TECHNICAL FIELD
The present invention relates to a control valve for
variable displacement compressors that are used in vehicle
air conditioners.
BACKGROUND ART
A typical variable displacement compressor includes a
control passage for connecting a discharge pressure zone with
a crank chamber. The pressure in the crank chamber is
adjusted to change the inclination of a cam plate.
Accordingly, the displacement is controlled.
Japanese Unexamined Patent Publication No. 4-119271
discloses a typical control valve for variable displacement
compressors. As shown in Fig. 7, this control valve has a
valve chamber 101 in a distal portion of a valve housing 102.
The valve chamber 101 is connected to a discharge pressure
zone by the upstream portion of a control passage 103. The
valve chamber 101 is also connected to a crank chamber by a
valve hole 104, a port 105 and the downstream portion of the
control passage 103. The valve hole 104 is formed axially in
the housing 102 and the port 105 is perpendicular to the
valve hole 104. A valve body 106 is housed in the valve
chamber 101 to open and close the valve hole 104.
A pressure sensing chamber 107 is formed adjacent to
the valve chamber 101 and is connected to a suction pressure
zone. A bellows 108 is housed in the pressure sensing
chamber 107 to detect the pressure of the suction pressure
zone. The pressure sensing chamber 107 is separated from the
valve chamber 101 by a dividing wall 102a. A guide hole 109
is formed in the dividing wall 102a to be continuous with the
valve hole 104. The chambers 101 and 107 are therefore
connected to each other. A rod 110 is slidably fitted in the
guide hole 109 to couple the bellows 108 with the valve body
106. The bellows 108 is deformed in accordance with the
suction pressure of the refrigerant gas. The deformation of
the bellows 108 is transmitted to the valve body 106 by the
rod 110.
A solenoid portion 111 is attached to a proximal
portion of the valve housing 102 and is coupled to the valve
body 106 by the bellows 108. The solenoid portion 111 is
excited and de-excited for changing the attraction force
between a fixed iron core 112 and a movable iron core 113.
Accordingly, the load acting on the valve body 106 is
changed. Therefore, the opening size of the control passage
103 is determined by the equilibrium of forces, such as the
force of the solenoid portion 111 and the force of the
bellows 108.
The pressure in the port 105 is relatively high and the
pressure in the pressure sensing chamber 107 is relatively
low. The rod 110 and the guide hole 109 are machined with
meticulous care for allowing the rod 110 to slide in the hole
109 and for preventing leakage of gas between the port 105
and the pressure sensing chamber 107. However, small
machining errors are inevitable, and the space between the
surface of the rod 110 and the surface of the guide hole 109
is different between a location near the port 105 and a
location near the pressure sensing chamber 107. Particularly,
when the space near the port 105 is smaller than the space
near the pressure sensing chamber 107, the pressure
difference between the port 105 and the pressure sensing
chamber 107 generates a lateral force acting on the rod 110.
The lateral force presses the rod 110 against the surface of
the guide hole 109, which increases the sliding resistance
between the rod 110 and the guide hole 109 (this phenomena
will hereafter be referred to as fluid fixation).
A recent trend is to reduce the size of the solenoid
portion 111 to reduce the size of the compressor. In a valve
having a small solenoid portion 111, the bellows 108 is
relatively small and the valve body 106 is moved by the
equilibrium of the difference between small forces, that is,
the force of the solenoid portion 111 and the force of the
bellows 108. Therefore, the control valve is easily affected
by an increase of the sliding resistance between the rod 110
and the guide hole 109 due to the fluid fixation. As a
result, even a small sliding resistance, which would be
negligible if the bellows 108 were large, causes hysteresis.
Therefore, the controllability of the displacement
significantly deteriorates.
DISCLOSURE OF THE INVENTION
The present invention was made in view of drawbacks in
the above described prior art. Accordingly, it is an
objective of the present invention to provide a control valve
for a variable displacement compressor that reduces sliding
resistance between a rod and a guide hole.
To achieve the foregoing objective, the present
invention provides a control valve for a variable
displacement compressor. The control valve includes a valve
body. The valve body opens and closes a control passage,
which connects a control pressure chamber with a suction
pressure zone or with a discharge pressure zone, to adjust
the opening size of the control passage for varying the
displacement of the compressor. The valve body is opened and
closed by a drive member. A dividing wall separates a
portion that accommodates the valve body from a portion that
accommodates the drive member. A guide hole is formed in the
dividing wall to communicate the valve body accommodating
portion with the drive member accommodating portion. A
sliding rod is located in the guide hole to operably couple
the valve body to the drive member. The control valve is
characterized by means for preventing fluid fixation. The
fluid fixation preventing means is located on at least one
of the outer surface of the rod and on the inner surface of
the guide hole.
The invention of the above structure has the means for
preventing fluid fixation between the rod and the guide hole,
which decreases the hysteresis of the control valve and
prevents deterioration of the displacement controlling
performance of the control valve.
In the above structure, the means may include a tapered
surface formed on at least one of the outer surface of the
rod and the inner surface of the guide hole such that the
space between the outer surface of the rod and the inner
surface of the guide hole widens toward one of the valve body
accommodating portion and the drive member accommodating
portion that has a higher pressure.
If the axis of the rod is displaced from the axis of
the guide hole for some reason, the rod receives a lateral
force, the direction of which is opposite to the displacement
direction. The misalignment of the axes is automatically
corrected.
In the above structures, the tapered surface may be one
of a plurality of tapered surfaces formed along the axial
direction of the rod.
In this structure, the cross-sectional area of the
space between the outer surface of the rod and the inner
surface of the guide hole changes in the axial direction in a
completed fashion and functions like a labyrinth seal. This
effectively prevents pressure leakage and refrigerant gas
leakage between the high pressure location and the low
pressure location.
In the above structure, the outer surface of the rod
may be tapered such that the diameter of the rod decreases
toward one of the valve body accommodating portion and the
drive member accommodating portion that has higher pressure.
This eliminates the necessity for tapering the inner wall of
the guide hole, which is formed in the dividing wall and has
a small cross-section, by inserting a tool into the guide
hole.
In the above structures, the means may include a
circumferential annular groove formed in at least one of the
outer surface of the rod and the inner surface of the guide
hole.
The annular groove circumferentially equalizes the
pressure in the space between the outer surface of the rod
and the inner surface of the guide hole. Accordingly, fluid
fixation does not occur between the rod and the guide hole.
If the annular groove is formed in the outer surface of
the rod, the groove is easily formed.
In the above structure, the drive member may include a
pressure sensing mechanism having a pressure sensing chamber
and a pressure sensing member located in the pressure sensing
chamber. The pressure sensing chamber is connected either
with the suction pressure zone or with the control pressure
chamber by a pressure introduction passage. The rod operably
couples the pressure sensing member with the valve body.
In this structure, the pressure sensing member is
deformed by pressure in the pressure sensing chamber, that is,
by either the pressure of the suction pressure zone or the
pressure in the control pressure chamber. The deformation is
transmitted to the valve body by the rod.
In the above structure, the drive member may include a
solenoid portion. The solenoid portion is excited and de-excited
to actuate a plunger accommodated in a plunger
chamber. The rod operably couples the plunger with the valve
body.
In this structure, the plunger is moved by excitation
and de-excitation of the solenoid portion. The movement of
the plunger is transmitted to the valve body by the rod.
In the above structure, the drive member may include a
pressure sensing mechanism and a solenoid portion. The
pressure sensing mechanism may include a pressure sensing
chamber and a pressure sensing member located in the pressure
sensing chamber. The pressure sensing chamber is connected
either with the suction pressure zone or with the control
pressure chamber by a pressure introduction passage. The
solenoid portion is excited and de-excited to actuate a
plunger accommodated in a plunger chamber. The rod may
include a first rod portion, which operably couples the
pressure sensing member with the valve body, and a second rod
portion, which operably couples the plunger with the valve
body.
In this structure, the opening size of the control
passage is determined by the position of the valve body,
which is determined by the equilibrium of the force of the
pressure sensing mechanism and the force of the solenoid
portion.
In the above structure, the control passage may connect
the discharge pressure zone with the control pressure chamber.
In this structure, the amount of refrigerant gas drawn
into the control pressure chamber is adjusted for controlling
the displacement. Highly pressurized gas is introduced into
the control valve. Fluid fixation between the rod and the
guide hole causes the rod to be pressed against the guide
hole by a greater force compared to a control valve that
adjusts the amount of refrigerant gas discharged from the
control pressure chamber to control the compressor
displacement. Therefore, the present invention has a great
advantage.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1A is a cross-sectional view of a control valve
according to a first embodiment of the present invention, in
which the outer surface of the rod is tapered;
Fig. 1B is a cross-sectional view of a control valve
according to the first embodiment, in which the inner surface
of the guide hole is tapered;
Figs. 1C and 1D are enlarged partial cross-sectional
views of the control valve according to the first embodiment,
in which the outer surface of the rod and the inner surface
of the guide hole are both tapered;
Fig. 2 is a cross-sectional view illustrating a
clutchless type variable displacement compressor;
Fig. 3 is an enlarged partial cross-sectional view
showing a compressor in which the displacement is minimum;
Fig. 4 is a diagram showing operation;
Fig. 5A is an enlarged partial cross-sectional view of
a displacement control valve according to a second embodiment,
in which a plurality of tapered surfaces are formed on the
outer surface of the rod;
Fig. 5B is an enlarged partial cross-sectional view of
a displacement control valve according to the second
embodiment, in which a plurality of tapered surfaces are
formed on the inner surface of the guide hole;
Fig. 5C is an enlarged partial cross-sectional view of
a displacement control valve according to the second
embodiment, in which a plurality of tapered surfaces are
formed on the outer surface of the rod and on the inner
surface of the guide hole;
Fig. 6A is a cross sectional view illustrating a
displacement control valve according to a third embodiment,
in which a plurality of annular grooves are formed on the
outer surface of the rod;
Fig. 6B is a cross sectional view illustrating a
displacement control valve according to the third embodiment,
in which a plurality of annular grooves are formed on the
inner surface of the guide hole;
Fig. 6C is a vertical cross sectional view illustrating
a displacement control valve according to the third
embodiment, in which a plurality of annular grooves are
formed both on the outer surface of the rod and on the outer
surface of the rod; and
Fig. 7 is a vertical cross-sectional view showing a
prior art displacement control valve.
BEST MODE FOR CARRYING OUT THE INVENTION
Displacement control valves used in variable
displacement compressors according to first to third
embodiments will now be described. The displacement control
valves of the first and second embodiments are used in a
clutchless type variable displacement compressor, while the
control valve according to the third embodiment is used in
another type variable displacement compressor. In the
descriptions of the second and third embodiments, only
differences from the first embodiment will be discussed.
Like or the same reference numerals are given to those
components that are like or the same as the corresponding
components of the first embodiment.
(FIRST EMBODIMENT)
First, the structure of the clutchless type variable
displacement compressor will be described.
As shown in Fig. 2, a front housing 11 is secured to
the front end face of a cylinder block 12. A rear housing 13
is secured to the rear end face of the cylinder block 12, and
a valve plate 14 is located between the rear housing 13 and
the cylinder block 12. The front housing 11 and the cylinder
block 12 define a control pressure chamber, which is a crank
chamber 15. A drive shaft 16 extends through the crank
chamber 15 and is rotatably supported by the front housing 11
and the cylinder block 12. A pulley 17 is rotatably
supported by the front housing 11. The pulley 17 is coupled
to the drive shaft 16. A belt 19 is engaged with the
periphery of the pulley 17 to directly couple the pulley 17
with a vehicle engine 20 without a clutch such as an
electromagnetic clutch.
A lug plate 22 is secured to the drive shaft 16 in the
crank chamber 15. A swash plate 23 is supported by the lug
plate 22 to slide axially and to incline with respect to the
axis L of the drive shaft 16. A hinge mechanism 24 is
located between the lug plate 22 and the swash plate 23. The
hinge mechanism 24 permits the swash plate 23 to incline with
respect to the axis L of the drive shaft 16 and to rotate
integrally with the drive shaft 16. As the radial center of
the swash plate 23 slides toward the cylinder block 12, the
inclination of the swash plate 23 decreases. A spring 26 for
decreasing the inclination is located between the lug plate
22 and the swash plate 23. The spring 26 urges the swash
plate 23 in the direction of disinclination of the swash
plate 23. The maximum inclination of the swash plate 23 is
defined by contact between the swash plate 23 and the lug
plate 22.
As shown in Fig. 3, an accommodation chamber 27 is
formed in the center of the cylinder block 12 and extends
along the axis L of the drive shaft 16. A sliding
cylindrical shutter 28 is accommodated in the accommodation
chamber 27. A spring 29 for opening a suction passage is
located between an end of the chamber 27 and the shutter 28
and urges the shutter 28 toward the swash plate 23.
The rear end portion of the drive shaft 16 is located
in the shutter 28. A radial bearing 30 is located between
the rear end portion of the drive shaft 16 and the inner wall
of the shutter 28. The radial bearing 30 slides with the
shutter 28 with respect to the drive shaft 16 along the axis
L.
A suction passage 32, which is part of the suction
pressure zone, is formed in the center of the rear housing 13
and the valve plate 14. The suction passage 32 communicates
with the accommodation chamber 27. A positioning surface 33
is defined on the valve plate 14 about an opening of the
passage 32. A shutting surface 34 is defined on an end of
the shutter 28. The shutting surface 34 contacts and
separates from the positioning surface 33 in accordance with
the position of the shutter 28. When the shutting surface 34
contacts the positioning surface 33, the surfaces 33, 34 seal
the interior of the accommodation chamber 27 from the suction
passage 32.
A thrust bearing 35 is located between the swash plate
23 and the shutter 28 such that the swash plate 23 slides
along the drive shaft 16. The thrust bearing 35 is urged by
the spring 29 and is normally held between the swash plate 23
and the shutter 28. As the swash plate 23 inclines toward
the shutter 28, the inclination of the swash plate 23 is
transmitted to the shutter 28 through the thrust bearing 35.
Accordingly, the shutter 28 is moved toward the positioning
surface 33 against the force of the spring 29 and the
shutting surface 34 of the shutter 28 contacts the
positioning surface 33. The contact between the shutting
surface 34 and the positioning surface 33 prevents the swash
plate 23 from being further inclined. In this state, the
swash plate 23 is at the minimum inclination, which is
slightly more than zero degrees.
Cylinder bores 12a are formed in the cylinder block 12.
A single-headed piston 36 is accommodated in each cylinder
bore 12a. Each piston 36 is coupled to the periphery of the
swash plate 23 by way of a pair of shoes 37. The pistons 36
are reciprocated by rotation of the swash plate 23.
A suction chamber 38, which forms part of suction
pressure zone, and a discharge chamber 39, which forms part
of discharge pressure zone, are defined in the rear housing
13. Suction ports 40, suction valve flaps 41, discharge
ports 42 and discharge valve flaps 43 are formed in the valve
plate 14. Each suction valve flap 41 opens and closes one of
the suction ports 40 and each discharge valve flap 43 opens
and closes one of the discharge ports 42. When moved from
the top dead center to the bottom dead center, each piston 36
draws refrigerant gas from the suction chamber 38 to the
associated cylinder bore 12a via the associated suction port
40 and the associated suction valve flap 41. Refrigerant gas
in each cylinder bore 12a is compressed to reach a
predetermined pressure as the associated piston 36 is moved
from the bottom dead center to the top dead center and is
discharged to the discharge chamber 39 via the associated
discharge port 42 and the associated discharge valve flap 43.
The suction chamber 38 communicates with the
accommodation chamber 27 via a communication hole 45. When
the shutting surface 34 of the shutter 28 contacts the
positioning surface 33, the communication hole 45 is
disconnected from the suction passage 32. A passage 46
axially extends in the drive shaft 16 to connect the crank
chamber 25 with the interior of the shutter 28. A pressure
release hole 47 is formed in the peripheral wall of the
shutter 28 to communicate the interior of the shutter 28 with
the accommodation chamber 27.
A control passage 48 connects the discharge chamber 39
with the crank chamber 15. A displacement control valve 49
is located in the control passage 48. The suction passage 32
is connected to the control valve 49 by a pressure
introduction passage 50.
The suction passage 32 draws refrigerant gas to the
suction chamber 38. A discharge outlet 51 discharges
refrigerant gas from the discharge chamber 39. The suction
passage 32 is connected to the discharge outlet 51 by an
external refrigerant circuit 52. The circuit 52 includes a
condenser 53, an expansion valve 54 and an evaporator 55. A
sensor 56 is located in the vicinity of the evaporator 55.
The sensor 56 detects the temperature of the evaporator 55
and sends the detected temperature information to a computer
57. The computer 57 is connected to a temperature adjuster
58, a sensor 59 and an air conditioner switch 60. The
temperature adjuster 58 sets the temperature in the passenger
compartment. The sensor 59 detects the temperature of the
passenger compartment.
The computer 57 receives various information including
a target temperature set by the temperature adjuster 58, the
temperature detected by the sensor 56, the temperature
detected by the sensor 59 and an ON/OFF signal from the air-conditioner
switch 60. Based on this information, the
computer 57 computes the value of a current supplied to a
drive circuit 61. Accordingly, the drive circuit 61 sends a
current having the computed value to the control valve 49.
In addition to the above listed data, the computer 57 may use
other data such as the temperature outside the compartment
and the engine speed for determining the magnitude of
electric current sent to the control valve 49.
The structure of the control valve 49 will now be
described.
As shown in Figs. 1A, 2 and 3, the control valve 49
includes a valve housing 71 and a solenoid portion 72. The
valve housing 71 and the solenoid portion 72 are coupled at
the center of the control valve 49. A valve chamber 73 is
defined between the valve housing 71 and the solenoid portion
72. The valve chamber 73 is connected to the discharge
chamber 39 through a port 77 and the upstream portion of the
control passage 48. A valve body 74 is accommodated in the
valve chamber 73. A valve hole 75 opens in the valve chamber
73 to face the valve body 74. The valve hole 75 extends
along the axis of the valve housing 71. A spring 76 is
located between the valve body 74 and the inner wall of the
valve chamber 73 to urge the valve body 74 in the direction
for opening the valve hole 75.
A pressure sensing chamber 84 is defined in the distal
portion of the valve housing 71. The pressure introduction
passage 50 is connected to the pressure sensing chamber 84.
Therefore, the pressure sensing chamber 84 is connected to
the suction passage 32 through a port 86 and the pressure
introduction passage 50. A pressure sensing member, which is
a bellows 87, is accommodated in the pressure sensing chamber
84.
A guide hole 88 is formed in a dividing wall 71a of the
valve housing 71, which divides the pressure sensing chamber
84 from the valve chamber 73. The guide hole 88 connects the
pressure sensing chamber 84 with the valve chamber 73. The
guide hole 88 is formed continuously with the valve hole 75.
A sliding rod 89 is located in the guide hole 88. The distal
end of the rod 89 is engaged with the bellows 87. The rod 89
is integral with the valve body 74 to operably couple the
bellows 87 with the valve body 74. A part of the rod 89 that
is connected to the valve body 74 has a small diameter to
define a gas passage in the valve hole 75.
A port 90 is formed in the dividing wall 71a between
the valve chamber 73 and the pressure sensing chamber 84.
The port 90 is perpendicular to the valve hole 75. The port
90 is connected to the crank chamber 15 through the
downstream portion of the control passage 48. That is, the
port 77, the valve chamber 73, the valve hole 75 and the port
90 form part of the control passage 48.
A plunger chamber 91 is defined in the solenoid portion
72. A fixed iron core 92 is fitted in the upper opening of
the plunger chamber 91. The fixed core 92 separates the
plunger chamber 91 from the valve chamber 73. A plunger,
which is a cup-shaped movable iron core 93, is accommodated
in the plunger chamber 91. The movable core 93 reciprocates
in the axial direction of the valve housing 71. A follower
spring 94 is located between the movable core 93 and the
bottom surface of the plunger chamber 91.
A guide hole 95 is formed in the fixed iron core 92,
which functions as a dividing wall, to connect the plunger
chamber 91 with the valve chamber 73. A sliding rod 96 is
integral with the valve body 74 and is fitted in the guide
hole 95. The end of the rod 96 that is closer to the movable
core 93 is pressed against the movable core 93 by the force
of the spring 76 and the follower spring 94. Therefore, the
movable core 93 and the valve body 74 are operably coupled to
each other by the rod 96.
A communication groove 81 is formed in the side of the
fixed core 92. A communication hole 82 is formed in the
valve housing 71. A small chamber 83 is defined between the
control valve 49 and an inner wall of the rear housing 13.
The plunger chamber 91 is connected to the port 90 through
the groove 81, the hole 82 and the chamber 83. That is, the
pressure in the plunger chamber 91 is the crank chamber
pressure, which is the same as the pressure in the port 90.
A cylindrical coil 97 is located radially outward of
both the fixed core 92 and the movable core 93. The coil 97
is connected to a drive circuit 61. The drive circuit 61
supplies current to the coil 97 in accordance with command
signals from the computer 57.
As shown in an enlarged oblong window A in Fig. 1A, the
part of the rod 89 that faces the inner surface 88a of the
guide hole 88 includes a cylindrical seal surface 89a and a
tapered surface 89b. The tapered surface 89b is adjacent to
the seal surface 89a and is closer to the port 90 (to the
valve body). The diameter of the tapered surface 89b
decreases toward the port 90. Therefore, the space between
the tapered surface 89b of the rod 89 and the inner surface
88a of the guide hole 88 is greater in the vicinity of the
port 90 than in the vicinity of the pressure sensing chamber
84 (drive member).
As shown in an enlarged oblong window B, part of the
rod 96 that faces the inner surface 95a of the guide hole 95
includes a cylindrical seal surface 96a and a tapered surface
96b. The tapered surface 96b is adjacent to the seal surface
96 and is closer to the valve chamber 73. The diameter of
the tapered surface 96b decreases toward the valve chamber 73.
Therefore, the space between the tapered surface 96b of the
rod 96 and the inner surface 95a of the guide hole 95 is
greater in the vicinity of the valve chamber 73 than in the
vicinity of the plunger chamber 91 (drive member).
The tapered surfaces 89b, 96b of the rods 89, 96 are
machined such that parts adjacent to the port 90 and the
valve chamber 73 have smaller diameters even if there are
machining errors. That is, this embodiment is characterized
in that the outer surfaces of the rods 89,96 are machined
such that the spaces between the surfaces of the rods 89, 96
and the inner surfaces 88a, 95a of the guide holes 88, 95
increase toward the high pressure locations. In the oblong
windows A, B, the tapered surfaces 89b, 96b are exaggerated
for purposes of illustration. Actually, the diameter
difference between each large diameter portion and the
corresponding small diameter portion is between a few micro
meters to a few tens of micro meters.
The operation of the displacement control valve 49 will
now be described.
When the air conditioner switch 60 is on, the computer
57 commands the solenoid portion 72 to be excited if the
temperature detected by the compartment temperature sensor 59
exceeds the target temperature set by the temperature
adjuster 58. Accordingly, a current is supplied to the coil
97 through the drive circuit 61, which generates an
attraction force between the cores 92, 93. The attraction
force is transmitted to the valve body 74 against the force
of the spring 76 and moves the valve body 74 in the direction
reducing the opening size of the valve hole 75.
When the solenoid portion 72 is excited, the bellows 87
is deformed in accordance with variation of the suction
pressure, which is applied to the pressure sensing chamber 84
from the suction passage 32 through the pressure introduction
passage 50. The deformation of the bellows 87 is transmitted
to the valve body 74 by the rod 89. The opening size of the
valve hole 75 is therefore determined by the equilibrium of
the force of the solenoid portion 72, the force of the
bellows 87 and the force of the spring 76.
When the temperature detected by the sensor 59 is far
higher than the temperature set by the adjuster 58, the
cooling load is great. The computer 57 controls the current
value to change the target suction pressure based on the
detected temperature and the target temperature.
Particularly, the computer 57 commands the drive circuit 61
to increase the magnitude of the current as the detected
temperature increases. A higher current magnitude increases
the attractive force between the fixed core 92 and the
movable core 93 thereby increasing the force that causes the
valve body 74 to close the valve hole 75. Accordingly, the
valve body 74 opens and closes the valve hole 75 at a lower
suction pressure. Therefore, a greater current magnitude
causes the control valve 49 to maintain a lower suction
pressure.
A smaller opening size of the valve hole 75 represents
less refrigerant gas supplied to the crank chamber 15 from
the discharge chamber 39 through the control passage 48. On
the other hand, refrigerant gas in the crank chamber 15 flows
to the suction chamber 38 through the passage 46, the
pressure release hole 47, the accommodation chamber 27 and a
communication hole 45, which lowers the pressure in the crank
chamber 15. Further, when the cooling load is great, the
pressure in the suction chamber 38 is high and the difference
between the pressure in the crank chamber 15 and the pressure
in the cylinder bores 12a is small. Accordingly, the
inclination of the swash plate 23 is increased.
When the cross-sectional area of the control passage 48
is zero, or when the end surface 74a of the valve body 74
contacts the inner wall of the valve chamber 73 to completely
close the valve hole 75, highly pressurized refrigerant gas
is not supplied from the discharge chamber 39 to the crank
chamber 15. The pressure in the crank chamber 15 is thus
substantially equalized with the pressure in the suction
chamber 38, which maximizes the inclination of the swash
plate 23. The compressor displacement is thus maximized.
When the temperature detected by the sensor 59 is close
to the temperature set by the adjuster 58, the cooling load
is small. The computer 57 commands the drive circuit 61 to
decrease the magnitude of the current as the detected
temperature decreases. A lower current magnitude decreases
the attractive force between the fixed core 92 and the
movable core 93 thereby decreasing the force that causes the
valve body 74 to close the valve hole 75. Accordingly, the
valve body 74 opens and closes the valve hole 75 at a higher
suction pressure. Therefore, a smaller current magnitude
causes the control valve 49 to maintain a higher suction
pressure.
A greater opening size of the valve hole 75 increases
the amount of refrigerant gas from the discharge chamber 39
to the crank chamber 15, which raises the pressure in the
crank chamber 15. When the cooling load is small, the
pressure in the suction chamber 38 is small and the
difference between the pressure in the crank chamber 15 and
the pressure in the cylinder bores 12a is great. Accordingly,
the inclination of the swash plate 23 is decreased.
As the cooling load approaches zero, the temperature of
the evaporator 55 drops to a frost forming temperature. When
the sensor 56 detects a temperature that is lower than or
equal to a predetermined temperature, the computer 57
commands the drive circuit 61 to de-excite the solenoid
portion 72. The predetermined temperature is a temperature
at which frost is likely to form in the evaporator 55.
Accordingly, current to the coil 97 is stopped and the
solenoid portion 72 is de-excited, which eliminates the
attraction force between the fixed core 92 and the movable
core 93.
The valve body 74 is then moved downward by the force
of the spring 76 against the force of the follower spring 94,
which acts on the valve body 74 through the movable core 93.
Eventually, the valve body 74 fully opens the valve hole 75.
Therefore, a great amount of highly pressurized refrigerant
gas is supplied to the crank chamber 15 from the discharge
chamber 39 through the control passage 48 and the pressure in
the crank chamber 15 is raised. The raised pressure in the
crank chamber 15 minimizes the inclination of the swash plate
23 as shown in Fig. 3.
When the switch 60 is turned off, the computer 57
commands the solenoid portion 72 to be de-excited. This also
minimizes the inclination of the swash plate 23.
As described above, the valve 49 is controlled in
accordance with the magnitude of the current supplied to the
coil 97 of the solenoid portion 72. When the magnitude of
the current is increased, the valve 49 regulates the control
passage 48 at a lower suction pressure. When the magnitude
of the current is decreased, on the other hand, the valve 49
regulates the control passage 48 at a higher suction pressure.
The inclination of the swash plate 23 is changed to maintain
the target suction pressure. Accordingly, the displacement
of the compressor is varied.
That is, the control valve 49 changes the target value
of the suction pressure in accordance with the value of the
current supplied thereto. Also, the valve 49 can cause the
compressor to operate at the minimum displacement for any
given suction pressure. A compressor equipped with the
control valve 49 varies the cooling ability of the
refrigerant circuit.
When the inclination of the swash plate 23 is minimum,
the shutting surface 34 of the shutter 28 abuts against the
positioning surface 33, which closes the suction passage 32.
In this state, the cross-sectional area of the suction
passage 32 is zero, and refrigerant gas cannot flow from the
external refrigerant circuit 52 to the suction chamber 38.
When the shutter 28 is at a closed position, at which the
shutter 28 disconnects the accommodation chamber 27 from the
suction passage 32, the inclination of the swash plate 23 is
minimized. The minimum inclination of the swash plate 23 is
slightly more than zero degrees. The shutter 28 is moved
between the positions for closing and opening the suction
passage 32 in accordance with the inclination of the swash
plate 23.
Since the minimum inclination angle is not zero degrees,
the discharge of the refrigerant gas in the cylinder bores
12a to the discharge chamber 38 is maintained. The
refrigerant gas sent to the discharge chamber 38 flows in the
control passage 48 and then enters the crank chamber 15. The
gas in the crank chamber 15 flows to the suction chamber 38
through the passage 46, the interior of the shutter, the
pressure release hole 47, the accommodation chamber 27 and
the communication hole 45. The gas in the suction chamber 38
is introduced in the cylinder bores 12a and is returned to
the discharge chamber 39.
That is, when the inclination of the swash plate 23 is
minimum, a circulation passage is formed in the compressor.
The circulation passage includes the discharge chamber 39,
which is discharge pressure zone, the control passage 48, the
crank chamber 15, the passage 46, the interior of the shutter
28, the pressure release hole 47, the accommodation chamber
27, the hole 45, the suction chamber 38, which is suction
pressure zone, and the cylinder bores 12a. Since the
pressures in the discharge chamber 39, the crank chamber 15
and the suction chamber 38 are different, refrigerant gas
circulates within the circulation passage. The circulation
of refrigerant gas causes lubricant oil contained in the gas
to lubricate the moving parts of the compressor.
The above embodiment has the following advantages.
(1) The space between the outer surface (89a, 89b) of
the rod 89 and the inner surface 88a of the guide hole 88 is
greater in the vicinity of the port 90, which is a high
pressure location, than in the vicinity of the pressure
sensing chamber 84, which is a low pressure location.
Therefore, fluid fixation between the rod 89 and the guide
hole 88 is prevented. Further, the hysteresis of the control
valve 49 is reduced, which prevents the displacement control
performance of the control valve 49 from deteriorating. As a
result, the size of the solenoid portion 72 is reduced, which
reduces the size of the compressor.
That is, if the axis of the rod 89 is displaced from
the axis of the guide hole 88 as shown in Fig. 4 for some
reason, the space between the outer surface (89a, 89b) of the
rod 89 and the inner surface 88a of the guide hole 88 is
narrower on the right side as viewed in Fig. 4. The pressure
distribution on the right side of the rod 89 suddenly drops
from the tapered surface 89b toward the seal surface 89a. On
the other hand, the space between the outer surface (89a,
89b) of the rod 89 and the inner surface 88a of the guide
hole 88 is wider on the left side of the rod 89 as viewed in
Fig. 4. The pressure distribution on the left side of the
rod 89 gradually decreases from the tapered surface 89b
toward the seal surface 89a. Accordingly, a lateral force,
the direction of which is opposite to the direction of the
displacement, acts on the rod 89. Therefore, the
displacement of the axis of the rod 89 from the axis of the
guide hole 88 is automatically corrected. (2) In the solenoid portion 72, the space between the
outer surface (96a, 96b) of the rod 96 and the inner surface
96a of the guide hole 96 is greater in the vicinity of the
valve chamber 73, which is a high pressure location, than in
the vicinity of the plunger chamber 91, which is a low
pressure location. The solenoid portion 72 therefore has the
advantage (1). (3) The compressor of this embodiment varies the
displacement by adjusting the amount of refrigerant gas
flowing into the crank chamber 15. The valve chamber 73 of
the control valve 49 receives highly pressurized discharge
refrigerant gas. Therefore, fluid fixation between the rod
96 and the guide hole 95 causes the rod 96 to be pressed
against the guide hole 95 by a greater force compared to a
control valve that adjusts the amount of refrigerant gas
discharged from the crank chamber 15 to control the
compressor displacement. The compressor of this embodiment
has a particular advantage since the control valve 49 has the
means for preventing fluid fixation.
In the first embodiment, the tapered surfaces are
formed on the rods 89, 96. However, as shown in enlarged
oblong windows A' and B' of Fig. 1B, tapered surfaces may be
formed in the guide holes 88, 95. According to this
structure, the spaces between the outer surface of the rods
89, 96 and the inner surfaces of the guide holes 88, 95 are
wider in the vicinity of the high pressure locations
compared to the vicinity of the low pressure locations. In
this case, the diameter of the tapered surfaces increase
toward the high pressure locations.
Further, as shown in enlarged oblong windows A'' and B''
of Figs. 1C and 1D, tapered surfaces may be formed both on
rods 89, 96 and the guide holes 88, 95. According to these
structures, the spaces between the outer surfaces of the
guide rods 89, 96 and the inner surface of the guide holes 88,
95 are wider in the vicinity of the high pressure locations
than in the vicinity of the low pressure locations.
However, it is preferred to form tapered surfaces on
the outer surface of the rods 89, 96 as shown in Fig. 1A.
This is because forming tapered surface on the guide holes is
troublesome. Specifically, the guide holes 88, 95 are formed
in the dividing walls 71a, 92. Then, a tool must be inserted
into the narrow guide holes 88, 95 to taper the inner
surfaces.
(SECOND EMBODIMENT)
Fig. 5A illustrates a second embodiment. In this
embodiment, the rods 89, 96 have axially arranged tapered
surfaces 89b, 96b, respectively. Thus, the space between
each tapered surface 89b, 96b and the corresponding inner
surface 88a, 95a increases in size toward the high pressure
locations (73, 90) from the low pressure zone (84, 91).
This embodiment has the same advantages as the first
embodiment. Further, the cross-sectional areas of the spaces
between the tapered surfaces 89b, 96b of the rods 89, 96 and
the inner surfaces 88a, 95a of the guide holes 88, 95 are
complicated in the axial directions. The spaces therefore
function as labyrinth seals. The structure thus prevents
refrigerant gas leakage between the high pressure location
(73, 90) and the low pressure location (84, 91), which
improves the displacement control performance of the control
valve 49.
As in the first embodiment, tapered surfaces may be
formed on the guide holes 88, 95 as shown in Fig. 5B instead
of the tapered surfaces on the rods 89, 96. As shown in Fig.
5C, tapered surfaces may be formed both on the rods 89, 96
and the guide holes 88, 95.
(THIRD EMBODIMENT)
Fig. 6A illustrates a third embodiment. A displacement
control valve 98 of this embodiment is used for a variable
displacement compressor (not shown) that is different from
the variable displacement compressor of the first and second
embodiments. The control valve 98 only functions as a
pressure sensing valve and includes a pressure sensing member,
which is a diaphragm 99.
As shown in an enlarged oblong window C, the valve 98
has a cylindrical rod 100 to operably couple the valve body
74 with the diaphragm 99. Annular grooves 100b are formed on
the outer surface 100a of the rod 100 to face the guide hole
88. The annular grooves 100b are axially arranged at equal
intervals.
The grooves 100b circumferentially equalize the
pressure in the space between the outer surface 100a of the
rod 100 and the inner surface 88a of the guide hole 88. As a
result, when the axis of the rod 100 is displaced from the
axis of the guide hole 88, fluid fixation between the rod 100
and the guide hole 88 is prevented. Thus, the third
embodiment has the advantage (1) of the first embodiment.
Instead of forming annular grooves on the outer surface
100a of the rod 100, annular grooves 88b may be formed on the
inner surface 88a of the guide hole 88 as shown in an
enlarged oblong window C' of Fig. 6B.
Further, as shown in an enlarged oblong window C'' of
Fig. 6C, annular grooves may be formed both on the outer
surface 100a of the rod 100 and on the inner surface 88a of
the guide hole 88.
However, it is preferred to form the annular grooves on
the outer surface 100a of the rod 100. This is because
forming annular grooves on the inner surface 88a of the guide
hole 88 is troublesome. Specifically, the guide hole 88 is
formed in the dividing walls 71a. Then, a tool must be
inserted into the narrow guide hole 88 to form annular
grooves.
Although several embodiments of the present invention
has been described herein, 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. For example, the present
invention may be embodied in a compressor that only has the
electromagnetic valve function 72.