Shaft sealing mechanism of compressor with mechanical seal

Details Shaft sealing mechanism of compressor with mechanical seal Shaft sealing mechanism of compressor with mechanical seal

2002-01-02

2004-02-10

Knight, Anthony (Department: 3676)

Seal for a joint or juncture

Seal between relatively movable parts

Relatively rotatable radially extending sealing face member

C277S369000, C277S359000, C277S388000, C277S389000

Reexamination Certificate

active

06688602

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a technique for shaft-sealing a circumference of a rotary shaft of a compressor of an air-conditioner using a mechanical seal.
BACKGROUND ART
FIG. 6
is a view showing a typical example of a conventional mechanical seal used as a shaft-seal means of a compressor of an air-conditioner for automobile use (a car air-conditioner) in which CO
2
gas is used as refrigerant. This type mechanical seal
200
is composed as follows. On the rotary shaft
101
of a gas compressor, the refrigerant of which is CO
2
gas, the rotary side sliding ring
201
is arranged via the O-ring
202
in such a manner that the rotary side sliding ring
201
is capable of moving in the axial direction and rotating together with the rotary shaft
101
. The stationary side sliding ring
203
, which cannot rotate, is airtightly arranged via the O-ring
204
on the seal housing
102
side of the gas compressor, the refrigerant of which is CO
2
gas. The rotary side sliding ring
201
is closely contacted with the stationary side sliding ring
203
by a pushing force generated by the spring
205
in the axial direction. When both the rings
201
and
203
are closely contacted with each other, the airtightly sealed sliding face
200
S is formed.
In this case, space A in the device, which is located on the right in the drawing and reaches the outer circumference of the airtightly sealed sliding face
200
S, is filled with an atmosphere of CO
2
gas containing refrigerating machine oil. Space B on the atmosphere side reaches the inner circumference of the airtightly sealed sliding face
200
S. The differential pressure &Dgr;p between space A in the device and space B on the atmosphere side changes in a range from 3 to 13 MPa. The rotary side sliding ring
201
is made of carbon sliding material having a self-lubrication property. The sliding protrusion
201
a,
which is continuously formed in the circumferential direction, of the rotary side sliding ring
201
is slidably contacted with the stationary side sliding ring
203
. The stationary side sliding ring
203
is made of sliding material of ceramics which is harder than the carbon sliding material described above.
According to the conventional mechanical seal
200
described above, the rotary side sliding ring
201
made of carbon sliding material, the Young's modulus of which is low, is deformed into a tapered-shape which is exaggeratedly shown in FIG.
7
. The reason why the rotary side sliding ring
201
is deformed into a tapered-shape will be explained as follows. The rotary side sliding ring
201
is given a displacement force as shown by arrow “f” by the differential pressure &Dgr;p acting in the radial direction on a portion close to the stationary side sliding ring
203
with respect to the O-ring
202
which is arranged on an inner circumference of the rotary side sliding ring
201
. Therefore, the portion of the rotary side sliding ring
201
close to the stationary side sliding ring
203
leans against the stationary side sliding ring
203
side. The sliding protrusion
201
a,
the bending strength of which is low from the viewpoints of profile and structure, further leans against the inner circumferential side by the differential pressure acting in the radial direction.
As a result, for example, in the case where a mechanical seal is used in which the rotary side sliding ring
201
is made of carbon sliding material, the outer diameter of the sliding protrusion
201
a
is approximately 20 mm and the width of the airtightly sealed sliding face
200
S in the radial direction is approximately 2 mm, partial abrasion is caused by sliding in which the quantity of abrasion in the outer circumferential portion of the sliding protrusion
201
a
is larger than that in the inner circumferential portion of the sliding protrusion
201
a
by about 1 to 3 fm (femto-meter).
Therefore, when displacement force “f” caused by differential pressure &Dgr;p is reduced according to the reduction of gas pressure of refrigerant CO
2
filled in space A in the device, as shown in
FIG. 8
, a tapered gap “g”, which is open onto the outer circumferential side (refrigerant gas CO
2
atmosphere side) is caused due to the above partial abrasion. Accordingly, when differential pressure &Dgr;p acts on this gap “g”, an intensity of force OP to open the airtightly sealed sliding face
200
S is increased.
When some refrigerating machine oil, which exists in the refrigerant gas CO
2
in a mist form, is introduced onto the airtightly sealed sliding face
200
S, an oil film is formed on the airtightly sealed sliding face
200
S. The thus formed oil film greatly contributes to the prevention of leakage of refrigerant CO
2
gas. When the tapered gap “g”, which is open onto the outer circumferential side as described above, is formed, the width of the airtightly sealed sliding face
200
S is remarkably decreased, and the oil film existing on the tightly sealed sliding face
200
S is remarkably decreased. Therefore, refrigerant CO
2
gas tends to leak from the device.
DISCLOSURE OF THE INVENTION
The present invention has been accomplished to solve the above problems. The primary technical task of the present invention is to prevent the collapse of an oil film on the airtightly sealed sliding face and suppress the leakage of refrigerant gas caused by the collapse of the oil film when deformation of the sliding ring and sliding protrusion caused by the pressure in the space in the device is reduced and partial abrasion on the airtightly sealed sliding face, which is caused by the deformation, is reduced.
The above technical task can be effectively accomplished by the present invention.
The present invention provides a shaft seal mechanism of a compressor with a mechanical seal, the mechanical seal comprising: a rotary side sliding ring supported by an outer circumferential face on a large diameter side of an annular step section formed on a rotary shaft of a compressor via a rotary side packing, the rotary side sliding ring being press-fit into the annular step section by gas pressure in the compressor; and a stationary side sliding ring, which is not rotated, airtightly fixed onto a seal housing side of the compressor via a stationary side packing in such a manner that the stationary side sliding ring can be moved in the axial direction, the stationary side sliding ring airtightly coming into contact with the rotary side sliding ring by a pushing force of a spring in the axial direction so as to form an airtightly sealed sliding face, wherein a space in the compressor in which gas to be sealed exists reaches an outer circumferential side of the airtightly sealed sliding face, the rotary side sliding ring is made of a self-lubrication sliding material, the stationary side sliding ring is made of a sliding material, the Young's modulus of which is higher that that of the self-lubrication sliding material, and a sliding protrusion extending from the rotary side sliding ring in the circumferential direction slidably comes into contact with the stationary side sliding ring. In this case, the self-lubrication sliding material, which is material of the rotary side sliding ring, is a carbon sliding material, a PTFE sliding material or a polyimide sliding material.
In the above structure, the rotary side sliding ring is given a deforming force in the leaning direction by a differential pressure between high gas pressure in the device and atmospheric pressure outside the device, however, this deforming force is canceled by a deforming force generated by a component force in the axial direction of the differential pressure acting on the annular step section of the rotary shaft in a pushing direction. Therefore, the occurrence of partial abrasion of the airtightly sealed sliding face, which is caused by a deformation of the rotary side sliding ring by leaning, can be suppressed. In this connection, the stationary side sliding ring is also given a deforming force in the leaning direction by the differential pressure in the same manner as that d

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