Air Compressor

Abstract

To provide a technique that enables recovery of oil stored in a gear casing without using a pump. A compressor 100 includes: a rotor 9 that compresses air; an electric motor 42 that drives the rotor 9; a gear that transmits the drive of the electric motor 42 to the rotor 9; a gear casing 22 that houses the gear; an oil tank 11 that stores oil separated from the compressed air; an oil supply passage 25 that extends from the oil tank 11 to the gear casing 22; an oil recovery passage 26 that extends from the gear casing 22 to a compressor intake portion 20; and an oil pressurizing passage 27 that extends from a discharge port 14b to the gear casing 22. Oil is supplied from the oil tank 11 to the gear casing 22 via the oil supply passage 25 by discharge pressure of the compressor 100, and the gear casing 22 is pressurized via the oil pressurizing passage 27 by the discharge pressure, thereby recovering oil from the gear casing 22 to the compressor intake portion 20 via the oil recovery passage 26.

Description

TECHNICAL FIELD

[0001] The present invention relates to an air compressor.BACKGROUND ART

[0002] An air compressor is known which compresses air by rotating a pair of male and female rotors arranged inside a casing. In such 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 from the male rotor via a timing gear or a helical groove.

[0003] As the transmission path between the motor and the male rotor, in addition to a direct connection structure, a structure in which drive is transmitted via gears in order to adjust the rotational speed is adopted. The gears are composed of a bull gear connected to the drive source and a pinion gear connected to the rotor. By forming a compression chamber with the grooves of the male and female rotors and the casing, the volume decreases due to rotation, and the pressure increases from atmospheric pressure to the user-specified pressure, and due to this structure, a negative pressure is generated at the intake portion of the casing.

[0004] Adjacent to the intake portion of the casing, there is a gear casing that houses gears, and inside the gear casing, oil for lubricating and cooling the gears is stored. In order to use the stored oil for cooling and lubricating the rotor compression chamber, a communication hole is provided between the gear casing and the casing, and a structure is known in which the oil inside the gear casing is recovered to the intake portion of the casing by the negative pressure at the intake portion of the casing.

[0005] On the other hand, there are cases where the oil inside the gear casing cannot be recovered by the negative pressure at the intake portion of the casing, as described above. For example, in a two-stage rotary screw compressor in which two pairs of male and female rotors are arranged vertically, the number of pinion gears connected to the male rotors increases, resulting in an increase in the volume of the gear casing that houses the bull gear and the pinion gears, and thus an increase in the amount of oil stored inside the gear casing.

[0006] Therefore, the negative pressure at the intake portion of the casing alone becomes insufficient to recover the oil in time, raising concerns about an increase in agitation resistance due to the gears being submerged in oil, as well as oil leakage toward the drive source.

[0007] Patent Document 1 discloses that lubricating oil stored in a gear case is pressure-fed to a lubricating oil heat exchanger via a lubricating oil pipe using an oil pump. The lubricating oil, which has been cooled to a predetermined temperature or lower by the lubricating oil heat exchanger, is sent to the discharge-side and intake-side compressor bearings via a lubricating oil pipe and an oil filter, and is thereaCITATION LISTPatent Document

[0008] Patent Document 1: WO 2015 / 198647SUMMARY OF THE INVENTIONProblems to be Solved by the Invention

[0009] In the technique disclosed in Patent Document 1, oil inside the gear casing is recovered using a pump; however, the rotor or dedicated motor that drives the pump often rotates at a constant speed, and therefore tends to maintain the same rotational speed during no-load operation of the compressor as during load operation. On the other hand, since the amount of oil supplied to the gears is determined by the discharge pressure acting on the oil, the amount of oil stored in the gear casing is smaller during no-load operation than during load operation.

[0010] Therefore, during no-load operation, the suction volume of the pump becomes larger than the amount of oil to be recovered by the pump, resulting in the oil containing air, which causes an increase in pump vibration. There is a risk that vibration of the pump is transmitted to the piping connected to the pump, thereby causing damage to the piping.

[0011] Accordingly, an object of the present invention is to provide a technique that enables recovery of oil stored in the gear casing without using a pump.SOLUTIONS TO PROBLEMS

[0012] In order to solve the above-described problem, one representative air compressor according to the present invention is an air compressor that compresses air drawn in through an intake portion and discharges the compressed air through a discharge port, and includes: a compressor that compresses the air; a drive source for driving the compressor; a gear for transmitting drive from the drive source to the compressor; a gear casing for housing the gear; an oil tank for storing oil separated from the compressed air; an oil supply passage that communicates from the oil tank to the gear casing; an oil recovery passage that communicates from the gear casing to the intake portion; and a pressurizing passage that communicates from the discharge port to the gear casing, wherein oil is supplied from the oil tank to the gear casing via the oil supply passage by the discharge pressure of the air compressor, and the gear casing is pressurized via the pressurizing passage by the discharge pressure, thereby recovering the oil in the gear casing to the intake portion via the oil recovery passage.EFFECTS OF THE INVENTION

[0013] According to the present invention, oil stored in the gear casing can be recovered without using a pump.

[0014] Other problems, configurations, and advantages not described above will become apparent from the following description of embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a diagram illustrating an example of the configuration of the air compressor according to Embodiment 1.

[0016] FIG. 2 is a diagram illustrating an example of the internal configuration of the compressor main body according to Embodiment 1.

[0017] FIG. 3 is a diagram illustrating an example of the internal configuration of the compressor main body according to Embodiment 2.

[0018] FIG. 4 is a diagram illustrating an example of the internal configuration of the compressor main body according to Embodiment 3.MODE FOR CARRYING OUT THE INVENTION

[0019] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.Embodiment 1

[0020] FIG. 1 is a diagram illustrating an example of the configuration of an air compressor 100 (hereinafter referred to as “compressor 100”) according to Embodiment 1.

[0021] FIG. 2 is a diagram illustrating an example of the internal configuration of a compressor main body 2 according to Embodiment 1.

[0022] In the present embodiment, air is used as the compressed gas; however, the invention is not limited thereto, and other gases may also be used. The compressor 100 is a positive displacement compressor of the liquid-injection type in which a liquid (for example, oil) is supplied to the compression chamber, and in the present embodiment, an oil-injection screw compressor is applied. The present invention is not limited to this configuration, and a turbo-type compressor may also be used.

[0023] The compressor 100 includes a package 1, a compressor main body 2 disposed inside the package 1, and an electric motor 42 that drives the compressor main body 2. The compressor main body 2 is connected to the electric motor 42 via a bull gear 3, a first-stage gear 4, and a second-stage gear 5. By the rotation of the electric motor 42, the bull gear 3 rotates, and the rotation of the bull gear 3 is transmitted to the first-stage gear 4 and the second-stage gear 5, whereby the first-stage rotor 6 and the second-stage rotor 7 rotate, and outside air is drawn in from a compressor intake portion 20 of the compressor main body 2 and compressed.

[0024] Outside air may be taken in from outside the air compressor 100 through a compressor intake passage 8b that communicates with the outside of the air compressor 100, or may be taken in from inside the air compressor 100 without providing the compressor intake passage 8b.

[0025] In FIGS. 1 and 2, rotors 9 are arranged as vertically stacked sets of male and female rotors, and in each set, the male rotor is located on the front side and the female rotor is located on the rear side when viewed from the front of the drawing.

[0026] Although the drawings in the present embodiment illustrate an oil-cooled two-stage compressor, the invention is not limited thereto, and a single-stage liquid-cooled air compressor may also be used. In a two-stage compressor, the male and female rotors arranged in the upper portion are referred to as the first-stage compressor, and the male and female rotors arranged in the lower portion are referred to as the second-stage compressor. It is desirable 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 compresses the air from atmospheric pressure to 0.18 MPa, and the second-stage compressor compresses it to 0.75 MPa. In order to suppress the temperature increase associated with compression, compression is performed while injecting oil during the compression process.

[0027] The injected oil is carried together with the compressed air to an oil separator element 10, where it is separated (this is referred to as secondary separation). In addition, before reaching the oil separator element 10, the oil is separated by centrifugal force (this is referred to as primary separation) using a cylindrical region formed by a skirt 12 disposed inside an oil tank 11 and the inner peripheral surface of the oil tank 11.

[0028] The oil separated by primary separation is stored in the oil tank 11. On the other hand, the compressed air separated by secondary separation is discharged from a compressed air discharge port 17 to the outside of the air compressor 100 through a pressure-regulating check valve 43 and an aftercooler 13, and is supplied to the user.

[0029] Inside the oil tank 11, a pressure lower than the pressure at the discharge port 14b of the compressor main body 2 and higher than the pressure of the compressed air supplied to the user (for example, 0.7 MPa) acts. As a result, the oil stored in the oil tank 11 is carried to an oil cooler 15 via an oil passage 14a that connects the oil tank 11 to the oil cooler 15. The oil carried to the oil cooler 15 exchanges heat with cooling water 16 inside the oil cooler 15. After passing through an oil filter 18, the oil, having undergone heat exchange, is supplied from the oil filter 18 to the compressor main body 2 via an oil supply passage 25 connected to the compressor main body 2, in order to cool the compressor main body 2 and the gears (the bull gear 3, the first-stage gear 4, and the second-stage gear 5).

[0030] In this embodiment, the compressor 100 is provided 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 is lower than a predetermined temperature, the temperature control valve 19 switches the flow so that oil is supplied to the compressor main body 2 without undergoing heat exchange in the oil cooler 15. In this way, by controlling the lower limit of the temperature of the compressed air, the configuration prevents the generation of drain.

[0031] In addition, the oil separated by secondary separation is configured to be stored inside the oil separator element 10.

[0032] The oil separator element 10 is provided with an oil recovery passage 2 (8a) that communicates with the compressor intake portion 20 of the compressor main body 2. During operation of the compressor 100, the internal pressure of the oil separator element 10 is always maintained higher than the pressure in the compressor intake portion 20, and the pressure difference is utilized to recover the oil that has been secondarily separated to the compressor intake portion 20.

[0033] A suction throttling valve 21 is provided in the compressor intake portion 20 of the compressor main body 2. The suction throttling valve 21 is opened and closed by pressurizing and depressurizing a pipe (not shown) that connects the oil separator element 10 to the pressurizing chamber of the suction throttling valve 21, thereby switching between loaded operation and unloaded operation.

[0034] FIG. 2 is a diagram showing a state in which the electric motor 42, the gear casing 22, and the compressor main body 2 are connected, and only the flange portion of the electric motor 42 that is connected to the gear casing 22 is shown. A bull gear 3 is provided at the end of a shaft 23 connected to the electric motor 42. The bull gear 3 is in mesh with a first-stage gear 4 connected to the male rotor of the first-stage rotor 6 and a second-stage gear 5 connected to the female rotor of the second-stage rotor 7. Although not illustrated, the male and female rotors of the first-stage rotor 6 and the second-stage rotor 7 are in mesh with each other. By the rotation of the electric motor 42, the male rotors are rotated via the bull gear 3, the first-stage gear 4 and second-stage gear 5. The rotation of the male rotors causes the female rotors meshed therewith to rotate. By the rotation of both the male and female rotors, a compression volume is formed between the rotors and the casing 24 that houses the rotors, and air is compressed by the change in the compression volume caused by the rotation of the male and female rotors.

[0035] On the other hand, the bull gear 3, the first-stage gear 4, and the second-stage gear 5 increase in temperature due to friction between the rotating gears, and therefore it is necessary to apply oil to the gears for cooling and lubrication. Therefore, it is desirable to constantly supply oil to the gears. In this embodiment, in order to prevent contamination from adhering to the gears and to retain the oil supplied to the gears, the gears are arranged inside the gear casing 22.

[0036] However, since the connection portion of the oil recovery passage 26 with the compressor intake portion 20 is located higher than the connection portion with the gear casing 22, it is difficult to recover the oil from the gear casing 22 merely by arranging the oil recovery passage 26.

[0037] Accordingly, an oil pressurizing passage 27 is provided to communicate from the discharge port 14b of the second-stage rotor 7 to the inside of the gear casing 22. The inside of the gear casing 22 is pressurized through the oil pressurizing passage 27 by the discharge pressure of the compressor 100. As a result, the oil stored inside the gear casing 22 is recovered to the compressor intake portion 20 through the oil recovery passage 26.

[0038] At this time, in order to increase the pressure inside the gear casing 22, seal mechanisms 1 (30), 2 (31), and 3 (32), such as mechanical seals or oil seals, are provided at the portions where the shafts (shaft 23, shaft 28, and shaft 29) penetrate the gear casing 22, thereby forming a sealed structure inside the gear casing 22.

[0039] The oil that has passed through the oil cooler 15 and the oil filter 18 from the oil tank 11 is supplied to the gear casing 22 in order to cool the gears inside the gear casing 22 as well as the seal mechanisms 1 (30), 2 (31), and 3 (32).

[0040] Here, let P1 be the pressure at the compressor intake portion 20, P2 be the discharge pressure of the compressor 100, P3 be the pressure inside the gear casing 22, and P4 be the pressure of the oil supplied from the oil tank 11 to the inside of the gear casing 22.

[0041] If the pressure P3 inside the gear casing 22 becomes greater than the pressure P4 of the oil supplied from the oil tank 11 to the inside of the gear casing 22, the oil flowing from the oil tank 11 to the gear casing 22 flows backward, and oil does not flow into the gear casing 22. Therefore, P3 needs to be lower than P4.

[0042] Therefore, a pressure-reducing valve 33 is provided in the oil pressurizing passage 27, and the set pressure of the pressure-reducing valve 33 is adjusted so that P3<P4.

[0043] When the amount of compressed air used by the user decreases during full-load operation, the pressure on the compressed air discharge port 17 side increases. When the detection value of the pressure sensor 2 (39) disposed 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 throttling valve 21, initiating no-load operation by closing the suction throttling valve 21.

[0044] During no-load operation, since the pressure P1 at the compressor intake portion 20 becomes close to a vacuum, the relationship of P1>P3 can still be maintained even when the gear casing 22 is not pressurized, i.e., when P3 is at atmospheric pressure. As a result, oil can be recovered from inside the gear casing 22 through the oil recovery passage 26.

[0045] During no-load operation, since outside air is not taken in, the discharge pressure P2 is considered to become atmospheric pressure or lower. However, because the suction throttling valve 21 is not in a fully closed state, the discharge pressure P2 remains higher than atmospheric pressure (for example, 0.15 MPa). At this time, the pressure P4 decreases compared to that during full-load operation (assumed to be 0.75 MPa), for example, to 0.03 MPa. However, the pressure P4 remains above atmospheric pressure (assumed to be 0 MPa in gauge pressure). Therefore, oil can still be supplied from the oil tank 11 to the inside of the gear casing 22.

[0046] The passages communicating with the inside of the gear casing 22 include an oil supply passage 25 for supplying oil from the oil tank 11 to the inside of the gear casing 22, an oil recovery passage 26 for recovering oil from inside the gear casing 22 to the compressor intake portion 20, and an oil pressurizing passage 27 for pressurizing the inside of the gear casing 22 with the discharge pressure of the compressor 100.

[0047] During no-load operation, since the pressure in the compressor intake portion 20 approaches a vacuum pressure, oil inside the gear casing 22 is recovered, and the pressure P3 becomes lower than atmospheric pressure due to the effect of the negative pressure from the suction throttling valve 21. As a result, since P4>P3 is maintained, no backflow of oil occurs in the oil supply passage 25.

[0048] On the other hand, the oil pressurizing passage 27 is connected from the discharge port 14b to the inside of the gear casing 22. When the pressure at the discharge port 14b pressurizes the inside of the gear casing 22 through the oil pressurizing passage 27, the pressure P3 increases, and if P4<P3, there is a possibility that the oil flowing from the oil tank 11 to the gear casing 22 will flow backward. To prevent this, the oil pressurizing passage 27 is provided with a solenoid valve 35 having an open / close function. During no-load operation, the solenoid valve 35 is closed to prevent compressed air from the discharge port 14b from flowing into the inside of the gear casing 22.

[0049] As a method for closing the solenoid valve 35 during no-load operation, for example, the solenoid valve (not shown) provided in a control chamber pressurizing passage (not shown) that connects the oil tank 11 to the pressurizing chamber of the suction throttling valve 21 may be operated in synchronization with the same timing. This solenoid valve (not shown) is connected via wiring to a control board (not shown) and is actuated based on a no-load determination flag determined by the control board (not shown).

[0050] According to Embodiment 1, an oil pressurizing passage 27 is provided that connects the discharge port 14b of the second-stage rotor 7 to the inside of the gear casing 22, and the inside of the gear casing 22 is pressurized through the oil pressurizing passage 27 by the discharge pressure of the compressor 100. As a result, the oil stored inside the gear casing can be recovered without using a pump.

[0051] As a result, since vibration caused by air being sucked in by a pump does not occur during no-load operation, damage to the piping due to pump-induced vibration can be prevented. Furthermore, since no power is required to drive the pump, power consumption can be reduced.Embodiment 2

[0052] Embodiment 2 considers a case in which the pressure values P2 and P4 fluctuate during load operation depending on the operating conditions of the compressor 100.

[0053] The discharge pressure of the compressor 100 varies depending on the user's usage of the compressed air. The discharge pressure of the compressor 100 is determined by the flow rate of air through the discharge passage (not shown) at the outlet of the aftercooler 13 and the flow path resistance of the discharge passage (not shown) at the outlet of the aftercooler 13. When the user consumes air, the diameter of the discharge passage (not shown) at the outlet of the aftercooler 13 increases, causing the discharge pressure to decrease. On the other hand, when the user stops consuming air and the diameter of the discharge passage (not shown) at the outlet of the aftercooler 13 decreases or the discharge passage of the aftercooler 13 is blocked, the discharge pressure increases.

[0054] As the electric motor 42 used in the compressor 100, either an induction motor that operates at a constant rotational speed or a variable-speed motor utilizing inverter control is employed. In the case of a variable-speed motor, the rotational speed of the rotor 9 is varied in accordance with the amount (load factor) of compressed air used by the user. In a screw compressor, the higher the discharge pressure and the higher the rotational speed of the rotor 9, the greater the output of the electric motor 42 becomes.

[0055] Accordingly, in a variable-speed screw compressor, control is performed such that when the pressure exceeds a predetermined rated point (rotational speed of the rotor and discharge pressure), the rotational speed of the rotor 9 is reduced to suppress the increase in output of the electric motor 42. Furthermore, in a variable-speed screw compressor, when the pressure falls below the rated point, control is performed to increase the rotational speed of the rotor 9 within the allowable output range of the electric motor 42.

[0056] As described above, when operating a constant-speed or variable-speed type compressor, if the pressure P2 is assumed to fall below the rated point, it is also conceivable that the pressure P4 will simultaneously decrease. For example, when the rated point of P2 is set to 0.75 MPa, the pressure P4 is set to 0.3 MPa, and the pressure setting of the pressure-reducing valve 33 (i.e., P3) is set to 0.2 MPa, if P2 decreases to 0.45 MPa, then the pressure P4 will fall below the setting pressure of the pressure-reducing valve 33 (0.2 MPa), resulting in a relationship of P4<P3. Therefore, the flow of oil from the oil filter 18 to the gear casing 22 may reverse, making it impossible to supply oil.

[0057] To address such concerns, the set pressure of the pressure-reducing valve 33 is made adjustable in accordance with the pressure of P4.

[0058] FIG. 3 is a diagram showing an example of the internal configuration of the compressor main body 2 in Embodiment 2.

[0059] The compressor main body 2 shown in FIG. 3 is based on the configuration of FIG. 2, with a control board 37, a pressure sensor 3 (38), and a pressure sensor 2 (39) added.

[0060] The pressure sensor 2 (39) is the same as the pressure sensor 2 (39) shown in FIG. 1, and it is disposed at the outlet of the aftercooler 13 to detect the discharge pressure of the compressor 100.

[0061] The pressure sensor 3 (38) is disposed at the discharge port 14b and detects the discharge pressure P2 of the compressor 100.

[0062] The set pressure of the pressure-reducing valve 33 is changed in accordance with the value of the pressure sensor 2 (39). Alternatively, the set pressure of the pressure-reducing valve 33 may be changed based on the value of the pressure sensor 3 (38) provided at the discharge port 14b.

[0063] The pressure sensor 2 (39) or the pressure sensor 3 (38) is connected to the control board 37. Based on the value of the pressure sensor 2 (39) or the pressure sensor 3 (38), the control board 37 determines the set pressure of the pressure-reducing valve 33 using a pre-prepared table (not shown).

[0064] When the control board 37 determines the set pressure of the pressure-reducing valve 33, the set value is, for example, converted into a voltage, and the pressure-reducing valve 33 is instructed to change the set pressure accordingly. The pressure-reducing valve 33 may be, for example, a mechanism that adjusts the flow path of the oil pressurizing passage 27 by a solenoid (not shown), or a mechanism (not shown) that automatically adjusts the adjustment handle of a diaphragm-type pressure-reducing valve.

[0065] The set pressure of the pressure-reducing valve 33 is changed in accordance with the pressure P4. For example, when 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 adjusted to a value lower than P4. This maintains the relationship of P4>P3 and prevents the backflow of oil from the oil filter 18 to the gear casing 22.

[0066] The value of P4 may be read, for example, by a pressure sensor 1 (40) disposed in the oil supply passage 25.

[0067] Alternatively, without using the pressure sensor 1 (40), the relationship between the pressures P2 and P4 may be previously identified, and the pressure P4 may be estimated based on the measured value of P2 obtained by the pressure sensor 3 (38).

[0068] According to Embodiment 2, the control board 37 determines the set pressure of the pressure-reducing valve 33 based on the value from the pressure sensor 2 (39) or the pressure sensor 3 (38), thereby maintaining the relationship P4>P3 and preventing the reverse flow of oil from the oil filter 18 to the gear casing 22.Embodiment 3

[0069] FIG. 4 is a diagram illustrating an example of the internal configuration of the compressor main body 2 in Embodiment 3.

[0070] The compressor main body 2 shown in FIG. 4 includes, in addition to the configuration of FIG. 2, a pressure-reducing valve 2 (41) added to the oil supply passage 25 from the oil filter 18 to the gear casing 22.

[0071] Similar to Embodiment 2, this configuration assumes a case in which the discharge pressure P2 of the compressor 100 fluctuates depending on the user's usage of compressed air, and is structured to maintain the relationship P4>P3 even when P2 fluctuates. Embodiment 3 is an alternative embodiment to Embodiment 2.

[0072] In this embodiment, the set pressure of the pressure-reducing valve 33 is set to be lower than the set pressure of the pressure-reducing valve 2 (41). This allows the relationship P4>P3 to be maintained even when the pressure P2 fluctuates, without adding the function of automatically changing the set pressure of the pressure-reducing valve 33 according to the value from the pressure sensor 2 (39) or the pressure sensor 3 (38), as in Embodiment 2.

[0073] According to Embodiment 3, the set pressure of the pressure-reducing valve 33 is configured to be lower than that of the pressure-reducing valve 2 (41), so that the relationship P4>P3 can be maintained even if the pressure P2 fluctuates.REFERENCE SIGNS LIST

[0074] 1: Package, 2: Compressor main body, 3: Bull gear, 4: First-stage gear, 5: Second-stage gear, 6: First-stage rotor, 7: Second-stage rotor, 8a: Oil recovery passage 2, 8b: Compressor intake passage, 9: Rotor, 10: Oil separator element, 11: Oil tank, 12: Skirt, 13: Aftercooler, 14a: Oil passage, 15: Oil cooler, 16: Cooling water, 17: Compressed air discharge port, 18: Oil filter, 19: Temperature control valve, 20: Compressor intake portion, 21: Suction throttling valve, 22: Gear casing, 23: Shaft, 24: Casing, 25: Oil supply passage, 26: Oil recovery passage, 27: Oil pressurizing passage, 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: Electric motor, 43: Pressure-regulating check valve

Claims

1. An air compressor that compresses air taken in through an intake portion and discharges compressed air through a discharge port, comprising:a compressor that compresses the air,a drive source that drives the compressor,a gear that transmits drive of the drive source to the compressor,a gear casing that houses the gear,an oil tank that stores oil separated from the compressed air,an oil supply passage that extends from the oil tank to the gear casing,an oil recovery passage that extends from the gear casing to the intake portion, anda pressurizing passage that extends from the discharge port to the gear casing,wherein oil is supplied from the oil tank to the gear casing via the oil supply passage by the discharge pressure of the air compressor, andthe gear casing is pressurized via the pressurizing passage by the discharge pressure, thereby allowing oil in the gear casing to be recovered to the intake portion via the oil recovery2. The air compressor according to claim 1,wherein the gear includesa drive shaft portion connected to the drive source, anda compressor shaft portion connected to the compressor, andthe gear casing includesa sealing mechanism that seals portions through which the drive shaft portion and the compressor shaft portion penetrate.

3. The air compressor according to claim 2,wherein the pressurizing passage includesa pressure-reducing valve that adjusts the pressure of the gear casing so that pressure of the gear casing becomes lower than pressure of the oil supply passage.

4. The air compressor according to claim 3,wherein the pressure-reducing valveadjusts pressure in the gear casing so that, when pressure of the intake portion is P1, discharge pressure is P2, pressure in the gear casing is P3, and pressure in the oil supply passage is P4, the relationship P1<P3<P4<P2 is satisfied.

5. The air compressor according to claim 3,wherein the intake portion includesan intake valve that closes the intake portion during no-load operation of the air compressor, andthe pressurizing passage includesa solenoid valve that closes the pressurizing passage during no-load operation of the air compressor.

6. The air compressor according to claim 3,further comprising a pressure sensor that detects the discharge pressure, anda control unit that controls the pressure-reducing valve according to the discharge pressure.

7. The air compressor according to claim 3,wherein the oil supply passage comprisesa second pressure-reducing valve that adjusts pressure in the oil supply passage, andthe pressure-reducing valve and the second pressure-reducing valveadjust pressure in the gear casing and pressure in the oil supply passage so that pressure in the gear casing becomes lower than pressure in the oil supply passage.

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