# US 10,309,402 B2 · Oil-free screw compressor having atmosphere open hole formed in casing and communication hole formed in shaft seal device

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- Number: US 10,309,402 B2
- Document ID: US10309402B2
- Status: Granted
- Kind: B2
- Application number: 15/513,830
- Filed: 2015-09-24
- Published: 2017-10-26
- Granted: 2019-06-04
- Earliest claimed: 2014-09-29
- Assignees: Kobe Steel, Ltd.
- Applicants: Kobe Steel, Ltd.
- Inventors: Yoshio Yano; Toshiyuki Miyatake
- Web page: https://patentgrep.com/patent/US10309402B2

## CPC

- F04C 27/009: {Shaft sealings specially adapted for pumps}
- F04B 39/00: Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
- F04C 18/16: with helical teeth, e.g. chevron-shaped, screw type {(for non-parallel axes of movement F04C18/48)}
- F04C 27/00: Sealing arrangements in rotary-piston pumps specially adapted for elastic fluids
- F04C 27/02: Liquid sealing for high-vacuum pumps {or for compressors}
- F16J 15/40: by means of fluid
- F16J 15/441: {with floating ring}
- F04C 2220/12: Dry running
- F04C 2230/21: by casting
- F04C 2240/30: Casings or housings
- F04C 2240/50: Bearings
- F04C 2240/60: Shafts
- F04C: ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS (engines F03C); ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
- F04B: POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS (machines for liquids, or pumps, of rotary-piston or oscillating-piston type F04C; non-positive-displacement pumps F04D; pumping of fluid by direct contact of another fluid or by using inertia of fluid to be pumped F04F)
- F16J: PISTONS {(specially adapted for dampers F16F9/32)}; CYLINDERS; SEALINGS

## Abstract

An oil-free screw compressor includes: a casing having a rotor chamber; a bearing supporting rotary shafts of the screw rotors; a shaft seal device including an oil seal portion and an air seal portion; an atmosphere open hole formed in the shaft seal device; at least one communication hole formed in the rotary shaft; and an annular space communicating the atmosphere open hole with the at least one communication hole communicate with each other. The annular space includes an inner peripheral annular space formed on an inner peripheral side of the casing. Assuming an open cross-sectional area of the inner peripheral annular space as S1, a total open cross-sectional area of the communication holes as S2, an open cross-sectional area of the i-th communication hole out of the communication holes as S2i, and the number of communication holes as n (n being a natural number of 1 or more), a following relationship is satisfied. S ⁢ ⁢ 1 ≧ S ⁢ ⁢ 2 = ∑ i = 1 n ⁢ ⁢ S ⁢ ⁢ 2 ⁢ i

## Claims

### Claim 1

An oil-free screw compressor comprising:
a pair of female and male screw rotors which meshes with each other in a non-contact manner;
a casing having a rotor chamber in which the screw rotors are housed;
a bearing which supports rotary shafts of the screw rotors;
a shaft seal device which includes an oil seal portion disposed on a bearing side and an air seal portion disposed on a rotor chamber side and shaft-seals the rotary shafts;
an atmosphere open hole which is formed in the casing;
at least one communication hole which is formed in the shaft seal device in a state where the communication hole is positioned between the oil seal portion and the air seal portion; and
an annular space which makes the atmosphere open hole and the at least one communication hole communicate with each other, wherein
the annular space includes an inner peripheral annular space annularly formed on an inner peripheral side of the casing,
wherein an open cross-sectional area of the inner peripheral annular space in a partial cross section taken along an axial direction of the rotary shaft as S1, a total open cross-sectional area of the communication holes as S2, an open cross-sectional area of the i-th communication hole out of the communication holes as S2i, and a number of communication holes as n (n being a natural number of 1 or more), a following relationship is satisfied:
S
⁢
⁢
1
≧
S
⁢
⁢
2
=
∑
i
=
1
n
⁢
⁢
S
⁢
⁢
2
⁢
i
wherein the casing is formed of a cast product, and
a width of an opening portion of the inner peripheral annular space in the axial direction of the rotary shaft is larger than an opening diameter of the communication hole by an amount set by taking into account a manufacturing tolerance of the cast product.

### Claim 2 (depends on 1)

The oil-free screw compressor according to claim 1, wherein the annular space further includes an outer peripheral annular space which is disposed so as to opposedly face the inner peripheral annular space on an outer peripheral side of the shaft seal device, and has a larger width in the axial direction of the rotary shaft than the communication holes, and
wherein an open cross-sectional area of the outer peripheral annular space in a partial cross section taken along the axial direction of the rotary shaft as S3, a following relationship is satisfied
S
=
S
⁢
⁢
1
+
S
⁢
⁢
3
≧
S
⁢
⁢
2
=
∑
i
=
1
n
⁢
⁢
S
⁢
⁢
2
⁢
i
.

### Claim 3 (depends on 2)

The oil-free screw compressor according to claim 2, wherein
the casing is formed of a cast product, and
a width of an opening portion of the inner peripheral annular space in the axial direction of the rotary shaft is larger than a width of an opening portion of the outer peripheral annular space in the axial direction of the rotary shaft by an amount set by taking into account a manufacturing tolerance of the cast product.

### Claim 4 (depends on 3)

The oil-free screw compressor according to claim 3, wherein
the casing is formed of a cast product,
the inner peripheral annular space has: an inner peripheral annular groove; and tapered expanding portions having a tapered shape which are formed on both end sides of the inner peripheral annular groove in the axial direction of the rotary shaft, and
the inner peripheral annular groove has an approximately semicircular shape in partial cross section taken along the axial direction of the rotary shaft.

### Claim 5 (depends on 4)

The oil-free screw compressor according to claim 4, wherein the tapered expanding portions respectively have an inclination angle and a height set by taking into account a projecting height of an O-ring mounted on an outer peripheral side of the shaft seal device.

### Claim 6 (depends on 2)

The oil-free screw compressor according to claim 2, wherein
the casing is formed of a cast product,
the inner peripheral annular space has: an inner peripheral annular groove; and tapered expanding portions having a tapered shape which are formed on both end sides of the inner peripheral annular groove in the axial direction of the rotary shaft, and
the inner peripheral annular groove has an approximately semicircular shape in partial cross section taken along the axial direction of the rotary shaft.

### Claim 7 (depends on 6)

The oil-free screw compressor according to claim 6, wherein the tapered expanding portions respectively have an inclination angle and a height set by taking into account a projecting height of an O-ring mounted on an outer peripheral side of the shaft seal device.

### Claim 8 (depends on 1)

The oil-free screw compressor according to claim 1, wherein
the casing is formed of a cast product,
the inner peripheral annular space has: an inner peripheral annular groove; and tapered expanding portions having a tapered shape which are formed on both end sides of the inner peripheral annular groove in the axial direction of the rotary shaft, and
the inner peripheral annular groove has an approximately semicircular shape in partial cross section taken along the axial direction of the rotary shaft.

### Claim 9 (depends on 8)

The oil-free screw compressor according to claim 8, wherein the tapered expanding portions respectively have an inclination angle and a height set by taking into account a projecting height of an O-ring mounted on an outer peripheral side of the shaft seal device.

### Claim 10 (depends on 1)

The oil-free screw compressor according to claim 1, wherein
the casing is formed of a cast product,
the inner peripheral annular space has: an inner peripheral annular groove; and tapered expanding portions having a tapered shape which are formed on both end sides of the inner peripheral annular groove in the axial direction of the rotary shaft, and
the inner peripheral annular groove has an approximately semicircular shape in partial cross section taken along the axial direction of the rotary shaft.

### Claim 11 (depends on 10)

The oil-free screw compressor according to claim 10, wherein the tapered expanding portions respectively have an inclination angle and a height set by taking into account a projecting height of an O-ring mounted on an outer peripheral side of the shaft seal device.