U.S. patent application number 10/648867 was filed with the patent office on 2004-03-11 for air conditioner.
Invention is credited to Hibino, Sokichi, Kayukawa, Hiroaki, Mizutani, Hideki, Murase, Masakazu.
Application Number | 20040045305 10/648867 |
Document ID | / |
Family ID | 31986357 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040045305 |
Kind Code |
A1 |
Murase, Masakazu ; et
al. |
March 11, 2004 |
Air conditioner
Abstract
An air conditioner has a refrigerant circuit, a control valve, a
detector, a calculator, a suction pressure sensor and a compressor
controller. The refrigerant circuit includes a variable
displacement compressor. First and second pressure monitoring
points are located in the refrigerant circuit. The control valve
includes an actuator and a pressure sensing mechanism that has a
pressure sensing member and a valve body. The detector detects
cooling load information in the refrigerant circuit. The calculator
calculates a target pressure in a relatively low pressure region in
the refrigerant circuit in response to the detected cooling load
information. The suction pressure sensor detects actual pressure in
the reiatively low pressure region in the refrigerant circuit. The
compressor controller controls the actuator to eliminate a
differential between the calculated target pressure and the
detected actual pressure.
Inventors: |
Murase, Masakazu;
(Kariya-shi, JP) ; Kayukawa, Hiroaki; (Kariya-shi,
JP) ; Mizutani, Hideki; (Kariya-shi, JP) ;
Hibino, Sokichi; (Kariya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154
US
|
Family ID: |
31986357 |
Appl. No.: |
10/648867 |
Filed: |
August 27, 2003 |
Current U.S.
Class: |
62/217 ;
62/224 |
Current CPC
Class: |
F25B 2600/023 20130101;
F25B 49/022 20130101; F04B 2027/1813 20130101; F25B 2400/076
20130101; F04B 2205/05 20130101; F25B 2700/2106 20130101; F25B
2700/21173 20130101; F25B 2500/19 20130101; F04B 2027/1854
20130101; F04B 2205/01 20130101; F25B 2700/2104 20130101; F04B
2027/1827 20130101; F04B 2027/185 20130101; F25B 2700/1933
20130101; F04B 27/1804 20130101; F04B 2027/1895 20130101 |
Class at
Publication: |
062/217 ;
062/224 |
International
Class: |
F25B 041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 5, 2002 |
JP |
2002-260427 |
Claims
What is claimed is:
1. An air conditioner comprising: a refrigerant circuit including a
variable displacement compressor, first and second pressure
monitoring points being located in the refrigerant circuit; a
control valve for adjusting its opening degree so as to vary a
displacement of the compressor, the control valve including: a
valve body; a pressure sensing mechanism operatively connected to
the valve body, the pressure sensing mechanism including a pressure
sensing member autonomically detecting a pressure differential
between the first and second pressure monitoring points, the
pressure sensing member moving in response to variation of the
pressure differential, whereby the valve body is moved to vary the
displacement of the compressor so as to cancel the variation of the
pressure differential; and an actuator for changing a set pressure
differential in such a manner that force applied to the valve body
is changed by an external command, the set pressure differential
being a reference value of a motion for determining a position of
the valve body by the pressure sensing mechanism; a detector for
detecting cooling load information in the refrigerant circuit; a
first calculator for calculating a target pressure in a relatively
low pressure region in the refrigerant circuit in response to the
detected cooling load information; a suction pressure sensor for
detecting actual pressure in the relatively low pressure region in
the refrigerant circuit; and a compressor controller for
controlling the actuator to eliminate a first differential between
the calculated target pressure and the detected actual
pressure.
2. The air conditioner according to claim 1, wherein the
refrigerant circuit further includes an evaporator, the air
conditioner further comprising: a second calculator for calculating
target after-evaporator temperature of air that has passed through
the evaporator based upon the detected cooling load information;
and an evaporator sensor for detecting actual after-evaporator
temperature of the air that has passed through the evaporator,
wherein the compressor controller controls the actuator to
eliminate the first differential when a second differential between
the calculated target after-evaporator temperature and the detected
actual after-evaporator temperature is greater than a first
predetermined value, wherein the compressor controller controls the
actuator to eliminate the second differential when the second
differential is equal to or smaller than the first predetermined
value.
3. The air conditioner according to claim 1, wherein force based
upon a third differential between a discharge pressure in the
refrigerant circuit and pressure in a crank chamber of the
compressor affects positioning of the valve body in the control
valve.
4. The air conditioner according to claim 1, wherein the first
predetermined value is 2 degrees centigrade.
5. The air conditioner according to claim 1, wherein the
refrigerant circuit further includes an evaporator, the control
valve including an electromagnetic actuator, electromagnetic force
generated by the electromagnetic actuator being adjusted by
controlling a duty ratio of supplied electric current, the air
conditioner further comprising: a second calculator for calculating
target after-evaporator temperature of air that has passed through
the evaporator based upon the detected cooling load information;
and an evaporator sensor for detecting actual after-evaporator
temperature of the air that has passed through the evaporator,
wherein the compressor controller controls the actuator to
eliminate a second differential between the detected actual
after-evaporator temperature and the calculated target
after-evaporator temperature when the duty ratio is greater than a
second predetermined value, wherein the compressor controller
controls the actuator to eliminate the first differential when the
duty ratio is equal to or smaller than the second predetermined
value.
6. The air conditioner according to claim 1, wherein the
refrigerant circuit further includes an evaporator, the compressor
defining a suction chamber inside, the first pressure monitoring
point is located in a suction pressure region between the
evaporator and the suction chamber including the evaporator and the
suction chamber, while the second pressure monitoring point is
located downstream to the first pressure monitoring point in the
suction pressure region.
7. The air conditioner according to claim 1, wherein the compressor
is a swash plate type.
8. The air conditioner according to claim 1, wherein the detector
includes a temperature setting device, a sensor for detecting a
compartment temperature, a sensor for detecting ambient temperature
and a sensor for detecting solar irradiance.
9. An air conditioner comprising: a refrigerant circuit including a
variable displacement compressor and an evaporator, first and
second pressure monitoring points being located in the refrigerant
circuit; a control valve for adjusting its opening degree so as to
vary a displacement of the compressor, the control valve including:
a pressure sensing mechanism including: a pressure sensing member
autonomically detecting a pressure differential between the first
and second pressure monitoring points; and a valve body operatively
connected to the pressure sensing member, the pressure sensing
member moving in response to variation of the pressure
differential, whereby the valve body is moved to vary the
displacement of the compressor so as to cancel the variation of the
pressure differential; and an actuator for changing a set pressure
differential in such a manner that force applied to the valve body
is changed by an external command, the set pressure differential
being a reference value of a motion for determining a position of
the valve body by the pressure sensing mechanism; a detector for
detecting cooling load information in the refrigerant circuit; a
first calculator for calculating target surface temperature on the
evaporator in response to the detected cooling load information; a
surface temperature sensor for detecting actual surface temperature
on the evaporator; and a compressor controller for controlling the
actuator to eliminate a first differential between the calculated
target surface temperature and the detected actual surface
temperature.
10. The air conditioner according to claim 9, further comprising: a
second calculator for calculating target after-evaporator
temperature of air that has passed through the evaporator based
upon the detected cooling load information; and an evaporator
sensor for detecting actual after-evaporator temperature of the air
that has passed through the evaporator, wherein the compressor
controller controls the actuator to eliminate the first
differential when a second differential between the target
after-evaporator temperature and the detected actual
after-evaporator temperature is greater than a predetermined value,
wherein the compressor controller controls the actuator to
eliminate the second differential when the second differential is
equal to or smaller than the predetermined value.
11. A method of controlling an air conditioner including a
refrigerant circuit and a control valve, the refrigerant circuit
having a variable displacement compressor, the control valve
adjusting its opening degree so as to vary a displacement of the
compressor, the method comprising the steps of: detecting cooling
load information in the refrigerant circuit; calculating target
pressure in a relatively low pressure region in the refrigerant
circuit based upon the detected cooling load information; detecting
actual pressure in the relatively low pressure region in the
refrigerant circuit; and controlling the control valve so as to
eliminate a first differential between the calculated target
pressure and the detected actual pressure.
12. The method of controlling the air conditioner according to
claim 11, wherein the refrigerant circuit further includes an
evaporator, the controlling step including: calculating target
after-evaporator temperature of air that has passed through the
evaporator; detecting actual after-evaporator temperature of the
air that has passed through the evaporator; comparing a second
differential between the calculated target after-evaporator
temperature and the detected actual after-evaporator temperature
with a first predetermined value; controlling the control valve to
eliminate the first differential when the second differential
exceeds the first predetermined value; and controlling the control
valve to eliminate the second differential when the second
differential is within the first predetermined value.
13. A method of controlling an air conditioner including a
refrigerant circuit and a control valve, the refrigerant circuit
having a variable displacement compressor and an evaporator, the
control valve adjusting its opening degree so as to vry a
displacement of the compressor, the method comprising the steps of:
detecting cooling load information in the refrigerant circuit;
calculating target surface temperature on the evaporator in the
refrigerant circuit based upon the detected cooling load
information; detecting actual surface temperature of the evaporator
in the refrigerant circuit; and controlling the control valve so as
to eliminate a differential between the calculated target surface
temperature and the detected actual surface temperature.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an air conditioner with a
refrigerant circuit including a variable displacement compressor
and a control valve for adjusting an opening degree in connection
with variation in displacement of the compressor.
[0002] Generally, target temperature of air that has just passed
through an evaporator (target after-evaporator temperature) is
determined based upon cooling load information, such as ambient
temperature, temperature in a compartment of a vehicle and solar
irradiance. Then, the displacement of the variable displacement
compressor is adjusted by a feedback control based upon the target
after-evaporator temperature and actual after-evaporator
temperature detected by an evaporator sensor.
[0003] A variable displacement swash plate type compressor is
widely used for an on-vehicle variable displacement compressor, and
a displacement control mechanism for controlling the displacement
of the compressor is provided for the compressor. With respect to a
control valve of the displacement control mechanism, a position of
a valve body is determined by a balance between force from a
pressure sensing mechanism and force from an electromagnetic
actuator so that pressure in a crank chamber is adjusted to
determine the inclination angle of the swash plate, for example, as
disclosed on page 8 through 11 and FIG. 3 in Unexamined Japanese
Patent Publication No. 2001-173556.
[0004] Namely, the pressure sensing mechanism senses a pressure
differential between two pressure monitoring points arranged in a
refrigerant circuit by a pressure sensing member such as bellows
and applies force based on the pressure differential to the valve
body. The electromagnetic actuator strengthens and weakens the
force applied to the pressure sensing member by an external control
so that the set pressure differential between the two pressure
monitoring points is optionally varied. The pressure differential
governs internally mechanical motion of the pressure sensing
mechanism. The external control of the electromagnetic actuator,
that is, the variation in the set pressure differential of the
control valve, is exerted based upon the target after-evaporator
temperature and the detected after-evaporator temperature. In other
words, when the detected after-evaporator temperature exceeds the
target after-evaporator temperature, the set pressure differential
is increased so that the displacement of the compressor increases.
On the contrary, when the detected after-evaporator temperature is
lower than the target after-evaporator temperature, the set
pressure differential is reduced so that the displacement of the
compressor reduces.
[0005] The pressure differential between the two monitoring points
in the refrigerant circuit reflects the amount of refrigerant that
flows in the refrigerant circuit. Accordingly, the amount of
refrigerant that flows in the refrigerant circuit directly relates
to load torque of the compressor, and the control valve directly
controls the amount of refrigerant. For example, a computer for
controlling a vehicle engine easily and properly estimates torque
required for driving the compressor or an auxiliary machine based
upon the set pressure differential (electrical signal) sent to the
electromagnetic actuator of the control valve. As a result, the
output of the engine is appropriately adjusted, and fuel
consumption of the engine is reduced.
[0006] The electromagnetic actuator is capable of generating a
small amount of electromagnetic force that can balance with a small
amount of force based on the pressure differential between the two
monitoring points. Accordingly, even if carbon dioxide is used as
refrigerant, that is, even if pressure in the refrigerant circuit
is much higher than the pressure when fluorocarbon is used as
refrigerant, the enlarged electromagnetic actuator or the enlarged
control valve is restrained. Namely, when the control valve of a
variable set suction pressure type in which the pressure sensing
mechanism operates based upon absolute value of the suction
pressure requires to employ an especially large electromagnetic
actuator that can generate a large amount of electromagnetic force
balancing with a large amount of force based upon the suction
pressure when the suction pressure increases due to the carbon
dioxide refrigerant.
[0007] An unwanted feature is that the control valve detects the
pressure differential that does not reflect thermal load of the
evaporator and internally and autonomically adjusts the
displacement of the compressor by the feedback control.
Accordingly, the set pressure differential is changed by the
external control based upon the variation in the detected
after-evaporator temperature due to the variation in the thermal
load of the evaporator. The variation in the after-evaporator
temperature slowly responds to the variation in the thermal load of
the evaporator. For example, even if the thermal load of the
evaporator rapidly varies, the above control valve cannot rapidly
vary the displacement of the compressor. As a result, it takes a
long time that the after-evaporator temperature reaches the target
after-evaporator temperature so that air-conditioning feeling is
deteriorated. Therefore, there is a need for an air conditioner
that provides an excellent air-conditioning feeling.
SUMMARY OF THE INVENTION
[0008] In accordance with the present invention, an air conditioner
has a refrigerant circuit, a control valve, a detector, a first
calculator, a suction pressure sensor and a compressor controller.
The refrigerant circuit includes a variable displacement
compressor. First and second pressure monitoring points are located
in the refrigerant circuit. The control valve adjusts its opening
degree so as to vary a displacement of the compressor. The control
valve includes an actuator and a pressure sensing mechanism that
has a pressure sensing member and a valve body. The pressure
sensing member autonomically detects a pressure differential
between the first and second pressure monitoring points. The valve
body is operatively connected to the pressure sensing member. The
pressure sensing member moves in response to variation of the
pressure differential, whereby the valve body is moved to vary the
displacement of the compressor so as to cancel the variation of the
pressure differential. The actuator changes a set pressure
differential in such a manner that force applied to the valve body
is changed by an external command. The set pressure differential is
a reference value of a motion for determining a position of the
valve body by the pressure sensing mechanism. The detector detects
cooling load information in the refrigerant circuit. The calculator
calculates target pressure in a relatively low pressure region in
the refrigerant circuit in response to the detected cooling load
information. The suction pressure sensor detects actual pressure in
the relatively low pressure region in the refrigerant circuit. The
compressor controller controls the actuator to eliminate a
differential between the calculated target pressure and the
detected actual pressure.
[0009] Alternatively, in accordance with the present invention, an
air conditioner has a refrigerant circuit, a control valve, a
detector, a first calculator, a surface temperature sensor and a
compressor controller. The refrigerant circuit includes a variable
displacement compressor and an evaporator. First and second
pressure monitoring points are located in the refrigerant circuit.
The control valve adjusts its opening degree so as to vary a
displacement of the compressor. The control valve includes an
actuator and a pressure sensing mechanism that has a pressure
sensing member and a valve body. The pressure sensing member
autonomically detects a pressure differential between the first and
second pressure monitoring points. The valve body is operatively
connected to the pressure sensing member. The pressure sensing
member moves in response to variation of the pressure differential,
whereby the valve body is moved to vary the displacement of the
compressor so as to cancel the variation of the pressure
differential. The actuator changes a set pressure differential in
such a manner that force applied to the valve body is changed by an
external command. The set pressure differential is a reference
value of a motion for determining a position of the valve body by
the pressure sensing mechanism. The detector detects cooling load
information in the refrigerant circuit. The first calculator
calculates target surface temperature on the evaporator in response
to the detected cooling load information. The surface temperature
sensor detects actual surface temperature on the evaporator. The
compressor controller controls the actuator to direct a control
target to eliminate a first differential between the calculated
target surface temperature and the detected actual surface
temperature.
[0010] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The features of the present invention that are believed to
be novel are set forth with particularity in the appended claims.
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:
[0012] FIG. 1 is a longitudinal cross-sectional view of a variable
displacement swash plate type compressor according to a preferred
embodiment of the present invention;
[0013] FIG. 2 is a longitudinal cross-sectional view of a control
valve of the compressor according to the preferred embodiment of
the present invention; and
[0014] FIG. 3 is a flow chart of an air-conditioning control
according to the preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] A preferred embodiment of the present invention will now be
described with reference to FIGS. 1 through 3. The preferred
embodiment applies the present invention to a vehicle air
conditioner.
[0016] Now referring to FIG. 1, the diagram illustrates a
longitudinal cross-sectional view of a variable displacement swash
plate type compressor C according to the preferred embodiment of
the present invention. A housing 11 of the compressor C defines a
crank chamber or a swash plate chamber 12. A drive shaft 13 is
rotatably supported by the housing 11 and extends through the crank
chamber 12. The drive shaft 13 is operatively coupled to an
internal combustion engine E or a drive source for traveling a
vehicle through a power transmission mechanism PT.
[0017] The power transmission mechanism PT may be a clutch
mechanism, such as an electromagnetic clutch, that is selective to
transmit and disrupt power by an external electric control or may
be a constantly transmitting clutchless mechanism, such as the
combination of a belt and a pulley, that has no such clutch
mechanism. Incidentally, a clutchless type power transmission
mechanism is employed in the preferred embodiment.
[0018] A lug plate 14 is arranged in the crank chamber 12 and is
fixedly connected to the drive shaft 13 so as to rotate integrally
with. The crank chamber 12 accommodates a swash plate 15. The swash
plate 15 is supported by the drive shaft 13 so as to slide and
incline relative to the drive shaft 13. A hinge mechanism 16 is
interposed between the lug plate 14 and the swash plate 15.
Accordingly, the swash plate 15 is coupled to the lug plate 14
through the hinge mechanism 16 so that it synchronously rotates
with the lug plate 14 and the drive shaft 13 and inclines relative
to the drive shaft 13.
[0019] A plurality of cylinder bores 11 a (only one of them shown
in the drawing) is defined in the housing 11, and each of the
cylinder bores 11a accommodates a single-headed piston 17 so as to
reciprocate. Each of the pistons 17 engages the outer periphery of
the swash plate 15 through a pair of shoes 18. Accordingly, the
rotation of the swash plate 15 in accordance with the rotation of
the drive shaft 13 is converted to the reciprocation of the pistons
17 through the shoes 18.
[0020] A compression chamber 20 is defined in the rear side of the
cylinder bore 11a and is surrounded by the piston 17 and a valve
port assembly 19 provided in the housing 11. A suction chamber 21
and a discharge chamber 22 are defined in the rear side of the
housing 11.
[0021] Refrigerant gas in the suction chamber 21 is introduced into
each compression chambers 20 through a suction port 23 by pushing
aside a suction valve 24 as each piston 17 moves from its top dead
center to its bottom dead center. The suction ports 23 and the
suction valves 24 are formed in the valve port assembly 19. The
refrigerant gas introduced in the compression chamber 20 is
compressed to a predetermined pressure value as the piston 17 moves
from its bottom dead center to its top dead center. Then, the
compressed refrigerant gas is discharged to the discharge chamber
22 through a discharge port 25 by pushing aside a discharge valve
26.
[0022] Still referring to FIG. 1, a bleed passage 27 and a supply
passage 28 are provided in the housing 11. The bleed passage 27
interconnects the crank chamber 12 and the suction chamber 21. The
supply passage 28 interconnects the discharge chamber 22 and the
crank chamber 12. In the housing 11, a control valve CV is arranged
in the supply passage 28.
[0023] The adjustment of the opening degree of the control valve CV
controls a balance between the amount of discharged gas into the
crank chamber 12 through the supply passage 28 and the amount of
refrigerant gas out of the crank chamber 12 through the bleed
passage 27 so that pressure in the crank chamber 12 is determined.
A pressure differential between the crank chamber 12 and the
compression chambers 20 through the pistons 17 varies in response
to variation in the pressure in the crank chamber 12. Thus, the
inclination angle of the swash plate 15 is varied, and the stroke
of the pistons 17, that is, the displacement of the compressor C is
adjusted.
[0024] When the pressure in the crank chamber 12 is reduced, the
inclination angle of the swash plate 15 increases so that the
displacement of the compressor C increases. The two-dotted line of
the swash plate 15 in FIG. 1 indicates a state where the lug plate
14 contacts the swash plate 15 to regulate its further inclination,
that is, the swash plate 15 is at its maximum inclination angle. On
the contrary, when the pressure in the crank chamber 12 is
increased, the inclination angle of the swash plate 15 reduces so
that the displacement of the compressor C reduces. The solid line
of the swash plate 15 in FIG. 1 indicates a state where the swash
plate 15 is at its minimum inclination angle.
[0025] Still referring to FIG. 1, the refrigerant circuit of the
vehicle air conditioner includes the above described compressor C
and an external refrigerant circuit 30. The external refrigerant
circuit 30 includes a condenser 31, an expansion valve 32 and an
evaporator 33.
[0026] A first pressure monitoring point P1 is located in the
discharge chamber 22. A second pressure monitoring point P2 is
located at a predetermined distance from the first pressure
monitoring point P1 toward the side of the condenser 31 (the
downstream side) in a refrigerant passage. A differential between a
pressure PdH at the first pressure monitoring point P1 and a
pressure PdL at the second pressure monitoring point P2 reflects
the flow rate of refrigerant in the refrigerant circuit. The first
pressure monitoring point P1 communicates with the control valve CV
through a first pressure introducing passage 35. The second
pressure monitoring point P2 communicates with the control valve CV
through a second pressure introducing passage 36 (See FIG. 2).
[0027] Now referring to FIG. 2, the diagram illustrates a
longitudinal cross-sectional view of the control valve CV according
to the preferred embodiment of the present invention. A valve
housing 41 of the control valve CV defines a valve chamber 42, a
communication passage 43 and a pressure sensing chamber 44. A rod
45 is arranged in the valve chamber 42 and the communication
passage 43 so as to move in its axial direction (the vertical
direction in the drawing). The upper end of the rod 45 inserted in
the communication passage 43 separates the communication passage 43
from the pressure sensing chamber 44. The valve chamber 42
communicates with the discharge chamber 22 through the upstream
portion of the supply passage 28. The communication passage 43
communicates with the crank chamber 12 through the downstream
portion of the supply passage 28. The valve chamber 42 and the
communication passage 43 constitute a portion of the supply passage
28.
[0028] A valve body portion 46 is formed at the middle portion of
the rod 45 and is located in the valve chamber 42. A step at a
boundary between the valve chamber 42 and the communication passage
43 forms a valve seat 47, and the communication passage 43 serves
as a kind of valve hole. As the rod 45 moves from the lowest
position shown in FIG. 2 to the highest position where the valve
body portion 46 seats the valve seat 47, the communication passage
43 is shut. Namely, the valve body portion 46 of the rod 45
functions as a valve body for adjusting the opening degree of the
supply passage 28.
[0029] A pressure sensing mechanism includes a pressure sensing
member 48 and the pressure sensing chamber 44. The pressure sensing
member or a bellows spring 48 is accommodated in the pressure
sensing chamber 44. The upper end of the pressure sensing member 48
is secured to the valve housing 41. The upper end of the rod 45 is
fitted into the lower end of the pressure sensing member 48. The
inside of the pressure sensing chamber 44 is separated into a first
pressure chamber 49 and a second pressure chamber 50 by the
pressure sensing member 48, which forms a cylinder with an opening
at one end. The first pressure chamber 49 and the second pressure
chamber 50 are respectively defined inside and outside the pressure
sensing member 48. The pressure PdH at the first pressure
monitoring point P1 is applied to the first pressure chamber 49
through the first pressure introducing passage 35. The pressure PdL
at the second pressure monitoring point P2 is applied to the second
pressure chamber 50 through the second pressure introducing passage
36.
[0030] An electromagnetic actuator 51 for changing set pressure
differential is provided in the lower side of the valve housing 41.
The electromagnetic actuator 51 includes a plunger housing 52 in
the middle of the valve housing 41. The plunger housing 52 forms a
cylinder with an opening at one end. A center post or a fixed core
53 is fixedly fitted at the opening on the upper side of the
plunger housing 52. A plunger chamber 54 is defined at the lower
region in the plunger housing 52 by fitting the center post 53.
[0031] A plunger or a movable core 56 is accommodated in the
plunger housing 54 so as to move in its axial direction. A guide
hole 57 extends through the middle of the center post 53 along its
axial direction. The lower end of the rod 45 is located in the
guide hole 57 so as to move in its axial direction. The lower end
of the rod 45 contacts the upper end of the plunger 56 in the
plunger chamber 54.
[0032] A coil spring 60 is accommodated in the plunger chamber 54
between the bottom end of the plunger housing 52 and the plunger
56. The coil spring 60 urges the plunger 56 toward the rod 45. The
rod 45 is urged toward the plunger 56 by the spring property of the
pressure sensing member or the bellows spring 48. Accordingly, the
plunger 56 and the rod 45 regularly move upward and downward
together. Incidentally, the bellows spring 48 has a greater spring
force than the coil spring 60.
[0033] A coil 61 is wound outside the outer circumference of the
plunger housing 52 and ranges from the center post 53 to the
plunger 56. The coil 61 is supplied with electric current from a
drive circuit 78 in response to a command of an air conditioner ECU
or a compressor controller 72 for controlling the air conditioner.
Electromagnetic force (electromagnetic attraction) corresponding to
the amount of electric current supplied from the drive circuit 78
to the coil 61 is generated between the plunger 56 and the center
post 53, and the electromagnetic force is transmitted to the rod 45
through the plunger 56. Incidentally, the electric current supplied
to the coil 61 is controlled by adjusting applied voltage. A pulse
width modulation (PWM) control is employed to adjust the applied
voltage.
[0034] The opening degree of the control valve CV or the position
of the valve body portion 46 of the rod 45 is determined as
follows.
[0035] Still referring to FIG. 2, when no current is supplied to
the coil 61 (duty ratio Dt=0%), downward urging force of the
bellows spring 48 dominantly determines the position of the rod 45.
Accordingly, the rod 45 is positioned at the lowest position so
that the valve body portion 46 fully opens the communication
passage 43. Therefore, the pressure in the crank chamber 12 becomes
maximum in accordance with the present condition, and the pressure
differential between the crank chamber 12 and the compression
chambers 20 through the pistons 17 becomes large. Then, the
inclination angle of the swash plate 15 is minimum so that the
displacement of the compressor C is minimum.
[0036] When the coil 61 is supplied with electric current that is
greater than the minimum duty ratio Dt(min) in the effective range
of the duty ratio (Dt(min)>0%), the upward electromagnetic force
and the urging force of the coil spring 60 exceed the downward
urging force of the bellows spring 48 so that the rod 45 initiates
to move upwardly. In this state, the upward electromagnetic force
and the upward urging force of the coil spring 60 oppose downward
pressing force based upon the pressure differential .DELTA.Pd
(=PdH-PdL) and the downward urging force of the bellows spring 48.
Then, the position of the valve body portion 46 of the rod 45 is
determined based upon a balance among the above upward and downward
urging forces. Thus, the displacement of the compressor C is
adjusted.
[0037] For example, when the rotational speed of the engine E slows
down to reduce the flow rate of refrigerant gas in the refrigerant
circuit, the downward urging force based upon the pressure
differential .DELTA.Pd weakens so that the upward urging force at
the moment cannot maintain the balance between the upward and
downward urging forces that act on the rod 45. Accordingly, the
valve body portion 46 of the rod 45 moves upwardly to reduce the
opening degree of the communication passage 43 so that the pressure
in the crank chamber 12 tends to reduce. Therefore, the swash plate
15 inclines to increase its inclination angle, and the displacement
of the compressor C increases. The increased displacement increases
the flow rate of refrigerant gas in the refrigerant circuit so that
the pressure differential .DELTA.Pd increases.
[0038] On the contrary, when the rotational speed of the engine E
speeds up to increase the flow rate of refrigerant gas in the
refrigerant circuit, the downward urging force based upon the
pressure differential .DELTA.Pd strengthens so that the upward
electromagnetic force at the moment cannot maintain the balance
between the upward and downward urging forces that act on the rod
45. Accordingly, the valve body portion 46 of the rod 45 moves
downwardly to increase the opening degree of the communication
passage 43 so that the pressure in the crank chamber 12 tends to
increase. Therefore, the swash plate 15 inclines to reduce its
inclination angle, and the displacement of the compressor C
reduces. The reduced displacement reduces the flow rate of
refrigerant gas in the refrigerant circuit so that the pressure
differential .DELTA.Pd reduces.
[0039] Furthermore, when the duty ratio Dt supplied to the coil 61
is increased to strengthen the upward electromagnetic force, the
force based upon the pressure differential .DELTA.Pd at the moment
cannot maintain the balance between the upward and downward urging
forces. Therefore, the valve body portion 46 of the rod 45 moves
upwardly to reduce the opening degree of the communication passage
43 so that the displacement of the compressor C increases. As a
result, the flow rate of refrigerant gas the refrigerant circuit
increases, and the pressure differential .DELTA.Pd increases.
[0040] On the contrary, when the duty ratio Dt supplied to the coil
61 is reduced to weaken the upward electromagnetic force, the force
based upon the pressure differential .DELTA.Pd at the moment cannot
maintain the balance between the upward and downward urging forces.
Therefore, the valve body portion 46 of the rod 45 moves downwardly
to increase the opening degree of the communication passage 43 so
that the displacement of the compressor C reduces. As a result, the
flow rate of refrigerant gas the refrigerant circuit reduces, and
the pressure differential .DELTA.Pd reduces.
[0041] In summary, the control valve CV internally determines the
position of the valve body portion 46 of the rod 45 in response to
the variation in the pressure differential .DELTA.Pd so as to
maintain the set pressure differential (a target pressure
differential) of the pressure differential .DELTA.Pd determined by
the duty ratio Dt to the coil 61. Additionally, the set pressure
differential is externally changeable by adjusting the duty ratio
Dt to the coil 61.
[0042] Incidentally, the pressure in the crank chamber 12 is
applied to the plunger chamber 54 through a clearance between the
guide hole 57 and the rod 45. Accordingly, the pressure in the
plunger chamber 54 (the pressure in the crank chamber 12) is
applied to the rod 45 to close the valve hole. Meanwhile, the
pressure PdH in the discharge chamber 22 is applied to the upper
end of the valve body portion 46. Accordingly, force based upon a
pressure differential between the pressure PdH in the discharge
chamber 22 and the pressure in the crank chamber 12 also influences
on the determination of the position of the rod 45, in addition to
the force based upon the pressure differential .DELTA.Pd and the
force from the electromagnetic actuator 51. Namely, with respect to
the control valve CV, even if the duty ratio Dt supplied to the
coil 61 does not change, when there is a differential between the
pressure PdH in the discharge chamber 22 and the pressure in the
crank chamber 12, the set pressure differential varies a
little.
[0043] Still referring to FIG. 2, the information detector 77
includes an air conditioner switch or an A/C switch 79, a
temperature setting device 80, a compartment temperature sensor 81
for detecting temperature in a vehicle compartment, an ambient
temperature sensor 82 for detecting ambient temperature, a solar
irradiance sensor 85, a suction pressure sensor 83 and an
evaporator sensor 84.
[0044] The A/C switch 79 is an ON-OFF switch of the air
conditioner. The temperature setting device 80 is a device by which
a passenger sets temperature in the vehicle compartment (set
temperature Tset). The compartment temperature sensor 81 is a
device for detecting temperature Tr in the vehicle compartment. The
ambient temperature sensor 82 is a device for detecting ambient
temperature Tam. The solar irradiance sensor 85 is a device for
detecting solar irradiance Ts. The suction pressure sensor 83 is a
device for detecting a pressure Ps(x) in a relatively low pressure
region in the refrigerant circuit, such as a suction pressure
region (for example, the suction chamber 21, the inside of a
conduit near the relatively low pressure region of the external
refrigerant circuit 30 and an adjacent outlet of refrigerant gas in
the evaporator 33). The evaporator sensor 84 is a device for
detecting temperature Te(x) of air that is just passed through the
evaporator 33.
[0045] Particularly, a cooling load information detector includes
the temperature setting device 80, the compartment temperature
sensor 81, the ambient temperature sensor 82 and the solar
irradiance sensor 85. The cooling load information detector detects
cooling load information in the refrigerant circuit, such as the
set temperature Tset, the compartment temperature Tr, the ambient
temperature Tam and the solar irradiance Ts.
[0046] The air conditioner ECU 72 adjusts the duty ratio Dt of the
control valve CV, that is, the set pressure differential of the
control valve CV, in response to the information detected by the
information detector 77. Incidentally, The air conditioner ECU 72
not only controls the control valve CV but also, for example,
controls air quantity by a conventional manner for adjusting the
rotational speed of a blower motor (not shown) in response to the
information detected by the information detector 77.
[0047] Now referring to FIG. 3, the diagram illustrates a flow
chart of an air-conditioning control according to the preferred
embodiment of the present invention. When the engine E is started,
the air conditioner ECU 72 exerts various initialization in
accordance with an initial program at a step 101 (S101). For
example, the air conditioner ECU 72 sets "0" as an initial value to
the duty ratio Dt of the control valve CV (Namely, no electric
current is supplied to the coil 61). The ON/OFF state of the A/C
switch 79 is observed until it is turned on at S102. When the A/C
switch 79 is turned on, the air conditioner ECU adjusts the duty
ratio Dt of the control valve CV to the minimum duty ratio Dt(min)
at S103 so as to start up the internally mechanical control
function of the control valve CV (a function for maintaining the
set pressure differential).
[0048] Required blowing temperature Ta0 of the air conditioner is
calculated at S104 based upon the cooling load information (Tset,
Tr, Tam and Ts) that is sent from the temperature setting device
80, the compartment temperature sensor 81, the ambient temperature
sensor 82 and the solar irradiance sensor 85. The air conditioner
ECU 72 serves as a calculator for calculating the target
after-evaporator temperature at S105 and calculates the target
after-evaporator temperature Te(set) from the calculated required
blowing temperature Ta0 with reference to map data that are
previously memorized. The air conditioner ECU 72 compares the
calculated target after-evaporator temperature Te(set) with the
after-evaporator temperature Te(x) detected by the evaporator
sensor 84 and judges whether or not a differential between Te(set)
and Te(x) is equal to or less than a predetermined value (for
example, 2 degrees centigrade) at S106.
[0049] When the judgment of S106 is false, that is, when the
differential between Te(set) and Te(x) exceeds the predetermined
value, the air conditioner ECU 72 revises the duty ratio Dt of the
control valve CV so as to change the target value to the suction
pressure Ps(x) detected by the suction pressure sensor 83.
[0050] Namely, the air conditioner ECU 72 serves as a calculator
for calculating a target suction pressure at S107 and calculates a
target suction pressure Ps(set) from the target after-evaporator
temperature Te(set) calculated at S105 with reference to map data
that are previously memorized. The air conditioner ECU 72 judges
whether or not the suction pressure Ps(x) detected by the suction
pressure sensor 83 is greater than the calculated target suction
pressure Ps(set) at S108. When the judgment of S108 is false, the
air conditioner ECU 72 judges whether or not the detected suction
pressure Ps(x) is smaller than the target suction pressure Ps(set).
When the judgment of S109 is also false, the detected suction
pressure Ps(x) is equal to the target suction pressure Ps(set).
[0051] Thereby, even if the air conditioner ECU 72 does not change
the duty ratio Dt of the control valve CV, it soon judges the
differential between the target after-evaporator temperature
Te(set) and the detected after-evaporator temperature Te(x) becomes
within the predetermined value and switches a process to S116
without sending a command to change the duty ratio Dt to the drive
circuit 78. Namely, as the duty ratio Dt of the control valve CV is
changed, the suction pressure Ps(x) varies at first, and then the
after-evaporator temperature Te(x) varies at a certain interval
from the variation of the suction pressure Ps(x).
[0052] The air conditioner ECU 72 judges whether or not the A/C
switch 79 is turned off at S116. When the judgment of S116 is
false, the air conditioner ECU 72 switches a process to S104. On
the contrary, when the judgment of S116 is true, the air
conditioner ECU 72 switches a process to S101 so that the control
valve CV is in a non-energized state. Thus, the displacement of the
compressor C becomes minimum.
[0053] When the judgment of S108 is true, the thermal load on the
evaporator 33 is regarded to be relatively large so that the air
conditioner ECU 72 increases the duty ratio Dt by the unit quantity
of .DELTA.D at S110 and commands the drive circuit 78 to change the
duty ratio Dt to a revised duty ratio (Dt+.DELTA.D). Accordingly,
the opening degree of the control valve CV reduces a little so that
the displacement of the compressor C increases. Then, the heat
removal performance rises at the evaporator 33, and not only the
suction pressure Ps(x) but also the after-evaporator temperature
Te(x) tends to reduce.
[0054] When the judgment of S109 is true, the thermal load on the
evaporator 33 is regarded to be relatively small so that the air
conditioner ECU 72 reduces the duty ratio Dt by the unit quantity
of .DELTA.D at S111 and commands the drive circuit 78 to change the
duty ratio Dt to a revised duty ratio (Dt-.DELTA.D). Accordingly,
the opening degree of the control valve CV increases a little so
that the displacement of the compressor C reduces. Then, the heat
removal performance falls at the evaporator 33, and not only the
suction pressure Ps(x) but also the after-evaporator temperature
Te(x) tends to increase. Additionally, the air conditioner ECU 72
switches S110 and S111 to S116.
[0055] As described above, S110 and/or S111 directs a control
target to eliminate the differential between the detected suction
pressure Ps(x) and the target suction pressure Ps(set). Even if the
differential between the detected after-evaporator temperature
Te(x) and the target after-evaporator temperature Te(set) largely
exceeds the predetermined value (for example, 2 degrees
centigrade), the differential is rapidly lessened in such a manner
that the duty ratio Dt is revised at S110 and/or S111. Accordingly,
as coupled with the internally mechanical adjustment of the opening
degree of the control valve CV, the differential between the
detected after-evaporator temperature Te(x) and the target
after-evaporator temperature Te(set) rapidly fits within the
predetermined value.
[0056] When the differential between the detected after-evaporator
temperature Te(x) and the target after-evaporator temperature
Te(set) is within the predetermined value by a process for revising
the duty ratio Dt at S110 and/or S111, the judgment of S106 is
true. When the judgment of S106 is true, a process for revising the
duty ratio Dt of the control valve CV is directed to eliminate the
differential between the detected after-evaporator temperature
Te(x) and the target after-evaporator temperature Te(set).
[0057] Namely, the air conditioner ECU 72 judges whether or not the
after-evaporator temperature Te(x) detected by the evaporator
sensor 84 is greater than the calculated target after-evaporator
temperature Te(set) at S112. When the judgment of S112 is false,
the air conditioner ECU 72 judges whether or not the detected
after-evaporator temperature Te(x) is smaller than the target
after-evaporator temperature Te(set) at S113. When the judgment of
S113 is also false, the detected after-evaporator temperature Te(x)
is equal to the target after-evaporator temperature Te(set) so that
the duty ratio Dt need not be changed for varying cooling
performance. Therefore, the air conditioner ECU 72 switches a
process to S116 without sending a command for changing the duty
ratio Dt to the drive circuit 78.
[0058] When the judgment of S112 is true, the thermal load on the
evaporator 33 is regarded to be relatively large so that the air
conditioner ECU 72 increases the duty ratio Dt by the unit quantity
of .DELTA.D at S114 and commands the drive circuit 78 to change the
duty ratio Dt to a revised duty ratio (Dt+.DELTA.D). Accordingly,
the opening degree of the control valve CV reduces a little so that
the displacement of the compressor C increases. Then, the heat
removal performance rises at the evaporator 33, and the
after-evaporator temperature Te(x) tends to reduce.
[0059] When the judgment of S113 is true, the thermal load on the
evaporator 33 is regarded to be relatively small so that the air
conditioner ECU 72 reduces the duty ratio Dt by the unit quantity
of .DELTA.D at S115 and commands the drive circuit 78 to change the
duty ratio Dt to a revised duty ratio (Dt-.DELTA.D). Accordingly,
the opening degree of the control valve CV increases a little so
that the displacement of the compressor C reduces. Then, the heat
removal performance falls at the evaporator 33, and the
after-evaporator temperature Te(x) tends to increase. Additionally,
the air conditioner ECU 72 switches S114 and S115 to S116.
[0060] As described above, S114 and/or S115 directs a control
target to eliminate the differential between the detected
after-evaporator temperature Te(x) and the target after-evaporator
temperature Te(set). Even if the differential between the detected
after-evaporator temperature Te(x) and the target after-evaporator
temperature Te(set) exceeds the predetermined value, the
differential is gradually optimized in such a manner that the duty
ratio Dt is revised at S114 and/or S115. Accordingly, as coupled
with the internally mechanical adjustment of the opening degree of
the control valve CV, the detected after-evaporator temperature
Te(x) converges in high accuracy around the target after-evaporator
temperature Te(set).
[0061] According to the preferred embodiment, the following
advantageous effects are obtained.
[0062] (1) The air conditioner ECU 72 revises the duty ratio Dt of
the control valve CV so as to direct a control target to eliminate
the differential between the detected suction pressure Ps(x) and
the target suction pressure Ps(set). The suction pressure Ps(x) is
physical quantity that responds to the variation of the thermal
load on the evaporator 33 more rapidly than the after-evaporator
temperature Te(x). Accordingly, for example, the displacement of
the compressor C is rapidly varied in response to the rapid
variation of the thermal load on the evaporator 33 due to the rapid
variation of the rotational speed of the blower motor (air
quantity). As a result, the after-evaporator temperature Te(x)
rapidly approaches the target after-evaporator temperature Te(set)
so that air conditioning feeling becomes satisfactory.
[0063] (2) The control valve CV is configured to subtly vary the
set pressure differential when the differential between the
pressure PdH in the discharge chamber 22 and the pressure in the
crank chamber 12 differs, even if the duty ratio Dt supplied to the
coil 61 are the same. Accordingly, in a conventional manner, for
example, even if the rotational speed of the engine E (the
compressor C) rapidly varies due to rapid acceleration of a vehicle
and the like, that is, even if the flow rate of refrigerant gas in
the refrigerant circuit rapidly varies, an external control in
response to the variation of the detected after-evaporator
temperature Te(x) due to the above rapid variation changes a set
pressure differential to deal with the above rapid variation.
Namely, the process for revising the duty ratio Dt of the control
valve CV directs a control target to eliminate the differential
between the detected after-evaporator temperature Te(x) and the
target after-evaporator temperature Te(set). The above revising
process still has the same problem as the prior art mentioned in
the background of the invention when the rotational speed of the
engine E rapidly varies. Namely, it takes a relatively long time
that the after-evaporator temperature Te(x) approaches the target
after-evaporator temperature Te(set). Thereby, air conditioning
feeling is deteriorated.
[0064] However, the air conditioner ECU 72 in the preferred
embodiment directs a control target to eliminate the differential
between the detected suction pressure Ps(x) and the target suction
pressure Ps(set) and revises the duty ratio Dt of the control valve
CV. The suction pressure Ps(x) is physical quantity that responds
to the variation of the rotational speed of the engine E more
quickly than, for example, the after-evaporator temperature Te(x).
Accordingly, the displacement of the compressor C is quickly varied
in response to the rapid variation of the rotational speed of the
engine E, and the after-evaporator temperature Te(x) quickly
approaches the target after-evaporator temperature Te(set). As a
result, even if the rotational speed of the engine E rapidly
varies, air conditioning feeling is satisfactory.
[0065] (3) When the differential between the target
after-evaporator temperature Te(set) and the detected
after-evaporator temperature Te(x) is relatively small, the air
conditioner ECU 72 directs a control target to eliminate the
detected after-evaporator temperature Te(x) and the target
after-evaporator temperature Te(set) and revises the duty ratio Dt
of the control valve CV. Accordingly, the detected after-evaporator
temperature Te(x) converges in high accuracy around the target
after-evaporator temperature Te(set) so that air conditioning
feeling is further improved.
[0066] The present invention is not limited to the embodiment
described above but may be modified into the following alternative
embodiments.
[0067] In alternative embodiments to those of the above preferred
embodiment, referring to FIG. 2, the suction pressure sensor 83 is
changed to a surface temperature sensor 86 for detecting surface
temperature T.sub.ST (temperature of a heat exchanging fin) of the
evaporator 33. Additionally, a portion of the process for revising
the duty ratio Dt of the control valve CV by the air conditioner
ECU 72, particularly, the several steps (S107 through S111) in the
flow chart in FIG. 3 are changed to steps (S107', S108', S109',
S110, and S111) as follows.
[0068] Now referring to FIG. 4, the diagram illustrates a potion of
flow chart that is modified from that of FIG. 3. The air
conditioner ECU 72 serves as a calculator for calculating target
surface temperature T.sub.ST(set) at S107' and calculates the
target surface temperature T.sub.ST(set) from the target
after-evaporator temperature Te(set) calculated at S105 with
reference to map data that are previously memorized. The air
conditioner ECU 72 judges whether or not the surface temperature
T.sub.ST(x) detected by the surface temperature sensor 86 is
greater than the calculated target surface temperature
T.sub.ST(set) at S108'. When the judgment of S108' is false, the
air conditioner ECU 72 judges whether or not the detected surface
temperature T.sub.ST(x) is smaller than the target surface
temperature T.sub.ST(set) at S109'. When the judgment of S109' is
also false, the detected surface temperature T.sub.ST(x) is equal
to the target surface temperature T.sub.ST(set).
[0069] Thereby, the air conditioner ECU 72 soon judges the
differential between the target after-evaporator temperature
Te(set) and the detected after-evaporator temperature Te(x) is
within the predetermined value (for example, 2 degrees centigrade)
without changing the duty ratio Dt of the control valve CV and
switches a process to S116 without commanding the drive circuit 78
to change the duty ratio Dt. Namely, as the duty ratio Dt of the
control valve CV is changed, the surface temperature T.sub.ST(x) of
the evaporator 33 varies at first. Then, the after-evaporator
temperature Te(x) varies at a certain interval from the variation
of the surface temperature T.sub.ST(x).
[0070] When the judgment of S108' is true, the thermal load on the
evaporator 33 is regarded to be relatively large so that the air
conditioner ECU 72 increases the duty ratio Dt by the unit quantity
of .DELTA.D at S110 and commands the drive circuit 78 to change the
duty ratio Dt to a revised duty ratio (Dt+.DELTA.D). Accordingly,
the opening degree of the control valve CV reduces a little so that
the displacement of the compressor C increases. Then, the heat
removal performance rises at the evaporator 33, and the surface
temperature T.sub.ST(x) of the evaporator 33 and the
after-evaporator temperature Te(x) tend to reduce.
[0071] When the judgment of S109' is true, the thermal load on the
evaporator 33 is regarded to be relatively small so that the air
conditioner ECU 72 reduces the duty ratio Dt by the unit quantity
of .DELTA.D at S111 and commands the drive circuit 78 to change the
duty ratio Dt to a revised duty ratio (Dt-.DELTA.D). Accordingly,
the opening degree of the control valve CV increases a little so
that the displacement of the compressor C reduces. Then, the heat
removal performance falls at the evaporator 33, and the surface
temperature T.sub.ST(x) of the evaporator 33 and the
after-evaporator temperature Te(x) tend to increase.
[0072] The surface temperature T.sub.ST(x) of the evaporator 33 is
physical quantity that responds to the variation of the thermal
load on the evaporator 33 more quickly than the after-evaporator
temperature Te(x). Accordingly, the same advantageous effects to
those mentioned in the paragraphs (1) through (3) of the preferred
embodiment are obtained.
[0073] In the above preferred embodiment, when the differential
between the detected after-evaporator temperature Te(x) and the
target after-evaporator temperature Te(set) is within the
predetermined value, the air conditioner ECU 72 directs a control
target to eliminate the differential between the detected
after-evaporator temperature Te(x) and the target after-evaporator
temperature Te(set) and revises the duty ratio Dt of the control
valve CV. Furthermore, when the differential between the detected
after-evaporator temperature Te(x) and the target after-evaporator
temperature Te(set) exceeds the predetermined value, the air
conditioner ECU 72 directs a control target to eliminate the
differential between the detected suction pressure Ps(x) and the
target suction pressure Ps(set) and revises the duty ratio Dt of
the control valve CV. In alternative embodiments to those of the
above preferred embodiment, irrespective of the differential
between the target after-evaporator temperature Te(set) and the
detected after-evaporator temperature Te(x), the air conditioner
ECU 72 directs a control target to eliminate the differential
between the detected suction pressure Ps(x) and the target suction
pressure Ps(set) and revises the duty ratio Dt of the control valve
CV. Namely, for example, S106 and S112 through S115 are omitted
from the flow chart in FIG. 3 in the above preferred embodiment.
Even so, when the rotational speed of the engine E or the thermal
load on the evaporator 33 rapidly varies, the displacement of the
compressor C is quickly varied so that air conditioning feeling is
satisfactory.
[0074] In alternative embodiments to those of the above preferred
embodiment, referring to FIG. 5, the diagram illustrates a portion
of flow chart that is modified from that of FIG. 3. The control
target in connection with the process for revising the duty ratio
Dt(x) of the control valve CV is changed in response to large and
small of the set pressure differential of the control valve CV,
that is, large and small of the duty ratio Dt(x) supplied to the
coil 61. Namely, when the duty ratio Dt(x) of the control valve CV
is within the predetermined value Dt(set), that is, when the flow
rate of refrigerant gas in the refrigerant circuit is controlled in
a relatively large flow rate range, the air conditioner ECU 72
directs a control target to eliminate the differential between the
detected after-evaporator temperature Te(x) and the target
after-evaporator temperature Te(set) and revises the duty ratio
Dt(x) of the control valve CV. On the contrary, when the duty ratio
Dt(x) is less than the predetermined value Dt(set), that is, when
the flow rate of refrigerant gas in the refrigerant circuit is
controlled in a relatively small flow rate range, the air
conditioner ECU 72 directs a control target to eliminate the
differential between the detected suction pressure Ps(x) and the
target suction pressure Ps(set) and revises the duty ratio Dt(x) of
the control valve CV.
[0075] Thereby, a control of the flow rate in the refrigerant
circuit is stable in a relatively small flow rate range so that air
conditioning feeling is satisfactory. Namely, the control valve CV
is configured to detect the pressure differential .DELTA.Pd between
the pressure monitoring points in the refrigerant circuit and
internally and autonomically exerts a feedback control of the
displacement of the compressor C. Accordingly, when the flow rate
of refrigerant gas in the refrigerant circuit is relatively small,
the variation of the pressure differential .DELTA.Pd in response to
the variation of the flow rate of refrigerant gas is relatively
small (not clear) so that the internally mechanical control of the
control valve CV does not properly function. As a result, when the
air conditioner ECU 72 directs a control target to eliminate the
differential between the detected after-evaporator temperature
Te(x) and the target after-evaporator temperature Te(set) for
revising the duty ratio Dt(x) of the control valve CV, the flow
rate control of the refrigerant circuit in a relatively small flow
rate range becomes unstable due to a slow response of the detected
after-evaporator temperature Te(x) in response to the revising of
the duty ratio Dt(x).
[0076] In alternative embodiments to those of the above preferred
embodiment, referring to FIG. 1, a first pressure monitoring point
P1' is located at a suction pressure region between the evaporator
33 and the suction pressure chamber 21 including the evaporator 33
and the suction pressure chamber 21 in the refrigerant circuit,
while a second pressure monitoring point P2' is located downstream
to the first pressure monitoring point P1' in the same suction
pressure region.
[0077] In alternative embodiments to those of the above preferred
embodiment, the control valve CV employs a bleed side control valve
that adjusts the pressure in the crank chamber 12 by adjusting the
opening degree of the bleed passage 27 instead of the supply
passage 28.
[0078] In alternative embodiments to those of the above preferred
embodiment, the variable displacement compressor employs a wobble
type.
[0079] 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 of the appended claims.
* * * * *