim 3, wherein: The pressure reducing valve can adjust the pressure of the gear box so that when the pressure of the intake part is P1, the discharge pressure is P2, the pressure of the gear box is P3, and the pressure of the oil supply path is P4, P1<P3<P4<P2 is satisfied.

5. The air compressor according to claim 3, wherein: The air intake portion includes an air intake valve that closes the air intake portion when the air compressor is operating without load. The pressurized flow path includes a solenoid valve that closes the pressurized flow path when the air compressor operates without load.

6. The air compressor according to claim 3, wherein: The pressure reducing valve includes a pressure sensor for detecting the discharge pressure and a control unit for controlling the pressure reducing valve according to the discharge pressure.

7. The air compressor according to claim 3, wherein: The oil supply flow path includes a second pressure reducing valve for adjusting the pressure of the oil supply flow path. The pressure reducing valve and the second pressure reducing valve can adjust the pressure of the gear box and the pressure of the oil supply flow path so that the pressure of the gear box is lower than the pressure of the oil supply flow path.

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