OIL FEEDING TYPE COMPRESSOR

Abstract

 An oil feed type compressor includes a compressor body (2) that compresses a gas while oil is being injected therein, a first oil separator (6) that separates oil from the compressed gas delivered from the compressor body (2), a second oil separator (8) that further separates oil from the compressed gas from which the oil has been separated by the first oil separator (6), the second oil separator (8) having a reservoir (8bd) for storing the separated oil, a delivery pipe system (90) through which the compressed gas from which the oil has been separated by the second oil separator (8) flows, an oil discharge passage (10) that discharges the oil having been stored in the reservoir (8bd) from the reservoir (8bd), a valve body (10a) included in the oil discharge passage (10), and a controller (11) that controls the opening of the valve body (10a) over time.

Description

Technical Field

[0001] The present invention relates to an oil feed type compressor.

Background Art

[0002] Oil feed type compressors mix air, which is sucked in from the intake side of a compressor body when the compressor body is actuated, with lubricating oil and compress the air-oil mixture to a predetermined pressure. Oil is separated (primary separation) from the compressed air-oil mixture by an oil separator (first oil separator), and then the separated oil is further separated (secondary separation) by an oil separating element (second oil separator), after which the compressed air is caused to flow via a cooler, etc. to a delivery passage.

[0003] Further, the oil separated by the first oil separator is retrieved by an oil tank disposed in a lower portion of the first oil separator. The oil in the oil tank is pressure-fed to the intake side of the compressor body under the pressure of the compressed air in the oil tank, so that the oil is returned to the compressor body.

[0004] An oil feed type compressor where oil separated by a second oil separator by way of secondary separation is returned to a compressor body is disclosed in Patent Document 1, for example. According to the oil feed type compressor disclosed in Patent Document 1, oil dropped to an element head disposed in a lower portion of the second oil separator is pressure-fed from an oil retrieval hole formed in the element head to the intake side of the compressor body under the pressure of the compressed air, so that the oil is returned to the compressor body.

Prior Art Document

Patent Document

[0005] Patent Document 1: JP-2003-120565-A

Summary of the Invention

Problems to be Solved by the Invention

[0006] The oil retrieved from the oil retrieval hole is discharged by the pressure of the compressed air in the second oil separator. The compressed air that is discharged together with the oil is, however, liable to waste part of the compressed air produced by the compressor body, and represents one of the factors for reducing the efficiency of the air compressor.

[0007] In order to minimize the amount of compressed air discharged upon oil retrieval, it may be proposed to reduce the diameter of the pipe of a return channel for returning oil from the oil retrieval hole to the air compressor body or to provide the return channel with an orifice for restricting the oil flow (further reduce the diameter of the orifice, etc.). However, the pipe may become clogged, resulting in a retrieval failure. Therefore, there are certain limitations on efforts to reduce the diameter of the pipe.

[0008] Especially, small-size oil feed type compressors tend to have a small amount of oil retrieved from an oil retrieval hole, reflecting a small amount of delivered air. Therefore, even if the diameter of a return channel is reduced, the amount of discharged compressed air is relatively large, and the reduction in the performance of the compressors may not be improved.

[0009] With the configuration that makes it possible to operate the compressor body at variable speeds, e.g., in a case where an electric motor having a power converter (inverter) is used as the drive source of the compressor body, when the compressor body is operated under a low load, since the amount of discharged compressed air remains unchanged though a small amount of oil is retrieved from the oil retrieval hole, reflecting a small amount of delivered air, the performance of the compressors tends to be lowered.

[0010] The present invention has been made in view of the above problems. It is an object of the present invention to provide an oil feed type compressor that reduces the amount of compressed air discharged when oil separated by a second oil separator is retrieved, restraining a reduction in the efficiency of compression.

Means for Solving the Problems

[0011] In order to achieve the above object, there is provided in accordance with the present invention an oil feed type compressor including a compressor body that compresses a gas while oil is being injected therein, a first oil separator that separates oil from the compressed gas delivered from the compressor body, a second oil separator that further separates oil from the compressed gas from which the oil has been separated by the first oil separator, the second oil separator having a reservoir for storing the separated oil, a delivery pipe system through which the compressed gas from which the oil has been separated by the second oil separator flows, an oil discharge passage that discharges the oil having been stored in the reservoir from the reservoir, a valve body included in the oil discharge passage, and a controller that controls an opening of the valve body over time.

[0012]  There is also provided in accordance with the present invention an oil feed type compressor including a compressor body that compresses a gas while oil is being injected therein, a first oil separator that separates oil from the compressed gas delivered from the compressor body, a second oil separator that further separates oil from the compressed gas from which the oil has been separated by the first oil separator, the second oil separator having a reservoir for storing the separated oil, a delivery pipe system through which the compressed gas from which the oil has been separated by the second oil separator flows, an oil discharge passage that discharges the oil having been stored in the reservoir from the reservoir, a valve body included in the oil discharge passage, and a controller that controls an opening of the valve body on the basis of a load ratio and operating time of the compressor body.

[0013] There is also provided in accordance with the present invention an oil feed type compressor including an oil feed type compressor including a compressor body that compresses a gas while oil is being injected therein, a first oil separator that separates oil from the compressed gas delivered from the compressor body, a second oil separator that further separates oil from the compressed gas from which the oil has been separated by the first oil separator, the second oil separator having a reservoir for storing the separated oil, a delivery pipe system through which the compressed gas from which the oil has been separated by the second oil separator flows, an oil discharge passage that discharges the oil having been stored in the reservoir from the reservoir, a valve body included in the oil discharge passage, a pressure sensor that detects a pressure in the delivery pipe system, and a controller that controls an opening of the valve body over time, in which the controller controls a timing to constrict the opening of the valve body on the basis of the pressure detected by the pressure sensor while the valve body is being open.

Advantages of the Invention

[0014] According to the present invention, in the oil feed type compressor, the amount of compressed air discharged when the oil separated by the second oil separator is retrieved is reduced, thereby restraining the compression efficiency from being reduced.

Brief Description of the Drawings

[0015] 

FIG. 1 is a schematic view illustrating the configuration of oil feed type compressors according to first and third embodiments of the present invention.

FIG. 2 is a timing chart of a process of controlling the opening of a valve body that is carried out by a controller of the oil feed type compressor according to the first embodiment of the present invention.

FIG. 3 is a schematic view illustrating the configuration of oil feed type compressors according to second and third embodiments of the present invention.

FIG. 4 is a graph illustrating changes over time in a load ratio of a compressor body and a timing chart of a process of controlling the opening of a valve body that is carried out by a controller of the oil feed type compressor according to the second embodiment of the present invention.

FIG. 5 is a graph illustrating changes over time in a pressure detected by a pressure sensor and a timing chart of a process of controlling the opening of a valve body that is carried out by a controller of the oil feed type compressor according to the third embodiment of the present invention.

FIG. 6 is a graph illustrating changes over time in a load ratio of a compressor body, the graph illustrating changes over time in the pressure detected by the pressure sensor, and the timing chart of the process of controlling the opening of the valve body that is carried out by the controller of the oil feed type compressor according to the third embodiment of the present invention.

Modes for Carrying Out the Invention

[0016] The configuration and operation of oil feed type compressors according to first through third embodiments of the present invention will be described hereinbelow with reference to the drawings. Identical reference characters denote identical parts throughout views.

(First Embodiment)

[0017] FIG. 1 is a schematic view illustrating the configuration of an oil feed type compressor 1A according to the first embodiment of the present invention. The oil feed type compressor 1A includes a compressor body 2, an electric motor 3, an intake filter 4, an intake valve 5, a first oil separator 6, an oil supply system 7, a second oil separator (oil separator) 8, a delivery pipe system 9, an oil discharge passage 10, and a controller 11.

[0018] The compressor body 2 is a section for producing compressed air, and has a pair of screw rotors 2a and 2b (one depicted in FIG. 1) that mesh with each other and a casing (not depicted) for housing the pair of screw rotors 2a and 2b therein. The screw rotors 2a and 2b meshing with each other and the casing are combined with each other in making up a compression chamber (not depicted) as a closed space.

[0019] The electric motor 3 acts as a drive source for driving the screw rotors 2a and 2b of the compressor body 2. When the electric motor 3 drives the pair of screw rotors 2a and 2b, the compression chamber moves in an axial direction (a leftward direction in FIG. 1) of the screw rotors 2a and 2b, successively performing an air intake stroke, an air compression stroke, and an air delivery stroke. Specifically, the compression chamber sucks in air through the intake filter 4 and the intake valve 5 that are disposed on an intake side of the compressor body 2, compresses the air, and delivers the compressed air into the first oil separator 6 disposed on a delivery side of the compressor body 2. The compression chamber is supplied with oil from the oil supply system 7, for dissipating the heat generated when the air is compressed, sealing the compression chamber, and lubricating the screw rotors 2a and 2b.

[0020] The first oil separator 6 includes, for example, a swirl-separation-type gas-liquid separator for primarily separating oil from the compressed air by way of centrifugal separation. The first oil separator 6 has a swirling flow passage (not depicted) formed therein for swirling the compressed air. The oil that has been primarily separated is stored in an oil tank 6a in a lower portion of the first oil separator 6.

[0021] The oil supply system 7 includes pipes, etc. interconnecting the oil tank 6a and the compressor body 2, and injects the oil having been stored in the oil tank 6a into the compression chamber of the compressor body 2 under the pressure difference between the compressed air in the first oil separator 6 and the air sucked into the compressor body 2. One or more holes for injecting oil into the compression chamber are provided in a downstream portion of the oil supply system 7, and the oil is ejected or sprayed into the compression chamber. When the oil is ejected from the multiple holes, the oil streams from the multiple holes may be caused to collide with each other, so that the oil can be sprayed into the compression chamber.

[0022] The oil supply system 7 includes an oil cooler 7a for cooling the oil and an oil filter 7b that is disposed downstream of the oil cooler 7a and removes impurities from the oil. The oil cooler 7a cools the oil by exchanging heat with cooling air produced by a cooling fan 13 that is rotated by a fan motor 12.

[0023] The oil separator 8 secondarily separates a mist of oil contained in the compressed air from which the oil has been primarily separated. The oil separator 8 is held in fluid communication with an upper portion of the first oil separator 6, so that the compressed air from which the oil has been primarily separated by the first oil separator 6 can be introduced into the oil separator 8.

[0024] The oil separator 8 includes an element 8a acting as a filter for filtering out the mist of oil contained in the compressed air from which the oil has been primarily separated, a head 8b having a recess (not depicted) in which a lower portion of the element 8a is fitted, and a case 8c covering the element 8a and coupled to the head 8b.

[0025] The element 8a includes a tubular filter made of nonwoven fabric, a mesh of metal, a combination thereof, or the like and having upper and lower open ends. The element 8a has its lower end fitted in the recess in the head 8b, and a side surface and its upper end covered with the case 8c.

[0026] The head 8b includes a part for causing the compressed air from which the oil has been primarily separated to flow into one side (an outer circumferential side in the present embodiment) of the element 8a and causing the compressed air from which the oil has been secondarily separated to be delivered from another side (an inner circumferential side in the present embodiment) of the element 8a. The head 8b has the recess in which the lower portion of the element 8a is fitted, an inlet fluid passage 8ba, a delivery pipe 8bb, an outlet fluid passage 8bc, a reservoir 8bd, a discharge hole (not depicted), and a discharge fluid passage 8be.

[0027] The inlet fluid passage 8ba includes a fluid passage held in fluid communication with the first oil separator 6 and allows the compressed air from which the oil has been primarily separated by the first oil separator 6 to flow into the element 8a. The delivery pipe 8bb includes a pipe that extends upwardly from the center of the head 8b and has an upper end opening positioned within the element 8a placed on the head 8b. The upper end opening of the delivery pipe 8bb should preferably be positioned near the upper end of the element 8a such that the oil that has been secondarily separated and dropped does not flow into the delivery pipe system 9 by being dragged upwardly by the stream of the compressed air.

[0028] The outlet fluid passage 8bc includes a fluid passage held in fluid communication with the delivery pipe 8bb and the delivery pipe system 9. The compressed air from which the oil has been secondarily separated by the element 8a is delivered via the delivery pipe 8bb and the outlet fluid passage 8bc into the delivery pipe system 9.

[0029] The reservoir 8bd includes a part for storing therein the oil filtered out of the compressed air by the element 8a and dropped from the element 8a. The reservoir 8bd is formed around the delivery pipe 8bb by the bottom surface and inner side surface of the recess of the head 8b and the outer circumferential wall surface of the delivery pipe 8bb that extends upwardly from the bottom surface of the recess. The oil stored in the reservoir 8bd tends to be dragged upwardly by the stream of the compressed air that has passed through the element 8a and to be delivered together with the compressed air from the upper end opening of the delivery pipe 8bb. Therefore, the reservoir 8bd includes a hollow cylindrical shield plate (not depicted) held in contact with a lower portion of the inner circumferential side of the element 8a, for example, in order to prevent the stream of the compressed air that has passed through the element 8a from dragging upwardly the oil stored in the reservoir 8bd.

[0030]  The discharge hole includes a hole provided in a lower portion (a bottom portion in the present embodiment) of the reservoir 8bd and is held in fluid communication with the discharge fluid passage 8be. The discharge fluid passage 8be includes a fluid passage that provides fluid communication between the reservoir 8bd and the oil discharge passage 10 via the discharge hole. The discharge fluid passage 8be allows the oil having been stored in the reservoir 8bd to be delivered into the oil discharge passage 10 under the pressure of the compressed air in the oil separator 8.

[0031] The case 8c includes a hollow cylindrical tube having a top plate and a lower open end. The case 8c covers the element 8a and has the lower open end coupled to the head 8b. The region where the head 8b and the case 8c are coupled to each other is sealed to safeguard against the leakage of the compressed air and the oil.

[0032] The delivery pipe system 9 includes pipes, etc. that are connected to the outlet fluid passage 8bc of the oil separator 8 and deliver the compressed air from which the oil has been secondarily separated by the oil separator 8 to the user side. The delivery pipe system 9 includes a check valve 9a positioned downstream of the oil separator 8, a pressure sensor 9b positioned between the oil separator 8 and the check valve 9a, and an after cooler 9c that is positioned downwardly of the check valve 9a and cools the compressed air.

[0033] The check valve 9a prevents the compressed air from flowing back from the user side to the oil separator 8. The pressure sensor 9b detects the pressure of the compressed air delivered from the oil separator 8. The after cooler 9c cools the compressed air by exchanging heat with cooling air produced by the cooling fan 13. Therefore, the user is supplied with the compressed air that has been cooled.

[0034] The oil discharge passage 10 includes pipes, etc. interconnecting the reservoir 8bd and the compressor body 2 through the discharge fluid passage 8be of the head 8b. The oil having been stored in the reservoir 8bd is pressed by the pressure of the compressed air in the oil separator 8 and is discharged from the oil discharge passage 10 via the discharge hole and the discharge fluid passage 8be. According to the present embodiment, the oil discharge passage 10 is connected to the intake side of the compressor body 2, allowing the compressor body 2 to retrieve the oil discharged from the oil discharge passage 10. The oil discharge passage 10 includes a valve body 10a for selectively opening and closing the oil discharge passage 10.

[0035] The valve body 10a includes a solenoid valve whose opening is controlled over time by the controller 11. The solenoid valve as the valve body 10a may be a normally open ON-OFF solenoid valve, for example. However, though a normally open ON-OFF solenoid valve may be used as the valve body 10a according to the present embodiment, the valve body 10a is not limited to such a valve body. The valve body 10a may alternatively be a valve body capable of selecting three or more levels of opening including an intermediate level "OPEN (including slightly open)" or "CLOSED (including slightly closed)," for example. In other words, the valve body 10a may be configured to permit (partly permit) the stored oil to flow or may restrict (partly inhibit) the stored oil from flowing.

[0036] The controller 11 includes a section for controlling the oil feed type compressor 1A in various fashions. The controller 11 performs various control modes for the oil feed type compressor 1A according to cooperation between a CPU and programs. Part of the controller 11 may be of an analog configuration. According to the present embodiment, the controller 11 includes a user interface (not depicted) for entering pressure setting values and various setting values, and controls the electric power supplied to the electric motor 3 and the fan motor 12 and the opening of the valve body 10a on the basis of entered values.

[0037] Next, a process of controlling the opening of the valve body 10a that is carried out by the controller 11 according to the present embodiment will be described with reference to FIG. 2. FIG. 2 is a timing chart of the process of controlling the opening of the valve body 10a that is carried out by the controller 11 of the oil feed type compressor 1A according to the present embodiment.

[0038] The controller 11 repeatedly keeps the valve body 10a at a first opening during a first period Tc and keeps the valve body 10a at a second opening larger than the first opening during a second period To after elapse of the first period Tc. Specifically, as illustrated in FIG. 2, the controller 11 transmits an ON signal to the valve body 10a during the first period Tc to keep the valve body 10a at "CLOSED" state. Then, during the second period To after elapse of the first period Tc, the controller 11 turns OFF the transmission of the signal to the valve body 10a to keep the valve body 10a at "OPEN" state. Further, during another first period Tc after elapse of the second period To, the controller 11 transmits an ON signal to the valve body 10a to keep the valve body 10a at "CLOSED" state. The controller 11 then repeats the above control process. Since the valve body 10a is a normally open ON-OFF solenoid valve, when the power is lost, the valve body 10a is kept at "OPEN" state, restraining the oil that has been secondarily separated by the element 8a and dropped therefrom from overflowing the reservoir 8bd.

[0039] The first period Tc is a time taken for a predetermined amount of oil to be stored in the reservoir 8bd, and the second period To is a time taken for the predetermined amount of oil that has been stored in the reservoir 8bd during the first period Tc to be discharged from the reservoir 8bd. The predetermined amount of oil stored in the reservoir 8bd may be equal to or less than an amount capable of restraining the oil having been stored in the reservoir 8bd from flowing back or flowing into the delivery pipe 8bb, for example.

[0040] Furthermore, the first period Tc is a time measured, which is taken for the oil to be stored up to the predetermined amount in the reservoir 8bd, for example, and the second period To is a time measured, which is taken for the predetermined amount of oil to be discharged from the reservoir 8bd, for example. The first period Tc and the second period To that have been measured are input to the controller 11 and stored therein. The controller 11 controls the opening of the valve body 10a on the basis of the first period Tc and the second period To that have been stored.

[0041] Consequently, in the oil feed type compressor 1A, during the first period Tc, the valve body 10a is "CLOSED" state, storing the oil up to the predetermined amount in the reservoir 8Bd. Furthermore, in the oil feed type compressor 1A, during the second period To after elapse of the first period Tc, the valve body 10a is "OPEN" state, allowing the predetermined amount of oil that has been stored in the reservoir 8bd to be discharged to the intake side of the compressor body 2 via the discharge hole, the discharge fluid passage 8be, and the oil discharge passage 10.

[0042] The second period To should preferably be equal to or longer than a time measured, which is taken for the predetermined amount of oil to be discharged from the reservoir 8bd, for the reasons described below. First, deterioration of the oil or the like may cause the oil flowing through the discharge hole, the discharge fluid passage 8be, and the oil discharge passage 10 to flow at a reduced rate, making the time taken for the predetermined amount of oil to be discharged from the reservoir 8bd longer than the measured time. Secondly, the element 8a may become clogged over time while it is in use, tending to reduce the amount of oil that can be retained by the element 8a, and hence increase the amount of oil dropped from the element 8a per unit time, with the result that the amount of oil stored in the reservoir 8bd may be increased.

[Advantages]

[0043] The oil feed type compressor 1A according to the present embodiment includes the compressor body 2 that compresses a gas while oil is being injected therein, the first oil separator 6 that separates oil from the compressed gas delivered from the compressor body 2, the second oil separator 8 that further separates oil from the compressed gas from which the oil has been .separated by the first oil separator, the second oil separator 8 having the reservoir 8bd for storing therein the separated oil, the delivery pipe system 9 through which the compressed gas from which the oil has been retrieved by the second oil separator 8 flows, the oil discharge passage 10 that discharges the oil having been stored in the reservoir 8bd from the reservoir 8bd, the valve body 10a included in the oil discharge passage 10, and the controller 11 that controls the opening of the valve body 10a over time.

[0044] Heretofore, the oil discharge passage 10 that discharges the oil from the reservoir 8bd includes an orifice having a constant opening through which the oil is continuously discharged together with the compressed air. However, the oil feed type compressor 1A that is configured as described above according to the present embodiment is able to control (change) the opening of the valve body 10a included in the oil discharge passage 10 over time. When the oil feed type compressor 1A according to the present embodiment is controlled to increase the time taken for the opening of the valve body 10a to be kept smaller than the opening of the orifice referred to above (the valve body 10a may be closed), the amount of compressed air discharged through the oil discharge passage 10 is made smaller than heretofore, restraining a reduction in the compression efficiency of the oil feed type compressor 1A.

[0045] Moreover, even if the oil feed type compressor 1A according to the present embodiment is reduced in size, further reducing the amount of compressed air delivered therefrom and the amount of dropped oil, the first period Tc may be increased to reduce the opening of the valve body 10a until oil is stored in the reservoir 8bd. After oil has been stored in the reservoir 8bd, the opening of the valve body 10a may be increased to discharge the oil stored in the reservoir 8bd within a predetermined time. Therefore, the amount of compressed air discharged together with oil can be reduced, restraining a reduction in the compression efficiency of the oil feed type compressor 1A.

[0046] Furthermore, even if the compressor body of the oil feed type compressor 1A according to the present embodiment undergoes a low load, reducing the amount of compressed air delivered therefrom and the amount of dropped oil, the first period Tc may be increased to reduce the opening of the valve body 10a until oil is stored in the reservoir 8bd. After oil has been stored in the reservoir 8bd, the opening of the valve body 10a may be increased to discharge the oil stored in the reservoir 8bd within a predetermined time. Therefore, the amount of compressed air discharged together with oil can be reduced, restraining a reduction in the compression efficiency of the oil feed type compressor 1A.

[0047] Moreover, the controller 11 of the oil feed type compressor 1A according to the present embodiment repeatedly keeps the valve body 10a at the first opening during the first period Tc and keeps the valve body 10a at the second opening To larger than the first period Tc during the second period To after elapse of the first period Tc. Therefore, the oil discharge passage 10 is restrained from being clogged and from failing to discharge the oil.

[0048] Furthermore, the controller 11 of the oil feed type compressor 1A according to the present embodiment closes the valve body 10a at the first opening and opens the valve body 10a at the second opening. Therefore, after the oil has been stored in the reservoir 8bd, the oil stored in the reservoir 8bd can be discharged. Consequently, the amount of compressed air discharged together with oil can be reduced, restraining a reduction in the compression efficiency of the oil feed type compressor 1A.

[0049] In addition, the controller 11 of the oil feed type compressor 1A according to the present embodiment controls the second period To as a time longer than the time taken for the oil, which has been stored in the reservoir 8bd during the first period Tc, to be discharged. Therefore, the oil having been stored in the reservoir 8bd during the first period Tc can be discharged during the second period To, restraining oil from remaining in the reservoir 8bd. Consequently, the oil is restrained from overflowing the reservoir 8bd.

[0050] Furthermore, the valve body 10a of the oil feed type compressor 1A according to the present embodiment includes a normally open ON-OFF solenoid valve. Thus, the flow rate of oil flowing through the oil discharge passage 10 can be controlled easily by the controller 11. Even if a situation in which the valve body 10a cannot be controlled occurs due to a power loss or the like, the valve body 10a becomes "OPEN" state, restraining oil from being stored in the reservoir 8bd and hence from overflowing the reservoir 8bd.

[0051] Moreover, the oil discharge passage 10 of the oil feed type compressor 1A according to the present embodiment has a downstream opening held in fluid communication with a low-pressure side of the compressor body 2, and discharges oil that has been secondarily separated from the compressed gas by the oil separator 8 to the low-pressure side of the compressor body 2. Therefore, the oil separated by the oil separator 8 is not discharged to the outside, but can be reused for compressing the gas in the compressor body 2.

[0052] Moreover, the second oil separator 8 of the oil feed type compressor 1A according to the present embodiment includes the tubular case 8c whose upper end is closed and whose lower end is open, the tubular filter (element 8a) positioned inside the case 8c and having upper and lower ends open, and the delivery pipe 8bb extending upwardly from a lower portion of the filter, having an upper end opening positioned within the filter, and held in fluid communication with the delivery pipe system 9. Consequently, the filter (element 8a) can be lifted upwardly by removing the case 8c for easy replacement.

[0053] The first oil separator 6 of the oil feed type compressor 1A according to the present embodiment includes a swirl-separation-type gas-liquid separator. The swirl-separation-type gas-liquid separator is of a simple structure and is of a low cost.

(Second Embodiment)

[0054] FIG. 3 is a schematic view illustrating the configuration of an oil feed type compressor 1B according to the second embodiment of the present invention. The oil feed type compressor 1B according to the present embodiment is different from the oil feed type compressor 1A according to the first embodiment as follows:

[0055] First, the oil feed type compressor 1B includes a variable-speed mechanism combined with the electric motor 3. In other words, whereas the oil feed type compressor 1A according to the first embodiment operates under constant-speed control, the oil feed type compressor 1B according to the present embodiment operates under variable-speed control.

[0056] Furthermore, since the oil feed type compressor 1B according to the present embodiment includes the variable-speed mechanism combined with the electric motor 3, the amount of oil stored in the reservoir 8bd varies according to the load ratio (rotational speed / maximum rotational speed × 100%) of the compressor body 2. Therefore, whereas the controller 11 of the oil feed type compressor 1A according to the first embodiment controls the opening of the valve body 10a over time, the controller 11 of the oil feed type compressor 1B according to the present embodiment controls the opening of the valve body 10a according to the load ratio and the operating time of the compressor body 2.

[0057] The variable-speed mechanism combined with the electric motor 3 includes an inverter 20, for example. The inverter 20 is electrically connected to the electric motor 3 and the controller 11, and coverts electric power to be supplied to the electric motor 3 in response to a command from the controller 11.

[0058] The controller 11 varies the amount of electric power to be supplied from the inverter 20 to the electric motor 3 depending on a pressure set by the user, on the basis of the pressure detected by the pressure sensor 9b, for thereby performing a variable-speed control process for the compressor body 2. The variable-speed control process may be a proportional control process (P control process), a proportional plus integration control process (PI control process), a PID control process representing the PI control process with a derivative control process (D control process) added thereto, a non-load operation control process, or the like.

[0059] The non-load operation control process is available in the following types. According to one type, when the pressure detected by the pressure sensor 9b is equal to or higher than a pressure set by the user, the intake valve 5 is "CLOSED" to limit the amount of air sucked into the compressor body 2. According to the other type, when the pressure detected by the pressure sensor 9b is equal to or higher than a pressure set by the user, the intake valve 5 is "CLOSED" and the rotational speed of the electric motor 3 is caused to be lowered to a predetermined rotational speed (e.g., a minimum rotational speed capable of maintain the pressure set by the user).

[0060] The inverter 20 of the oil feed type compressor 1B according to the present embodiment operates according to the above control process to vary the amount of electric power to be supplied to the electric motor 3 to control the load ratio of the compressor body 2. Although the oil feed type compressor 1B is controlled at variable speeds by the inverter 20 in the illustrated embodiment, the oil feed type compressor 1B may be controlled at variable speeds according to other control processes.

[0061] The oil feed type compressor 1B according to the present embodiment varies the load ratio of the compressor body 2 depending on the pressure set by the user, changing the amount of delivered compressed air. Therefore, the amount of oil that has been secondarily separated by the oil separator 8 and stored in the reservoir 8bd is varied by the load ratio of the compressor body 2 at the time of control of the oil feed type compressor 1B. When the opening of the valve body 10a is controlled over time, if the compressor body 2 is of a low load ratio, the amount of oil stored in the reservoir 8bd is lowered, increasing the amount of compressed air discharged together with the oil. In order to restrain the amount of compressed air from increasing, the opening of the valve body 10a is controlled depending on the load ratio of the compressor body 2.

[0062] FIG. 4 is a graph illustrating changes over time in the load ratio of the compressor body 2 and a timing chart of a process of controlling the opening of the valve body 10a that is carried out by the controller 11 of the oil feed type compressor 1B according to the present embodiment.

[0063] The amount of oil stored in the reservoir 8bd can be estimated from the load ratio and operating time of the compressor body 2. Consequently, the controller 11 according to the present embodiment controls the opening of the valve body 10a on the basis of the load ratio and operating time of the compressor body 2.

[0064] Specifically, the controller 11 keeps the valve body 10a at a first opening while an integrated value A1, A2, A3, A4 of the product of the load ratio and operating time of the compressor body 2 is less than a predetermined value. Then, the controller 11 keeps the valve body 10a at a second opening larger than the first opening for a predetermined period To when the integrated value A1, A2, A3, A4 of the product of the load ratio and operating time of the compressor body 2 has reached the predetermined value.

[0065] The amount of oil stored in the reservoir 8bd when the integrated value A1, A2, A3, A4 of the product of the load ratio and operating time of the compressor body 2 has reached the predetermined value may be equal to or less than an amount (allowable amount in the reservoir 8bd) capable of restraining the stored oil from flowing back or flowing into the delivery pipe 8bb. Moreover, the predetermined period To should preferably be equal to or longer than a time measured, which is taken for the predetermined amount of oil having been stored in the reservoir 8bd to be discharged therefrom, for the same reasons as those described above with respect to the second period To according to the first embodiment.

[Advantages]

[0066] The oil feed type compressor 1B according to the present embodiment includes the compressor body 2 that compresses a gas while oil is being injected therein, the first oil separator 6 that separates oil from the compressed gas delivered from the compressor body 2, the second oil separator 8 that further separates oil from the compressed gas from which the oil has been separated by the first oil separator 6, the second oil separator 8 having the reservoir 8bd for storing the separated oil, the delivery pipe system 9 through which the compressed gas from which the oil has been separated by the second oil separator 8 flows, the oil discharge passage 10 that discharges the oil having been stored in the reservoir 8bd from the reservoir 8bd, the valve body 10a included in the oil discharge passage 10, and the controller 11 that controls the opening of the valve body 10a on the basis of the load ratio and the operating time of the compressor body 2.

[0067] The amount of oil stored in the reservoir 8bd can be estimated from the load ratio and operating time of the compressor body 2. Consequently, in the oil feed type compressor 1B configured as described above according to the present embodiment, it is possible to prevent oil from overflowing the reservoir 8bd in excess of the allowable amount thereof and to make the amount of compressed air discharged through the oil discharge passage 10 smaller than heretofore by controlling the timing of opening the valve body 10a from the closed state depending on the increase in the amount of oil estimated from the load ratio and time. The compression efficiency of the oil feed type compressor can thus be restrained from deceasing.

[0068] Furthermore, the controller 11 of the oil feed type compressor 1B according to the present embodiment keeps the valve body 10a at the first opening while the integrated value A1, A2, A3, A4 of the product of the load ratio and operating time of the compressor body 2 is less than the predetermined value. Then, the controller 11 keeps the valve body 10a at the second opening larger than the first opening for the predetermined period when the integrated value of the product of the load ratio and operating time of the compressor body 2 has reached the predetermined value. Therefore, the oil discharge passage 10 is restrained from being clogged and from failing to discharge the oil.

[0069] With the oil feed type compressor 1B according to the present embodiment, the amount of oil stored in the reservoir 8bd until the integrated value A1, A2, A3, A4 of the product of the load ratio and operating time of the compressor body 2 has reached the predetermined value is equal to or less than the allowable amount of oil that can be stored in the reservoir 8bd. Consequently, the oil is restrained from overflowing the reservoir 8bd.

[0070] Furthermore, with the oil feed type compressor 1B according to the present embodiment, the predetermined period To, for which the valve body 10a is kept at the second opening that is larger than the first opening, is longer than the time taken for the amount of oil, which is stored in the reservoir 8bd until the integrated value of the product of the load ratio and operating time of the compressor body 2 has reached the predetermined value, to be discharged. Thus, the oil stored in the reservoir 8bd until the integrated value A1, A2, A3, A4 of the product of the load ratio and operating time of the compressor body 2 has reached the predetermined value can be discharged within the predetermined period To, and the oil is restrained from remaining in the reservoir 8bd. Consequently, the oil is restrained from overflowing the reservoir 8bd.

[0071] Moreover, the controller 11 of the oil feed type compressor 1B according to the present embodiment closes the valve body 10a at the first opening and opens the valve body 10a at the second opening. Therefore, after oil has been stored in the reservoir 8bd, the oil stored in the reservoir 8bd can be discharged. Consequently, the amount of compressed air discharged together with the oil is reduced, restraining a reduction in the compression efficiency of the oil feed type compressor.

(Third Embodiment)

[0072] FIGS. 1 and 3 are schematic views illustrating the configuration of an oil feed type compressor 1C according to a third embodiment of the present invention. FIG. 5 is a graph illustrating changes over time in the pressure detected by the pressure sensor 9b and a timing chart of a process of controlling the opening of the valve body 10a that is carried out by the controller 11 of the oil feed type compressor 1C according to the third embodiment of the present invention. FIG. 6 is a graph illustrating changes over time in a load ratio of the compressor body 2, the graph illustrating changes over time in the pressure detected by the pressure sensor 9b, and the timing chart of the process of controlling the opening of the valve body 10a that is carried out by the controller 11 of the oil feed type compressor 1C according to the third embodiment of the present invention.

[0073] The oil feed type compressor 1C according to the present embodiment is different from the oil feed type compressors 1A and 1B according to the first and second embodiments in that the controller 11 controls the timing to constrict the opening of the valve body 10a on the basis of the pressure detected by the pressure sensor 9b while the valve body 10a is being open.

[0074] Specifically, the controller 11 of the oil feed type compressors 1A and 1B according to the first and second embodiments keeps the valve body 10a at the second opening larger than the first opening during the period To, and after elapse of the period To, controls the valve body 10a to change to the first opening smaller than the second opening. On the other hand, the controller 11 of the oil feed type compressor 1C according to the present embodiment constricts the opening of the valve body 10a at the timing at which the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b that detects the pressure in the delivery pipe system 9 while the valve body 10a is being open has reached a predetermined value ΔP.

[0075]  In other words, the controller 11 of the oil feed type compressor 1C controls the valve body 10a to change to the first opening smaller than the second opening at the timing at which the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b has reached the predetermined value ΔP while the valve body 10a is being kept at the second opening.

[0076] Consequently, with the controller 11 of the oil feed type compressors 1A and 1B according to the first and second embodiments, the period To during which the valve body 10a is kept at the second opening is a predetermined time that is set. In contract, the controller 11 of the oil feed type compressor 1C controls periods (To1 through To3) during which the valve body 10a is kept at the second opening, on the basis of a reduction caused in the pressure in the delivery pipe system 9 by the compressed air being discharged after the oil stored in the reservoir 8bd has been discharged.

[0077] FIG. 5 illustrates the case in which the period during which the valve body 10a is kept at the first opening is controlled over time in the same manner as with the oil feed type compressor 1A according to the first embodiment. FIG. 6 illustrates the case in which the period during which the valve body 10a is kept at the first opening is controlled according to the load ratio and the operating time of the compressor body 2 in the same manner as with the oil feed type compressor 1B according to the second embodiment.

[0078] In addition, the oil feed type compressor 1C can cause the controller 11 to control so as to detect and inform about a clogging of the oil discharge passage 10 on the basis of the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b.

[0079] Specifically, the controller 11 issues notification about an abnormality when the period taken for the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b to reach the predetermined value ΔP from the time of the second opening of the valve 10a exceeds a predetermined period.

[0080] In order to prevent a malfunction, the controller 11 may alternatively operate as follows: The controller 11 records a count of events where the ratio ((P1 - P2)/To) of the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b to the elapsed time To does not reach a predetermined value. If the count has reached a predetermined count, the controller 11 issues notification about an abnormality.

[0081] As the means for issuing notification about an abnormality, various means and devices such as a display device provided to the controller 11 and caused to display an warning, a warning lamp emitting light when energized, and a speaker generating a warning sound may be employed.

[Advantages]

[0082] The oil feed type compressor 1C according to the present embodiment includes the compressor body 2 that compresses a gas while oil is being injected therein, the first oil separator 6 that separates oil from the compressed gas delivered from the compressor body 2, the second oil separator 8 that further separates oil from the compressed gas from which the oil has been separated by the first oil separator, the second oil separator 8 having the reservoir 8bd for storing the separated oil, the delivery pipe system 9 through which the compressed gas from which the oil has been retrieved by the second oil separator 8 flows, the oil discharge passage 10 that discharges the oil having been stored in the reservoir 8bd from the reservoir 8bd, the valve body 10a included in the oil discharge passage 10, the pressure sensor 9b that detects the pressure in the delivery pipe system 9, and the controller 11 that controls the opening of the valve body 10a over time, in which the controller 11 controls the timing to constrict the opening of the valve body 10a on the basis of the pressures P1 and P2 detected by the pressure sensor 9b while the valve body 10a is being open.

[0083] When the valve body 10a in the oil feed type compressor 1C configured as described above is opened, the pressure detected by the pressure sensor 9b is lowered as the amount of oil in the reservoir 8bd is reduced. Therefore, the valve body 10a is prevented from being continuously open ineffectively after the amount of oil remaining in the reservoir 8bd has become zero by controlling the timing to constrict the opening of the valve body 10a on the basis of the pressure detected by the pressure sensor 9b while the valve body 10a is being open. Since the amount of compressed air discharged through the oil discharge passage 10 is thus smaller than heretofore, a reduction in the compression efficiency of the oil feed type compressor 1C is restrained.

[0084] The controller 11 of the oil feed type compressor 1C according to the present embodiment constricts the opening of the valve body 10a when the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b while the valve body 10a is being open has reached the predetermined value ΔP. Therefore, even if the time over which the oil stored in the reservoir 8bd is discharged becomes longer than normal time due to a reduction in the fluid passage area which reduction may be caused by foreign matter clogging the oil discharge passage 10, the oil stored in the reservoir 8bd can reliably be discharged.

[0085] Furthermore, the controller 11 of the oil feed type compressor 1C according to the present embodiment closes the valve body 10a when the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b while the valve body 10a is being open has reached the predetermined value ΔP. Therefore, the amount of compressed air discharged through the oil discharge passage 10 is made smaller than heretofore, restraining a reduction in the compression efficiency of the oil feed type compressor 1C.

[0086] Moreover, the controller 11 of the oil feed type compressor 1C according to the present embodiment opens the valve body 10a after having closed the valve body 10a for a predetermined period and closes the valve body 10a when the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b while the valve body 10a is being open has reached the predetermined value ΔP. Consequently, after oil has been stored in the reservoir 8bd, the oil stored in the reservoir 8bd can be discharged. Therefore, the amount of compressed air discharged through the oil discharge passage is made smaller than heretofore, restraining a reduction in the compression efficiency of the oil feed type compressor 1C.

[0087] In addition, with the oil feed type compressor 1C according to the present embodiment, the predetermined period during which the valve body 10a is closed varies depending on the load ratio of the compressor body 2. Therefore, even if the oil feed type compressor 1C operates under variable-speed control, after a predetermined amount of oil has been stored in the reservoir 8bd, the oil can be discharged from the reservoir 8bd. The number of times that the oil is discharged is thus reduced. The amount of compressed air discharged as the oil is discharged is made smaller than heretofore, restraining a reduction in the compression efficiency of the oil feed type compressor 1C.

[0088] Furthermore, the controller 11 of the oil feed type compressor 1C according to the present embodiment issues notification about an abnormality when the period taken for the reduction (P1 - P2) in the pressure detected by the pressure sensor 9b to reach the predetermined value ΔP from the time of the opening of the valve 10a exceeds a predetermined period. The controller 11 can thus detect a clogging of the oil discharge passage 10 and issue notification about the detected clogging to tne user.

[0089] Moreover, the controller 11 of the oil feed type compressor 1C according to the present embodiment records a count of events where the ratio of the reduction in the pressure detected by the pressure sensor 9b to the elapsed time does not reach a predetermined value while the valve body 10a is being open, and issues notification about an abnormality if the count has reached a predetermined count. Therefore, the controller 11 can be restrained from detecting a clogging of the oil discharge passage 10 in error, and can accurately issue notification about a clogging of the oil discharge passage 10 to the user.

[0090]  In addition, the pressure sensor 9b of the oil feed type compressor 1C according to the present embodiment is disposed near the region where the delivery pipe system 9 is connected to the second oil separator 8. Consequently, the pressure sensor 9b can quickly detect a reduction in the pressure in the second oil separator 9.

[0091] The present invention is not limited to the embodiments described above, but covers various changes and modifications therein. For example, the above embodiments have been described in detail for an easier understanding of the present invention, and the present invention should not be limited to that including all the configurations described above. Some of the configurations of one of the embodiments may be replaced or combined with some of the configurations of the other embodiments. Furthermore, other configurations may be added to, may be deleted from, or may be replaced with some of the configurations of each of the above embodiments.

[0092] The configurations , functions, etc. described above may partly or wholly be implemented by hardware, e.g., integrated circuits designed to realize the configurations , functions, etc. Alternatively, the configurations , functions, etc. described above may be realized by software by a processor (microcomputer) interpreting and executing programs for realizing the functions. Information in the form of programs, tables, files, etc. for realizing the functions may be stored in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

[0093] The embodiments of the present invention may be available in a form as follows: Each of the oil feed type compressors 1A and 1B according to the first and second embodiments may incorporate the controlling details of the oil feed type compressor 1C according to the third embodiment.

[0094] In the first through third embodiments, the compressor body 2 has been described as being of the screw rotor type including the pair of screw rotors 2a and 2b. However, the present invention is not limited to such details. A compressor body may include a screw rotor (including a gate-rotor-combinable type) and a plurality of gate rotors, for example. Furthermore, a compressor body may be of the displacement type other than the screw rotor type (specifically, another rotary type such as a scroll type or a claw type, or a reciprocating type or the like).

[0095] In the first through third embodiments, the electric motor 3 has been described as the drive source. However, the present invention is not limited to such details. An internal combustion engine or a mechanism that utilizes natural energy such as wind power or hydraulic power may be used as the drive source.

[0096] In the first through third embodiments, the inverter 20 has been described as the variable-speed mechanism. However, the present invention is not limited to such details. If the drive source includes an internal combustion engine, then a transmission gear or a fuel supply control device may be used as the variable-speed mechanism. On the other hand, if the drive source includes a mechanism that utilizes natural energy such as wind power or hydraulic power, then a transmission gear or a clutch mechanism may be used as the variable-speed mechanism.

[0097] In the first through third embodiments, air has been described as a gas to be compressed. However, the present invention is not limited to such details. A gas to be compressed may be another gas such as nitrogen.

[0098] In the first through third embodiments, the controller 11 has been described as being incorporated in the oil feed type compressor. However, the present invention is not limited to such details. A control device spaced from the oil feed type compressor may remotely control the oil feed type compressor via a wired or wireless link. Moreover, some control features may be carried out by the controller 11 in the oil feed type compressor, whereas other control features may be carried out by a remote control device.

Description of Reference Characters

[0099] 

1A, 1B, 1C: Oil feed type compressor

2: Compressor body

3: Electric motor

6: First oil separator

8: Second oil separator (oil separator)

8a: Element

8b: Head

8ba: Inlet fluid passage

8bb: Delivery pipe

8bc: Outlet fluid passage

8bd: Reservoir

8be: Discharge fluid passage

8c: Case

9: Delivery pipe system

9a: Check valve

9b: Pressure sensor

10: Oil discharge passage

10a: Valve body

11: Controller

20: Inverter

Claims

1. An oil feed type compressor comprising:

a compressor body that compresses a gas while oil is being injected therein;

a first oil separator that separates oil from the compressed gas delivered from the compressor body;

a second oil separator that further separates oil from the compressed gas from which the oil has been separated by the first oil separator, the second oil separator having a reservoir for storing the separated oil;

a delivery pipe system through which the compressed gas from which the oil has been separated by the second oil separator flows;

an oil discharge passage that discharges the oil having been stored in the reservoir from the reservoir;

a valve body included in the oil discharge passage; and

a controller configured to control an opening of the valve body over time.

2. An oil feed type compressor comprising:

a compressor body that compresses a gas while oil is being injected therein;

a first oil separator that separates oil from the compressed gas delivered from the compressor body;

a second oil separator that further separates oil from the compressed gas from which the oil has been separated by the first oil separator, the second oil separator having a reservoir for storing the separated oil;

a delivery pipe system through which the compressed gas from which the oil has been separated by the second oil separator flows;

an oil discharge passage that discharges the oil having been stored in the reservoir from the reservoir;

a valve body included in the oil discharge passage; and

a controller configured to control an opening of the valve body on a basis of a load ratio and operating time of the compressor body.

3. An oil feed type compressor comprising:

a compressor body that compresses a gas while oil is being injected therein;

a first oil separator that separates oil from the compressed gas delivered from the compressor body;

a second oil separator that further separates oil from the compressed gas from which the oil has been separated by the first oil separator, the second oil separator having a reservoir for storing the separated oil;

a delivery pipe system through which the compressed gas from which the oil has been separated by the second oil separator flows;

an oil discharge passage that discharges the oil having been stored in the reservoir from the reservoir;

a valve body included in the oil discharge passage;

a pressure sensor that detects a pressure in the delivery pipe system; and

a controller that controls an opening of the valve body over time, wherein

the controller configured to control a timing to constrict the opening of the valve body on a basis of the pressure detected by the pressure sensor while the valve body is being open.

4. The oil feed type compressor according to claim 1, wherein
the controller repeatedly keeps the valve body at a first opening during a first period and keeps the valve body at a second opening larger than the first opening during a second period after elapse of the first period.

5. The oil feed type compressor according to claim 4, wherein
the controller closes the valve body at the first opening and opens the valve body at the second opening.

6. The oil feed type compressor according to claim 4, wherein
the controller controls the second period as a time longer than a time taken for the oil to be discharged, the oil having been stored in the reservoir during the first period.

7. The oil feed type compressor according to claim 2, wherein
the controller keeps the valve body at a first opening while an integrated value of a product of the load ratio and the operating time of the compressor body is less than a predetermined value, and keeps the valve body at a second opening larger than the first opening for a predetermined period when the integrated value of the product of the load ratio and the operating time of the compressor body has reached the predetermined value.

8. The oil feed type compressor according to claim 7, wherein
the controller closes the valve body at the first opening and opens the valve body at the second opening.

9. The oil feed type compressor according to claim 7, wherein
an amount of oil stored in the reservoir until the integrated value has reached the predetermined value is equal to or less than an allowable amount of oil that can be stored in the reservoir.

10. The oil feed type compressor according to claim 7, wherein
the predetermined period is longer than a time taken for the oil to be discharged, the oil being stored in the reservoir until the integrated value has reached the predetermined value.

11. The oil feed type compressor according to claim 3, wherein
the controller constricts the opening of the valve body when a reduction in the pressure detected by the pressure sensor while the valve body is being open has reached a predetermined value.

12. The oil feed type compressor according to claim 3, wherein
the controller opens the valve body after having closed the valve body for a predetermined period, and closes the valve body when a reduction in the pressure detected by the pressure sensor while the valve body is being open has reached a predetermined value.

13. The oil feed type compressor according to claim 12, wherein
the predetermined period varies according to a load ratio of the compressor body.

14. The oil feed type compressor according to claim 3, wherein
the controller issues notification about an abnormality when a period taken for a reduction in the pressure detected by the pressure sensor to reach a predetermined value from a time of opening of the valve body exceeds a predetermined period.

15. The oil feed type compressor according to claim 3, wherein
the controller records, while the valve body is being open, a count of events where a ratio of a reduction in the pressure detected by the pressure sensor to an elapsed time does not reach a predetermined value, and issues notification about an abnormality if the count has reached a predetermined count.

16. The oil feed type compressor according to claim 3, wherein
the pressure sensor is disposed near a region where the delivery pipe system is connected to the second oil separator.

17. The oil feed type compressor according to any one of claims 1 through 3, wherein
the valve body includes a normally open ON-OFF solenoid valve.

18. The oil feed type compressor according to any one of claims 1 through 3, wherein
the oil discharge passage has a downstream opening held in fluid communication with a low-pressure side of the compressor body, and discharges the oil that has been secondarily separated from the compressed gas by the second oil separator to the low-pressure side of the compressor body.

19. The oil feed type compressor according to any one of claims 1 through 3, wherein
the second oil separator has a tubular case whose upper end is closed and whose lower end is open, a tubular filter positioned inside the case and having upper and lower ends open, and a delivery pipe extending upwardly from a lower portion of the filter, having an upper end opening positioned within the filter, and being held in fluid communication with the delivery pipe system.

20. The oil feed type compressor according to any one of claims 1 through 3, wherein
the first oil separator includes a swirl-separation-type gas-liquid separator.

Drawing