JP7539828B2 - Shaft seal structure of oil-cooled screw compressor - Google Patents

Description

The present invention relates to a shaft seal structure for an oil-cooled screw compressor, and more specifically, to a shaft seal structure for preventing compressed gas from leaking from the rotor chamber through the gap between the discharge side rotor shaft and the shaft hole provided in the screw rotor of an oil-cooled screw compressor.

The oil-cooled screw compressor 100 houses a pair of male and female screw rotors 140, 150 that can mesh and rotate in a rotor chamber 111 formed in a casing, and compresses the gas to be compressed together with lubricating oil by the meshing rotation of the pair of screw rotors 140, 150 and discharges it as a gas-liquid mixed fluid. It is used to compress various types of gas.

As described above, this oil-cooled screw compressor 100 compresses the compressed gas together with lubricating oil and discharges it as a gas-liquid mixed fluid. Therefore, in order to supply compressed gas to the consumption side to which a pneumatic work machine or the like is connected, it is necessary to remove the lubricating oil from the gas-liquid mixed fluid discharged by the oil-cooled screw compressor 100.

As shown in FIG. 6, the oil-cooled screw compressor 100 is driven by a driving source 210 such as an engine or a motor, and the gas-liquid mixture fluid discharged from the oil-cooled screw compressor 100 is first introduced into a receiver tank 220 for gas-liquid separation, and the compressed gas from which the lubricating oil has been separated is then supplied to the consumer side via a check valve 221.

On the other hand, the lubricating oil recovered in the receiver tank 220 is supplied again to the compressor body via an oil supply pipe 224 equipped with an oil filter 222 and an oil cooler 223, utilizing the pressure within the receiver tank 220.

The lubricating oil supplied to the oil-cooled screw compressor 100 in this way is supplied to the compression space and used to lubricate, cool, and seal the compression space, and is also supplied to parts of the oil-cooled screw compressor 100 that require lubrication, such as shaft seals, bearings, and gear mechanisms, and is used to lubricate and seal each part.

In this oil-cooled screw compressor 100, in order to enable the screw rotors 140, 150 to mesh and rotate within the rotor chamber 111, rotor shafts 141, 142 (151, 152) are formed on both ends of the screw rotors 140, 150, and the rotor shafts are inserted into shaft holes formed in the casing, and each rotor shaft 141, 142 (151, 152) is rotatably supported by bearings 170 housed in a bearing chamber 132 that communicates with the shaft holes.

Then, to prevent the compressed gas compressed in the rotor chamber 111 by the meshing rotation of the screw rotor 140 (150) from leaking from the gap between the outer peripheral surface of the discharge side rotor shaft 142 (152) of the screw rotor 140 (150) and the inner peripheral surface of the shaft hole 131, the aforementioned shaft seal portion 134 is provided between the rotor chamber 111 and the bearing chamber 132 that houses the bearing 170 that supports the discharge side rotor shaft 142 (152).

As shown in FIG. 7, in the configuration of the shaft seal 134 in Patent Document 1, which is cited below, an endless annular oil supply groove 137 is provided on the outer circumferential surface of the discharge side rotor shaft 142 (152) between the bearing chamber 132 that houses the discharge side bearing 170 and the rotor chamber 111.

Then, lubricating oil from the receiver tank 220 described above is supplied to this oil supply groove 137 via the oil supply pipe 224 and the oil supply passage 193, and this lubricating oil seals the gap Δ' between the outer circumferential surface of the rotor shaft 142 and the inner circumferential surface of the shaft hole 131, thereby preventing compressed gas from leaking from the rotor chamber 111 through this gap Δ'.

The lubricating oil introduced into the gap Δ' between the outer circumferential surface of the rotor shaft 142 and the inner circumferential surface of the shaft hole 131 via the oil supply groove 137 is allowed to leak into the bearing chamber 132, so that the bearing 170 can also be oiled.

JP 2015-4306 A

In the shaft seal portion 134 described in Patent Document 1 described above, lubricating oil at approximately the same pressure as the discharge pressure of the oil-cooled screw compressor is supplied to the oil supply groove 137 provided on the outer peripheral surface of the rotor shaft 142 (152) to prevent the compressed gas in the rotor chamber 111 from leaking into the bearing chamber 132 through the aforementioned gap Δ'. This causes the pressure of this lubricating oil to balance with the pressure of the compressed gas attempting to leak from the rotor chamber 111 within the aforementioned gap Δ', preventing the compressed gas in the rotor chamber 111 from passing through the gap Δ'.

The lubricating oil supplied to the oil supply groove 137 of the rotor shaft 142 (152) is at approximately the same pressure as the discharge pressure of the oil-cooled screw compressor 100 as described above, so when the pressure of the compressed gas compressed in the rotor chamber 111 increases, as in the case of an oil-cooled screw compressor 100 set to high pressure, the oil supply pressure to the oil supply groove 137 of the rotor shaft 142 (152) also increases accordingly.

As a result, the amount of lubricating oil flowing into the bearing 170 through the gap Δ' between the outer circumferential surface of the rotor shaft 142 on the bearing chamber 132 side and the inner circumferential surface of the shaft hole 131 relative to the oil groove 137 due to the increase in oil supply pressure to the oil groove 137, and therefore the amount of oil supplied to the bearing 170, increases more than necessary.

In this way, if more lubricating oil than necessary is supplied to the bearing 170, the rotational resistance caused by the bearing 170 stirring the lubricating oil increases, resulting in increased power loss in the oil-cooled screw compressor 100.

In addition, the lubricating oil after lubricating the bearing 170 is recovered in the lubricating oil recovery chamber 135 provided on the outside of the bearing 170. However, if a configuration is adopted in which the lubricating oil recovered in this lubricating oil recovery chamber 135 is fed and recovered into the compression action space immediately after intake air confinement, which is at a lower pressure than the lubricating oil recovery chamber 135, the amount of lubricating oil introduced into the compression action space also increases, and the power loss caused by the screw rotor 140 (150) stirring this increased amount of lubricating oil also increases.

As an example of a method for preventing excessive oil supply to the bearing 170, as shown in FIG. 8, a cylindrical spacer 136 is attached to the rotor shaft 142 between the bearing chamber 132 and the rotor chamber 111, and the above-mentioned oil supply groove 137 is provided on the outer circumferential surface of this spacer 136. In addition, a plurality of endless annular labyrinth grooves 138', 139 having a rectangular cross section and formed continuously in the circumferential direction are formed on the outer circumferential surface of the spacer 136 on the rotor chamber 111 side and the outer circumferential surface of the spacer 136 on the bearing chamber 132 side with respect to the oil supply groove 137, thereby giving the spacer 136 the function as a labyrinth seal.

In this configuration, the lubricating oil passing through the gap Δ between the outer peripheral surface of the spacer 136 and the inner peripheral surface of the shaft hole 131 from the oil supply groove 137 toward the bearing chamber 132 side passes alternately through the throttling section formed between the labyrinth grooves 139 and the enlarged section formed within the labyrinth groove 139, as shown in Figure 8 (B), which causes pressure loss, making it possible to reduce the amount of lubricating oil flowing into the bearing 170 side.

However, if this configuration is used to reduce the amount of oil supplied to the bearing 170 of the oil-cooled screw compressor 100 set at high pressure without reducing the oil supply pressure to the oil supply groove 137, it is necessary to form a large number of labyrinth grooves 139 on the outer peripheral surface of the spacer 136 in order to generate a significant pressure loss corresponding to the increase in the discharge side pressure of the oil-cooled screw compressor 100. In order to secure this space, it is necessary to increase the length of the spacer 136, etc., and a major redesign of the shaft seal portion 134 involving dimensional changes, etc. is required.

Therefore, there is a demand for a shaft seal structure that can more efficiently reduce the amount of oil supplied to the bearing 170 by simply replacing the shaft seal spacer 136, for example, without requiring major design changes to the shaft seal portion 134, such as changing the length of the spacer 136.

Here, in order to reduce the amount of lubricating oil flowing into the bearing chamber 132, it is also possible to narrow the oil supply passage 193 that supplies lubricating oil into the oil supply groove 137.

However, if the amount of oil supplied to the oil supply groove 137 decreases, the pressure inside the oil supply groove 137 will no longer be able to resist the pressure of the compressed gas attempting to leak from the rotor chamber 111, and as a result, it will no longer be possible to prevent the compressed gas from leaking from the rotor chamber 111.

As shown in FIG. 8, a labyrinth groove 138' with a rectangular cross section is provided on the outer peripheral surface of the spacer 136 on the rotor chamber 111 side relative to the oil supply groove 137, and a pressure loss is also generated in the compressed gas leaking from the rotor chamber 111, thereby reducing the pressure of the lubricating oil supplied to the oil supply groove 137.

However, in the gap Δ between the outer peripheral surface of the spacer 136, which is located on the rotor chamber 111 side of the oil supply groove 137, and the inner peripheral surface of the shaft hole 131, not only is compressed gas introduced from the rotor chamber 111 side, as shown in FIG. 8(C), but lubricating oil is also introduced from the oil supply groove 137 side.

When the pressures of both fluids are balanced in this gap Δ, the compressed gas in the rotor chamber 111 cannot pass through the gap Δ, preventing leakage into the bearing chamber 132. However, as shown in FIG. 8(C), if a labyrinth groove 138' with a rectangular cross section and therefore a symmetrical shape is provided, this labyrinth groove 138' not only causes a pressure loss in the compressed gas flowing from the rotor chamber 111 to the oil supply groove 137, but also causes a pressure loss in the lubricating oil flowing from the oil supply groove 137 to the rotor chamber 111. Therefore, even if a labyrinth groove 138' with a rectangular cross section is provided, if the oil supply flow path that supplies lubricating oil to the oil supply groove 137 is narrowed to reduce the amount of lubricating oil supplied to the oil supply groove 137, it will no longer be possible to prevent leakage of compressed gas from the rotor chamber 111.

The inventors of the present invention therefore conducted extensive research and completed the present invention, based on the idea that if a greater pressure loss could be caused in the compressed gas flowing from the rotor chamber 111 side to the oil groove 137 than in the lubricating oil flowing from the oil groove 137 side to the rotor chamber 111 side by devising a cross-sectional shape of the labyrinth groove 138' formed on the outer circumferential surface of the spacer 136 located on the rotor chamber 111 side relative to the oil groove 137, it would be possible to prevent leakage of compressed gas from the rotor chamber 111 even if the oil pressure supplying the oil groove 137 is reduced.

In this way, the present invention aims to provide a shaft seal structure for an oil-cooled screw compressor that can prevent compressed gas in the rotor chamber from leaking into the bearing chamber even if the amount of oil supplied to the shaft seal is reduced, while maintaining the function of the shaft seal to prevent leakage of compressed gas from the rotor chamber, and therefore can widen the range of control over the amount of oil supplied to the bearings located adjacent to the shaft seal.

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 structure of the oil-cooled screw compressor 1 of the present invention is as follows:
A shaft seal structure for an oil-cooled screw compressor, in which a pair of male and female screw rotors 40, 50 are rotatably accommodated in a meshed state within a rotor chamber 11 formed within a casing 2, a shaft hole 31 into which a discharge side rotor shaft 42, 52 of the screw rotors 40, 50 is inserted, and a bearing chamber 32 is formed in the casing 2, communicating with the shaft hole 31 and accommodating bearings 70, 70 supporting the discharge side rotor shaft 42, 52, and a shaft seal portion 34 is provided between the rotor chamber 11 and the bearing chamber 32 to seal a gap Δ between an outer peripheral surface of the discharge side rotor shaft 42, 52 and an inner peripheral surface of the shaft hole 31,
an endless annular oil supply groove 37 is formed in the circumferential direction on the outer peripheral surface of the discharge side rotor shaft 42, 52 between the bearing chambers 32, 32 and the rotor chamber 11 and/or on the inner peripheral surface of the shaft hole 31 at the accommodation position of the rotor shaft 42, 52 (in the illustrated example, on the outer peripheral surface of a spacer 36 fitted onto the rotor shaft 42, 52 to form the outer peripheral surface of the rotor shaft 42, 52); and an oil supply passage 93 is provided in the casing 2 for supplying lubricating oil to the oil supply groove 37.
The labyrinth groove 38 has a cross-sectional shape which gradually expands from the oil groove 37 side toward the rotor chamber 11 side, thereby causing a greater pressure loss for the compressed gas flowing from the rotor chamber 11 side to the oil groove 37 side than for the lubricating oil flowing from the oil groove 37 side to the rotor chamber 11 side, and is characterized in that a plurality of endless annular labyrinth grooves 38 which are continuous in the circumferential direction are provided in parallel at predetermined intervals on the outer peripheral surface of the rotor shafts 42, 52 located on the rotor chamber 11 side of the oil groove 37 and/or the inner peripheral surface of the shaft hole 31 (in the illustrated example, the outer peripheral surface of the spacer 36 which forms the outer peripheral surface of the rotor shafts 42, 52) (see claim 1 and Figures 3 to 5).

A cylindrical spacer 36 may be provided that is fitted around the discharge side rotor shaft 42, 52 between the bearing chamber 32, 32 and the rotor chamber 11 to expand the outer diameter of the discharge side rotor shaft 42, 52 at that position, and the outer circumferential surface of the spacer 36 may be the outer circumferential surface of the discharge side rotor shaft 42, 52 (claim 2).

The labyrinth grooves 38 may also be provided in parallel at a predetermined interval on the outer circumferential surface of the discharge rotor shaft 42, 52 located on the bearing chamber 32 side relative to the oil supply groove 37 and/or on the inner circumferential surface of the shaft hole 31 (in the illustrated example, on the outer circumferential surface of the spacer 36 forming the outer circumferential surface of the discharge rotor shaft 42, 52) (see claim 3 and FIG. 3).

Alternatively, instead of the above configuration, a rectangular labyrinth groove 39 having a rectangular cross section and an endless annular shape that continues in the circumferential direction may be provided in parallel at a predetermined interval on the outer circumferential surface of the discharge side rotor shaft 42, 52 located on the bearing chamber 32 side relative to the oil supply groove 37 and/or on the inner circumferential surface of the shaft hole 31 (in the illustrated example, the outer circumferential surface of the spacer 36 that forms the outer circumferential surface of the discharge side rotor shaft 42, 52) (see claim 4 and Figure 4).

Furthermore, the outer peripheral surface of the discharge side rotor shaft 42, 52 on the bearing chamber 32 side relative to the oil supply groove 37 (in the illustrated example, the outer peripheral surface of the spacer 36 forming the outer peripheral surface of the discharge side rotor shaft 42, 52) and the inner peripheral surface of the shaft hole 31 may both be smooth surfaces without labyrinth grooves (see claim 5 and Figure 5).

By using the configuration of the present invention described above, the shaft seal portion 34 of the oil-cooled screw compressor 1 of the present invention can achieve the following remarkable effects:

By adopting a configuration (see Figures 3 to 5) in which a plurality of endless annular labyrinth grooves 38, which have a cross-sectional shape that gradually expands from the bearing chamber 32 side toward the rotor chamber 11 side and are continuous in the circumferential direction, are provided in parallel at predetermined intervals on the outer circumferential surface of the discharge side rotor shaft 42, 52 located on the rotor chamber 11 side relative to the oil supply groove 37 and/or the inner circumferential surface of the shaft hole 31 (in the illustrated example, the outer circumferential surface of the spacer 36 that forms the outer circumferential surface of the discharge side rotor shaft 42, 52), it is possible to prevent leakage of compressed gas from the rotor chamber 11 even when the amount of oil supplied to the oil supply groove 37 is reduced and the pressure of the lubricating oil in the oil supply groove 37 is set lower than the pressure of the compressed gas leaking from the rotor chamber 11.

In this way, it is possible to reduce the amount of oil supplied to the oil groove 37, which makes it possible to reduce the amount of oil supplied to the bearing 70 located adjacent to the shaft seal portion 34, and prevents excessive supply of lubricating oil to the bearing 70 even in an oil-cooled screw compressor 1 set at high pressure.

As a result, it is possible to prevent power loss caused by the bearing 70 stirring up excess lubricating oil, and by recovering excess lubricating oil supplied to the bearing 70 in the compression action space, it is possible to prevent power loss caused by an increase in the amount of lubricating oil stirred by the screw rotors 40, 50.

In addition to forming the labyrinth groove 38 described above on the rotor chamber 11 side of the oil supply groove 37, a configuration in which a labyrinth groove 38 of a similar structure is formed on the bearing chamber 32 side of the oil supply groove 37 (see FIG. 3), or a configuration in which a rectangular labyrinth groove 39 with a rectangular cross section is formed (see FIG. 4), can be adopted to reduce the amount of lubricating oil leaking into the bearing chamber 32 side through the gap Δ between the outer circumferential surface of the discharge side rotor shaft 42, 52 located on the bearing chamber 32 side of the oil supply groove 37 (in the illustrated example, the outer circumferential surface of the spacer 36 forming the outer circumferential surface of the discharge side rotor shaft 42, 52) and the inner circumferential surface of the shaft hole 31. This can further reduce the amount of oil supplied to the bearing 70 by the synergistic effect of the reduction in the amount of oil supplied to the oil supply groove 37 described above.

Furthermore, by adopting a configuration in which the outer peripheral surface of the discharge side rotor shaft 42, 52 on the bearing chamber 32 side (in the illustrated example, the outer peripheral surface of the spacer 36 forming the outer peripheral surface of the discharge side rotor shaft 42, 52) and the inner peripheral surface of the shaft hole 31 are both smooth surfaces with respect to the oil supply groove 37 (see FIG. 5), the amount of oil supplied to the bearing 70 can be reduced by only reducing the amount of oil supplied to the oil supply groove 37 described above, and by appropriately selecting and combining the configurations adopted for the bearing chamber side portion of the oil supply groove 37 from the configurations shown in FIG. 3 to FIG. 5, it is also possible to finely adjust the amount of oil supplied to the bearing 70.

1 is a cross-sectional plan view of an oil-cooled screw compressor to which the shaft seal structure of the present invention is applied; 1 is a front view, on a reduced scale, of an oil-cooled screw compressor to which the shaft seal structure of the present invention is applied; 3A is an enlarged view of the part indicated by the arrow III in FIG. 2 (the part surrounded by the dashed line), FIG. 3B is an enlarged explanatory view of the part indicated by the arrow B in FIG. 3A, and FIG. 3C is an enlarged explanatory view of the part indicated by the arrow C in FIG. 3A is an enlarged view showing a modified example of the portion indicated by the arrow III in FIG. 2 (the portion surrounded by a dashed line), and FIG. 3B is an enlarged explanatory view of the portion indicated by the arrow B in FIG. 3 is an enlarged view showing another modified example of the portion indicated by the arrow III in FIG. 2 (portion surrounded by a dashed line). FIG. 2 is an explanatory diagram of a compressor unit having an oil-cooled screw compressor as a compressor body. FIG. 2 is an explanatory diagram of a shaft seal of a conventional oil-cooled screw compressor (corresponding to FIG. 2 of Patent Document 1). FIG. 1A is an explanatory diagram assuming a structure in which a shaft seal spacer is provided in the shaft seal section and a labyrinth groove is provided in this spacer. FIG. 1B is an enlarged explanatory diagram of the part indicated by the arrow B in FIG. 1A. FIG. 1C is an enlarged explanatory diagram of the part indicated by the arrow C in FIG.

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

[Overall configuration of oil-cooled screw compressor]
Reference numeral 1 in Figs. 1 and 2 denotes an oil-cooled screw compressor to which the shaft seal structure of the present invention is applied, and this oil-cooled screw compressor 1 includes a casing 2 forming an outer shell.

The casing 2 comprises a rotor casing 10, a suction side casing 20 attached to the suction side end of the rotor casing 10 or formed integrally therewith, and a discharge side casing 30 attached to the discharge side end of the rotor casing 10. A pair of male and female screw rotors 40, 50 are housed in a rotor chamber 11 formed in the rotor casing 10 so as to mesh and rotate.

The suction side casing 20 attached to the suction side end of the rotor casing 10 has an axial hole formed therein to accommodate the suction side rotor shafts 41, 51 of the screw rotors 40, 50, and bearings 60, 60 are housed in the bearing chambers 21, 22 formed in communication with this axial hole, and the suction side rotor shafts 41, 51 of the male and female screw rotors 40, 50 are supported by these bearings 60, 60.

The suction side casing 20 also has a gear chamber 23 formed therein, which houses a speed increasing device 80 that increases the rotational driving force from a driving source such as a motor or engine (not shown) and inputs it to either the male or female screw rotor 40, 50.

As an example, this speed increasing device 80 includes a driven gear 81 fixed to the suction side rotor shaft of one of the screw rotors 40 or 50 (in this embodiment, the suction side rotor shaft 41 of the male rotor 40), a drive gear 82 that transmits a rotational driving force to this driven gear 81, and a drive shaft 83 that inputs a rotational driving force generated by a drive source to the drive gear 82. By making the diameter of the driven gear 81 smaller than that of the drive gear 82, the rotational driving force input via the drive shaft 83 is accelerated and transmitted to the suction side rotor shaft 41 of the male rotor 40, and the screw rotors 40, 50 can be rotated at an accelerated speed.

In addition, in the oil-cooled screw compressor 1 of the present invention, the speed-increasing device 80 and the gear chamber 23 are not essential components. In cases where the speed-increasing device is provided outside the oil-cooled screw compressor 1, or where the rotational driving force from the driving source is input at the same rotational speed without being increased, the speed-increasing device 80 and the gear chamber 23 are not provided, the suction side rotor shaft of either the male or female, for example the suction side rotor shaft 41 of the male rotor 40, may be protruded outside the machine through the casing and used as the drive shaft to input the rotational driving force from the engine or motor.

The discharge side end of the rotor casing 10 is covered by a discharge side casing 30 having shaft holes 31, 31 that accommodate the discharge side rotor shafts 42, 52 of the male rotor 40 and female rotor 50, and the discharge side rotor shafts 42, 52 of the screw rotors 40, 50 are supported by bearings 70 accommodated in bearing chambers 32, 32 formed in communication with the shaft holes 31, 31 of the discharge side casing 30.

The suction side casing 20 is formed with an intake port 24 (see Figure 2), and the compressed gas introduced through this intake port 24 is introduced into the compression action space defined by the pair of male and female screw rotors 40, 50 and the inner wall of the rotor chamber 11, where it is compressed together with the lubricating oil, and is discharged outside the machine through a discharge port 33 (see Figure 2) provided in the discharge side casing 30.

The bottom of the rotor casing 10 of this oil-cooled screw compressor 1 is provided with an oil supply port 12 (see FIG. 2) to which the oil supply pipe 224 from the receiver tank 220 described with reference to FIG. 6 is connected, and oil supply passages 91, 92, and 93 are formed in the wall thickness of the casing, communicating with this oil supply port 12, to supply lubricating oil to each part of the oil-cooled screw compressor 1 that requires oil.

In the illustrated embodiment, as shown in FIG. 2, oil supply passages 91, 92, and 93 are provided that branch off in three directions from the oil supply port 12, and one of them, 91, is connected to the compression action space after the intake air is trapped, so that lubricating oil can be supplied to the compression action space for lubrication, cooling, and sealing.

In addition, one of the remaining oil supply passages 92 extends through the thickness of the rotor casing 10 toward the suction side and reaches the suction side casing 20, and is connected to an oil supply nozzle 25 that injects lubricating oil into the gear chamber 23 in which the speed increasing device 80 is housed, thereby lubricating the speed increasing device 80 housed in the gear chamber 23 and the bearings 60, 60 housed in the bearing chambers 21, 22 that are provided in communication with the gear chamber 23.

This gear chamber 23 is connected to the rotor chamber 11 by a communication passage (not shown), and lubricating oil that accumulates in the gear chamber 23 above a certain oil level is introduced into the rotor chamber 11 through this communication hole (not shown) and compressed together with the gas to be compressed.

Furthermore, the remaining oil supply passage 93 extends through the thickness of the rotor casing 10 to the discharge side as shown in FIG. 2, then reaches the inside of the discharge side casing 30 and changes direction to a direction perpendicular to the axis of the discharge side rotor shafts 42, 52, so that it can supply lubricating oil to the discharge side shaft seals 34, 34 and the bearings 70, 70 provided adjacent to these shaft seals 34, 34.

The lubricating oil that lubricates the shaft seals 34, 34 and the bearings 70, 70 on the discharge side is introduced into the lubricating oil recovery chamber 35 provided on the outside of the bearings 70, 70, and is configured to be recovered into the compression action space via the lubricating oil recovery passage 94 (see Figure 1) that communicates with this lubricating oil recovery chamber 35.

[Shaft seal structure]
The discharge side casing 30 of the oil-cooled screw compressor 1 described with reference to Figures 1 and 2 is provided with shaft holes 31, 31 for accommodating the discharge side rotor shafts 42, 52, and the discharge side rotor shafts 42, 52 are rotatably supported by bearings 70, 70 accommodated in bearing chambers 32, 32 provided in communication with the shaft holes 31, 31.

The aforementioned shaft seals 34, 34 are provided between the bearing chambers 32, 32 and the rotor chamber 11 to prevent leakage of compressed gas from the rotor chamber 11.

Figure 3 shows an example of the configuration of the shaft seal 34 provided on the discharge side rotor shaft 42 of the male rotor 40.

As shown in FIG. 3, the outer diameter of the discharge-side rotor shaft 42 is slightly smaller than the inner diameter of the shaft hole 31 in the shaft seal portion 34, narrowing the gap Δ between the outer circumferential surface of the discharge-side rotor shaft 42 and the inner circumferential surface of the shaft hole 31 in this portion, and by sealing this gap Δ with lubricating oil as described below, leakage of compressed gas from the rotor chamber 11 is prevented.

The outer diameter of the discharge side rotor shaft 42 at the shaft seal portion 34 may be formed so that the outer diameter of the discharge side rotor shaft 42 itself at that position is slightly smaller than the inner diameter of the shaft hole 31, but in the embodiment shown in FIG. 3, a cylindrical spacer 36 for shaft sealing may be fitted onto the discharge side rotor shaft 42 at this position, and the outer diameter of the discharge side rotor shaft 42 may be expanded by this spacer 36 to form the aforementioned gap Δ between the outer peripheral surface of the spacer 36 and the inner peripheral surface of the shaft hole 31. In this case, the outer peripheral surface of the spacer 36 becomes the outer peripheral surface of the discharge side rotor shaft 42.

This spacer 36 is attached to the outer periphery of the discharge side rotor shaft 42 so that it rotates together with the discharge side rotor shaft 42 without contacting the inner periphery of the shaft hole 31. Lubricating oil is supplied to the gap Δ generated between the outer periphery of this spacer 36 and the inner periphery of the shaft hole 31 to close the gap Δ, thereby preventing leakage of compressed gas from the rotor chamber 11, and lubricating oil is leaked through this gap Δ to the bearing chamber 32 side to oil the bearing 70.

A continuous endless annular oil supply groove 37 is formed on the outer peripheral surface of the spacer 36 at the midpoint in the axial direction, and the oil supply groove 37 is connected to the oil supply passage 93 formed in the discharge side casing 30 in a direction perpendicular to the axial direction of the discharge side rotor shaft 42, so that lubricating oil pumped from a receiver tank can be supplied to the oil supply groove 37.

At least in the portion of the outer circumferential surface of the spacer 36 that is located closer to the rotor chamber 11 than the oil supply groove 37, a labyrinth groove 38 is provided in parallel at a predetermined interval, with a cross-sectional shape that gradually expands from the bearing chamber 32 side toward the rotor chamber 11 side, and is formed as an endless ring that continues in the circumferential direction. The surface of the spacer 36 in this portion is formed as a sawtooth cross section as a whole.

In the embodiment shown in FIG. 3, multiple labyrinth grooves 38 having such a cross-sectional shape (five in the illustrated example) are also provided parallel to each other at a predetermined interval on the outer peripheral surface of the spacer 36 located on the bearing chamber 32 side relative to the oil supply groove 37.

In this way, by forming a labyrinth groove 38 with a cross-sectional shape that gradually expands from the bearing chamber 32 side toward the rotor chamber 11 side, it is possible to prevent leakage of compressed gas from the rotor chamber 11 even when the amount of oil supplied to the oil supply groove 37 is reduced and the pressure of the lubricating oil in the oil supply groove 37 is set to a lower pressure than the pressure of the compressed gas attempting to leak from the rotor chamber 11.

The lubricating oil that is supplied to the oil supply groove 37 and flows from the oil supply groove 37 toward the bearing chamber 32 passes through the throttling section formed between the labyrinth grooves 38, as shown in the enlarged view of FIG. 3(B), and then reaches the enlarged section formed within the labyrinth groove 38, where the flow path expands suddenly. As a result, as in the case of providing a labyrinth groove with a rectangular cross section as described with reference to FIG. 8(B), the lubricating oil repeatedly passes through a flow path that expands suddenly from a throttling state, causing a pressure loss. By repeating this process, the amount of lubricating oil that passes through the gap Δ toward the bearing chamber 32 can be reduced.

Similarly, the compressed gas, which is a compressible fluid attempting to pass through the gap Δ between the outer peripheral surface of the spacer 36 and the inner peripheral surface of the shaft hole 31 from the rotor chamber 11 side toward the oil supply groove 37 side, also passes through a flow path that expands rapidly from the choke section to the expansion section and moves toward the oil supply groove 37 side as shown in Figure 3 (C), and as a result, it expands rapidly from a compressed state and undergoes a large pressure loss by repeating this process, just as in the case of a labyrinth groove with a rectangular cross section.

However, as the lubricating oil, which is an incompressible fluid flowing from the oil supply groove 37 toward the rotor chamber 11, passes through a flow path that gradually expands from the throttle section to the expansion section, the flow rate decreases while the pressure increases (Bernoulli's theorem). By repeating these steps, a state is reached where "compressed gas pressure ≦ lubricating oil pressure," making it possible to prevent compressed gas from leaking from the rotor chamber.

As a result, by attaching the spacer 36 to the discharge-side rotor shaft 42, with the rotor chamber 11 side being the side where the flow path area expands rapidly from the throttling section to the expansion section, and the bearing chamber 32 side being the side where the flow path area expands gradually from the throttling section to the expansion section, it is possible to counter the pressure of the compressed gas leaking from the rotor chamber 11 even if the oil supply pressure to the oil supply groove 37 is set to a pressure lower than the pressure of the compressed gas attempting to leak from the rotor chamber 11, and leakage of the compressed gas from the rotor chamber 11 can be prevented.

By reducing the amount of oil supplied to the oil supply groove 37 in this way, in the oil-cooled screw compressor 1 equipped with the shaft seal structure of the present invention, it is possible to reduce the amount of lubricating oil flowing from the oil supply groove 37 toward the bearing chamber 32 through the gap Δ between the outer peripheral surface of the spacer 36 and the inner peripheral surface of the shaft hole 31.

In addition, in the embodiment shown in FIG. 3, a labyrinth groove 38 having a cross-sectional shape similar to that provided between the rotor chamber 11 and the oil supply groove 37 is provided on the outer peripheral surface of the spacer 36 between the oil supply groove 37 and the bearing chamber 32, as described above, thereby reducing the amount of lubricating oil that passes through this portion and leaks into the bearing chamber 32.

By reducing the amount of oil supplied to the bearings 70 in this way, it was possible to prevent power loss caused by the bearings 70 stirring a large amount of lubricating oil, even in an oil-cooled screw compressor 1 set at high pressure.

In addition, by reducing the amount of oil supplied to the bearing 70, the amount of lubricating oil recovered in the compression space via the lubricating oil recovery chamber 35 and the lubricating oil recovery passage 94 (see Figure 2) after lubricating the bearing 70 is reduced, which makes it possible to prevent power loss caused by the screw rotors 40, 50 stirring up excess lubricating oil.

In the shaft seal portion 34 described above with reference to FIG. 3, the cross-sectional shape of the labyrinth groove 38 provided on the outer peripheral surface of the spacer 36 located on the bearing chamber 32 side relative to the oil supply groove 37, and the cross-sectional shape of the labyrinth groove 38 provided on the outer peripheral surface of the spacer 36 on the rotor chamber 11 side relative to the oil supply groove 37, are both gradually enlarged from the bearing chamber 32 side toward the rotor chamber 11 side.

Instead of this configuration, the labyrinth groove provided on the outer peripheral surface of the spacer 36 located on the bearing chamber 32 side relative to the oil supply groove 37 may be a rectangular labyrinth groove 39 with a rectangular cross section, as shown in Figure 4.

In the gap Δ between the outer peripheral surface of the spacer 36 on the bearing chamber 32 side relative to the oil supply groove 37 and the inner peripheral surface of the shaft hole 31, only the flow of lubricating oil occurs from the oil supply groove 37 toward the bearing chamber 32 side, and there is no need to consider the flow of fluid in the opposite direction. The shape of the labyrinth groove formed in this part can be any cross-sectional shape as long as it can reduce the amount of lubricating oil leaking into the bearing chamber 32 side.

In addition, when the labyrinth groove width and depth are the same, labyrinth groove 39, which has a rectangular cross-sectional shape, has a larger cross-sectional area at the expanding portion than labyrinth groove 38, which has a cross-sectional shape that gradually expands from the bearing chamber 32 side toward the rotor chamber 11 side. This causes the flow of lubricating oil passing through gap Δ to expand and contract more suddenly, resulting in a larger pressure loss and making it possible to further reduce the amount of lubricant passing through this portion.

Therefore, if it becomes necessary to further reduce the amount of oil supplied to the bearing 70, such a requirement can be met by forming the labyrinth groove 39, which has a rectangular cross section, on the bearing chamber 32 side relative to the oil supply groove 37 as shown in FIG. 4.

Furthermore, in the shaft seal portion 34 described with reference to Figures 3 and 4, labyrinth grooves 38, 39 are provided not only on the outer circumferential surface of the spacer 36 on the rotor chamber 11 side relative to the oil supply groove 37, but also on the outer circumferential surface of the spacer 36 on the bearing chamber 32 side relative to the oil supply groove 37. However, instead of this configuration, the outer circumferential surface of the spacer 36 on the bearing chamber 32 side relative to the oil supply groove 37 may be formed as a flat surface without labyrinth grooves, as shown in Figure 5.

With this configuration, the amount of oil supplied to the bearing 70 increases compared to the embodiment described with reference to Figures 3 and 4. However, since there are oil-cooled screw compressors 1 that require a relatively large amount of oil to be supplied to the bearing 70, such as oil-cooled screw compressors 1 that rotate the screw rotors 40, 50 at a relatively high rotational speed, the structure of the outer surface of the spacer 36 on the bearing chamber 32 side relative to the oil supply groove 37 can be appropriately selected from the configurations shown in Figures 3 to 5 according to the settings of the oil-cooled screw compressor 1, etc.

In the embodiments shown in Figures 3 to 5, the spacer 36 is made of a single cylindrical member. However, as an example, as shown as a modified example in Figure 5, the spacer 36 may be divided into two in the axial direction and formed by combining two members.

In this configuration, a labyrinth groove 38 with a cross-sectional shape that gradually expands from the bearing chamber 32 side toward the rotor chamber 11 side is formed on the outer peripheral surface of the portion 36a of the spacer 36 that is arranged on the rotor chamber 11 side.

On the other hand, the portion 36b arranged on the bearing chamber side may be prepared in advance with the labyrinth groove 38 shown in FIG. 3, the rectangular labyrinth groove 39 shown in FIG. 4, or without a labyrinth groove as shown in FIG. 5, and the spacer 36 may be formed by combining the portion 36b arranged on the bearing chamber side selected from these according to the settings of the oil-cooled screw compressor 1, etc.

Furthermore, in the embodiments described with reference to Figures 3 to 5, the oil supply groove 37, labyrinth groove 38, and rectangular labyrinth groove 39 are formed on the outer peripheral surface of the spacer 36. However, these may be formed on the inner peripheral surface of the shaft hole 31 at a position corresponding to the spacer 36, either in addition to or instead of being formed on the outer peripheral surface of the spacer 36, and the same effect can be obtained by adopting this configuration.

REFERENCE SIGNS LIST 1 oil-cooled screw compressor 2 casing 10 rotor casing 11 rotor chamber 12 oil supply port 20 suction side casing 21, 22 bearing chamber 23 gear chamber 24 intake port 25 oil supply nozzle 30 discharge side casing 31 shaft hole 32 bearing chamber 33 discharge port 34 shaft seal portion 35 lubricating oil recovery chamber 36 spacer 36a portion (of spacer) disposed on rotor chamber side 36b portion (of spacer) disposed on bearing chamber side 37 oil supply groove 38 labyrinth groove 39 rectangular labyrinth groove 40 male screw rotor 41 suction side rotor shaft 42 discharge side rotor shaft 50 female screw rotor 51 suction side rotor shaft 52 discharge side rotor shaft 60, 70 bearing 80 speed increasing device 81 driven gear 82 Drive gear 83 Drive shaft 91, 92, 93 Oil supply passage 94 Lubricating oil recovery passage 100 Oil-cooled screw compressor 111 Rotor chamber 131 Shaft hole 132 Bearing chamber 134 Shaft seal portion 135 Lubricating oil recovery chamber 136 Spacer 137 Oil supply groove 138', 139 Labyrinth groove 140, 150 Screw rotor 140a, 150a Discharge side end surface (of the screw rotor)
141, 142, 151, 152 Rotor shaft 170 Bearing 193 Oil supply passage 210 Driving source 220 Receiver tank 221 Check valve 222 Oil filter 223 Oil cooler 224 Oil supply pipe Δ Gap between outer circumferential surface of discharge side rotor shaft (spacer) and inner circumferential surface of shaft hole Δ' Gap between outer circumferential surface of rotor shaft and inner circumferential surface of shaft hole

Claims (5)

A shaft seal structure for an oil-cooled screw compressor, comprising: a pair of male and female screw rotors rotatably housed in a rotor chamber formed in a casing in an intermeshed state; a shaft hole into which a discharge side rotor shaft of the screw rotor is inserted; and a bearing chamber communicating with the shaft hole and housing a bearing for supporting the discharge side rotor shaft; and a shaft seal portion for sealing a gap between the outer peripheral surface of the discharge side rotor shaft and the inner peripheral surface of the shaft hole between the rotor chamber and the bearing chamber,
an endless annular oil supply groove is formed in the outer peripheral surface of the discharge side rotor shaft between the bearing chamber and the rotor chamber and/or in the inner peripheral surface of the shaft hole at the accommodation position of the discharge side rotor shaft, and an oil supply passage is provided in the casing for supplying lubricating oil to the oil supply groove,
a shaft seal structure for an oil-cooled screw compressor, characterized in that a plurality of endless annular labyrinth grooves continuing in the circumferential direction are provided in parallel at predetermined intervals on the outer peripheral surface of the discharge-side rotor shaft located on the rotor chamber side of the oil groove and/or the inner peripheral surface of the shaft hole, the labyrinth grooves having a cross-sectional shape that gradually expands from the oil groove side towards the rotor chamber side, thereby causing a greater pressure loss for the compressed gas flowing from the rotor chamber side to the oil groove side, than for the lubricating oil flowing from the oil groove side to the rotor chamber side. The shaft seal structure of an oil-cooled screw compressor according to claim 1, characterized in that a cylindrical spacer is provided between the bearing chamber and the rotor chamber, fitted onto the discharge rotor shaft to expand the outer diameter of the discharge rotor shaft at that position, and the outer circumferential surface of the spacer is the outer circumferential surface of the discharge rotor shaft. The shaft seal structure of an oil-cooled screw compressor according to claim 1 or 2, characterized in that the labyrinth grooves are further provided in parallel at predetermined intervals on the outer circumferential surface of the discharge rotor shaft located on the bearing chamber side relative to the oil supply groove and/or on the inner circumferential surface of the shaft hole. The shaft seal structure of an oil-cooled screw compressor according to claim 1 or 2, characterized in that a plurality of endless annular rectangular labyrinth grooves, each having a rectangular cross section and continuing in the circumferential direction, are provided parallel to each other at predetermined intervals on the outer circumferential surface of the discharge rotor shaft located on the bearing chamber side relative to the oil supply groove and/or on the inner circumferential surface of the shaft hole. 3. A shaft seal structure for an oil-cooled screw compressor according to claim 1, wherein the outer peripheral surface of the discharge-side rotor shaft on the bearing chamber side with respect to the oil supply groove and the inner peripheral surface of the shaft hole are both smooth surfaces.

Images