The present invention relates to a bearing structure
of a rotary valve in a swash plate type compressor suitable
for air-conditioning of a vehicle.
A reciprocative compressor as disclosed in Japanese
Unexamined Patent Publication No. Hei 6-137265 is known.
This compressor has a cylinder block having a plurality of
cylinder bores around the axial center, a shaft inserted
into an axial hole of the cylinder block, a plurality of
pistons which are coupled to a swash plate in a crank
chamber that operates together with the shaft and
reciprocate in the respective cylinder bores, and a housing
which has a suction chamber communicatable to the axial
hole of the cylinder block and a discharge chamber formed
in an outward area of the suction chamber and closes end
faces of the cylinder block. This type of compressor has
communication passages formed between the respective
cylinder bores and the axial hole of the cylinder block,
and a rotary valve coupled to the shaft in such a way as to
be rotatable in synchronism with the shaft. The rotary
valve has a suction passage for sequentially connecting the
communication passages of the individual cylinder bores in
a suction stroke to the suction chamber. The shaft is made
of an iron-based metal, and the rotary valve of an
aluminum-based metal. An engage hole is bored in one end
portion of the rotary valve. Attached to the engage hole
is a steel liner that has a base plate portion, which abuts
on one end of the shaft, and extruding pieces, which are
split from the base plate portion through selectively
bending and are fitted in the engage hole. The split
opening portion of the liner is fitted over an engage shaft
protruding from the shaft end.
Because the shaft and the rotary valve in such a
compressor are formed of different members, however, the
compressor has a larger number of components. To reduce
the number of the components, the shaft and the rotary
valve may be formed integrally. From the viewpoint of
securing the strength, the shaft is often made of an iron-based
metal having rigidity. In a case where the shaft and
the rotary valve may be formed integrally, therefore, the
rotary valve is likely to be made of an iron-based metal.
Generally, the housing is made of an aluminum-based metal
to become lighter. As the shaft rotates at a high speed,
therefore, the temperature of the slide surface between the
housing and rotary valve, which are made of different
metals, rises and the clearance between the housing and the
rotary valve increases due to the difference between their
coefficients of thermal expansion. The increased clearance
leads to gas leakage and a reduction in sealability, which
would lower the performance of the compressor.
Accordingly, it is an object of the present invention
to provide a swash plate type compressor which prevents an
increase in the clearance between the housing and the
rotary valve when the shaft rotates at a high speed.
A swash plate type compressor includes a housing
having a cylinder block. The cylinder block has a
plurality of cylinder bores around a shaft. The shaft is
rotatably supported in the housing. An suction pressure
area is formed in the housing. A plurality of pistons are
respectively inserted into the cylinder bores and
reciprocate in the respective cylinder bores via a swash
plate in accordance with rotation of the shaft to thereby
perform a suction stroke for taking a refrigerant gas in
the suction pressure area into a compression chamber formed
in each cylinder bore. The swash plate type compressor
comprises communication passages, a rotary valve, and a
sleeve. The communication passages is formed in the
cylinder block in such a way as to communicate with the
cylinder bores, respectively. The rotary valve is formed
integral with the shaft. The rotary valve has a suction
passage for connecting the communication passage of each
cylinder bore in the suction stroke to the suction pressure
area. The sleeve is provided on the rotary valve in the
cylinder block. The sleeve has a coefficient/of thermal
expansion closer to that of the shaft than that of the
cylinder block.
Other aspects and advantages of the invention will
become apparent from the following description, taken in
conjunction with the accompanying drawings, illustrating by
way of example the principles of the invention.
The invention, together with objects and advantages
thereof, may best be understood by reference to the
following description of the presently preferred
embodiments together with the accompanying drawings in
which:
Fig. 1 is a schematic cross-sectional view of a
compressor according to one embodiment of the invention
taken along the line B-B in Fig. 2; Fig. 2 is a cross-sectional view of the compressor
taken along the line A-A in Fig. 1; and Fig. 3 is a partly enlarged cross-sectional view
showing the details of the compressor in Fig. 1.
One embodiment of the present invention as embodied
into a swash plate type compressor which is used in a
vehicular air-conditioning system will be described below
with reference to Figs. 1 to 3.
As shown in Fig. 1, a front housing 11 is connected
to the front end of a cylinder block 12. A rear housing 13
is connected to the rear end of the cylinder block 12 via a
valve plate assembly 14. The front housing 11, the
cylinder block 12 and the rear housing 13 are fastened by
through bolts 11a (see Fig. 2) and constitute the housing
of the compressor. The front housing 11, the cylinder
block 12 and the rear housing 13 are made of an aluminum-based
metal. The coefficient of thermal expansion of
aluminum is about 19 to 23 x 10-6/°C. Note that the lefthand
side in Fig. 1 shows the frontward of the compressor,
and the right-hand side shows the rearward thereof.
The valve plate assembly 14 includes a main plate 14a,
a sub plate 14b stacked over the rear surface of the main
plate 14a and a retainer plate 14c stacked over the rear
surface of the sub plate 14b. The valve plate assembly 14
is connected to the cylinder block 12 at the front surface
of the main plate 14a.
A crank chamber 15 is defined between the front
housing 11 and the cylinder block 12. A shaft 16 is
rotatably supported between the front housing 11 and the
cylinder block 12 in such a way as to pass through the
crank chamber 15. The front end portion of the shaft 16 is
supported on the front housing 11 via a radial bearing 17.
A retaining hole 18 is formed nearly in the center of the
cylinder block 12. The rear end portion of the shaft 16 is
supported on a radial bearing 19 which is provided in the
retaining hole 18. A shaft seal 20 is provided at the
front end portion of the shaft 16. The shaft 16 is made of
an iron-based metal. The coefficient of thermal expansion
of iron is about 10 to 12 x 10-6/°C.
A plurality of cylinder bores 12a (only two shown in
Fig. 1) are formed in the cylinder block 12 in such a way
as to surround the shaft 16 at equiangles and equal
distances. One-headed pistons 21 are retained in a
reciprocative manner in the respective cylinder bores 12a.
The front opening of each cylinder bore 12a is closed by
the front surface of the associated piston 21, and the rear
opening of that cylinder bore 12a is closed by the front
surface of the valve plate assembly 14. A compression
chamber 22 is defined in each cylinder bore 12a and its
volume varies in accordance with the reciprocation of the
associated piston 21.
A lug plate 23 is fixed to the shaft 16 in the crank
chamber 15 in such a way as to be rotatable together with
the shaft 16. The lug plate 23 is abuttable on an inner
wall surface 11b of the front housing 11 via a thrust
bearing 24. The inner wall surface 11b supports the axial
weight originated from the compression repulsive force of
each piston 21 and restricts the forward slide movement of
the shaft 16.
A swash plate 25 is provided in the crank chamber 15
with the shaft 16 put through a through hole formed in the
swash plate 25. A hinge mechanism 26 is positioned between
the lug plate 23 and the swash plate 25. The hinge
coupling with the lug plate 23 via the hinge mechanism 26
and the support on the shaft 16 allow the swash plate 25 to
be rotatable in synchronism with the lug plate 23 and the
shaft 16, be slidable in the axial direction of the shaft
16 and be tiltable with respect to the shaft 16. The lug
plate 23 and the hinge mechanism 26 constitute a variable
displacement mechanism.
Each piston 21 is engaged with the peripheral portion
of the swash plate 25 via a shoe 27. The rotation of the
shaft 16 is converted into the reciprocating motion of the
pistons 21 via the swash plate 25 and the shoes 27.
The lug plate 23, the swash plate 25, the hinge
mechanism 26 and the shoes 27 constitute a crank mechanism
which converts the rotational movement of the shaft 16 to a
compression action to compress the refrigerant gas in the
compression chamber 22.
A restricting portion 28 is provided on the shaft 16
between the swash plate 25 and the cylinder block 12. The
restricting portion 28 is a ring-like member secured to the
outer surface of the shaft 16. The minimum inclination
angle of the swash plate 25 is defined by the abutment on
the restricting portion 28, while the maximum inclination
angle of the swash plate 25 is defined by the abutment on
the lug plate 23.
As shown in Fig. 1, a suction chamber 29 and a
discharge chamber 30 are defined in the rear housing 13.
Discharge ports 33 and discharge valves 34 which open and
close the respective ports 33 are formed in the valve plate
assembly 14 in association with the respective cylinder
bores 12a. Each cylinder bore 12a communicates with the
discharge chamber 30 via the respective discharge port 33.
The suction chamber 29 is connected to the discharge
chamber 30 via an external refrigeration circuit (not show).
An supply passage 35 which connects the crank chamber
15 to the discharge chamber 30 is formed in the cylinder
block 12 and the rear housing 13. Disposed in the supply
passage 35 is a control valve 36 which constitutes the
variable displacement mechanism. The control valve 36 is a
known solenoid valve. The control valve 36 provides a
valve chamber in the supply passage 35. The angle of
opening of the control valve 36 is adjustable by the amount
of the excitation current of the solenoid. The control
valve 36 also serves as a restrictor. Therefore, the
supply passage 35 is closed by the excitation of the
solenoid and is released by the deexcitation of the
solenoid.
The rear end portion of the shaft 16 forms a rotary
valve 37. The shaft 16 is integral with the rotary valve
37 so that as the shaft 16 rotates, the rotary valve 37
rotates together with the shaft 16. The shaft 16 and the
rotary valve 37 are made of the same iron-based metal. A
circulation passage 38 is formed in the shaft 16 and the
rotary valve 37. An oil separator 39, which separates oil
from the refrigerant gas, is provided at the rear end
portion of the circulation passage 38, i.e., nearly the
center portion of the rotary valve 37. Coating is applied
to the surfaces of the shaft 16 and the rotary valve 37.
An inlet 38a of the circulation passage 38 is formed
in the rearward of the radial bearing 17. The rear end
portion of the circulation passage 38 is widened by the oil
separator 39 and forms a communication chamber 41b. The
rear end of the communication chamber 41b is connected to
the suction chamber 29 in such a way that the refrigerant
gas flows there. Accordingly, the circulation passage 38
constitutes a bleed passage which connects the crank
chamber 15 to the suction chamber 29.
The inner surface of the oil separator 39 is inclined
in such a way that the inside diameter of the oil separator
39 becomes larger toward the rear end, which is the
downstream side to the flow of the refrigerant gas from the
crank chamber 15 to the suction chamber 29, from the distal
end which is the upstream side. The diameter of the oil
separator 39 is the largest at the rear end.
A communication hole 41a which communicates with the
circulation passage 38 from the side is formed in the
rotary valve 37, as shown in Fig. 1. As the rotary valve
37 rotates in the direction of the arrow in Fig. 2 in
accordance with the rotation of the shaft 16, communication
passages 42 of the cylinder bores 12a communicate with the
communication hole 41a. The communication hole 41a and the
communication chamber 41b constitute a suction passage 41.
The suction passage 41 is provided on a rearer end
side (the downstream side or right-hand side in Fig. 1) to
the shaft 16 than the oil separator 39. One end of the
communication passage 42 communicates with the associated
cylinder bore 12a and the other end of the passage 42 is
located in a position corresponding to the suction passage
41 (communication hole 41a). When the rotary valve 37
rotates, the communication passage 42 of the cylinder bore
12a in a suction stroke communicates with the suction
passage 41, while the communication passage 42 of the
cylinder bore 12a in a discharge stroke does not
communicate with the suction passage 41. At this time, the
slide surface (sealed portion) between the rotary valve 37
and the cylinder block 12 is sealed in an air-tight manner.
The slide surface between the rotary valve 37 and the
cylinder block 12 is formed by a sleeve 43. The sleeve 43
is fitted in the cylinder block 12 by casting or press
fitting. The sleeve 43 is made of an iron-based metal
which has a coefficient of thermal expansion closer to
those of the shaft 16 and the rotary valve 37.
The action of the compressor with the above-described
structure will be discussed below.
As the shaft 16 rotates, the swash plate 25 rotates
together with the shaft 16 via the lug plate 23 and the
hinge mechanism 26. The rotational motion of the swash
plate 25 is converted to the reciprocating motion of the
pistons 21 via the shoes 27. As this driving continues,
the suction, compression and discharge of the refrigerant
are repeated one after another in the compression chamber
22. The refrigerant is supplied to the suction chamber 29
from the external refrigeration circuit, is fed into the
compression chamber 22 (suction stroke), is compressed by
the movement of the associated piston 21 (compression
stroke) and is discharged to the discharge chamber 30 via
the associated discharge port 33 (discharge stroke). The
discharged refrigerant is fed out to the external
refrigeration circuit via a discharge passage.
Then, a control apparatus (not shown) adjusts the
degree of opening of the control valve 36 or the degree of
opening of the supply passage 35 in accordance with the
refrigerant load, thereby changing the state of
communication of the discharge chamber 30 with the crank
chamber 15.
When the refrigerant load is large, the degree of
opening of the supply passage 35 is reduced, thereby
decreasing the flow rate of the refrigerant gas to be
supplied to the crank chamber 15 from the discharge chamber
30. As the amount of the refrigerant gas to be supplied to
the crank chamber 15 is reduced, the pressure in the crank
chamber 15 gradually drops due to the escape of the
refrigerant gas to the suction chamber 29 via the
circulation passage 38 or the like. As a result, the
difference between the pressure in the crank chamber 15 and
the pressure in each cylinder bore 12a via the associated
piston 21 becomes smaller, so that the swash plate 25 is
displaced in the direction of increasing the inclination
angle (leftward in Fig. 1). Therefore, the amount of the
stroke of the piston 21 increases, thus making the
discharge volume greater.
When the refrigerant load becomes smaller, on the
other hand, the degree of opening of the control valve 36
is increased, thereby increasing the flow rate of the
refrigerant gas to be supplied to the crank chamber 15 from
the discharge chamber 30. When the amount of the
refrigerant gas to be supplied to the crank chamber 15
exceeds the escape amount of the refrigerant gas to the
suction chamber 29 via the circulation passage 38, the
pressure in the crank chamber 15 gradually rises.
Consequently, the difference between the pressure in the
crank chamber 15 and the pressure in each cylinder bore 12a
via the associated piston 21 becomes larger, so that the
swash plate 25 is displaced in the direction of decreasing
the inclination angle (rightward in Fig. 1). The amount of
the stroke of the piston 21 therefore decreases, thus
reducing the discharge volume.
The refrigerant gas which is fed toward the suction
chamber 29 via the circulation passage 38 is whirled in
accordance with the rotation of the oil separator 39. This
causes the centrifugal separation of the oil from the
refrigerant gas. The separated oil is discharged out of
the oil separator 39 by the centrifugal force or the like
based on the rotation of the oil separator 39. The
discharged oil is supplied between the rotary valve 37 and
the cylinder block 12 and between the piston 21 and the
associated cylinder bore 12a via the suction passage 41 and
the associated communication passage 42.
Part of the refrigerant gas, from which the oil has
been separated in the oil separator 39, is supplied to the
suction chamber 29 via the communication chamber 41b. The
refrigerant gas supplied to the suction chamber 29 (this
gas has a small amount of oil mixed therein) is discharged
to the external refrigeration circuit via the associated
compression chamber 22 and the discharge chamber 30.
As the shaft 16 and the rotary valve 37 rotate
together, the refrigerant gas in the suction chamber 29 is
sucked into each cylinder bore 12a via the suction passage
41 of the shaft 16 and the communication passage 42 of that
bore 12a in the suction stroke. Because the suction of the
refrigerant gas continues in each cylinder bore 12a
smoothly and stably, a pressure loss becomes extremely
small.
The sleeve 43 serves as a rotary valve receiving
portion of the cylinder block 12. The sleeve 43 is formed
by casting or press fitting in the cylinder block 12. When
the shaft 16 rotates at a high speed, the rotary valve 37
slides with respect to the sleeve 43, raising the
temperature of the slide surface therebetween. Since the
rotary valve 37 and the sleeve 43 are both made of an iron-based
metal and their coefficients of thermal expansion are
almost equal to each other, the clearance between the
rotary valve 37 and the sleeve 43 can be prevented from
increasing.
The above-mentioned embodiment have the following
advantages.
The rotary valve 37 and the shaft 16 are integrally
formed of an iron-based metal and the sleeve 43 is made of
an iron-based metal whose coefficient of thermal expansion
is closer to that of the shaft 16 (and the rotary valve 37).
This can reduce the number of components and prevents an
increase in the clearance between the slide surfaces of the
rotary valve 37 and the sleeve 43, which would be caused by
a temperature rise at the time the shaft 16 rotates at a
high speed. This prevents gas leakage from the clearance
and a reduction in the performance of the compressor. The
sleeve 43 maintains the sealability between the rotary
valve 37 and the cylinder block 12 over a long period of
time. It is therefore possible to smoothly rotate the
rotary valve 37 and suppress sliding noise of the rotary
valve 37.
The rotary valve 37 and the sleeve 43 are made of an
iron-based metal, which is excellent in rigidity over an
aluminum-based metal. This can ensure a high strength.
Coating is applied to the surfaces of the shaft 16
and the rotary valve 37. The coating can prevent burning
of the shaft 16 and the rotary valve 37 when they rotate
together.
The control valve 36 is provided in the supply
passage 35. The control valve 36 can control the pressure
in the crank chamber 15 by using the high pressure in the
discharge chamber 30. Thus, discharge volume can be
controlled with high accuracy.
The inner surface of the oil separator 39 is inclined
in such a way that the inside diameter of the oil separator
39 becomes larger from the upstream side toward the
downstream of the flow of the refrigerant gas with respect
to the flow of the refrigerant gas. This facilitates the
oil adhered to the inner surface of the oil separator 39 to
be discharged outside from the downstream of the oil
separator 39 by the centrifugal force at the time the shaft
16 rotates.
It should be apparent to those skilled in the art
that the present invention may be embodied in many other
specific forms without departing from the spirit or scope
of the invention. Particularly, it should be understood
that the invention may be embodied in the following forms.
The iron-based metal for the sleeve can be any metal
as long as its coefficient of thermal expansion is close to
that of the iron-based metal for the shaft. For example,
such iron-based metals available include gray cast iron (11
to 12 x 10-6/°C), ductile iron (11 to 12 x 10-6/°C) and Ni-resist
D-3 (8 to 9 x 10-6/°C). In this case, similar
advantages to those obtained when iron is used are also
obtained.
Since the coefficient of thermal expansion of
aluminum is approximately 19 to 23 x 10-6/°C and the
coefficient of thermal expansion of iron is approximately
10 to 12 x 10-6/°C, the coefficient of thermal expansion of
the iron-based metal for the sleeve can lie in a range of
approximately 7 to 15 x 10-6/°C.
The sleeve may be made of any material other than a
metal, as long as its coefficient of thermal expansion is
close to that of the iron-based metal for the shaft. That
is, a resin or ceramics may be used in place of a metal.
Of ceramics, alumina which has a coefficient of thermal
expansion of 6 to 8 x 10-6/°C and zirconia which has a
coefficient of thermal expansion of 9 to 11 x 10-6/°C can be
used, for example. Those of various kinds of engineering
plastics whose coefficients of thermal expansion are near
10 to 13 x 10-6/°C may be used. In this case, advantages
similar to those mentioned above are also obtained.
The suction chamber 29, which is provided in the rear
housing 13, may be omitted. In this case, the refrigerant
is led directly into the communication chamber 41b, which
constitutes an suction pressure area.
The radial bearing 19 may be omitted. The shaft 16
may be supported by the sleeve 43 only.
The compressor may be a wobble type variable
displacement compressor.
The compressor may be a double-headed piston type
compressor.
Therefore, the present examples and embodiments are
to be considered as illustrative and not restrictive and
the invention is not to be limited to the details given
herein, but may be modified within the scope and
equivalence of the appended claims.
A shaft (16) and a rotary valve (37), which are
formed integrally, are made of an iron-based metal while a
cylinder block (12) is made of an aluminum-based metal. A
sleeve (43) forms a slide surface between the cylinder
block (12) and the rotary valve (37) when the shaft (16)
and the rotary valve (37) rotate together. The sleeve (43)
has a coefficient of thermal expansion closer to those of
the shaft (16) and the rotary valve (37) than that of the
cylinder block (12). This structure prevents an increase
in the clearance between the housing and the rotary valve,
due to the increased temperature at the time the shaft
rotates at a high speed, and prevents gas leakage and a
reduction in sealability.