JP2024130382A - Shaft seal device - Google Patents

Abstract

To provide a shaft seal device which can be used at a high speed and can exert a high sealing property even during rotation stop.SOLUTION: One end of a cylinder 62 formed in a shaft seal 61 is inserted into a gear chamber 131, and a cylindrical piston is inserted into the cylinder 62, and is movable between a first movement position which is a movement position corresponding to a pressure (negative pressure) inside the gear chamber 131 when an output shaft 51 of a motor is rotated, and a second movement position which is a movement position corresponding to a pressure (pressure of ambient air pressure or more) inside the gear chamber 131 when the motor is stopped. When the output shaft 51 is rotated, a seal material 66 is moved away from a stepped part 22a and sealing is performed by a non-contact seal part 68 formed by a fine interval δ between an inner periphery of the piston 63 and an outer periphery of a rotational shaft 20. When the output shaft 51 is stopped, sealing is performed by a contact seal part 69 in which the seal material 66 is moved to the second movement position and seals a gap S between one end surface 63a of the piston 63 and the stepped part 22a.SELECTED DRAWING: Figure 3

Description

The present invention relates to a shaft seal device, and more specifically, to a shaft seal device used to seal the gap between the inner circumference of a shaft hole and the outer circumference of a rotating shaft in various devices that have a shaft hole in a casing and a rotating shaft inserted into the shaft hole.

In equipment such as screw compressors that house a rotating body such as a screw rotor in a rotor chamber formed inside a casing, a rotating shaft such as a rotor shaft protruding from the end of the screw rotor is inserted into a shaft hole provided in the casing, and the gap between the inner circumference of the shaft hole and the outer circumference of the rotating shaft is sealed with a shaft seal device, a process known as "shaft sealing."

By sealing the shaft in this way, it is possible to prevent leakage of fluid from the rotor chamber depending on the shaft seal position, to prevent the lubricating oil supplied to the bearings that support the rotor shaft from entering the rotor chamber, and to prevent leakage outside the machine.

The seals installed in this shaft sealing device include non-contact seals such as labyrinth seals and viscoseals (screw seals), and contact seals such as lip seals and mechanical seals.

As an example of a shaft seal device that employs a non-contact seal, Patent Document 1, which is listed below, discloses a shaft seal device 360 that seals between the inner circumference of a shaft hole 310 provided in a casing on the suction side of an oil-free screw compressor and the outer circumference of a rotor shaft 320.

As shown in FIG. 9, this shaft seal device 360 has an air seal portion 361 that seals gas, an oil thrower seal portion 362 that seals oil from the bearing 330, and a seal box portion 363 provided between the air seal portion 361 and the oil thrower seal portion 362, and the seal box portion 363 is open to the atmosphere via an air vent hole 364.

In addition, Patent Document 2, which is listed below, describes a shaft seal device 460 that seals the shaft seal on the discharge side of a screw compressor by combining a non-contact seal and a contact seal.

As shown in FIG. 10, this shaft seal device 460 is configured such that, in the space between the outer periphery of the rotor shaft 420 of the screw rotor 402 and the inner periphery of the shaft hole 410, a first non-contact seal 461, a second non-contact seal 462, and a lip seal 463 are arranged in that order from the screw rotor 402 side, and an oil supply passage 465 that supplies lubricating oil to a first seal space 464 between the first non-contact seal 461 and the second non-contact seal 462 is connected, and a communication hole 467 is provided that connects the second seal space 466 between the second non-contact seal 462 and the lip seal 463 to a space below the withstand pressure of the lip seal 463 (opening to the atmosphere).

JP 2011-256828 A JP 2009-287413 A

In the shaft seal device 360 described in the above-mentioned Patent Document 1, the air seal portion 361 prevents compressed gas from leaking from the rotor chamber, and the oil cutter seal portion 362 prevents the lubricating oil supplied to the bearing 330 from entering the rotor chamber.

However, the air seal portion 361 and the oil thrower seal portion 362 used in the shaft seal device 360 of Patent Document 1 are both non-contact seals that perform sealing through a small gap formed between them and the rotor shaft 320.

Since this type of non-contact seal does not come into contact with the outer surface of the rotor shaft 320, there is almost no friction, making it suitable for sealing a rotating shaft that rotates at high speeds, such as the rotor shaft 320 of an oil-free screw compressor. However, because it is non-contact, it has a lower ability to seal fluids than a contact seal.

In addition, even when using a dynamic pressure type non-contact seal such as Viscoseal, which improves sealing performance by utilizing the dynamic pressure generated by the rotation of the rotating shaft, the leakage prevention effect is greatly reduced when the rotating shaft is rotating at a low speed or is stopped.

For this reason, although the shaft seal device 360 described in Patent Document 1 employs a viscoseal (screw seal) as the oil cutter seal portion 362, when the rotation of the screw rotor is stopped as the compression operation is stopped, the leakage prevention effect of the oil cutter seal portion decreases and it becomes impossible to prevent leakage of lubricating oil from the bearing 330, and there is a risk that the lubricating oil supplied to the bearing 330 will seep into the rotor chamber side of the oil-free screw compressor, where the intrusion of oil must be avoided.

In contrast, the shaft seal device 460 described in the above-mentioned Patent Document 2 uses a lip seal 463 to seal against leakage of lubricating oil from the bearing 430.

This lip seal 463 has a lip made of an elastic material such as synthetic rubber, and the tip of the lip is pressed against the outer circumference of the rotor shaft 420, which is the rotating shaft, to create a seal without any gaps. This has the advantage that it has a higher airtightness than a non-contact seal and can be sealed even when the rotor shaft 420 is stopped rotating.

As a result, the configuration described in Patent Document 2 makes it possible to prevent the lubricating oil supplied to the bearing 430 from entering the rotor chamber even when the rotor shaft 420 has stopped rotating by stopping the operation of the screw fluid machine.

However, the lip seal 463 that seals against oil leakage from the bearing 430 in the shaft sealing device 460 described in Reference 2 has a structure in which the tip of the synthetic rubber lip is pressed against the outer periphery of the rotor shaft 420 as described above. Therefore, when used to seal a rotating shaft that rotates at high speeds, for example at a peripheral speed of more than 20 m/s, such as in an oil-free screw compressor that requires the screw rotor to rotate at high speeds, there is a drawback in that it cannot be used to seal a high-speed rotating shaft because it will be damaged by frictional heat, wear, etc.

In the shaft seal device 460 described in Patent Document 2, in order to compensate for the drawbacks of the lip seal 463 and enable sealing of a rotating shaft rotating at high speed, lubricating oil is supplied to the first seal space 464 formed between the first non-contact seal 461 and the second non-contact seal 462, and lubricating oil leaked from the second non-contact seal 462 is supplied to the lip seal 463, thereby preventing deterioration and damage caused by overheating of the lip seal 463 and successfully increasing the rotational speed of the rotor shaft 420 (paragraph [0023] of Patent Document 2).

Thus, in the configuration described in Patent Document 2, the shaft seal device 460 employs a contact seal (lip seal) 463, making it possible to seal a high-speed rotating shaft. However, to achieve this, the shaft seal device 460 must be provided with a total of three seals, consisting of two non-contact seals 461, 462 and one contact seal 463, and an oil supply passage 465 and a communication hole 467 must be drilled into the casing, making the structure of the shaft seal device 460 complex.

Furthermore, in order for the lip seal 463 to be applicable to sealing a high-speed rotating shaft, it is essential to supply oil to the first seal space 464. Therefore, when the screw rotor 402 stops rotating and the pressure in the rotor chamber on the discharge side drops, there is a risk that the lubricating oil supplied to the first seal space 464 will enter the rotor chamber.

For this reason, although the shaft seal device 460 described in Patent Document 2 can be used as a shaft seal device for an oil-cooled screw compressor that compresses the compressed gas together with lubricating oil, its applications are limited, such as not being able to be used as a shaft seal device for an oil-free screw compressor that compresses the compressed gas without oil in order to obtain compressed gas that does not contain oil.

As described above, a shaft seal device consisting only of a non-contact seal has the advantage that it can be used to seal a high-speed rotating shaft, but it has lower leakage prevention performance compared to a shaft seal device equipped with a contact seal, and even if an attempt is made to improve leakage prevention performance by adopting a dynamic pressure type non-contact seal, it is difficult to prevent leakage during low-speed rotation, especially when the rotation is stopped.

On the other hand, a shaft seal device that uses a contact seal instead of or in addition to a non-contact seal can improve leakage prevention performance and can seal the shaft seal even when the rotating shaft is stopped, but it cannot be used to seal a rotating shaft that rotates at high speeds, or if it is used to seal such a rotating shaft that rotates at high speeds, the structure becomes complicated, as it requires oiling the friction parts, and its uses are restricted, as it cannot be used as a shaft seal device for oil-free screw compressors.

The present invention was made to eliminate the drawbacks of the above-mentioned conventional technology, and aims to provide a shaft seal device that can be used to seal a high-speed rotating shaft, while still providing high sealing performance even during low-speed rotation or when the rotation is stopped.

Below, the means for solving the problem are described together with the reference symbols used in the description of the embodiment of the invention. These reference symbols are described to clarify the correspondence between the description of the claims and the description of the embodiment of the invention, and needless to say, are not used in a restrictive manner in interpreting the technical scope of the present invention.

In order to achieve the above object, the shaft seal device 60 of the present invention comprises:
A shaft seal device 60 for sealing a gap between an inner peripheral surface of the shaft hole 61 and an outer peripheral surface of the rotating shaft 20 of an apparatus having a shaft hole 61 formed in a casing 10 and a rotating shaft 20 inserted into the shaft hole 61,
A cylinder 62 is formed concentrically with the rotating shaft 20 within the shaft hole 61, and one end of the cylinder 62 is connected to a variable pressure space 15, which is a space within the casing 10 in which the internal pressure changes with the change in the rotation speed of the rotating shaft 20.
A cylindrical piston having an opening 64 at the center through which the rotating shaft 20 is inserted with a small gap δ is inserted into the cylinder 62, and the rotating shaft 20 is movable in the axial direction between a first movement position which is a movement position corresponding to the pressure in the pressure change space 15 when the rotating shaft 20 exceeds a predetermined rotation speed, and a second movement position which is a movement position corresponding to the pressure in the pressure change space 15 when the rotating shaft is at or below the predetermined rotation speed; a stepped portion 22a is formed on the rotating shaft 20 so as to closely face one end face 63a of the piston 63 with a predetermined gap S therebetween, and an endless annular sealing material 66 is attached to either one or both of the one end face 63a and/or the stepped portion 22a of the piston 63 and surrounding the outer periphery of the rotating shaft 20;
When the piston 63 is in the second moving position, the seal member 66 forms a contact seal portion 69 that seals the space S between the one end face 63 a of the piston 63 and the step portion 22 a in a contact state,
When the piston 63 moves to the first moving position, the seal between the one end face 63a of the piston 63 and the step portion 22a is released and sealing is performed by the non-contact seal portion 68 formed by the minute gap δ between the inner surface of the piston 63 and the outer periphery of the rotating shaft 20 (claim 1).

The shaft seal device 60 configured as above may be provided with a biasing means 70 such as a spring that biases the piston 63 to the first movement position or the second movement position (Claim 2).

It is preferable to provide a spiral groove 22b on the outer peripheral surface of the rotating shaft 20 in a portion facing the inner peripheral surface of the piston 63 in the first moving position (claim 3).

In this case, it is preferable that the rotating shaft 20 is configured to have a rotating shaft body 21 and a collar 22 fitted onto the rotating shaft body 21, and that the step portion 22a and the spiral groove 22b are formed on the collar 22 (claim 4).

Furthermore, the shaft seal device 60 configured as described above can be provided with a stopper portion 90 that abuts against the outer peripheral portion 63a' of the one end face 63a of the piston 63 in the second movement position (claim 5).

In the shaft seal device 60 of the present invention described above, when the rotation speed of the rotating shaft 20 exceeds a predetermined rotation speed, the piston 63 moves to the first moving position, one end face 63a of the piston 63 separates from the step portion 22a, and the seal provided by the sealing material 66 is released, and sealing is performed only by the non-contact seal portion 68 formed by the minute gap δ formed between the inner surface of the piston 63 and the outer surface of the rotating shaft.

On the other hand, when the rotation speed of the rotating shaft 20 is below a predetermined rotation speed (including stopping and reversing the rotation), the piston 63 moves to the second movement position, one end face 63a of the piston 63 is positioned close to the step portion 22a, and the gap between one end face 63a of the piston 63 and the step portion 22a is sealed by the sealing material 66, forming a contact seal portion 69.

As a result, in the shaft seal device 60 of the present invention, when the rotating shaft 20 exceeds a predetermined rotation speed, i.e. when it is rotating at high speed, only the non-contact seal portion 68 seals, and the seal material 66 does not seal. Therefore, even when used to seal a high-speed rotating shaft, problems such as burning or wear of the seal material 66 do not occur. On the other hand, when the rotation speed of the rotating shaft 20 falls below a predetermined rotation speed (including stopping and reverse rotation), the seal material 66 seals the gap between one end face 63a of the piston 63 and the step portion 22a, forming a contact seal portion 69, which is formed by sealing the gap between the end face 63a of the piston 63 and the step portion 22a, thereby achieving a high level of sealing that cannot be achieved by the non-contact seal portion 68.

In this way, the present invention has been able to provide an innovative shaft seal device 60 that retains the advantages of both non-contact and contact seals while eliminating the disadvantages of both seals.

In a configuration in which a spiral groove 22b is formed on the outer periphery of the rotating shaft 20 in a portion facing the inner periphery of the piston 63 in the first moving position, the generation of dynamic pressure accompanying the rotation of the rotating shaft 20 can improve the sealing performance of the non-contact seal portion 68 when the rotating shaft 20 rotates.

The rotating shaft 20 is configured to include a rotating shaft body 21 and a collar 22 fitted onto the rotating shaft body 21, and the collar 22 is formed with the step portion 22a and the spiral groove 22b. Even if the spiral groove 22b is scratched by dirt getting caught and the sealing performance of the non-contact seal portion 68 is reduced, or if the sealing performance of the contact seal portion 69 is reduced due to wear of the step portion 22a (wear of the seal material 66 if a seal material 66 is provided on the step portion 22a side), it is possible to relatively easily restore the condition before the damage or wear occurred by simply replacing the collar 22 portion without replacing the entire rotating shaft 20.

By providing a stopper portion 90 that abuts against the outer peripheral portion 63a' of the one end face 63a of the piston 63 in the second movement position to restrict the movement of the piston 63, the gap S formed between the one end face 63a of the piston 63 in the second movement position and the step portion 22a is always constant, and the amount of pressure applied by the seal material 66 against the step portion 22a (the one end face 63a of the piston 63 when the seal material 66 is provided on the step portion 22a side) can be made constant.

This prevents the sealing material 66 from being pressed down too hard, making the structure less susceptible to deterioration.

In addition, by maintaining a constant distance S between one end face 63a of the piston 63 and the step portion 22a in this manner, it is possible to reduce the likelihood of damage, etc., even when a lip seal, which has a relatively low strength but high conformability to the surface of the rotating shaft 20 and high sealing performance, is used as the sealing material 66 that seals that portion.

1 is a cross-sectional view of a screw compressor equipped with a shaft sealing device of the present invention. FIG. 2 is an enlarged view of a shaft seal device portion in the screw compressor of FIG. 1 . 3A is an enlarged view of the upper portion of the shaft seal device of FIG. 2, in which (A) shows a state in which the piston is in a first movement position, and (B) shows a state in which the piston is in a second movement position. 1A is an enlarged view of the upper part of a shaft sealing device in a modified example (an example in which a spiral groove and a step portion are formed directly on the rotating shaft), where (A) shows the piston in a first moving position, and (B) shows the piston in a second moving position. 1A and 1B are enlarged views of the upper part of a shaft seal device in a modified example (an example in which the piston is operated by utilizing the negative pressure generated in the variable pressure space), in which (A) shows the piston in the second movement position, and (B) shows the piston in the first movement position. 1A and 1B are enlarged views of the upper part of a shaft sealing device in a modified example (an example in which the shaft sealing device is used to seal the discharge side of a screw compressor), in which (A) shows the piston in a second movement position, and (B) shows the piston in a first movement position. 1A and 1B are enlarged views of the upper portion of a shaft seal device in a modified example (a configuration in which a stopper portion is provided that abuts against the outer peripheral portion of one end face of the piston), in which (A) shows the piston in a first moving position, and (B) shows the piston in a second moving position. 11A and 11B are enlarged views of the upper portion of a shaft sealing device in a modified example (modified example of a stopper portion), in which (A) shows the piston in a first movement position, and (B) shows the piston in a second movement position. FIG. 1 is an explanatory diagram of a conventional shaft seal device (corresponding to FIG. 1 of Patent Document 1). FIG. 2 is an explanatory diagram of a conventional shaft seal device (corresponding to FIG. 2 of Patent Document 2).

Below, an embodiment of the present invention will be described with reference to the attached drawings.

In the embodiment described below, the shaft seal device 60 of the present invention is used to seal the shaft of a screw compressor 1, but the application of the shaft seal device 60 of the present invention is not limited to the screw compressor 1, and it can be applied to various known devices as long as the device has a space (variable pressure space) in the casing where the internal pressure changes in response to changes in the rotational speed of the rotating shaft.

[Overall configuration of screw compressor]
FIG. 1 shows the overall configuration of a screw compressor 1 equipped with a shaft sealing device 60 of the present invention.

The casing 10 of this screw compressor 1 is composed of a rotor casing 11, a suction side casing 13 provided at the suction side end of the rotor casing 11, and a discharge side casing 12 attached to the discharge side end of the rotor casing 11. A pair of male and female screw rotors 2, 3 are housed in a rotor chamber 113 formed in the rotor casing 11 so that they can mesh and rotate.

The rotor casing 11 is formed in a cylindrical shape that opens the rotor chamber 113 at the discharge end, and has an axial hole formed at the suction end to accommodate the suction side rotor shafts 2b, 3b of the screw rotors 2, 3. A bearing is housed in the bearing chamber formed in this axial hole, and this bearing supports the suction side rotor shafts 2b, 3b of the male and female screw rotors 2, 3.

A gear chamber 131 is formed in the suction side casing 13 provided at the suction side end of the rotor casing 11, and this gear chamber 131 houses a speed increasing device 30 that increases the rotational driving force from the motor 50 and inputs it to either the male or female screw rotor 2, 3.

This speed increasing device 30 is, for example, composed of a driven gear 31 attached to the suction side rotor shaft of one of the screw rotors 2 or 3 (in the illustrated embodiment, the suction side rotor shaft 2b of the male rotor 2) and a driving gear 32 with a larger diameter than the driven gear 31. The tip of the output shaft 51 of the motor 50 is inserted into the gear chamber 131 through the shaft hole 61 provided in the suction side casing 13, and the aforementioned driving gear 32 is attached to the tip of the output shaft 51 of the motor 50. The rotational driving force input via the output shaft 51 of the motor 50 is accelerated and transmitted to the suction side rotor shaft 2b of the male rotor 2, and the screw rotors 2 and 3 can be rotated at an accelerated speed.

The discharge side end of the rotor casing 11 is covered by a discharge side casing 12 that has an axial hole that accommodates the discharge side rotor shafts 2a, 3a of the male rotor 2 and female rotor 3, and the discharge side rotor shafts 2a, 3a of the screw rotors 2, 3 are supported by bearings housed in a bearing chamber formed in the axial hole of the discharge side casing 12.

The rotor casing 11 is formed with an intake port (not shown) and an intake space 117 that communicates with the intake port. The compressed gas introduced into the intake space 117 of the rotor chamber 113 through the intake port (not shown) is introduced into the compression action space defined by the pair of male and female screw rotors 2, 3 and the inner wall of the rotor chamber 113, where it is compressed, and is then discharged outside the machine through a discharge port (not shown) provided at the discharge end of the rotor casing 11.

[Shaft seal device]
The suction side casing 13 of the screw compressor 1 constructed as described above has a shaft hole 61 that is penetrated by the output shaft 51 of the motor 50, as shown in Figures 2 and 3, and the gap between the inner surface of this shaft hole 61 and the outer periphery of the output shaft 51 is sealed by the shaft seal device 60 of the present invention.

Therefore, in the embodiment shown in Figures 1 to 3, the output shaft 51 of the motor 50 is the rotating shaft 20 to be sealed by the shaft seal device 60 of the present invention.

In the shaft seal device 60 of the present invention, a cylinder 62 is formed in the aforementioned shaft hole 61, which is concentric with the output shaft 51 of the motor 50, which is the rotating shaft 20. One end of this cylinder 62 is connected to the gear chamber 131 formed in the suction side casing 13, and the other end is connected to the space outside the casing.

The gear chamber 131, to which one end of the cylinder 62 is connected, is in communication with the suction space 117 (see FIG. 1) formed in the rotor casing 11, and is therefore slightly negative relative to atmospheric pressure when the screw rotors 2 and 3 are rotating. On the other hand, when the motor 50 is stopped and the screw rotors 2 and 3 are stopped from rotating, the compressed gas that was being compressed expands and flows back into the suction space 117 (the screw rotors 2 and 3 may rotate slightly in the opposite direction during this backflow), causing the pressure in the gear chamber 131, which is in communication with the suction space 117, to rise. In the illustrated embodiment, the gear chamber 131, which is in communication with one end of the cylinder 62, is a pressure-changing space 15 in which the internal pressure rises from a negative pressure to a pressure above atmospheric pressure when the rotational speed of the motor output shaft 51, which is the rotating shaft 20, exceeds a predetermined rotational speed (circumferential speed 0 m/s) and when it is below that rotational speed (circumferential speed 0 m/s or a state in which it rotates slightly in the opposite direction, which is a negative rotational speed).

In this way, a cylindrical piston 63 that moves back and forth in the axial direction of the rotating shaft 20 is housed in the cylinder 62, one end of which is connected to the gear chamber 131, which is the pressure change space 15, so as not to rotate within the cylinder 62, as shown in Figures 2 and 3.

In the center of this piston 63, an opening 64 is formed with a diameter slightly larger than the outer diameter of the rotating shaft 20. By inserting the rotating shaft 20 into this opening 64 and storing it in the cylinder 62, a minute gap δ is formed between the inner surface of the opening 64 of the piston 63 and the outer periphery of the rotating shaft 20, which is necessary to allow the rotating shaft 20 to rotate.

The gap between the outer circumferential surface of the piston 63 and the inner circumferential surface of the cylinder 62 is sealed by an O-ring 65 to prevent fluid from leaking through the gap.

The portion of the rotating shaft 20 located inside the shaft hole 61 has a step 22a formed by changing the outer diameter of the rotating shaft 20 at that portion, and an endless ring-shaped seal material 66 is attached to one end face 63a of the piston 63 that faces this step 22a so as to surround the outer periphery of the rotating shaft 20.

In the illustrated embodiment, the seal 66 is attached to one end surface 63a of the piston 63, but the seal 66 may be attached to the step portion 22a side instead, or the seal 66 may be attached to both one end surface 63a of the piston 63 and the step portion 22a.

The seal material 66 can be any of a variety of known seal materials made of elastic materials such as synthetic rubber, and is not limited to the example shown in the figure. Lip seals and other seal materials can also be used. Depending on the application of the shaft seal device 60, a metal seal material may also be used.

In the cylinder 62, the piston 63 is configured to be movable between a predetermined first movement position, which is a movement position corresponding to the pressure in the pressure change space 15 (gear chamber 131) when the rotating shaft 20 (output shaft 51) is in a rotational state exceeding a predetermined rotational speed, and a predetermined second movement position, which is a movement position corresponding to the pressure in the pressure change space 15 (gear chamber 131) when the rotating shaft 20 (output shaft 51) is in a state of being equal to or lower than the predetermined rotational speed. In the illustrated embodiment, a shaft hole cover 67 is provided to cover the outer peripheral portion of the end of the shaft hole 61 on the gear chamber 131 side, and the movement position shown in FIG. 3(A) where the other end face 63b of the piston 63 abuts against this shaft hole cover 67 is set as the first movement position. When the piston 63 is in the first movement position, the seal material 66 provided on one end face 63a of the piston 63 is separated from the step portion 22a provided on the rotating shaft 20 and is in a non-contact state, and sealing is performed only by the non-contact seal portion 68 formed by the minute gap δ formed between the inner peripheral surface of the piston 63 and the outer peripheral surface of the rotating shaft 20.

In this embodiment, in order to improve the sealing performance of the non-contact seal portion 68, a spiral groove 22b is formed on the outer peripheral surface of the rotating shaft 20 at least in the portion facing the inner peripheral surface of the piston 63 in the first moving position, and a flow of fluid toward the gear chamber 131 is generated in the small gap δ of the non-contact seal portion 68 by the rotation of the rotating shaft 20. However, such a spiral groove 22b is not necessarily provided, or a labyrinth groove (not shown) may be formed instead of the spiral groove 22b.

In addition, these spiral grooves 22b and labyrinth grooves (not shown) may be formed on the inner surface of the piston 63.

On the other hand, as shown in FIG. 3(B), the seal material 66 provided on one end face 63a of the piston 63 abuts against the step portion 22a, and the movement position in which the gap S between one end face 63a of the piston 63 and the step portion 22a is sealed by the seal material 66 is defined as the second movement position, and by the movement of the piston 63 to the second movement position, the gap S between one end face 63a of the piston 63 and the step portion 22a is blocked by the seal material 66, forming a contact seal portion 69.

In this embodiment, as shown in FIG. 3, the rotating shaft 20 is structured to include a rotating shaft body 21 and a collar 22 fitted onto the rotating shaft body 21, and the collar 22 is formed with the spiral groove 22b and step portion 22a. However, instead of this structure, as shown in FIG. 4, the rotating shaft 20 may be formed as an integral structure without a collar, and the spiral groove 22b and step portion 22a may be provided directly on the rotating shaft 20.

However, in the configuration shown in FIG. 3, in which the spiral groove 22b and the step portion 22a are provided on the collar 22 fitted onto the rotating shaft body 21, even if the spiral groove 22b is damaged by dirt getting caught in it, or if the step portion 22a is damaged and the sealing material 66 cannot be brought into close contact, reducing the sealing performance, it is economical to deal with this by replacing only the collar 22 without replacing the entire rotating shaft 20.

In addition, in the configuration shown in Figures 1 to 3, which is provided with a shaft seal device 60 to prevent leakage of lubricating oil from the gear chamber 131, which is the pressure change space 15, a spacer 23 is attached to the outer periphery of the rotating shaft body 21 on the machine outer side relative to the collar 22, and an oil cutter groove is provided by providing an annular irregularity on the outer periphery of this spacer 23.

However, as shown in Figure 4, it is not necessary to provide such a spacer 23 or oil drain groove.

The reference numeral 70 in Figs. 2 to 4 denotes a spring provided as a biasing means for biasing the piston 63. This biasing means 70 may be provided only when the piston 63 cannot be moved back and forth between the first and second movement positions by the pressure change in the variable pressure space 15 (gear chamber 131) alone, which changes in response to the change in the rotational speed of the rotating shaft 20.

In the configuration of the embodiment shown in Figures 3 and 4, the gear chamber 131, which is the pressure change space 15, becomes negative pressure when the rotating shaft 20 is rotating, and the piston 63 can be moved to the first movement position shown in Figure 3 (A) by suction caused by this negative pressure when the rotating shaft 20 is rotating without providing a biasing means 70. When the rotation of the rotating shaft 20 is stopped, the pressure in the gear chamber 131 increases due to the backflow of the compressed fluid during compression, so that the piston 63 can be moved to the second movement position shown in Figure 3 (B) without providing a biasing means 70. However, in order to make the operation of the piston 63 more stable, a compression spring is provided as the biasing means 70 to bias the piston 63 toward the first movement position.

However, as will be described in detail later, the biasing direction of the biasing means 70 can be appropriately selected according to the pressure change in the variable pressure space 15 and the direction of the fluid to be sealed, so that the piston 63 can be moved to the first movement position when the rotational speed of the rotating shaft 20 exceeds a predetermined rotational speed, and moved to the second movement position when the rotational speed is equal to or lower than the predetermined rotational speed.

[Action, etc.]
The operation of the shaft seal device 60 (see FIGS. 1 to 3) of the present invention, which is provided in the space between the shaft hole 61 provided in the suction side casing 13 of the screw compressor 1 having the configuration shown in FIG. 1 and the rotating shaft 20 which is the output shaft 51 of the motor 50, will be described as follows.

When the output shaft 51 of the motor 50, which is the rotating shaft 20, is rotating, and therefore when the screw rotors 2 and 3 housed in the rotor casing 11 are rotating, the meshing rotation of the screw rotors 2 and 3 creates a negative pressure in the suction space 117, and the pressure in the gear chamber 131 that communicates with this suction space 117 also becomes negative.

The cylinder 62 formed in the shaft hole 61 of the suction side casing 13 has one end connected to the gear chamber 131, which is the pressure change space 15, and the other end connected to the outside of the machine, which is a space at atmospheric pressure. Therefore, when the output shaft (rotating shaft) 51 of the motor 50 is rotating (a state in which the circumferential speed exceeds 0 m/s, which is a predetermined rotation speed), the piston 63 is in a state in which it has moved to the first moving position shown in FIG. 3(A) by suction due to the negative pressure in the gear chamber 131, which is the pressure change space 15 (and the biasing force of the biasing means 70, if a biasing means 70 is provided), and one end face 63a of the piston 63 and the step portion 22a are separated, and the seal material 66 is not in contact with the step portion 22a.

As a result, when the rotating shaft 20 rotates, the shaft seal device 60 seals only the non-contact seal portion 68 formed by the minute gap δ between the inner circumferential surface of the piston 63 and the outer circumferential surface of the rotating shaft 20, and the seal material 66 is not in contact with the stepped portion 22a. This prevents the seal material 66 from deteriorating due to burning or wear, even when the rotation speed of the output shaft 51 of the motor 50, which is the rotating shaft 20, is high (for example, a peripheral speed of 20 m/s or more).

On the other hand, when the motor 50 is stopped, the screw rotors 2 and 3 stop rotating and the compressed gas that was in the process of being compressed in the compression space starts to flow back toward the suction space 117, causing the pressure in the suction space 117 and the gear chamber 131 (transformed pressure space 15) connected to the suction space 117 to rise.

In addition, the screw rotors 2 and 3 may rotate slightly in the reverse direction due to the backflow of the compressed gas, and such reverse rotation of the screw rotors 2 and 3 may also cause the output shaft 51 of the motor 50, which is the rotating shaft 20, to rotate in the reverse direction (negative rotation speed).

In this way, when the rotation speed of the output shaft 51 of the motor 50, which is the rotating shaft 20, falls below a predetermined rotation speed (circumferential speed 0 m/s), the pressure in the gear chamber 131, which is the pressure change space 15, increases, and a force is applied to the piston 63 in the cylinder 62 to move it to the second movement position shown in Figure 3 (B). When this force exceeds the biasing force of the biasing means 70, the piston 63 moves to the second movement position.

When the piston 63 moves to this second movement position, the seal material 66 provided on one end face 63a of the piston 63 is pressed against the step portion 22a, and the gap S between the one end face 63a of the piston 63 and the step portion 22a is sealed by the seal material 66, forming a contact seal portion 69.

This makes it possible to prevent the leakage of lubricating oil that would otherwise leak out along with the air in the gear chamber 131 through the minute gap δ between the inner surface of the piston 63 and the outer periphery of the rotating shaft 20 (the rotating shaft collar 22).

In this way, in the configuration of the shaft seal device 60 shown in Figures 1 to 3, when the output shaft 51 of the motor (rotating shaft 20) rotates, sealing is performed by the non-contact seal portion 68, and the seal material 66 is separated from the step portion 22a, so that even when used to seal a high-speed rotating shaft, the seal material 66 can be prevented from being damaged by frictional heat or wear. On the other hand, when the rotation of the output shaft 51 of the motor (rotating shaft 20) stops (including a slight reversal after stopping), the seal material 66 is pressed against the step portion 22a to perform a highly airtight seal, resulting in a shaft seal device 60 that combines the advantages of both a non-contact seal and a contact seal.

In the above explanation given with reference to Figures 1 to 4, the shaft seal device 60 of the present invention is described as an example of a configuration in which the lubricating oil in the gear chamber 131 provided on the suction side of the screw compressor 1 is prevented from leaking outside the machine when the screw compressor 1 is stopped. However, the use of the shaft seal device 60 of the present invention is not limited to this, and various modifications are possible.

As an example, FIG. 5 shows an example in which a shaft hole 61 is provided at the suction end of the casing of a screw compressor 1, penetrating the inside and outside of the casing 10, and the gap between the outer periphery of the rotor shaft 2b of the male rotor inserted into this shaft hole 61 and the inner periphery of the shaft hole 61 is sealed with the shaft seal device 60 of the present invention.

In this example, as shown in FIG. 5, the shaft seal device 60 of the present invention is provided between the bearing 80 provided in the shaft hole 61 and the suction space 117, preventing the lubricating oil supplied to the bearing 80 from entering the suction space 117 formed in the rotor chamber 113.

Therefore, in the shaft seal device 60 shown in Figure 5, the rotor shaft 2b of the male rotor is the rotating shaft 20 to be sealed, and the suction space 117 to which one end of the cylinder 62 is connected is the variable pressure space 15 that provides the operating pressure to the piston 63.

In the embodiment shown in FIG. 5, a compression spring is provided as the biasing means 70 to bias the piston to the second movement position shown in FIG. 5(A).

In this way, by providing the shaft seal device 60 of the present invention in the position shown in FIG. 5, when the rotor shaft 2b (rotating shaft 20) is stopped or is rotating at a relatively low speed, the pressure in the suction space 117 (variable pressure space 15) is atmospheric pressure or a slight negative pressure, so that the force of the biasing means 70 presses the seal material 66 against the step portion 22a, and sealing is performed by the contact seal portion 69.

In contrast, when the rotation speed of the rotor shaft 2b (rotating shaft 20) increases, and therefore the rotation speed of the screw rotor increases and the negative pressure in the suction space 117 (pressure change space 15) increases, the cylinder 63 moves to the first movement position shown in FIG. 5(B), the seal material 66 moves away from the step portion 22a, and the seal at the contact seal portion 69 is released, and sealing is performed only by the non-contact seal portion 68 formed in the minute gap δ formed between the inner surface of the cylinder 63 and the outer surface of the rotating shaft (rotor shaft 2b).

This prevents the seal material 66 from deteriorating due to heat or wear, even when the rotor shaft 2b, which is the rotating shaft 20, is rotated at high speed.

After that, when the rotation of the rotor shaft 2b, which is the rotating shaft 20, stops and the screw rotor stops rotating, the pressure in the suction space 117 (pressure change space) increases due to the backflow of the compressed gas that was being compressed, and the piston 63 moves again to the second movement position shown in Figure 5 (A) and the gap between one end face 63a of the piston 63 and the step portion 22a is sealed with the sealing material 66, thereby sealing with the contact seal portion 69, and it is also possible to prevent the lubricating oil supplied to the bearing 80 from spraying out of the casing 10 due to the pressure increase in the suction space 117.

Furthermore, in the embodiment described above, the end of the cylinder 62 on the first moving position side (left side of the page) is connected to the pressure change space 15. However, instead of this configuration, as shown in FIG. 6, the end of the cylinder 62 on the second moving position side (right side of the page) may be used as one end connected to the pressure change space 15.

The embodiment shown in Figure 6 is an example in which the discharge side rotor shaft 2a of the male rotor 2 of a screw compressor is used as the drive shaft, and the shaft seal device 60 of the present invention is provided between the bearing 81 in the shaft hole 61 provided as a through hole in the discharge side casing 12 and the rotor chamber 113, thereby preventing the lubricating oil supplied to the bearing 81 attached in the shaft hole 61 from entering the rotor chamber 113.

In this configuration, the biasing means 70 is a tension spring that biases the piston 63 to the second movement position shown in Figure 6 (A).

By providing the shaft seal device 60 of the present invention at the above position, when the rotor shaft 2a on the discharge side, which is the rotating shaft 20, is stopped rotating, the pressure on the discharge side of the rotor chamber 113, which is the variable pressure space 15, is at atmospheric pressure, and the piston 63 is moved to the second movement position shown in Figure 6 (A) by the biasing force of the biasing means 70, and the seal material 66 is pressed against the step portion 22a to form a contact seal portion 69.

When the screw rotor starts to rotate by rotating the discharge side rotor shaft (rotating shaft) 2a from this state, the pressure on the discharge side of the rotor chamber 113, which is the pressure change space 15, rises and the piston 63 moves to the first moving position shown in FIG. 6(B) against the biasing force of the biasing means 70, causing the sealing material 66 to move away from the step portion 22a, releasing the sealing state by the contact seal portion 59, and switching to sealing by the non-contact seal portion 68 formed by the minute gap δ formed between the inner surface of the piston 63 and the outer surface of the rotating shaft (rotor shaft 2a).

Thus, even in the configuration shown in FIG. 6, the contact seal portion 69 can provide a seal when the rotor shaft 2a, which is the rotating shaft 20, is stopped from rotating. However, when the rotor shaft 2a starts to rotate, the seal material 66 moves away from the step portion 22a, and the seal at the contact seal portion 69 is released. Therefore, even when the rotor shaft 2a is rotated at high speed, it is possible to prevent the seal material 66 from deteriorating due to frictional heat or wear.

In the shaft seal device 60 of the present invention described above, a configuration example is shown in which a biasing means 70 is provided to bias the piston 63 to the first movement position or the second movement position. However, in the configuration example of the shaft seal device 60 described with reference to Figures 1 to 4, for example, when the rotation of the rotating shaft 20 (drive shaft 51) causes negative pressure in the gear chamber 131, which is the pressure change space 15, as described above, even if such a biasing means 70 is not provided, it is possible to move the piston 63 between the first movement position and the second movement position in response to changes in the rotational speed of the rotating shaft, and the biasing means 70 is not necessarily required.

In addition, in the illustrated example, a configuration for sealing the rotating shaft 20 arranged horizontally has been described, but when the shaft sealing device 60 of the present invention is used to seal an equipment in which the rotating shaft 20 can be arranged vertically, the movement of the piston 63 to either the first moving position or the second moving position may be performed using gravity instead of the biasing by the biasing means 70 described above, and depending on the configuration of the equipment to which the shaft sealing device 60 of the present invention is applied, the biasing means 70 may not necessarily be provided.

[Modifications]
In the embodiments described above with reference to Figures 1 to 6, a configuration is adopted in which the position where the piston 63 cannot move because the sealing material 66 provided on one end face 63a of the piston 63 is pressed against the step portion 22a, is the second movement position described above.

However, with this configuration, the seal material 66 may be pressed against the step portion 22a more strongly than necessary, and if the rotating shaft 20 is rotated (including in the reverse direction) in this state, deterioration of the seal material 66 may still occur.

In order to prevent the sealing material 66 from being pressed against the step portion 22a more strongly than necessary, in the embodiment shown in FIG. 7, a stopper portion 90 is provided that abuts against the outer peripheral portion 63a' of one end face 63a of the piston 63 in the second movement position shown in FIG. 7(B). When the piston 63 moves to the second movement position, the outer peripheral portion 63a' of one end face 63a of the piston 63 abuts against the stopper portion 90 to restrict the movement, so that a constant distance is maintained between one end face 63a of the piston 63 and the step portion 53a.

In the embodiment shown in FIG. 7, the outer peripheral portion 63a' of one end face 63a of the piston 63 is made to protrude to the right side of the page to form a protrusion, and this protrusion is abutted against a stopper portion 90 consisting of the end wall on the outer side of the cylinder 62, making it possible to stop the movement of the piston 63 at the second movement position.

In addition, as long as the stopper portion 90 can abut against the outer peripheral portion 63a' of one end face 63a of the piston 63 to restrict the movement of the piston 63, it may be formed by moving the position of the outer end wall of the cylinder 62 that constitutes the stopper portion 90 to the inner side of the machine, as shown in FIG. 8 as a modified example, instead of the configuration shown in FIG. 7 in which a protrusion is provided on the outer peripheral portion 63a' of one end face 63a of the piston 63, and is not limited to the example shown in the figure as long as it can maintain a constant distance S between the one end face 63a of the piston 63 and the step portion 22a.

However, as explained with reference to FIG. 7, in a configuration in which a protrusion is provided on the outer peripheral portion 63a' of one end face 63a of the piston 63, it is possible to provide a bearing material (wear ring) 65' in addition to the O-ring 65 on the outer peripheral surface of the piston 63 to increase the lubrication of the piston 63 and to improve the sealing of the gap between the outer peripheral surface of the piston 63 and the inner peripheral surface of the cylinder 62 by preventing eccentricity of the piston and protecting the O-ring 65, thereby improving the sealing against leakage of fluid through the gap between the outer peripheral surface of the piston 63 and the inner peripheral surface of the cylinder 62.

1 Screw compressor 2 Screw rotor (male)
2a Discharge side rotor shaft (male screw rotor)
2b Intake side rotor shaft (male screw rotor)
3 Screw rotor (female)
3a Discharge side rotor shaft (female screw rotor)
3b Intake side rotor shaft (female screw rotor)
REFERENCE SIGNS LIST 10 Casing 11 Rotor casing 113 Rotor chamber 117 Suction space 12 Discharge side casing 13 Suction side casing 131 Gear chamber 15 Pressure change space 20 Rotating shaft 21 Rotating shaft main body 22 Collar 22a Step portion 22b Spiral groove 23 Spacer 30 Speed increasing device 31 Driven gear 32 Driving gear 50 Motor 51 Output shaft 60 Shaft seal device 61 Shaft hole 62 Cylinder 63 Piston 63a One end face (of the piston)
63a': Outer circumferential portion of one end face 63b: Other end face 64: Opening (of piston)
65 O-ring 65' Bearing material (wear ring)
66 Sealing material 67 Shaft hole cover 68 Non-contact seal portion 69 Contact seal portion 70 Urging means (spring)
Reference Signs List 80, 81 Bearing 90 Stopper portion 310 Shaft hole 320 Rotor shaft 330 Bearing 360 Shaft seal device 361 Air seal portion 362 Oil thrower seal portion 363 Seal box portion 364 Atmospheric release hole 402 Screw rotor 410 Shaft hole 420 Rotor shaft 430 Bearing 460 Shaft seal device 461 First non-contact seal 462 Second non-contact seal 463 Lip seal 464 First seal space 465 Oil supply passage 466 Second seal space 467 Communication hole δ Micro gap S Spacing (between one end face of the piston and the step portion)

Claims (5)

A shaft seal device for sealing a gap between an inner peripheral surface of a shaft hole formed in a casing and an outer peripheral surface of a rotating shaft of an equipment having a rotating shaft inserted into the shaft hole,
a cylinder is formed in the axial hole and is concentric with the rotating shaft, and one end of the cylinder is connected to a variable pressure space, which is a space in the casing in which the internal pressure changes with the change in the rotation speed of the rotating shaft;
A cylindrical piston having an opening at the center through which the rotating shaft is inserted with a small gap is inserted into the cylinder, and the piston is movable in the axial direction of the rotating shaft between a first movement position which is a movement position corresponding to the pressure in the variable pressure space when the rotating shaft is rotating at a speed exceeding a predetermined rotational speed, and a second movement position which is a movement position corresponding to the pressure in the variable pressure space when the rotating shaft is rotating at a speed equal to or lower than the predetermined rotational speed,
a step portion is formed on the rotating shaft so as to closely face one end face of the piston with a predetermined gap therebetween at the second moving position, and an endless annular seal material surrounding an outer periphery of the rotating shaft is attached to either one or both of the one end face of the piston and/or the step portion;
When the piston is in the second moving position, the sealing material forms a contact seal portion that seals the gap between the one end face of the piston and the step portion in a contact state,
A shaft seal device characterized in that, when the piston moves to the first moving position, the seal between the one end face of the piston and the step portion is released and sealing is performed by a non-contact seal portion formed by the minute gap between the inner surface of the piston and the outer periphery of the rotating shaft. The shaft seal device according to claim 1, characterized in that it is provided with a biasing means for biasing the piston to the first movement position or the second movement position. The shaft seal device according to claim 1 or 2, characterized in that a spiral groove is formed on the outer peripheral surface of the rotating shaft in a portion facing the inner peripheral surface of the piston in the first moving position. The shaft seal device according to claim 3, characterized in that the rotating shaft comprises a rotating shaft body and a collar fitted onto the rotating shaft body, and the step portion and the spiral groove are formed on the collar. 3. The shaft seal device according to claim 1, further comprising a stopper portion which abuts against an outer peripheral portion of said one end face of said piston at said second movement position.

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