JP3796656B2 - Oil supply type screw compressor and its control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oil supply type screw compressor and a control method thereof, and more particularly, to a technique for recovering oil from a shaft seal device.
[0002]
[Prior art]
Conventionally, it has a pair of male and female screw rotors whose axes are parallel to each other and the torsional directions are reversed, and a bore that accommodates these screw rotors through a minute gap, and an inlet port on one end surface of this bore However, there is known a rotation speed control oil supply type screw compressor including a casing having a discharge port formed on the other end face, and provided with an inverter for adjusting a load and a suction valve. In this rotational speed control oil supply type screw compressor, a male (male) rotor has an intake side shaft end extended to the outside of the casing for driving, and a pulley or a coupling is attached. Inside the casing is a bearing that supports the rotor, and this bearing is lubricated for lubrication. For this reason, a shaft seal device is provided where the Osloter intake side shaft passes through the casing, and sealing is performed so that the lubricating oil does not leak out of the casing. However, since there is a slight leakage of lubricating oil from the shaft seal device, a groove for temporarily storing the leaked lubricant oil is provided outside the shaft seal device, and this groove is provided on the primary side of the intake valve ( The recovery piping connected to the inlet side) was used to recover the lubricating oil accumulated in the groove using the differential pressure between the negative pressure generated by the air passing through the intake valve and the atmospheric pressure outside the shaft seal device. .
[0003]
Moreover, as a prior art of the lubricating oil collection | recovery apparatus from a shaft seal apparatus, there exists a technique of Unexamined-Japanese-Patent No. 9-88860, for example.
[0004]
[Problems to be solved by the invention]
In the above prior art, oil leaked from the shaft seal device is collected in the groove outside the shaft seal, sucked up by the negative pressure generated on the primary side of the suction valve through the recovery pipe, and compressed again through the suction valve. It is collected in the machine body.
[0005]
The suction throttle valve method, which is a general capacity adjustment method for air compressors, adjusts the opening of the intake valve steplessly from fully open to fully closed in order to adjust the air volume. Even so, there is sufficient negative pressure on the primary side of the intake valve for recovery of the lubricating oil.
[0006]
On the other hand, in the case of the rotational speed control method, the capacity adjustment in accordance with the amount of air used is performed by changing the rotational speed of the compressor body, so that the opening degree of the intake valve is not adjusted. Therefore, the negative pressure on the primary side of the suction valve for collecting the lubricating oil does not change the opening degree of the suction valve, so that the lower the load, the lower the rotational speed when the full load state is maximized, and the lower the lubricating oil collecting capacity. . FIG. 4 shows the relationship between the compressor speed and the compressor suction negative pressure. As shown in FIG. 4, the recovery piping that has exhibited the lubricating oil recovery capability with sufficient negative pressure during full load operation also reduces the rotation speed of the compressor body as the user's air consumption decreases, resulting in a low rotation speed. As a result, the amount of air passing through the intake valve decreases, and the negative pressure on the primary side of the intake valve decreases. Since the suction valve opening remains constant throughout the rotation speed control range, the negative pressure on the secondary side similarly decreases at low rotation speeds. Therefore, in the operating range below a certain rotation speed A, the negative pressure on the primary side of the intake valve sufficient for recovery of the lubricating oil cannot be secured, resulting in insufficient recovery capability. For this reason, if the operation state below a certain load region continues, there is a possibility that sufficient lubricating oil recovery capability cannot be exhibited. In addition, the lubricating oil that could not be recovered may scatter to the outside, adhere to the driving belt, and cause a slip.
[0007]
An object of the present invention is to eliminate a load region where the recovery capability of lubricating oil leaked from a shaft seal device of an oil supply type screw compressor of a rotational speed control system is insufficient.
[0008]
[Means for Solving the Problems]
In order to maintain the recovery capability of the lubricating oil, the negative pressure at the downstream end of the recovery pipe may be maintained. The inventors of the present invention have focused on the fact that if the recovery pipe is connected to the secondary side of the suction valve, the negative pressure at the downstream end of the recovery pipe can be maintained by closing the suction valve, leading to the present invention.
[0009]
That is, in order to achieve the above object, the present invention has a suction valve that can be opened and closed by remote control, and in an oil supply type screw compressor that performs capacity control by changing the number of revolutions, it leaks outside the shaft seal device. A storage means such as a groove provided for storing lubricating oil, a recovery pipe connecting the storage means and the primary side of the suction valve, and a check valve connecting the secondary side of the recovery pipe and the suction valve A recovery pipe branch pipe connected through the recovery pipe and a lubricating oil recovery control means for closing the suction valve for a predetermined time when it is determined that the recovery oil capacity of the recovery pipe is insufficient. Features.
[0010]
Judgment of whether the recovery pipe has insufficient lubricating oil recovery capability depends on whether the compressor rotational speed is lower than the predetermined rotational speed, or the suction valve pressure is higher than the predetermined pressure. It is possible to use a criterion such as whether or not the oil level of the groove portion is higher than a predetermined position.
[0011]
Further, it is desirable that the recovery pipe branch pipe is provided with a throttle mechanism in order to adjust the recovery capability.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a system diagram of a rotational speed control oil supply type screw compressor of the present embodiment (however, an oil separation device, an oil supply system, etc. are omitted). The illustrated rotational speed control oil supply type screw compressor includes an oil supply type screw compressor body 1, a drive motor 7 that drives the oil supply type screw compressor body 1, an inverter 8 that controls the rotation speed of the electric motor 7, and an oil supply. Type open and close intake valve 2 coupled to the air suction side of the main body of the screw compressor 1 and lubricating oil recovery control as lubricating oil recovery control means for opening and closing the intake valve 2 based on a signal output from the inverter 8 The apparatus 9 includes an oil supply type screw compressor main body 1 and a recovery pipe 4 and a recovery pipe branch pipe 4A that connect the suction valve.
[0013]
The oil-feeding screw compressor main body 1 has a pair of male and female screw rotors whose axes are parallel to each other and whose torsion directions are opposite to each other, and a bore that accommodates these screw rotors through a minute gap. And a casing having an air inlet at one end surface and a discharge port at the other end surface. For driving, a male (male) rotor has an intake side shaft end extended to the outside of the casing, and a pulley or a coupling is attached (FIG. 2 shows an example in which the pulley is attached). Inside the casing is a bearing that supports the rotor, and this bearing is lubricated for lubrication. For this reason, the shaft seal device 3 is provided where the Osloter intake side shaft passes through the casing, and seals so that the lubricating oil does not leak out of the casing. However, since there is a slight leakage of the lubricating oil from the shaft seal device 3, a mechanical seal external groove 11 for temporarily storing the leaked lubricant oil is provided outside the shaft seal device.
[0014]
FIG. 2 is a partially broken side view showing the oil supply type screw compressor main body 1 and the suction valve 2 coupled to the oil supply type screw compressor main body 1. The intake valve 2 is configured to allow the air flowing in from the lateral direction to flow out downward, and the valve body 24 abuts the lower surface of the valve seat 25 formed in a direction orthogonal to the outflow direction to close the valve. It is like that. A cylinder 26 having a hollow portion is provided above the valve seat 25 with an axis line in the vertical direction, and a piston 24A that slides up and down along the axis line is provided in the hollow portion. A piston rod extending in the axial direction is coupled to the lower surface of the piston 24A. The piston rod penetrates the lower end of the cylinder 26 and is coupled to the upper surface of the valve body 24. Inside the cylinder, a spring 23 is provided between the lower surface of the piston 24A and the bottom surface of the cylinder to urge the piston 24A upward. Further, as shown in the drawing, a step portion having an inner diameter smaller than the outer diameter of the piston 24A is formed at the lower portion of the cylinder, and this is the lower limit of the lowering of the piston 24A. A gap serving as an air flow path is provided between the lower end portion of the cylinder 26 and the valve seat 25. In the valve open state, air flowing in from the lateral direction flows into the opening of the valve seat through this gap. It is supposed to be.
[0015]
The piston 24 </ b> A moves up and down by the resultant force of the pressure applied to the upper and lower surfaces thereof and the elastic force of the spring 23, and the valve body 24 takes two open / close positions. Although not shown in the cylinder, there are provided a pressure line for introducing the discharge air of the compressor to a portion (lower section) below the lower limit of lowering of the piston 24A, and an exhaust line for releasing the internal pressure of the lower section. Each is equipped with a solenoid valve. Similarly, a part (upper section) above the upper limit position of the cylinder is provided with a pressure line for introducing the discharge air of the compressor and an exhaust line for releasing the internal pressure of the upper part. A solenoid valve is installed. The lower section, the pressurization pipe connected to the upper section, and the solenoid valve of the exhaust pipe are controlled to be opened and closed by the lubricant recovery control device 9. In addition, the pressurization pipe line which introduces the discharge air of the compressor to the lower section is omitted, the solenoid valve of the pressurization pipe connected to the upper section is closed, the solenoid valve of the exhaust pipe is opened, and the valve body is operated by the force of the spring It is also possible to configure the valve to close by raising 24.
[0016]
A mechanical seal external groove 11 provided in the vicinity of the shaft seal device 3 of the intake side shaft of the oil supply type screw compressor main body 1 and the primary side (intake valve primary side port 21) of the intake valve 2 are the recovery pipe 4 The recovery pipe 4 and the secondary side (suction valve secondary side port 21) of the suction valve 2 are connected via a check valve 5 via a recovery pipe branch pipe 4A. Here, the “primary side of the intake valve” refers to the upstream side of the internal valve seat, and the “secondary side” refers to the downstream side of the valve seat and the inlet of the compression chamber. The check valve 5 stops the flow from the suction valve 2 toward the recovery pipe 4. Further, a throttle 6 for adjusting the recovery capability is provided between the check valve 5 and the suction valve 2, but may be omitted depending on circumstances.
[0017]
During normal operation, the intake valve is in a fully open state, and closed operation (a system that operates while restricting intake air and releasing compressed air to the outside. Effective in reducing power consumption. Also called decompression operation / purge operation. ) Sometimes the valve is fully closed. In addition, when the compressor is stopped, the intake valve is fully closed, and a check function that prevents the lubricating oil that has flown back in the compressor body from leaking outside is also achieved.
[0018]
FIG. 3 is a partial cross-sectional view when a mechanical seal is used in the shaft seal device. A shaft seal device 3 such as a mechanical seal is provided on the intake side shaft of the oil supply type screw compressor main body 1 and includes a mechanical seal external groove 11 for temporarily storing lubricating oil leaked from the outside. The recovery pipe 4 connects the bottom of the mechanical seal external groove 11 to the primary port 21 of the intake valve 2.
[0019]
With this configuration, the lubricating oil accumulated in the mechanical seal outer groove 11 is collected in the suction valve 2 by utilizing the differential pressure between the negative pressure generated by the air passing through the suction valve 2 and the atmospheric pressure outside the shaft seal device.
[0020]
The operation of the embodiment having the above configuration will be described below.
[0021]
In the compressor stop state, the electromagnetic valve of the pressurizing line that introduces the discharge air of the compressor to the upper section is opened, and the electromagnetic valve of the exhaust line that releases the internal pressure of the upper section is closed. On the other hand, the solenoid valve of the pressurizing line for introducing the discharge air of the compressor into the lower section is closed, and the solenoid valve of the exhaust line for releasing the internal pressure of the lower section is opened. The valve body 24 is lifted by being biased by the spring 23, and the suction valve 2 is closed.
[0022]
When the compressor is started, the secondary side of the suction valve 2 becomes negative pressure, and the air in the compressor is compressed and introduced into the upper section, and the force in the valve opening direction due to this pressure difference is the force of the spring 23. It becomes stronger than that and the valve body 24 descends. That is, the suction valve 2 is opened and normal operation is started.
[0023]
As shown in FIG. 4, a negative pressure sufficient for recovery of the lubricating oil cannot be secured in an operation region of a certain rotation speed A or less, resulting in insufficient recovery. In the case of the rotational speed control method, there is a minimum rotational speed that can be controlled (B in FIG. 4), and capacity control based on the rotational speed at a rotational speed lower than that is not performed. In the present embodiment, the rotational speed A at which the recovery capability cannot be maintained is stored in advance in the lubricating oil recovery control device 9, and a signal indicating the operating rotational speed is output from the inverter 8 to the lubricating oil recovery control device 9. The lubricant recovery control device 9 constantly monitors the operating rotational speed based on the signal output from the inverter 8.
[0024]
FIG. 5 shows an operation control time chart of the lubricant recovery according to the present embodiment. The lubricating oil recovery control device 9 starts a built-in timer for switching operation when the operating rotational speed that is constantly monitored falls below the rotational speed A, and switches to a closed operation after the time T1 has elapsed. At the time of switching, the lubricant recovery control device 9 opens the solenoid valve of the pressurization line in the lower section and closes the solenoid valve of the exhaust section, closes the solenoid valve of the pressurization line in the upper section and exhausts the exhaust pipe. Open the solenoid valve. That is, in the closed operation, the intake valve 2 is fully closed and the intake air becomes zero. In this state, no negative pressure is generated on the suction valve primary side, but the suction valve 2 is fully closed, so that the secondary side negative pressure is sufficient, and this secondary side negative pressure passes through the check valve 5. Therefore, the recovery of the lubricating oil is continued.
[0025]
The closing operation continuation time T2 for the recovery of the lubricating oil is set in advance in consideration of the oil storage amount and the oil recovery capability during the closing operation, and the switching time T1 and the continuation time T2 to the closing operation are the lubricating oil recovery control. Store in advance in the device. The closing operation duration time T2 may be about 15 to 60 seconds. The switching time T1 to the closed operation avoids a situation in which the operation is switched to the closed operation when the rotation speed instantaneously becomes equal to or lower than the rotation speed A near the rotation speed A and immediately exceeds the rotation speed A. Therefore, it is set in order to keep the driving stability.
[0026]
When switching to the closed operation, the lubricant recovery control device 9 resets and starts the built-in timer, and again returns to the rotational speed control after the closed operation duration time T2 has elapsed. At this time, the lubricating oil recovery control device 9 closes the electromagnetic valve of the pressurization line in the lower section and opens the electromagnetic valve of the exhaust line, and opens the electromagnetic valve of the pressurization line in the upper section and closes the exhaust pipe. Close the solenoid valve. As a result, the suction valve 2 is opened, and the suction and compression of air are resumed.
[0027]
Since the supply of compressed air to the compressed air load side is temporarily stopped during the closed operation, when switching to the closed operation, if the discharge pressure is once increased and then switched to the closed operation, only the increased pressure Since extra air is supplied to the load side, the compressed air usage time on the load side can be gained, and the closing operation time can be increased, which is effective.
[0028]
In the above embodiment, the compressor rotational speed is monitored and switched to a closed operation. However, since the lubricant recovery uses the compressor negative pressure, a vacuum sensor for measuring the negative pressure is provided on the primary side of the suction valve 2. The system may be switched to the closed operation when the negative pressure set in the attaching and lubricating oil recovery control device 9 is reached. In this case, since the collection control is directly performed with the negative pressure generated in the suction valve 2, the collection accuracy is improved, and individual setting (rotation speed setting) according to the compressor model is not required, so that parts can be shared. There are also secondary benefits. The vacuum sensor that measures the negative pressure may be attached to the secondary side of the suction valve 2, but if it is attached to the secondary side, it will be exposed to a rapid pressure change every time it switches to the closed operation, in terms of maintaining the life. Not desirable.
[0029]
Further, a sensor is provided for detecting the oil amount at a location where the oil leaked from the shaft seal device such as the mechanical seal outer groove 11 is stored, and when the sensor outputs a signal indicating a predetermined upper limit oil amount, the sensor is closed. It is good also as a system switched to driving | operation. In this case, as a method for returning to normal operation, either a method for returning to normal operation by a timer or a method for returning to normal operation when a sensor outputs a signal indicating a predetermined oil amount can be adopted. .
[0030]
The lubricating oil recovery structure can be achieved by simply providing a recovery pipe to the secondary side of the suction valve. However, by providing the recovery pipe 4 and the recovery pipe branch pipe 4A, the lubricating oil can be supplied when the compressor is stopped. This has the effect of preventing leakage. During operation, the compressor main body has a pressure gradient from a substantially atmospheric pressure state on the suction side to a high pressure state on the discharge side, and when stopped in this state, compressed air / lubricating oil on the discharge side flows backward to the suction side. Usually, the valve body 24 in the suction valve 2 is completely closed earlier than the reverse flow speed, and control is performed so that air and lubricating oil do not leak out of the compressor body. Although the check pipe 5A is attached to the recovery pipe branch pipe 4A connected to the suction valve secondary side where the high-pressure compressed air / lubricating oil flows backward as described above, a slight amount is caused by the delay in closing the check valve 5. There is a leak. This leakage becomes pressure pulsation and starts to flow back to the recovery pipe 4, but the pressure is dispersed at the point where it joins the pipe to the suction valve primary side, and does not reach the mechanical seal outer groove 11. Therefore, the lubricating oil does not jump out of the mechanical seal outer groove 11 and the periphery of the mechanical seal outer groove is kept clean.
[0031]
【The invention's effect】
Lubricating oil can be collected from the shaft seal device in the entire range of rotation speed control.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of the present invention.
FIG. 2 is a piping connection system diagram showing details of a portion of the embodiment shown in FIG. 1;
FIG. 3 is a partial sectional view showing details of a shaft seal device portion of the embodiment shown in FIG. 2;
FIG. 4 is a conceptual diagram showing the relationship between compressor rotation speed and suction negative pressure.
FIG. 5 is a lubricating oil recovery control time chart according to the embodiment of the present invention.
[Explanation of symbols]
1 Oil supply screw compressor body 2 Suction valve 3 Shaft seal device (mechanical seal)
4 Recovery Pipe 4A Recovery Pipe Branch Pipe 5 Check Valve 6 Restrictor 7 Electric Motor 8 Inverter 9 Lubricating Oil Recovery Controller 11 Mechanical Seal External Groove 21 Suction Valve Primary Port 22 Suction Valve Secondary Port 23 Spring 24 Valve Body 24A Piston 25 Valve seat 26 Cylinder

Claims (6)

In an oil supply type screw compressor having a suction valve that can be opened and closed by remote operation and performing capacity control by changing the number of revolutions, a storage means for temporarily storing lubricating oil leaked from a shaft seal device of a rotor, and the storage A recovery pipe for connecting the inlet and the inlet side of the intake valve to recover the lubricating oil of the storage means to the inlet side of the intake valve, and connecting the recovery pipe and the outlet side of the intake valve via a check valve When the recovery pipe branch pipe for recovering the lubricating oil in the storage means to the outlet side of the suction valve and the recovery oil collecting power of the recovery pipe are determined to be insufficient, the suction pipe is set for a preset time. And a lubricating oil recovery control means for closing the valve. 2. The oil supply type screw compressor according to claim 1, wherein when the compressor rotation speed is lower than a predetermined rotation speed, the lubricating oil recovery control means has insufficient lubricating oil recovery power of the recovery pipe. A lubricated screw compressor, characterized in that it is configured to determine. 2. The oil supply type screw compressor according to claim 1, wherein when the pressure on the suction valve entrance side becomes higher than a predetermined pressure, the lubricant recovery control means lacks the lubricant recovery force of the recovery pipe. It is comprised so that it may judge that it is having, The oil supply type screw compressor characterized by the above-mentioned. 2. The oil supply type screw compressor according to claim 1, wherein the lubricating oil recovery control means has a shortage of lubricating oil recovery power in the recovery pipe when the oil level position of the storage means becomes higher than a predetermined position. It is comprised so that it may judge that it is having, The oil supply type screw compressor characterized by the above-mentioned. The oil supply type screw compressor of any one of Claims 1-4 WHEREIN: The throttle mechanism was provided in the said piping piping for collection | recovery, The oil supply type screw compressor characterized by the above-mentioned. A suction valve that can be opened and closed by remote operation, a storage means for temporarily storing lubricating oil leaked from the shaft seal device of the rotor, a recovery pipe connecting the inlet side of the suction valve, the recovery pipe and the suction In a control method for an oil-fed screw compressor that includes a recovery pipe branch pipe that connects the outlet side of a valve via a check valve, and performs capacity control by changing the rotation speed, the rotation speed of the compressor is set in advance. A control method for an oil supply type screw compressor, wherein the suction valve is closed for a preset time when the rotation speed falls below a predetermined rotational speed.

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