JP7107730B2 - Operation control method for oil-flooded screw compressor and oil-flooded screw compressor - Google Patents

Description

The present invention relates to an operation control method for an oil-cooled screw compressor, and an oil-cooled screw compressor capable of executing the control method.

The oil-cooled screw compressor 100 accommodates a pair of male and female screw rotors in a cylinder formed in a casing so as to be able to mesh and rotate. A compressor body 130 that compresses the compressed gas together with the cooling oil and discharges it as a gas-liquid mixed fluid, and introduces the gas-liquid mixed fluid discharged from the compressor body 130 to mix the compressed gas and the cooling oil. A separate receiver tank 160 and a driving source such as an engine or a motor (engine 150 in the illustrated example) for inputting rotational driving force to the rotor shaft of the compressor main body 130 are provided (see FIG. 6).

Then, the gas-liquid mixed fluid from the compressor body 130 introduced into the receiver tank 160 is primarily separated into compressed gas and cooling oil in the receiver tank 130, and the separated cooling oil is stored in the oil cooler 163 and the oil filter 162. The compressed gas from which the cooling oil has been separated is introduced again into the injection port of the compressor main body 130 through the oil supply passage 164 provided with the oil separator 160a. After being further removed, it is supplied to the consumption side to which a pneumatic working machine (not shown) is connected.

In such an oil-cooled screw compressor 100, a suction control valve 111 is provided in the suction passage 137 of the compressor body 130, and when the pressure in the receiver tank 160 changes due to changes in the consumption of compressed gas on the consumption side, suction The pressure in the receiver tank 160 is set in advance by changing the opening of the intake passage 137 of the compressor body 130 by the control valve 111 and the rotational speed of the drive source such as the engine or motor (the engine 150 in the illustrated example). By performing “capacity control” that controls the pressure to approach a predetermined pressure, it is configured to be able to supply compressed gas at a stable pressure to the consumer side.

In this "capacity control", normally, when the pressure in the receiver tank 160 is lower than the preset reference pressure Ps, the suction control valve 111 fully opens the suction passage 137 of the compressor main body 130 and rotates the drive source 150. Full-load operation is performed with the speed set to the rated rotation speed Rr, and when the pressure in the receiver tank 160 reaches the no-load operation pressure Pu set as a pressure higher than the reference pressure Ps, the suction control valve 111 fully closes the intake passage 137 of the compressor main body 130, and reduces the rotation speed of the engine 150 to the no-load rotation speed Ru set as a predetermined lower speed than the rated rotation speed Rr to perform no-load operation. (unload operation).

In the oil-flooded screw compressor 100, the operation state is switched between the two operation states of full-load operation and no-load operation. and the no-load operating pressure Pu, the opening of the suction control valve 111 is set to a predetermined position between full open and full close according to the pressure in the receiver tank 160, and/or the rotation of the drive source 150 There is also an intermediate load operation in which the speed is set to a predetermined speed between the rated rotation speed Rr and the no-load rotation speed Ru, and the operation is performed in an intermediate load state between the full-load operation and the no-load operation described above. , and the oil-cooled screw compressor 100.

In this manner, since the oil-flooded screw compressor 100 switches the operating state according to the pressure in the receiver tank 160, the consumption of the compressed gas on the consumption side stops, and the pressure in the receiver tank 160 rises to no effect. When the load operation pressure Pu is reached, the operation shifts to the no-load operation described above, and when the pressure in the receiver tank 160 becomes equal to or lower than the reference pressure Ps due to the consumption of compressed air being resumed on the consumption side from the no-load operation state, full load operation is performed. return to driving.

Here, in the known general oil-cooled screw compressor 100, when returning from no-load operation to full-load operation, the rotational speed of the drive source 150 rises from the no-load rotational speed Ru to the rated rotational speed Rr. However, since it takes a certain amount of time to increase the rotation speed in this way, the pressure in the receiver tank 160 rises to the reference pressure when a large amount of compressed air starts and continues to be consumed during no-load operation. If the pressure drops significantly below Ps, it will take a long time to return to the reference pressure Ps, causing inconveniences such as stopping the pneumatic working machine connected to the consumption side.

In order to solve such a problem, Patent Document 1 described later discloses that the rotation speed of the engine 150, which is the drive source, is always set to a high rotation speed (for example, the rated rotation speed) regardless of the pressure change in the receiver tank 160. It is proposed that the intake control valve 111 is fixed and the capacity is controlled only by opening and closing the intake control valve 111 .

JP-A-2002-168177

As in the engine-driven compressor 100 described in Patent Document 1 above, in a configuration in which the rotation speed of the engine 150 is fixed at a high rotation speed even during no-load operation, a large amount of compressed gas is generated on the consumption side during no-load operation. Even if the pressure in the receiver tank 160 suddenly drops due to the start of consumption of By preventing the pressure in the receiver tank 160 from dropping significantly below the reference pressure Ps, it is possible to supply compressed gas with a stable pressure to the consumption side, and therefore the air working machine connected to the consumption side can Stopping or the like can be prevented.

However, in the configuration of the engine-driven compressor 100 described in Patent Document 1, compared to the configuration of a known general engine-driven compressor that reduces the rotation speed of the engine during no-load operation, the compressor body 130 The replacement cycle of the bearings provided in the

That is, the rotor shafts of the male and female screw rotors of the compressor body 130 described above are supported by bearings. When the surface and the rolling surface of the rolling elements are subjected to repeated compressive stress, flaking (a phenomenon in which the surface layer peels off in scales) occurs due to fatigue of the material, making it unusable.

The "life" of a bearing is defined as the "total number of rotations" until this flaking occurs, and it is necessary to replace the bearing before this "life" is reached. In a configuration in which the engine 150 is driven at a high rotation speed even during no-load operation, such as the cold screw compressor 100, a known general engine drive configuration in which the rotation speed of the engine 150 is reduced during no-load operation is used. Compared to the type compressor 100, the "total number of revolutions" at which flaking occurs is reached within a short operating time, shortening the bearing replacement cycle and complicating maintenance work.

In order to reduce the frequency of bearing replacement and eliminate the complexity of maintenance work while maintaining a high rotation speed of the engine 150 during no-load operation, a dynamic load rating (a rated life is obtained at 1 million rotations) is required. It is conceivable to use a bearing with a high dynamic load rating, such as a constant load applied to the bearing in the direction and magnitude). The use of bearings not only increases the price of oil-cooled screw compressors, but also increases maintenance costs due to the periodic replacement of expensive bearings.

In addition, in the configuration in which the engine 150 is driven at a high rotation speed during no-load operation, compared to a known screw compressor that operates the engine 150 at a low rotation speed during no-load operation, the compressor body 130 and the operating noise of the engine 150 increases, noise increases during no-load operation.

Therefore, there is a demand for a structure capable of suppressing or reducing the increase in noise even when the motor is operated at a high rotational speed during no-load operation.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to eliminate the drawbacks of the prior art described above. Therefore, even if a large amount of compressed gas starts to be consumed during no-load operation, the pressure in the receiver tank will drop significantly and air work will not be possible. It is an object of the present invention to provide an operation control method for an oil-cooled screw compressor capable of preventing the machine from stopping, etc., and an oil-cooled screw compressor capable of executing the control method.

Means for solving the problems are described below together with symbols used in the mode for carrying out the invention. This code is for clarifying the correspondence between the description of the claims and the description of the mode for carrying out the invention, and needless to say, it is used restrictively for the interpretation of the technical scope of the present invention. It is not something that can be done.

In order to achieve the above object, the operation control method of the oil-cooled screw compressor 1 of the present invention comprises:
A compressor body 30, a receiver tank 60 for introducing compressed gas discharged from the compressor body 30, a driving source 50 for driving the compressor body 30, and opening and closing a suction passage 37 of the compressor body 30. A suction control device 10 is provided, and when the pressure in the receiver tank 60 is lower than a predetermined reference pressure Ps, full-load operation is performed with the suction flow path 37 fully opened, and the pressure in the receiver tank 60 is set to the reference pressure Ps. In an oil-cooled screw compressor 1 that shifts to no-load operation with the suction passage 37 fully closed when a predetermined no-load operating pressure Pu higher than the pressure Ps is reached,
The no-load rotation speed Ru, which is the rotation speed of the drive source 50 during the no-load operation, is variable,
During the no-load operation, the compressed gas in the receiver tank 60 is released from the suction port of the compressor body 30 through the negative pressure relief flow path 82 communicating between the receiver tank 60 and the suction port of the compressor body 30 . Execute the negative pressure relaxation process introduced to
A flow rate adjusting means 80 is provided for adjusting the flow rate of the compressed gas flowing in the negative pressure relaxation flow path 82, and the introduction amount of the compressed gas introduced into the compressor main body 30 during the negative pressure relaxation process is controlled by the no-load rotation speed. When Ru is set to a relatively low rotational speed, the flow rate adjusting means 80 is adjusted so as to relatively decrease, and when the no-load rotational speed Ru is set to a relatively high rotational speed, it is relatively increased. It is characterized in that it is adjusted by the flow rate adjusting means 80 (Claim 1).

The compressor main body 30 can be a multi-stage compressor main body 30,
The introduction of the compressed gas in the negative pressure relaxation process can be performed to the suction port of the low-pressure stage compressor main body 31 and/or the suction port of the high-pressure stage compressor main body 32 that constitutes the compressor main body 30 (claim 2, Figures 1 and 3).

Further, when the compressor main body 30 is a multi-stage compressor main body 30,
When the no-load rotation speed Ru is set to a relatively low rotation speed, the introduction of the compressed gas is controlled by the suction port of the low-pressure stage compressor main body 31 constituting the compressor main body 30 (low-pressure stage compression in the illustrated example). By performing only the suction flow path 37) communicating with the suction port of the machine body 31, the amount of compressed gas to be introduced is relatively reduced,
When the no-load rotational speed Ru is set to a relatively high rotational speed, the compressed gas is introduced into the compressor main body 30 at the suction port of the low-pressure stage compressor main body 31 and the suction port of the high-pressure stage compressor main body 32. (In the illustrated example, the intermediate flow path 33 that communicates with the suction port of the high-pressure stage compressor main body 32) can be made to relatively increase the amount of compressed gas to be introduced. 3, see FIGS. 4 and 5).

Furthermore, in the configuration in which the compressed gas is introduced into the suction port of the high-pressure stage compressor main body 32, the pressure on the suction side of the high-pressure stage compressor main body 32 The pressure in the flow path 33) is measured, and the introduction amount of the compressed gas to the suction port of the high-pressure stage compressor body 32 is adjusted so that the pressure on the suction side of the high-pressure stage compressor body 32 becomes a predetermined pressure. (See claim 4 and FIG. 5).

Further, the no-load rotation speed Ru may be set in multiple steps or steplessly (see claim 5 and FIG. 5).

In addition, the oil-cooled screw compressor 1 of the present invention is
A compressor body 30, a receiver tank 60 for introducing compressed gas discharged from the compressor body 30, a driving source 50 for driving the compressor body 30, and opening and closing a suction passage 37 of the compressor body 30. A suction control device 10 is provided, and when the pressure in the receiver tank 60 is lower than a predetermined reference pressure Ps, full-load operation is performed with the suction flow path 37 fully opened, and the pressure in the receiver tank 60 is set to the reference pressure Ps. In an oil-cooled screw compressor 1 that shifts to no-load operation with the suction passage 37 fully closed when a predetermined no-load operating pressure Pu higher than the pressure Ps is reached,
No-load rotation speed setting means (rotation speed selector switch 21 or rotation speed setting volume 22 in the illustrated example) for setting the no-load rotation speed, which is the rotation speed of the drive source 50 during the no-load operation;
a negative pressure relief flow path 82 communicating between the receiver tank 60 and the suction port of the compressor body 30;
a flow rate adjusting means 80 provided in the negative pressure relief flow path 82;
Control means (controller 70 in the illustrated example) for controlling the flow rate adjusting means 80 according to the no-load rotation speed set by the no-load rotation speed setting means 21 or 22,
The control means 70
When the no-load rotation speed set by the no-load rotation speed setting means 21 or 22 is a relatively low rotation speed, the flow rate of the compressed gas flowing through the negative pressure relief passage 82 is relatively reduced. controlling the flow rate adjusting means 80,
When the no-load rotation speed set by the no-load rotation speed setting means is a relatively high rotation speed, the flow rate adjustment is performed so that the flow rate of the compressed gas flowing through the negative pressure relief flow path 82 relatively increases. It is characterized by controlling means 80 (Claim 6).

In the oil-cooled screw compressor 1 configured as described above, the compressor main body 30 can be a multi-stage compressor main body 30,
One end of the negative pressure relaxation flow path 82 communicates with the receiver tank 60, and the other end is connected to the suction port of the low-pressure stage compressor main body 31 constituting the compressor main body 30 (low-pressure stage compressor main body in the illustrated example). It may be configured to communicate with a suction passage 37 communicating with the suction port of 31 (see claim 7, FIGS. 1 and 3).

Further, when the compressor main body 30 is a multi-stage compressor main body 30,
One end of the negative pressure relaxation passage 82 is communicated with the receiver tank 60, and the other end is branched, and one of the branched passages 83 is connected to the main body of the low-pressure stage compressor constituting the main body 30 of the compressor. 31 (in the illustrated example, the suction flow path 37 communicating with the suction port of the low-pressure stage compressor main body 31), and the other flow path 84 is connected to the suction port of the high-pressure stage compressor main body 32 (illustrated In the example, the other flow path 84 communicates with the intermediate flow path 33 that communicates with the suction port of the high-pressure stage compressor main body 32, and an opening/closing means for opening and closing the other flow path 84 (the electromagnetic valve 98 in the illustrated example). , an electropneumatic valve 99) may form the flow rate adjusting means 80 (see claim 8, FIGS. 4 and 5).

In this case, a pressure detecting means (pressure sensor 72 in the illustrated example) for detecting the pressure in the suction port of the high-pressure stage compressor main body 32 is provided, and the opening degree of the opening/closing means for opening/closing the other flow path 84 is adjusted. A possible flow rate control valve (electropneumatic valve 99 in the illustrated example) is used, and the control means 70 adjusts the pressure on the suction side of the high-pressure stage compressor main body 32 to a predetermined pressure based on the pressure detected by the pressure detection means 72. The flow rate control valve 99 may be configured to be controlled so that

Furthermore, as the no-load rotation speed setting means, the no-load rotation speed can be set in multiple stages or steplessly (see rotation speed setting volume 22 in FIG. 5). 5).

According to the configuration of the present invention described above, the following remarkable effects can be obtained according to the present invention.

By making the no-load rotation speed Ru, which is the rotation speed of the drive source 50 during no-load operation, variable, the no-load rotation speed Ru can be made high (for example, the rated rotation speed) only when necessary. , the oil-cooled screw compressor 1 could be operated at a low cost with reduced fuel consumption or power consumption, compared to the case where the no-load rotation speed Ru is always high.

Furthermore, during the no-load operation, a negative pressure relaxation process is executed to introduce the compressed gas in the receiver tank 60 into the suction port of the compressor main body 30. The introduction amount of the compressed gas to be introduced is relatively decreased when the no-load rotation speed Ru is set to a relatively low rotation speed, and is relatively reduced when the no-load rotation speed Ru is set to a relatively high rotation speed. As a result, the suction side pressure of the compressor body 30 rises during no-load operation at a high rotation speed, and the pressure on the suction side and the suction side increases compared to the case of no-load operation at a low rotation speed. By reducing the pressure difference on the discharge side, both the axial and radial loads generated in the bearings 36a to 36g that support the rotor shaft of the screw rotor could be reduced.

As a result, even when the rotational speed during no-load operation is set to a high rotational speed, it is possible to prevent the bearing replacement cycle from being shortened without using a bearing with a high dynamic load rating.

Moreover, since the negative pressure on the suction side of the compressor main body 30 is alleviated by the negative pressure reducing process, the oil-cooled screw compressor 1 that can reduce the noise of the compressor main body 30 can be provided. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of an oil-cooled screw compressor according to one embodiment of the present invention; FIG. 2 is an explanatory diagram showing a modification of FIG. 1 (a modification of the suction control device 10 and the compressor main body 30); FIG. 2 is an explanatory diagram showing a modification of FIG. 1 (an example in which the ECU 51 in FIG. 1 is changed to a mechanical governor 52); FIG. 4 is an explanatory diagram of an oil-cooled screw compressor according to another embodiment of the present invention; FIG. 4 is an explanatory diagram of an oil-cooled screw compressor according to still another embodiment of the present invention; Explanatory drawing of the conventional oil-cooled screw compressor.

Hereinafter, an oil-cooled screw compressor 1 of the present invention will be described with reference to the accompanying drawings.

1. Embodiment 1
[Overall configuration of oil-cooled screw compressor]
Reference numeral 1 in FIG. 1 denotes an oil-cooled screw compressor of the present invention. ), provided with a receiver tank 60 for storing the compressed gas discharged from the compressor main body 30, and after storing the compressed gas discharged from the compressor main body 30 in the receiver tank 60, through the check valve 61 It is configured to supply power to a consumption side to which a pneumatic working machine (not shown) is connected.

The engine-driven compressor 1, which is the object of operation control in the present invention, is an oil-cooled screw compressor that compresses gas to be compressed together with lubricating oil for lubrication, cooling, and sealing of the compression working space as a compressor main body 30. By introducing the compressed gas discharged by the compressor body 30 together with the lubricating oil into the receiver tank 60, the compressed gas and the lubricating oil are separated from the gas and liquid, and the lubricating oil is separated. After the compressed gas is passed through the oil separator 60a, it is supplied to the consumption side, and the lubricating oil recovered in the receiver tank 60 is passed through the oil supply channel 64 having the oil filter 62 and the oil cooler 63. By supplying oil to the compressor body 30 again, the lubricating oil can be circulated.

[Compressor body]
In the illustrated embodiment, the compressor main body 30 provided in the oil-cooled screw compressor 1 is a so-called "two-stage compressor", and the discharge port of the low-pressure stage compressor main body 31 arranged on the upper side of the page is is communicated with the suction port of the high-pressure stage compressor body 32 arranged at the bottom of the paper surface through the intermediate flow path 33, so that the compressed gas compressed by the low-pressure stage compressor body 31 is further transferred to the high-pressure stage compressor body. 32 can be compressed.

Each compressor main body 31, 32 of the low-pressure stage and the high-pressure stage has a rotor chamber in its casing, and a pair of male and female screw rotors 34, 34 supported at both ends by bearings (36a to 36g) in the rotor chamber. '; 34, 35' (in FIG. 1, the other rotors 34', 35' are hidden behind the one rotor 34, 35) are accommodated so as to be rotatable in mesh with each other, and the screw rotors 34, 35 Rotational drive force from a drive source such as an engine or a motor (engine 50 in the illustrated example) can be input to the rotor shaft through a speed increasing device 40 .

The casing of this oil-cooled screw compressor 1 has a suction passage 37 that communicates with the suction port of the low-pressure stage compressor body 31 described above, a discharge port of the low-pressure stage compressor body and a suction port of the high-pressure stage compressor body. and a discharge passage 38 communicating with the discharge port of the high-pressure stage compressor main body 32 are formed, and the compressed gas introduced through the suction passage 37 flows into the low-pressure stage compressor After being compressed by the main body 31 and discharged, it is further compressed by the high-pressure stage compressor main body 32 and introduced into the above-described receiver tank 60 via the discharge flow path 38 .

Although the oil-cooled screw compressor 1 shown in FIG. 1 has been described as having a two-stage compressor main body 30 as the compressor main body 30, the oil-cooled screw compressor 1 of the present invention It is not limited to the configuration provided with the two-stage compressor body 30, but may be provided with a single-stage compressor body as shown in FIG. It can also be applied to those provided with a machine body.

In the embodiment shown in FIG. 1, the compressor main body 30 has a speed increasing device 40, but the structure of the present invention has a compressor main body 30 without the speed increasing device 40. It can also be applied to an oil-cooled screw compressor, and is not limited to the illustrated configuration.

[Capacity control device]
In the oil-flooded screw compressor 1 configured as described above, in order to be able to supply compressed gas of stable pressure to the consumption side, the compressor main body A capacity control is provided that controls the intake air of 30 and controls the rotational speed of the engine 50 .

In order to perform such capacity control, the illustrated oil-cooled screw compressor 1 is provided with a suction control device 10 for controlling the opening and closing of the suction passage 37 of the compressor body 30 and a speed control device 10 for controlling the rotation speed of the engine 50 . A controller is provided.

(1) Suction Control Device In the embodiment shown in FIG. It comprises a lever 12 , an air cylinder 13 which is an actuator for operating the butterfly valve 11 , and a connecting rod 14 which connects the piston rod of the air cylinder 13 and the lever 12 .

The operation of the suction control device 10 is controlled by a controller 70, which is control means, according to pressure changes in the receiver tank 60. In order to enable the control of the suction control device 10 by the controller 70, an oil-cooled screw compression The machine 1 is provided with a pressure sensor 71 which is pressure detecting means for detecting the pressure in the receiver tank 60 .

In addition, a control channel 81 having one end communicating with the receiver tank 60 is provided so that the above-described intake control device 10 can be operated using the pressure in the receiver tank 60 as the operating pressure. The other end is communicated with the air cylinder 13 described above, and the controller 70 opens and closes the electropneumatic valve 91 provided in the control flow path 81 in response to the pressure in the receiver tank 60 detected by the pressure sensor 71 described above. The intake control device 10 can control the opening and closing of the intake passage 37 of the compressor body 30 and the opening by controlling the opening.

The controller 70 stores a preset reference pressure Ps, compares the pressure in the receiver tank 60 detected by the pressure sensor 71 with the reference pressure Ps, and detects when the pressure detected by the pressure sensor 71 exceeds the reference pressure Ps. , a control signal for opening the electropneumatic valve 91 is output based on a preset correspondence relationship.

That is, the correspondence relationship between the pressure difference between the detected pressure and the reference pressure Ps and the opening degree of the electro-pneumatic valve is set in advance, and the controller 70 responds to the pressure difference between the detected pressure and the reference pressure Ps as described above. By changing the signal strength of the control signal, the internal passage of the electropneumatic valve 91 is closed when the pressure difference is 0 or less (detected pressure is less than the reference pressure), and the opening of the electropneumatic valve is reduced when the pressure difference is small. , and outputs a control signal to increase the opening when the pressure difference is large.

When the pressure of the compressed air supplied to the air cylinder 13 of the intake control device 10 is low, that is, the opening degree of the electropneumatic valve 91 is small and the pressure in the control flow path 81 on the secondary side of the electropneumatic valve 91 is low. Occasionally, the rod of the air cylinder 13 contracts and the butterfly valve 11 opens the suction passage 37 of the compressor body 30, while the opening of the electro-pneumatic valve 91 is large and the secondary side of the electro-pneumatic valve 91 is closed. When the pressure in the control channel 81 increases and the pressure of the compressed air supplied to the air cylinder 13 increases, the rod of the air cylinder 13 extends and the butterfly valve 11 closes or completely closes the intake channel 37. .

As a result, when the pressure in the receiver tank 60 is below the predetermined reference pressure Ps, the controller 70 operates the suction control device 10 so that the suction flow path 37 of the compressor body 30 is fully opened. When the pressure reaches the no-load operating pressure Pu set as a predetermined pressure higher than the reference pressure Ps, the operation of the suction control device 10 is controlled so that the suction passage 37 of the compressor body 30 is fully closed. do.

In the illustrated embodiment, the suction control device 10 is configured by the butterfly valve 11, the air cylinder 13, and the connecting rod 14 and lever 12 that connect them. As long as it can control the air intake of the compressor main body 30, various known structures can be adopted.

As an example, FIG. 2 shows an example in which the suction control device 10 is configured by a normally open suction control valve 11'.

The intake control valve 11' is configured to close the intake passage 37 of the compressor main body 30 by introducing the compressed gas in the receiver tank 60 into the closed valve pressure receiving chamber 15. In this embodiment, the air intake passage 17 communicating with the intake passage 37 of the compressor body 30 is formed by the space formed in the body (valve box) 16, and the air intake passage 17 is provided with By seating the valve body 18 on the valve seat 17a, the intake passage 17 is closed, and thus the intake passage 37 of the compressor main body 30 can be closed.

(2) Speed control device The engine 50 described above has an engine control unit (hereinafter referred to as "ECU") 51 that receives a rotational speed instruction signal output from the controller 70 and controls the rotational speed of the engine 50. The controller 70 described above outputs a rotational speed instruction signal to the ECU 51 based on a correspondence relation stored in advance.

Therefore, in the embodiment of FIG. 1, the controller 70 and the ECU 51 implement a speed control device for controlling the rotational speed of the engine.

In the embodiment shown in FIG. 1, the no-load operation speed setting means is configured by a rotational speed selector switch 21, which is a two-position selector switch. 70 sets the no-load rotation speed to a predetermined low-speed no-load rotation speed LRu, and when it is operated to the "high" position on the right side of the paper surface, it is set as a predetermined high rotation speed with respect to the low-speed no-load rotation speed LRu. set to the high no-load rotation speed HRu.

This high speed no-load rotation speed HRu can be appropriately set within a speed range higher than the low speed no-load rotation speed LRu. It may be set as the load rotational speed HRu.

As an example, in the oil-cooled screw compressor 1 shown in FIG. 1, when the rotation speed selector switch 21 is set to "low speed", the lowest value (for example, 1100 min ^-1 ) of the rotation speed range of the engine 50 is set as the low rotation speed LRu. , when the speed selector switch is set to "high speed", the rated rotational speed (for example, 1900 min ^-1 ) of the engine 50 is set to the high speed no-load rotational speed HRu.

The controller 70 detects the pressure in the receiver tank 60 detected by the pressure sensor 71 and the reference pressure Ps when the low-speed no-load rotation speed LRu is selected and when the high-speed no-load rotation speed HRu is selected. The correspondence relationship between the difference and the rotational speed instruction signal output to the ECU 51 of the engine 50 is stored, and the controller 70 controls the rotational speed of the engine 50 when the pressure difference is 0 or less (the detected pressure is equal to or less than the reference pressure). is output to the ECU 51, and the pressure difference is set as a predetermined high pressure with respect to the reference pressure. When the value indicating that the no-load operating pressure Pu has been reached, the rotation speed of the engine 50 is set to either high or low no-load rotation speed (HRu or LRu) set by the rotation speed selector switch 21. to the ECU 51.

In the embodiment shown in FIG. 1, the speed control of the engine 50 is controlled by the ECU 51 based on the rotation speed command signal of the controller 70. However, instead of the ECU 51 in FIG. The engine 50 is provided with a mechanical governor 52 and an air cylinder 53 which is an actuator for operating the mechanical governor 52. A control flow path 81 is communicated with the air cylinder 53 so that the pressure in the receiver tank 60 causes the mechanical A governor 52 may be operated to control the rotation speed of the engine 50 .

In the embodiment shown in FIG. 3, a pressure regulating valve 92 is provided instead of the electropneumatic valve 91 provided in the control flow path 81 in the configuration shown in FIG. When the pressure regulating valve 92 begins to open the control flow path 81 and the pressure in the receiver tank 60 reaches the no-load operating pressure Pu, the control flow path 81 is fully opened. Instead of the electrical control by the controller 70 based on the above, the opening/closing of the control flow path 81 is mechanically controlled.

In this case, an electromagnetic valve 93 is provided in the control flow path 81 on the primary side of the air cylinder 53 that operates the mechanical governor 52, and when the rotational speed selector switch 21 is operated to the "high speed" side, the controller By configuring to output to the electromagnetic valve 93 a signal that causes the closing operation to be performed, the rotation speed of the engine does not change due to the pressure change in the receiver tank 60, and the suction flow path 37 of the compressor body 30 is closed. The no-load operation, which is performed in the state where the engine is stopped, may be configured to be performed at a high speed (rated rotation speed).

In the embodiment shown in FIG. 1, the no-load rotation speed is selected by the rotation speed selector switch 21 from either the low-speed no-load rotation speed LRu or the high-speed no-load rotation speed HRu. Although an example has been shown, instead of the rotational speed selector switch 21, which is a two-position selector switch, a volume switch (rotational speed setting volume 22) such as a variable resistor is used as shown in FIG. Alternatively, it may be configured so that it can be set steplessly.

[Negative pressure relief channel]
The receiver tank 60 and the suction passage 37 of the compressor body 30 are communicated by a negative pressure relief passage 82 having a vacuum relief valve 94. When the suction control device 10 closes the suction passage 37, , the compressed gas in the receiver tank 60 is introduced to relieve the negative pressure in the intake passage 37 .

A vacuum relief valve 94 provided in the negative pressure relief flow path 82 has an inlet port 94a, an exhaust port 94b, and a pressure receiving port 94c communicating with the pressure receiving chamber. The discharge port 94b communicates with the suction flow path 37 of the compressor body 30, and the pressure receiving port 94c communicates with the control flow path 81 on the secondary side of the electropneumatic valve 91. When compressed air is introduced into the pressure receiving chamber through the pressure receiving port 94c, the passage formed inside opens and the inlet port 94a and the discharge port 94b communicate with each other.

Therefore, when the pressure in the receiver tank 60 exceeds the reference pressure Ps and the electro-pneumatic valve 91 opens and the compressed gas in the receiver tank 60 is introduced into the control flow path 81 on the secondary side of the electro-pneumatic valve 91, suction control The apparatus 10 closes the suction passage 37 of the compressor main body 30, and at the same time, the compressed gas is introduced into the pressure receiving chamber of the vacuum relief valve 94 to open the negative pressure relief passage 82, and the compressed gas in the receiver tank 60 is released. It is designed to be introduced into the suction flow path 37 of the compressor main body 30 .

On the secondary side of the vacuum relief valve 94, the negative pressure relief passage 82 is provided with a main passage 82a having a throttle 95 and a sub-passage 82b bypassing the throttle 95. By providing the electromagnetic valve 96, the auxiliary passage 82b can be opened and closed.

The controller 70 closes the solenoid valve 96 provided in the sub-passage 82b when the rotation speed selector switch 21 is switched to "low speed", and closes the solenoid valve 96 provided in the sub-passage 82b when it is switched to "high speed". 96 is configured to output a signal to open 96, and the amount of compressed gas introduced into the compressor main body 30 through the negative pressure relief passage 82 can be relatively increased at high speed compared to at low speed. configured to allow

Therefore, in the embodiment shown in FIG. 1, the auxiliary passage 82b and the electromagnetic valve 96 that opens and closes the auxiliary passage 82b constitute flow rate adjusting means 80 for changing the flow rate of the compressed gas passing through the negative pressure relief passage 82. As shown in FIG.

[Action and effect]
In the oil-flooded screw compressor 1 shown in FIG. If there is a risk that the pressure in the receiver tank 60 will drop significantly from the reference pressure Ps due to the delay in the startup of the rotation speed of the engine 50 when the consumption of compressed gas is started, this is the no-load rotation speed setting means. A high speed no-load rotation speed (rated rotation speed in this embodiment) is selected as the no-load rotation speed by operating the rotation speed selector switch 21 .

By operating the rotation speed changeover switch 21, the controller 70 outputs a signal to open the electromagnetic valve 96 provided in the sub-passage 82b of the negative pressure relaxation flow passage 82. FIG.

The controller 70 monitors the pressure in the receiver tank 60 based on the detection signal from the pressure sensor 71, and outputs a signal to close the electropneumatic valve 91 until the pressure in the receiver tank 60 reaches the reference pressure Ps. , to the ECU 51, a rotational speed command signal of the rated rotational speed Rr.

As a result, the oil-cooled screw compressor 1 is operated at full load, in which the engine 50 is operated at the rated rotational speed Rr with the suction flow path 37 of the compressor body 30 being fully opened by the suction control device 10. conduct.

In this way, since the electro-pneumatic valve 91 is closed during full-load operation, the vacuum relief valve 94 is also closed. Nor is the compressed gas in the tank 60 introduced.

When the pressure in the receiver tank 60 rises and exceeds the reference pressure Ps due to the continuation of such full-load operation, the controller 70 detects the pressure detected by the pressure sensor 71 and the reference pressure Ps based on the correspondence relationship stored in advance. An opening degree signal corresponding to the pressure difference of Ps is output to the electropneumatic valve 91 .

As a result, the electro-pneumatic valve 91 opens the control passage 81, the compressed gas in the receiver tank 60 is introduced into the air cylinder 13 of the intake control device 10, and the intake passage 37 of the compressor main body 30 is opened by the intake control device 10. At the same time as the closing operation is started, the introduction of compressed gas into the pressure receiving chamber of the vacuum relief valve 94 is started, the vacuum relief valve 94 is opened, and the compressed gas in the receiver tank 60 is released through the negative pressure relief flow path 82 to the compressor. It is introduced into the suction channel 37 of the main body 30 .

Based on the detection signal of the pressure sensor 71, the controller 70 changes the signal output to the electropneumatic valve 91 according to the pressure rise in the receiver tank 60 to increase the opening of the electropneumatic valve 91. , the suction control device 10 throttles the suction passage 37 of the compressor main body 30, and when the pressure in the receiver tank 60 reaches a predetermined no-load operating pressure Pu, the suction control device 10 closes the suction passage of the compressor main body 30. 37 is fully closed to shift to no-load operation.

However, the controller 70 changes the no-load rotation speed Ru to the high no-load rotation speed HRu (“rated rotation speed” in this embodiment) in response to the operation of the rotation speed selector switch 21 to the “high voltage” side. , the rotational speed of the engine 50 does not decrease even if it shifts to no-load operation, and a rotational speed instruction signal is sent to the ECU 51 of the engine 50 to maintain the high speed no-load rotational speed HRu (rated rotational speed). Output.

In this way, when "high speed" is set by the rotational speed changeover switch 21, the engine 50 maintains operation at a high rotational speed even after transitioning to no-load operation. Since the vacuum relief valve 94 opens the negative pressure relief passage 82 and the controller 70 opens the solenoid valve 96 provided in the sub passage 82b of the negative pressure relief passage 82, the compressed gas in the receiver tank 60 is released. , through both the main passage 82 a and the sub passage 82 b of the negative pressure relief passage 82 and into the suction passage 37 of the compressor body 30 .

As a result, even if the compressor main body 30 is rotated at a high speed during no-load operation, the suction flow path 37 of the compressor main body 30 does not absorb as much as in the case of the "low speed" setting in which the solenoid valve 96 is closed. Since the amount of compressed gas introduced into the flow path 37 increases and the pressure difference between the suction side and the discharge side of the compressor body 30 is greatly reduced, the thrust direction and axial direction pressure applied to the bearings 36a to 36g are reduced. Both loads can be reduced.

As a result, it is possible to delay and offset the increase in rolling fatigue progression speed of the bearing that accompanies the increase in rotational speed by reducing the load, thereby preventing shortening of the bearing replacement cycle.

In addition, it is expected that the increase in the amount of compressed gas introduced into the suction passage 37 of the compressor body 30 will reduce the negative pressure on the suction side of the compressor body 30, resulting in an increase in the noise of the compressor body 30. can be suppressed.

2. Embodiment 2
As described above, in the configuration of the oil-cooled screw compressor 1 described with reference to FIG. The arrangement has been described as being only via path 37 .

On the other hand, in the embodiment shown in FIG. 4, the other end of the negative pressure relief channel 82, one end of which communicates with the receiver sink 60, is branched into two directions, and one of the branch channels 83 is connected via the suction channel 37. The intermediate flow path 33 communicates with the suction port of the low-pressure stage compressor main body 31 at the same time, and the other branch flow path 84 communicates between the discharge port of the low-pressure stage compressor main body 31 and the suction port of the high-pressure stage compressor main body 32. communicates with

A solenoid valve 98 is provided in the other branch flow path 84 communicating with the intermediate flow path 33, and when the rotational speed selector switch 21 is set to "high speed" as the no-load rotation speed, the other branch flow path 84 is closed. The electromagnetic valve 98 is opened to introduce compressed gas into the suction port of the high-pressure stage compressor main body 32 .

Therefore, in the embodiment shown in FIG. 4, by opening and closing the other branch flow path 84 with the solenoid valve 98, the flow rate of the compressed gas that passes through the negative pressure relief flow path 82 and is introduced into the compressor body 30 is reduced. A variable flow rate adjusting means 80 is configured.

Other configurations are the same as those of the oil-cooled screw compressor 1 in FIG.

With the configuration of the oil-cooled screw compressor 1 shown in FIG. , when the pressure in the receiver tank 60 is equal to or lower than the reference pressure Ps, the electro-pneumatic valve 91 is closed. A rotation speed instruction signal is output to make the rotation speed equal to the rated rotation speed Rr, and full load operation is performed.

When the pressure in the receiver tank 60 exceeds the reference pressure Ps due to the continuation of full-load operation, the controller 70 expands the opening of the electropneumatic valve 91 in response to this pressure increase, thereby When the pressure in the control passage 81 on the side rises and the suction control device 10 begins to close the suction passage 37 of the compressor body 30, and the pressure in the receiver tank 60 reaches a predetermined no-load operating pressure Pu, the compression The suction flow path 37 of the machine main body 30 is fully closed and the operation shifts to no-load operation.

However, since the controller 70 sets the no-load rotation speed Ru to the high-speed no-load rotation speed HRu (the rated rotation speed in this embodiment) in accordance with the selection by the rotation speed selector switch 21, the rotation speed of the engine 50 is set to full-load operation. Maintain the same rotation speed.

Also, when the pressure in the control flow path 81 on the secondary side of the electro-pneumatic valve 91 increases due to the opening of the electro-pneumatic valve 91 and the compressed gas is supplied to the pressure receiving chamber of the vacuum relief valve 94, the vacuum relief valve 94 is closed. The internal passage is opened, and the compressed gas in the receiver tank 60 is introduced into the suction passage 37 of the compressor main body 30 via one branch passage 83 of the negative pressure relief passage 82 .

In this way, when the no-load operation rotational speed is set to "high", by introducing the compressed gas to the suction side of the high-pressure stage compressor main body 32 via the intermediate flow path 33, the high-pressure stage compressor The pressure difference between the suction side and the discharge side of the main body 32 can be reduced, and a larger load than the bearings 36a to 36c of the low pressure stage compressor main body 31 is applied to the bearings 36d to 36g of the high pressure stage compressor main body 32. The load can be suitably reduced, and even when no-load operation is performed at a high rotational speed, the replacement cycle of the bearings 36d to 36g that support the rotor shaft of the high-pressure stage compressor main body 32 is shortened. could be prevented.

By introducing the compressed gas into the intermediate flow path 33, the pressure difference between the suction flow path 37 and the discharge side (intermediate flow path 33) of the low-pressure stage compressor main body 31 during no-load operation is reduced to the intermediate flow path 33. On the other hand, it becomes larger than when the compressed gas is not introduced.

However, the pressure difference between the suction side and the discharge side of the low-pressure stage compressor main body 31 (the pressure difference between the suction flow path 37 and the intermediate flow path 33) during no-load operation is not only is it sufficiently small compared to the pressure difference (pressure difference between the intermediate flow path 33 and the discharge flow path 38), but also compared to the pressure difference between the suction side and the discharge side of the low-pressure stage compressor main body 31 during full load operation. Even if the pressure difference between the suction side and the discharge side of the low-pressure stage compressor main body 31 increases somewhat by introducing compressed gas into the intermediate flow path 33 during no-load operation, , the load applied to the bearings 36a to 36c of the low-pressure stage compressor main body 31 is still small, which does not shorten the replacement cycle.

On the other hand, the pressure difference between the suction side and the discharge side of the high-pressure stage compressor main body 32 (the pressure difference between the intermediate flow path 33 and the discharge flow path 38) during no-load operation is larger than that during full-load operation. Therefore, during no-load operation, a large load is applied to the bearings 36d to 36g of the high-pressure stage compressor body 32 in both the thrust direction and the axial direction. 32 is driven at a high rotational speed, the replacement cycle of the bearings 36d-36g is greatly shortened.

Therefore, as in the present embodiment, compressed gas is introduced into the intermediate flow path 33 during no-load operation, and the pressure in the intermediate flow path is increased to increase the pressure difference ( By reducing the load on the bearings 36d to 36g by reducing the pressure difference between the intermediate flow path 33 and the discharge flow path 38, the load on the bearings 36d to 36g of the high-pressure stage compressor main body 32, which is subjected to a larger load, is reduced. It can extend the replacement cycle.

As a result, even if the compressor body was rotated at high speed during no-load operation, it was possible to prevent the replacement cycle of the bearings 36a to 36g from being shortened compared to the case where no-load operation was performed only at low speed. It should be noted that in the configuration of the present embodiment described with reference to FIG. Although the configuration in which the compressed gas in the receiver tank 60 is introduced through the negative pressure relief flow path 82 to both of the suction ports (intermediate flow path 33) of the high pressure stage compressor main body 32 Since the introduction of the compressed gas into the suction port of the low-pressure stage compressor body 31 is effective in reducing the load applied to the bearing, for example, in the configuration described with reference to FIG. ) is communicated with the suction port (intermediate flow path 33) of the high-pressure stage compressor main body 32, and the introduction of the compressed gas into the compressor main body 30 is controlled by the high-pressure stage compression It may be constructed so as to be carried out through the suction port of the machine main body 32 .

3. Embodiment 3
In the configuration of the oil-cooled screw compressor 1 of Embodiment 2 described with reference to FIG. In addition, an electromagnetic valve 98 is provided in the other branch flow path 84 for introducing the compressed gas into the intermediate flow path 33, and is configured to control only the opening and closing of the other branch flow path 84.

In contrast, in the embodiment shown in FIG. 5, the rotation speed selector switch 21 is configured as a rotation speed setting volume 22 that can be switched in multiple positions or steplessly by a variable resistor or the like, and the no-load rotation speed can be set in multiple steps or steplessly. It is configured so that it can be set in stages.

In addition, an electro-pneumatic valve 99 is provided in the other branch flow path 84 for introducing the compressed gas into the intermediate flow path 33, and a control signal from the controller 70 not only controls the opening and closing of the other branch flow path 84, but also , and a pressure detection means (pressure sensor) 72 for detecting the pressure in the intermediate flow path 33 communicating between the low-pressure stage compressor main body 31 and the high-pressure stage compressor main body 32 is provided.

As a result, the controller 70 closes the electropneumatic valve 99 when the rotation speed setting volume 22 is operated to set the no-load rotation speed to the lowest rotation speed, and the rotation speed setting volume 22 is changed from the lowest rotation speed to the high rotation speed side. When it is operated to set a high rotation speed, a predetermined high rotation speed is set as the no-load rotation speed with respect to the minimum speed rotation according to the operation amount of the rotation speed setting volume 22 .

The controller 70 controls the opening degree of the electropneumatic valve 99 provided in the other branch flow path 84 so that the pressure in the intermediate flow path 33 detected by the pressure sensor 72 becomes a predetermined pressure. do.

In this way, when the no-load rotation speed is set to a rotation speed higher than the lowest rotation speed by operating the rotation speed setting volume 22, the negative pressure relaxation passage 82 opens and the suction passage of the low-pressure stage compressor body 31 opens. 37, the compressed gas is also introduced to the suction port of the high-pressure stage compressor main body 32 via the other branch flow path 84 and the intermediate flow path 33. The pressure difference between the suction side and the discharge side of the stage compressor body 32 is also reduced, and the load applied to the bearings 36a to 36g of the low-pressure stage compressor body 31 and the high-pressure stage compressor body 32 is reduced. Even when the compressor body 30 is operated at a high rotational speed, the replacement cycle of the bearings 36a to 36g need not be shorter than the replacement cycle for no-load operation only at a low speed. 4, which is the same as the case of the oil-cooled screw compressor 1 introduced as the second embodiment described above.

In addition, in the oil-cooled screw compressor 1 of this embodiment (Embodiment 3), by adopting the rotation speed setting volume 22, the no-load rotation speed can be set in multiple stages or steplessly. The no-load rotation speed can be set according to the amount of compressed gas consumed by the pneumatic work equipment and the operating conditions. There is a risk that the pressure in the tank will drop below the standard pressure, but if the no-load operation is performed at the rated speed, the performance will be excessive. Since it can be appropriately set in a range higher than the value and lower than the rated rotation speed, it is also advantageous in that it is possible to optimize fuel consumption, power consumption, etc. during no-load operation.

Moreover, the pressure in the intermediate flow path 33 is detected and controlled so that the pressure in the intermediate flow path 33 is within a predetermined pressure range even if the setting of the no-load rotation speed changes. To suitably prevent the occurrence of inconvenience such as excessive introduction into the flow path 33 and increase in power consumption for recompressing the introduced compressed gas in the high-pressure stage compressor main body 32 and power consumption during no-load operation. was made.

1 oil-cooled screw compressor 10 suction control device 11 suction control valve (butterfly valve)
11' intake control valve (normally open type)
12 lever 13 actuator (air cylinder)
Reference Signs List 14 connecting rod 15 valve closing pressure receiving chamber 16 body 17 intake path 17a valve seat 18 valve body 21 rotation speed selector switch (no-load rotation speed setting means)
22 rotation speed setting volume (no-load rotation speed setting means)
30 Compressor main body 31 Low-pressure stage compressor main body 32 High-pressure stage compressor main body 33 Intermediate passages 34, 35 (34', 35') Screw rotors 36a to 36g Bearings 37 Suction passage 38 Discharge passage 40 Speed increasing device 50 Engine 51 Engine control unit (ECU)
52 mechanical governor 53 actuator (air cylinder)
60 receiver tank 60a oil separator 61 check valve 62 oil filter 63 oil cooler 64 oil supply passage 70 controller (control means)
71 pressure detection means (pressure sensor) (for receiver tank)
72 pressure detection means (pressure sensor) (for intermediate flow path)
80 flow rate adjusting means 81 control channel 82 negative pressure relaxation channel 82a main channel 82b auxiliary channel 83 one branch channel 84 other branch channel 91, 99 electropneumatic valve 92 pressure regulating valve 93, 96, 98 solenoid valve 94 Vacuum relief valve 94a Inlet 94b Outlet 94c Pressure receiving port 95, 97 Throttle 100 Oil-cooled screw compressor 111 Suction control valve 130 Compressor body 137 Suction flow path 150 Drive source (engine)
160 receiver tank 160a oil separator 162 oil filter 163 oil cooler 164 oil supply passage Ps reference pressure Pu no-load operating pressure Rr rated rotation speed Ru no-load rotation speed HRu high-speed no-load rotation speed LRu low-speed no-load rotation speed

Claims (10)

a compressor body, a receiver tank for introducing compressed gas discharged from the compressor body, a drive source for driving the compressor body, and a suction control device for opening and closing a suction flow path of the compressor body, When the pressure in the receiver tank is lower than the predetermined reference pressure, full-load operation is performed with the suction passage fully opened, and the pressure in the receiver tank reaches a predetermined no-load operating pressure higher than the reference pressure. In an oil-cooled screw compressor that shifts to no-load operation with the suction passage fully closed when
variable no-load rotation speed, which is the rotation speed of the drive source during no-load operation;
Negative pressure for introducing the compressed gas in the receiver tank to the suction port of the compressor body through a negative pressure relief passage that communicates between the receiver tank and the suction port of the compressor body during the no-load operation. Execute the mitigation process,
A flow rate adjusting means is provided for adjusting the flow rate of the compressed gas flowing in the negative pressure relaxation flow path, and the introduction amount of the compressed gas introduced into the compressor main body during the negative pressure relaxation process is adjusted relative to the no-load rotational speed. When setting the rotation speed to a relatively low speed, the flow rate adjusting means adjusts the flow rate to relatively decrease, and when the no-load rotation speed is set to a relatively high rotation speed, the flow rate adjusting means adjusts to relatively increase. An operation control method for an oil-cooled screw compressor, characterized by: the compressor body is a multi-stage compressor body,
2. The method according to claim 1, wherein the introduction of the compressed gas in the negative pressure relaxation process is performed to an intake port of a low-pressure stage compressor main body and/or an intake port of a high-pressure stage compressor main body constituting the compressor main body. and an operation control method for an oil-cooled screw compressor. the compressor body is a multi-stage compressor body,
When the no-load rotation speed is set to a relatively low rotation speed, the compressed gas is introduced only to the suction port of the main body of the low-pressure stage compressor that constitutes the main body of the compressor. Relatively reduce the amount of gas,
When the no-load rotation speed is set to a relatively high rotation speed, the introduction of the compressed gas into the compressor body is directed to both the suction port of the low-pressure stage compressor body and the suction port of the high-pressure stage compressor body. 2. The operation control method for an oil-flooded screw compressor according to claim 1, wherein the amount of compressed gas to be introduced is relatively increased by performing the operation. measuring the pressure on the suction side of the main body of the high-pressure stage compressor, and introducing the amount of the compressed gas into the suction port of the main body of the high-pressure stage compressor so that the pressure on the suction side of the main body of the high-pressure stage compressor becomes a predetermined pressure; 4. The method for controlling the operation of an oil-cooled screw compressor according to claim 3, wherein the adjustment is performed. The operation control method for an oil-cooled screw compressor according to any one of claims 1 to 4, wherein the no-load rotation speed can be set in multiple stages or steplessly. a compressor body, a receiver tank for introducing compressed gas discharged from the compressor body, a drive source for driving the compressor body, and a suction control device for opening and closing a suction flow path of the compressor body, When the pressure in the receiver tank is lower than the predetermined reference pressure, full-load operation is performed with the suction passage fully opened, and the pressure in the receiver tank reaches a predetermined no-load operating pressure higher than the reference pressure. In an oil-cooled screw compressor that shifts to no-load operation with the suction passage fully closed when
no-load rotation speed setting means for setting a no-load rotation speed, which is the rotation speed of the drive source during the no-load operation;
a negative pressure relief flow path communicating between the receiver tank and the suction port of the compressor body;
a flow rate adjusting means provided in the negative pressure relief channel;
Control means for controlling the flow rate adjusting means according to the no-load rotation speed set by the no-load rotation speed setting means,
the control means,
When the no-load rotation speed set by the no-load rotation speed setting means is a relatively low rotation speed, the flow rate adjusting means relatively decreases the flow rate of the compressed gas flowing through the negative pressure relief passage. to control
When the no-load rotation speed set by the no-load rotation speed setting means is a relatively high rotation speed, the flow rate adjusting means relatively increases the flow rate of the compressed gas flowing through the negative pressure relief passage. An oil-cooled screw compressor characterized by controlling the compressor body is a multi-stage compressor body,
7. The oil according to claim 6, wherein one end of said negative pressure relief passage communicates with said receiver tank, and the other end thereof communicates with a suction port of a main body of a low-pressure stage compressor constituting said main body of said compressor. Cold screw compressor. the compressor body is a multi-stage compressor body,
One end of the negative pressure relaxation passage is communicated with the receiver tank, the other end is branched, and one of the branched passages is connected to the suction port of the main body of the low-pressure stage compressor that constitutes the main body of the compressor. and the other flow path is connected to the suction port of the main body of the high-pressure stage compressor, and the flow rate adjusting means is formed by the other flow path and the opening/closing means for opening and closing the other flow path. 7. An oil-cooled screw compressor according to claim 6. A pressure detecting means for detecting the pressure in the suction port of the high-pressure stage compressor main body is provided, and the opening and closing means for opening and closing the other flow path is an adjustable flow rate control valve, and the control means detects the pressure. 9. An oil-cooled screw compressor according to claim 8, wherein said flow control valve is controlled so that the pressure on the suction side of said high-pressure stage compressor main body becomes a predetermined pressure based on the pressure detected by said means. An oil-cooled screw compressor according to any one of claims 6 to 9, wherein said no-load rotation speed setting means can set said no-load rotation speed in multiple stages or steplessly.

Images