U.S. patent application number 09/777596 was filed with the patent office on 2001-10-11 for control apparatus and control method for variable displacement compressor.
Invention is credited to Adaniya, Taku, Kawaguchi, Masahiro, Kimura, Kazuya, Matsubara, Ryo, Ota, Masaki, Suitou, Ken.
Application Number | 20010027659 09/777596 |
Document ID | / |
Family ID | 18554794 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010027659 |
Kind Code |
A1 |
Ota, Masaki ; et
al. |
October 11, 2001 |
Control apparatus and control method for variable displacement
compressor
Abstract
An improved control apparatus for controlling the displacement
of a variable displacement compressor. A control valve includes an
operating rod, which is urged by a force based on a differential
pressure between two pressure monitoring points, which are located
in a refrigeration circuit. The control valve causes the compressor
to seek a target displacement. A computer limits the target
displacement when the demand for cooling is decreasing to improve
fuel economy and to extend the life of the compressor.
Inventors: |
Ota, Masaki; (Kariya-shi,
JP) ; Kimura, Kazuya; (Kariya-shi, JP) ;
Kawaguchi, Masahiro; (Kariya-shi, JP) ; Suitou,
Ken; (Kariya-shi, JP) ; Matsubara, Ryo;
(Kariya-shi, JP) ; Adaniya, Taku; (Kariya-shi,
JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154
US
|
Family ID: |
18554794 |
Appl. No.: |
09/777596 |
Filed: |
February 6, 2001 |
Current U.S.
Class: |
62/228.3 ;
417/222.2 |
Current CPC
Class: |
F04B 2205/07 20130101;
F04B 2027/1813 20130101; F04B 27/1804 20130101; F04B 2027/1827
20130101; F04B 2027/1859 20130101; F04B 2027/1854 20130101; F04B
49/065 20130101 |
Class at
Publication: |
62/228.3 ;
417/222.2 |
International
Class: |
F04B 001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 2000 |
JP |
2000-029549 |
Claims
What is claimed is:
1. A control apparatus for controlling discharge capacity of a
variable displacement compressor included in a refrigeration
circuit of an air conditioner, said refrigeration circuit including
an evaporator, said control apparatus comprising: a differential
pressure detector for detecting a differential pressure between two
pressure monitoring points set to said refrigeration circuit, on
which the discharge capacity of the variable displacement
compressor is reflected; a temperature sensor for detecting a
cooling state of said evaporator as temperature information; a set
differential pressure calculator for calculating a set differential
pressure which becomes a control target of a differential pressure
between the two pressure monitoring points, based on a temperature
detected by the temperature sensor of said evaporator and a target
temperature which is a control target of the temperature of said
evaporator; a limit value setting device for setting a limit value
to the differential pressure between the two pressure monitoring
points when the temperature detected by the temperature sensor of
said evaporator is lowered from the state higher than a threshold
temperature which is set to higher than the target temperature to
the state lower than the threshold temperature, and for releasing
the setting of the limit value when the temperature detected by the
temperature sensor of said evaporator is raised from the state
lower than the threshold temperature to the state higher than the
threshold temperature; a set differential pressure setting device
for comparing the set differential pressure calculated by said set
differential pressure calculator with the limit value set by said
limit value setting device, for dealing with the set differential
pressure in itself if the discharge capacity of the variable
displacement compressor which the set differential pressure
represents is less than that of the variable displacement
compressor which the limit value represents, and for dealing with
the limit value as a new set differential pressure if the discharge
capacity of the variable displacement compressor which the set
differential pressure represents is greater than that of the
variable displacement compressor which the limit value represents;
and a compressor control mechanism for controlling the discharge
capacity of the variable displacement compressor so that the
differential pressure detected by the differential pressure
detector approaches to the set differential pressure from said set
differential pressure setting device.
2. The control apparatus according to claim 1, wherein said
threshold temperature comprises an upper limit temperature and a
lower limit temperature which are different from each other,
wherein said limit value setting device for setting a limit value
to the differential pressure between the two pressure monitoring
points when the temperature detected by the temperature sensor of
said evaporator is lowered from the state higher than the lower
limit temperature to the state lower than the lower limit
temperature, and for releasing the setting of the limit value when
the temperature detected by the temperature sensor of said
evaporator is raised from the state lower than the upper limit
temperature to the state higher than the upper limit
temperature.
3. The control apparatus according to claim 1, wherein said
temperature sensor of the evaporator is arranged in the vicinity of
the evaporator, and detects the temperature of air passed through
the evaporator.
4. The control apparatus according to claim 1, wherein said control
apparatus further comprises a temperature setting device which can
adjust a target temperature of said evaporator.
5. The control apparatus according to claim 1, further comprising a
means for magnifying the differential pressure between the two
pressure monitoring points, the means is arranged between the two
pressure monitoring points.
6. The control apparatus according to claim 5, wherein said means
is a fixed throttle.
7. The control apparatus according to claim 1, wherein said
compressor is a swash plate type variable displacement compressor
which stroke of a piston can be changed by controlling an internal
pressure of a crank chamber.
8. The control apparatus according to claim 1, wherein said
compressor is a wobble type variable displacement compressor in
which stroke of a piston can be changed by controlling an internal
pressure of a crank chamber.
9. A control apparatus for controlling discharge capacity of a
variable displacement compressor included in a refrigeration
circuit of an air conditioner, said refrigeration circuit including
an evaporator, said control apparatus comprising: a compressor
control mechanism for controlling the discharge capacity of the
compressor in accordance with a differential pressure between two
pressure monitoring points set to said refrigeration circuit, said
differential pressure reflecting the discharge capacity of the
variable displacement compressor; a temperature sensor for
detecting a cooling state of said evaporator as temperature
information; and a computer for calculating a set differential
pressure which becomes a control target of a differential pressure
between the two pressure monitoring points, based on a temperature
detected by the temperature sensor of said evaporator and a target
temperature which is a control target of the temperature of said
evaporator, wherein said compressor control mechanism controls the
discharge capacity of the variable displacement compressor so that
the differential pressure approaches to the set differential
pressure, wherein said computer sets a limit value to the
differential pressure between the two pressure monitoring points
when the temperature detected by the temperature sensor of said
evaporator is lowered from the state higher than a threshold
temperature, which is set to higher than the target temperature, to
the state lower than the threshold temperature, and releases the
setting of the limit value when the temperature detected by the
temperature sensor of said evaporator is raised from the state
lower than the threshold temperature to the state higher than the
threshold temperature, wherein said computer compares the set
differential pressure with the limit value when the limit value is
set, deals with the set differential pressure in itself if the
discharge capacity of the variable displacement compressor which
the set differential pressure represents is less than that of the
variable displacement compressor which the limit value represents,
and deals with the limit value as a new set differential pressure
if the discharge capacity of the variable displacement compressor
which the set differential pressure represents is greater than that
of the variable displacement compressor which the limit value
represents.
10. The control apparatus according to claim 9, wherein said
threshold temperature comprises an upper limit temperature and a
lower limit temperature which are different from each other,
wherein said computer sets a limit value to the differential
pressure between the two pressure monitoring points when the
temperature detected by the temperature sensor of said evaporator
is lowered from the state higher than the lower limit temperature
to the state lower than the lower limit temperature, and releases
the setting of the limit value when the temperature detected by the
temperature sensor of said evaporator is raised from the state
lower than the upper limit temperature to the state higher than the
upper limit temperature.
11. The control apparatus according to claim 9, wherein said
temperature sensor of the evaporator is arranged in the vicinity of
the evaporator, and detects the temperature of air passed through
the evaporator.
12. The control apparatus according to claim 9, wherein said
control apparatus further comprises a temperature setting device
which can adjust the target temperature of said evaporator.
13. The control apparatus according to claim 9, further comprising
a means for magnifying the differential pressure between the two
pressure monitoring points, the means arranged between the two
pressure monitoring points.
14. The control apparatus according to claim 13, wherein said means
is a fixed throttle.
15. The control apparatus according to claim 9, wherein said
compressor is a swash plate type variable displacement compressor
in which stroke of a piston can be changed by controlling an
internal pressure of a crank chamber.
16. The control apparatus according to claim 9, wherein said
compressor is a wobble type variable displacement compressor in
which stroke of a piston can be changed by controlling an internal
pressure of a crank chamber.
17. A method for controlling discharge capacity of a variable
displacement compressor included in a refrigeration circuit of an
air conditioner, said refrigeration circuit including an
evaporator, said method comprising the steps of: detecting a
differential pressure between two pressure monitoring points set to
said refrigeration circuit, on which the discharge capacity of the
variable displacement compressor is reflected; detecting a cooling
state of said evaporator as temperature information; calculating a
set differential pressure which becomes a control target of a
differential pressure between the two pressure monitoring points
based on said temperature information and a target temperature
which is a control target of the temperature of said evaporator;
setting a limit value to the differential pressure between the two
pressure monitoring points when said temperature information is
lowered from the state higher than a threshold temperature which is
set to higher than the target temperature to the state lower than
the threshold temperature, and releasing the setting of the limit
value when the detected temperature is raised from the state lower
than the threshold temperature to the state higher than the
threshold temperature; comparing said set differential pressure
with the limit value set, dealing with the set differential
pressure in itself if the discharge capacity of the variable
displacement compressor which the set differential pressure
represents is less than that of the variable displacement
compressor which the limit value represents, and dealing with the
limit value as a new set differential pressure if the discharge
capacity of the variable displacement compressor which the set
differential pressure represents is greater than that of variable
displacement compressor which the limit value represents; and
controlling the discharge capacity of the variable displacement
compressor so that the differential pressure approaches to said set
differential pressure.
18. The control method according to claim 17, wherein said
threshold temperature comprises an upper limit temperature and a
lower limit temperature which are different from each other,
wherein said step of setting or releasing said limit value includes
the step of setting the limit value to the differential pressure
between the two pressure monitoring points when the temperature
information from said evaporator is lowered from the state higher
than the lower limit temperature to the state lower than the lower
limit temperature, and releasing the setting of the limit value
when the detected temperature is raised from the state lower than
the upper limit temperature to the state higher than the upper
limit temperature.
19. The control method according to claim 17, wherein said step of
detecting a cooling state of said evaporator as temperature
information detects the temperature of air passed through the
evaporator.
20. The control method according to claim 17, wherein the target
temperature of said evaporator can be adjusted.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an apparatus and a method
for controlling discharge capacity of a variable displacement
compressor of an automotive air conditioner.
[0002] Generally, a refrigerant circuit of an automotive air
conditioner includes a condenser, an expansion valve, an
evaporator, and a compressor. The compressor draws and compresses
refrigerant gas from the evaporator and discharges the refrigerant
gas to the condenser. The evaporator transfers heat to refrigerant
passing through the refrigerant circuit from air flowing inside a
vehicle. Since the heat of the air passing through the evaporator
is transmitted to the refrigerant passing through the evaporator in
accordance with the size of the air conditioning load, the pressure
of the refrigerant gas at the outlet, or downstream end of the
evaporator, reflects the size of the air conditioning load.
[0003] A swash plate type variable displacement compressor, which
has been widely used in vehicles, is provided with a capacity
control mechanism, which is operated to hold the pressure of the
outlet of the evaporator (hereinafter referred to as the suction
pressure (Ps)) to a predetermined target value (hereinafter
referred to as the set suction pressure). The capacity control
mechanism feedback controls the discharge capacity of the
compressor, or the angle of the swash plate, using the suction
pressure Ps as a control index such that the flow rate of the
refrigerant corresponds to the size of the air conditioning load. A
typical example of a capacity control mechanism is an internal
control valve. The internal control valve detects the suction
pressure Ps with a pressure-sensing member, such as bellows or a
diaphragm, and adjusts the pressure (the crank pressure) of a swash
plate chamber (or crank chamber) by using displacement of the
pressure-sensing member to position a valve body. The position of
the valve body determines the angle of the swash plate.
[0004] In addition, since a simple internal control valve, which
reacts only to the suction pressure, is not able to cope with a
demand for minute air conditioning control, a set suction pressure
variable type control valve in which the set suction pressure can
be changed by external electric control, is needed. For example, a
set suction pressure variable type control valve changes the set
suction pressure by using an actuator, the force of which is
electrically controllable. For example, the actuator may be an
electronic solenoid. The actuator increments or decrements the
force acting on the pressure-reducing member, which determines the
set suction pressure of the internal control valve.
[0005] However, in controlling the discharge capacity using an
absolute value of the suction pressure as an index, the real
suction pressure cannot reach the set suction pressure immediately,
even though the set suction pressure is changed electrically. In
other words, whether the actual suction pressure follows the change
of the set suction pressure responsively depends on the heat load
of the evaporator. Therefore, though the set suction pressure is
gradually adjusted by the electric control, the change of the
discharge capacity of the compressor is delayed or the discharge
capacity is not changed continuously and smoothly, and the change
of the discharge capacity often becomes rapid.
SUMMARY OF THE INVENTION
[0006] An objective of the present invention is to provide a
control apparatus and a control method of a variable displacement
compressor which can improve the control property and responsivity
of the discharge capacity.
[0007] In accordance with one aspect of the present invention,
there is provided a control apparatus for controlling discharge
capacity of a variable displacement compressor included in a
refrigeration circuit of an air conditioner, said refrigeration
circuit including an evaporator, said control apparatus comprising:
a differential pressure detector for detecting a differential
pressure between two pressure monitoring points set to said
refrigeration circuit, on which the discharge capacity of the
variable displacement compressor is reflected; a temperature sensor
for detecting a cooling state of said evaporator as temperature
information; a set differential pressure calculator for calculating
a set differential pressure which becomes a control target of a
differential pressure between the two pressure monitoring points,
based on a temperature detected by the temperature sensor of said
evaporator and a target temperature which is a control target of
the temperature of said evaporator; a limit value setting device
for setting a limit value to the differential pressure between the
two pressure monitoring points when the temperature detected by the
temperature sensor of said evaporator is lowered from the state
higher than a threshold temperature which is set to higher than the
target temperature to the state lower than the threshold
temperature, and for releasing the setting of the limit value when
the temperature detected by the temperature sensor of said
evaporator is raised from the state lower than the threshold
temperature to the state higher than the threshold temperature; a
set differential pressure setting device for comparing the set
differential pressure calculated by said set differential pressure
calculator with the limit value set by said limit value setting
device, for dealing with the set differential pressure in itself if
the discharge capacity of the variable displacement compressor
which the set differential pressure represents is less than that of
the variable displacement compressor which the limit value
represents, and for dealing with the limit value as a new set
differential pressure if the discharge capacity of the variable
displacement compressor which the set differential pressure
represents is greater than that of the variable displacement
compressor which the limit value represents; and a compressor
control mechanism for controlling the discharge capacity of the
variable displacement compressor so that the differential pressure
detected by the differential pressure detector approaches to the
set differential pressure from said set differential pressure
setting device.
[0008] In accordance with another aspect of the present invention,
there is provided a method for controlling discharge capacity of a
variable displacement compressor included in a refrigeration
circuit of an air conditioner, said refrigeration circuit including
an evaporator, said method comprising the steps of: detecting a
differential pressure between two pressure monitoring points set to
said refrigeration circuit, on which the discharge capacity of the
variable displacement compressor is reflected; detecting a cooling
state of said evaporator as temperature information; calculating a
set differential pressure which becomes a control target of a
differential pressure between the two pressure monitoring points
based on said temperature information and a target temperature
which is a control target of the temperature of said evaporator;
setting a limit value to the differential pressure between the two
pressure monitoring points when said temperature information is
lowered from the state higher than a threshold temperature which is
set to higher than the target temperature to the state lower than
the threshold temperature, and releasing the setting of the limit
value when the detected temperature is raised from the state lower
than the threshold temperature to the state higher than the
threshold temperature; comparing said set differential pressure
with the limit value set, dealing with the set differential
pressure in itself if the discharge capacity of the variable
displacement compressor which the set differential pressure
represents is less than that of the variable displacement
compressor which the limit value represents, and dealing with the
limit value as a new set differential pressure if the discharge
capacity of the variable displacement compressor which the set
differential pressure represents is greater than that of variable
displacement compressor which the limit value represents; and
controlling the discharge capacity of the variable displacement
compressor so that the differential pressure approaches to said set
differential pressure.
[0009] Other aspects and advantages of the present 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
[0010] 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:
[0011] FIG. 1 is a cross-sectional view of a swash plate type
variable displacement compressor;
[0012] FIG. 2 is a diagram schematically showing a refrigeration
circuit;
[0013] FIG. 3 is a cross-sectional view of a control valve;
[0014] FIG. 4 is a flow chart illustrating a control method of the
control valve; and
[0015] FIG. 5 is a graph showing the relationship between a
post-temperature of the evaporator and an upper limit value of a
duty ratio.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The control apparatus of a swash plate type variable
displacement compressor of a refrigeration circuit of an automotive
air conditioner according to the present invention will hereafter
be described with reference to FIGS. 1 to 5.
[0017] The Swash Plate Type Variable Displacement Compressor
[0018] As shown in FIG. 1, the swash plate type variable
displacement compressor (hereinafter referred to as the compressor)
includes a cylinder block 11, a front housing 12 fixed to the front
end of the cylinder block 11, and a rear housing 14 securely fixed
to the rear end of the cylinder block 11 through a valve/port
forming body 13. A crank chamber 15 is surrounded by the cylinder
block 11 and the front housing 12. A drive shaft 16 extends through
the crank chamber 15 so that the drive shaft 16 is rotatably
supported by the cylinder block 11 and the front housing 12. A lug
plate 17 is integrally and rotatably fixed to the drive shaft 16 in
the crank chamber 15.
[0019] The front end of the drive shaft 16 is operatively connected
to an automotive engine Eg, which functions as an external drive
source, through a power transmitting mechanism PT. The power
transmitting mechanism PT may be a clutch mechanism (for example,
an electronic clutch), which can engage and disengage the clutch
electronically or it may be a clutchless mechanism, which does not
have a clutch mechanism (for example, the transmission may be a
combination of a belt and a pulley). In the present invention, a
clutchless type power transmitting mechanism PT is used.
[0020] The swash plate 18, which functions as a cam plate, is
accommodated in the crank chamber 15. The swash plate 18 slides on
the surface of the drive shaft 16 in the axial direction, and the
swash plate 18 inclines with respect to the axis of the drive shaft
16. A hinge mechanism 19 is located between the lug plate 17 and
the swash plate 18. Accordingly, the swash plate 18 is driven
integrally with the lug plate 17 and the drive shaft 16 by the
hinge mechanism 19.
[0021] Cylinder bores 20 (only one cylinder bore is shown) are
arranged about the drive shaft 16 in the cylinder block 11. A
single-head type piston 21 is accommodated in each cylinder bore
20. The front and rear openings of the cylinder bores 20 are closed
by the valve/port forming body 13 and the piston 21, and a
compression chamber, the volume of which is changed in accordance
with the piston motion is defined in each cylinder bore 20. Each
piston 21 is connected to the periphery of the swash plate 18
through a set of shoes 28. Accordingly, rotation of the swash plate
18 by the rotation of the drive shaft 16 is converted to
reciprocation of the pistons 21 by the shoes 28.
[0022] A suction chamber 22, which is included in a suction
pressure Ps region and a discharge chamber 23, which is included in
a discharge pressure Pd region, are defined by the valve/port
forming body 13 and the rear housing 14, as shown in FIG. 1. Also,
when the piston 21 moves from top dead center to bottom dead
center, the refrigerant gas of the suction chamber 22 is drawn into
the corresponding cylinder bore 20 (compression chamber) through a
corresponding suction port 24 and a corresponding suction valve 25
of the valve/port forming body 13. The refrigerant gas drawn into
the cylinder bores 20 is compressed to a predetermined pressure by
movement of the pistons 21 from bottom dead center to top dead
center and is then discharged to the discharge chamber 23 through
the discharge ports 26 and the discharge valves 27 of the
valve/port forming body 13.
[0023] The angle of inclination of the swash plate 18 (the angle
formed between the swash plate 18 and an imaginary plane that is
perpendicular to the drive shaft 16) can be adjusted by changing
the relationship between internal pressure (crank pressure Pc) of
the crank chamber 15, which is the back pressure of the pistons 21,
and the internal pressure of the cylinder bores 20 (compression
chambers). In the present embodiment, the angle of inclination of
the swash plate 18 is adjusted by changing the crank pressure
Pc.
[0024] The Refrigeration Circuit
[0025] As shown in FIGS. 1 and 2, the refrigeration circuit of the
automotive air conditioner includes the compressor and a external
refrigerant circuit 35. The external refrigerant circuit 35
includes a condenser 36, a thermostatic expansion valve 37, and an
evaporator 38. The opening degree of the expansion valve 37 is
feedback controlled based on an evaporation pressure (the discharge
pressure of the evaporator 38) and the temperature detected by a
temperature sensor 37a placed at the outlet side, or the downstream
side, of the evaporator 38. The expansion valve 37 supplies the
evaporator 38 with liquid refrigerant, the pressure of which
corresponds to the heat load, and adjusts the flow rate of the
refrigerant in the external refrigerant circuit 35. A downstream
pipe 39 connects the suction chamber 22 of the compressor with the
outlet of the evaporator 38 in the downstream region of the
external refrigerant circuit 35. An upstream pipe 40 connects the
discharge chamber 23 of the compressor with the inlet of the
condenser 36 in the upstream region of the external refrigerant
circuit 35. The compressor draws and compresses the refrigerant gas
from the downstream region of the external refrigerant circuit 35
to the suction chamber 25 and discharges the compressed gas to the
discharge chamber 23 connected to the upstream region of the
external refrigerant circuit 35.
[0026] However, as the flow rate of the refrigerant flowing through
the refrigerant circulator is increased, the pressure loss per unit
length of the circuit, or the pipe, is also increased. That is, the
pressure loss (differential pressure) between a first pressure
monitoring point P1 and a second pressure monitoring point P2 in
the refrigerant circuit correlates with the flow rate of the
refrigerant in the refrigerant circulator. Accordingly, to detect
the difference (PdH-PdL) between the gas pressure (PdH) of the
first pressure monitoring point P1 and the gas pressure (PdL) of
the second pressure monitoring point P2, the flow rate of the
refrigerant in the refrigerant circuit must be indirectly detected.
In the present embodiment, the first pressure monitoring point PI
(the high pressure point) is any point in the discharge chamber 23
corresponding to the most upstream region of the upstream pipe 40.
The second pressure monitoring point P2 (the low pressure point) is
a point in the upstream pipe 40 that is spaced from the first
pressure monitoring point by a predetermined distance.
[0027] In addition, the flow rate of the refrigerant in the
following refrigerant circuit can be represented as the product of
the rotating speed of the drive shaft 16 and the discharge amount
(the discharge capacity) of the refrigerant gas per unit rotation
of the drive shaft 16 in the compressor. The rotating speed of the
drive shaft 16 can be calculated from the pulley rate of the power
transmitting mechanism PT and the rotating speed of the automotive
engine Eg (the output shaft). In other words, when the rotating
speed of the automotive engine Eg is constant, the flow rate of the
refrigerant in the refrigerant circuit is increased when the
discharge capacity of the compressor is increased, and the flow
rate of the refrigerant in the refrigerant circuit is decreased
when the discharge capacity of the compressor is decreased. On the
contrary, when the discharge capacity of the compressor is
constant, the flow rate of the refrigerant in the refrigerant
circuit is increased when the rotating speed of the automotive
engine Eg is increased, and the flow rate of the refrigerant in the
refrigerant circulator is decreased when the rotating speed of the
automotive engine Eg is decreased.
[0028] A fixed throttle 43 is arranged between the pressure
monitoring points P1 and P2 in the upstream pipe 40. The throttle
43 increases the differential pressure between the points P1 and
P2. The fixed throttle 43 increases the differential pressure
PdH-PdL between the two points P1 and P2, though the pressure
monitoring points P1 and P2 are not far apart from each other.
Since the fixed throttle 43 is located between the pressure
monitoring points P1, P2, the second pressure monitoring point P2
can be positioned in the vicinity of the compressor (the discharge
chamber 23), and a second detecting passage 42, which extends
between a control valve 46 mounted in the compressor and the second
pressure monitoring point P2, can be shortened.
[0029] The Crank Pressure Control Mechanism
[0030] As shown in FIGS. 1 and 2, the crank pressure control
mechanism, for controlling the crank pressure Pc of the compressor,
includes a release passage 31, a first pressure sensing passage 41,
a second pressure sensing passage 42, a supply passage 44, a
control valve 46. The release passage 31 communicates the crank
chamber 15 with the suction chamber 22. The first pressure sensing
passage 41 connects the first pressure monitoring point P1 of the
refrigerant circuit with the control valve 46. The second pressure
sensing passage 42 connects the second pressure detecting point P2
of the refrigerant circuit with the control valve 46. The supply
passage 44 connects the control valve 46 with the crank chamber
15.
[0031] By adjusting the opening degree of the control valve 46, the
relationship between the flow rate of high pressure discharge gas
flowing from the second pressure monitoring point P2 to the crank
chamber 15 through the second pressure sensing passage 42 and the
supply passage 44 and the flow rate of gas discharged from the
crank chamber 15 to the suction chamber 22 through the release
passage 31 is controlled, which determines the crank pressure Pc.
The difference between the internal pressure of the cylinder bores
20 and the crank pressure Pc varies in accordance with variation of
the crank pressure Pc, and the inclination of the swash plate 18
varies accordingly. The stroke of each piston 21, of the discharge
capacity, is adjusted in accordance with the inclination angle of
the swash plate 18.
[0032] The Control Valve
[0033] As shown in FIG. 3, the control valve 46 includes an inlet
valve portion 51 at the top and a solenoid portion 52 at the
bottom. The solenoid portion 52 is also called an electric drive
portion. The valve portion 51 adjusts the opening degree
(throttling amount) of the supply passage 44. The solenoid portion
52 is an electronic actuator for controlling an operating rod 53,
which is arranged in the control valve 45, based on external
electric current control. The operating rod 53 includes a divider
portion 54, a connecting portion 55, a valve portion 56, or valve
body, and a guiding rod portion 57. The valve portion 56 is located
at the upper end of the guiding rod portion 57.
[0034] A valve housing 58 of the control valve 46 includes a cap
58a, an upper body 58b, which forms a main outer wall of the inlet
valve portion 51, and a lower body 58c, which forms a main outer
wall of the solenoid portion 52. A valve chamber 59 and a
communicating passage 60 are formed in the upper body 58b of the
valve housing 58. A high pressure chamber 65 is formed between the
upper body 58b and the cap 58a, which is threaded to the upper body
58b. The operating rod 53 is arranged to move in the valve chamber
59, the communicating passage 60, and the high pressure chamber 65
in an axial direction of the valve housing 58. The valve chamber 59
and the communicating passage 60 can communicate in accordance with
the position of the operating rod 53.
[0035] A bottom wall of the valve chamber 59 is provided by a top
end surface of a fixed core 70 of the solenoid portion 52. A first
radial port 62 extends through the main wall of the valve housing
58 surrounding the valve chamber 59. The first radial port 62
connects the valve chamber 59 with the second pressure monitoring
point P2 through the second pressure sensing passage 42.
Accordingly, the low pressure PdL of the second monitoring point P2
is applied to the valve chamber 59 through the second pressure
sensing passage 42 and the first port 62. A second port 63 is
arranged to extend radially through the main wall of the valve
housing 58 surrounding the communication passage 60. The second
port 63 connects the communicating passage 60 with the crank
chamber 15 through the supply passage 44. Accordingly, the valve
chamber 59 and the communicating passage 60 form a part of the
supply passage 44 that passes through the control valve and applies
the pressure of the second pressure monitoring point P2 to the
crank chamber 15.
[0036] The valve portion 56 of the operating rod 53 is located in
the valve chamber 59. The diameter of the aperture of the
communicating passage 60 is larger than that of the connecting
portion 55 of the operating rod 53 so that gas flows smoothly. A
step located at the boundary between the communicating passage 60
and the valve chamber 59 functions as a valve seat 64, and the
communicating passage 60 is a valve aperture. When the operating
rod 53 moves from the location shown in the drawings (the lowest
position) to the highest position, where the valve portion 56 is
seated against the valve seat 64, the communicating passage 60 is
blocked. In other words, the valve portion 56 of the operating rod
53 can adjust the opening degree of the supply passages 44.
[0037] The divider portion 54 of the operating rod 53 is fitted
into the high pressure chamber 65. The divider portion 54 serves as
a partition between the high pressure chamber 65 and the
communicating passage 60. Therefore the high pressure chamber 65
does not communicate with the communicating passage 60
directly.
[0038] A third port 67 is formed in the main wall of the valve
housing 58 surrounding the high pressure chamber 65. The high
pressure chamber 65 always communicates with the discharge chamber
23, which is the location of the first pressure monitoring point
P1, through the third port 67 and the first pressure sensing
passage 41. Accordingly, the high pressure PdH is applied to the
high pressure chamber 65 through the first pressure sensing passage
41 and the third port 67. A return spring 68 is accommodated in the
high pressure chamber 65. The return spring 68 applies axial force
to the divider portion 54 (or to the operating rod 53).
[0039] The solenoid portion 52 includes a cylindrical barrel 69
having a bottom. The fixed core 70 is fitted into the top portion
of the barrel 69, and the barrel 69 forms a plunger chamber 71. A
plunger (the moving core) 72 is accommodated in the plunger chamber
71 and is moveable in the axial direction. A guiding hole 73 is
formed in the fixed core 70. The guiding rod portion 57 of the
operating rod 53 is fitted in the guiding hole 73 and is moveable
in the axial direction. A clearance (not shown) is formed between
the internal wall surface of the guiding hole 73 and the guiding
rod portion 57. Thus, the valve chamber 59 always communicates with
the plunger 71 through the clearance. In other words, the low
pressure of the valve chamber 59, that is, the pressure PdL of the
second pressure monitoring point P2, is applied to the plunger
chamber 71.
[0040] The lower end of the guiding rod portion 57 is fixed to the
plunger 72. Accordingly, the operating rod 53 moves integrally with
the plunger 72. A buffer spring 74 is located in the plunger
chamber 71. The elastic force of the buffer spring 74 urges the
plunger 72 toward the fixed core 70, which urges the operating rod
53 in an upward direction in the drawings. The force of the buffer
spring 74 is smaller than that of the return spring 68.
[0041] A coil 75 is wound in the vicinity of the plunger 72 and the
fixed core 70 in a range that covers them. The coil 75 is supplied
with a driving signal from a driving circuit 82, based on a command
from a computer 81, and the coil 75 generates an electronic force
F, the magnitude of which depends on the level of the driving
signal. The plunger 72 is attracted to the fixed core 70 by the
electronic force F, and the operating rod 53 moves upward. The
current flowing to the coil 75 is varied by adjusting the voltage
applied to the coil 75. In the present embodiment, to adjust the
voltage applied to the coil 75, a duty control method has been
employed.
[0042] In addition, the high pressure PdH of the high pressure
chamber 65 is applied to the operating rod 53 in the downward
direction of FIG. 3, as is the force f1 of the return spring 68.
Also, the low pressure PdL is applied to the guide rod portion 57
in the upward direction. The control valve 46 includes a
differential pressure sensor (the pressure chamber 65, the plunger
chamber 71, and the operating rod 53), which uses the differential
pressure .DELTA.P (.DELTA.Pd=(PdH-PdL)) to determine the position
of the valve portion 56. On the other hand, the electronic force F
generated between the fixed core 70 and the plunger 72 is applied
to the operating rod 53 in the upward direction, like the force f2
of the buffer spring 74. In other words, the adjustment of the
opening degree of the control valve 46, namely, the adjustment of
the opening degree of the communicating passage 60, is internally
performed based on changes of the differential pressure between the
two points .DELTA.Pd, and at the same time, is externally performed
based on changes of the electronic force F.
[0043] That is, if the electronic force F is constant, when the
rotating speed of the engine Eg is decreased to decrease the flow
rate of the refrigerant in the refrigerant circuit, the downward
force based on the differential pressure between the two points
.DELTA.Pd is decreased. Thus the downward force acting on the
operating rod 53 against the electronic elastic force F is reduced.
Accordingly, the operating rod 53 moves upwardly, and the force of
the return spring 68 increases. The valve portion 56 of the
operating rod 53 is relocated to a position where the upward and
downward forces are rebalanced. As a result, the opening degree of
the communicating passage 60 is reduced, and the crank pressure Pc
is reduced. Consequently, the difference between the internal
pressure of the cylinder bores 20 and the crank pressure Pc is
reduced, and the angle of the inclination of the swash plate 18 is
increased. As a result, the discharge capacity of the compressor is
increased. When the discharge capacity of the compressor is
increased, the flow rate of refrigerant in the refrigerant circuit
is increased, and the differential pressure between the two points
.DELTA.Pd is increased.
[0044] On the contrary, when the rotating speed of the automotive
engine Eg is increased to increase the flow rate of the refrigerant
in the refrigeration circuit, the downward force based on the
differential pressure .DELTA.Pd is increased. Accordingly, the
operating rod 53 moves downwardly, the downward force of the return
spring 68 is reduced, and the valve portion 56 of the operating rod
53 is relocated to a position where the upward and downward forces
are rebalanced. As a result, the opening degree of the
communicating passage 60 is increased, and the crank pressure Pc is
increased. Also, the difference between the internal pressure of
the cylinder bores 20 and the crank pressure Pc is increased, and
the angle of the inclination of the swash plate 18 is decreased.
Thus, the discharge capacity of the compressor is decreased. When
the discharge capacity of the compressor is decreased, the flow
rate of the refrigerant in the refrigeration circuit is decreased,
and the differential pressure .DELTA.Pd is decreased.
[0045] In addition, for example, if the electronic force F is
increased by increasing the duty ratio Dt to the coil 75, the
operating rod 53 moves upwardly against the force of the return
spring 68, and the valve portion 56 of the operating rod 53 is
relocated at a position where the upward and downward forces are
rebalanced. Accordingly, the opening degree of the control valve
46, namely, the opening degree of the communicating passage 60 is
reduced, and the discharge capacity of the compressor is increased.
As a result, the flow rate of the refrigerant in the refrigerant
circulator is increased, and the differential pressure .DELTA.Pd is
also increased.
[0046] On the contrary, if the electronic force F is decreased by
decreasing the duty ratio Dt, the operating rod 53 moves downwardly
and the force of the return spring 68 is reduced. Consequently, the
valve portion 56 of the operating rod 53 is relocated at a position
where the upward and downward forces on the rod 53 are rebalanced.
Accordingly, the opening degree of the communicating passage 60 is
increased, and the discharge capacity of the compressor is
decreased. As the result, the flow rate of the refrigerant in the
refrigerant circulator is decreased, and the differential pressure
.DELTA.Pd is also decreased.
[0047] In other words, the control valve 46 in FIG. 3 positions the
operating rod 53 in accordance with the differential pressure
.DELTA.Pd to hold a control target (the target differential
pressure) of the differential pressure .DELTA.Pd, which is
determined by the electronic force F.
[0048] The Control Scheme
[0049] As shown in FIGS. 2 and 3, the automotive air conditioner
includes the computer 81, which performs overall control. The
computer 81 includes a CPU, a ROM, a RAM, and an I/O interface. The
A/C switch 83 (the ON/OFF switch of the air conditioner operated by
passengers), an internal air temperature sensor 84 for detecting
the temperature of the passenger compartment, a temperature setting
unit 85 for setting the compartment temperature, and a
post-temperature sensor 86 of the evaporator are connected to the
input terminal of the I/O interface of the computer 81. The
evaporator air temperature sensor 86 is located in the vicinity of
the exit side of the evaporator 38 and detects the temperature of
the air cooled by passing through the evaporator 38. A driving
circuit 82 is connected to the output terminal of the I/O interface
of the computer 81.
[0050] The computer 81 calculates an appropriate duty ratio Dt,
which indicates the set differential pressure, based on various
kinds of external information, which is provided by respective
sensors 83-86, and commands the driving circuit 82 to output the
driving signal, which represents the duty ratio Dt. The driving
circuit 82 outputs the driving signal that represents the commanded
duty ratio Dt to the coil 75 of the control valve 46. The
electronic force F of the solenoid portion 52 of the control valve
46 is changed in accordance with the duty ratio of the driving
signal.
[0051] The duty control method of the control valve 46 by the
computer 81 will be described hereinafter with reference to the
flow chart of FIG. 4.
[0052] If an ignition switch (or a start switch) of the vehicle is
turned ON, the computer 81 is supplied with power and starts the
operating process. In the first step S101 (steps are sometimes
referred to as S101 and so on), the computer 81 performs various
initialization steps in accordance with an initial program. For
example, the duty ratio Dt is initially set to 0%, and the upper
limit value DtMax of the duty ratio Dt is set to 100%. By setting
the upper limit value DtMax of the duty ratio to 100%, the
magnitude of the electronic force F, that is, the set differential
pressure, which is used to adjust the valve opening degree of the
control valve 46, can be reduced as far as the physical limit of
the control valve 46. Also, the upper limit value DtMax is changed
between 100% and a value less than 100%, for example, 40-60% (50%
in the present embodiment). Setting the upper limit value DtMax to
50% limits the cooling capability of the air conditioner.
[0053] In the step S102, the ON/OFF state of the A/C switch 83 is
monitored until the A/C switch 83 is turned ON. When the A/C switch
83 is turned ON, in step S103, the computer 81 determines the
cooling state of the evaporator 38 based on the set temperature
information from the temperature setting unit 85 or the temperature
information from the compartment air temperature sensor 84. In
other words, a target temperature Te(set) of the evaporator air
temperature Te(t) is calculated in the range of 3-12.degree. C.
Accordingly, the compartment air temperature sensor 84 and the
temperature setting unit 85, together with the computer 81, form a
temperature setting device for setting the target temperature the
target temperature Te(set).
[0054] In step S104, the computer 81 determines whether the
temperature Te(t) detected by the evaporator air temperature sensor
86 is greater than the target temperature Te(set). If the
determination of the step S104 is NO, the computer 81 determines in
step S105 whether the detected temperature Te(t) is less than the
target temperature Te(set). If the determination of step S105 is
also NO, since the detected temperature Te(t) is equal to the
target temperature Te(set), the duty ratio Dt is not changed.
[0055] If the determination of step S104 is YES, the computer 81
increases the duty ratio Dt by the unit amount .DELTA.D in step
S106. When the driving signal Dt+.DELTA.D is output from the
driving circuit 82 to the coil 75 of the control valve 46 as
described above, the flow rate of the refrigerant in the
refrigerant circulator is increased, and the cooling performance of
the evaporator 38 increases, and the evaporator air temperature
Te(t) decreases. If the determination of step S105 is YES, the
computer 81 decreases the duty ratio Dt by the unit amount .DELTA.D
in step S107. When the driving signal Dt-.DELTA.D is output from
the driving circuit 82 to the coil 75 of the control valve 46 as
described above, the flow rate of the refrigerant in the
refrigerant circulator is decreased, the cooling performance of the
evaporator 38 decreases, and the evaporator air temperature Te(t)
increases.
[0056] After the duty ratio Dt is changed in the above-described
manner, the computer 81 determines whether the temperature Te(t)
detected by the evaporator air temperature sensor 86 is outside of
a predetermined threshold temperature range (for example,
15-16.degree. C.) and, if so, changes the upper limit value DtMax
of the duty ratio Dt. The threshold temperature range
(15-16.degree. C.) is greater than the set range (3-12.degree. C.)
of the target temperature Te(set).
[0057] That is, in step S108, the computer 81 determines whether
the present set upper limit value DtMax is 100% or 50%. If the
upper limit value DtMax is determined to 100% in step S108, the
computer determines in step S109 whether the temperature Te(t)
detected by the evaporator air temperature sensor 86 is less than
the lower limit temperature (15.degree. C.) of the threshold
temperature range (15-16.degree. C.) If the determination of step
S109 is NO, the upper limit value remains at 100%. On the contrary,
if the determination of step S109 is YES, the upper limit value
DtMax is changed from 100% to 50% in step S110.
[0058] In addition, if the upper limit value DtMax is determined to
be 50% in step S108, the computer determines in step S111 whether
the temperature Te(t) detected by the evaporator air temperature
sensor 86 is greater than the upper limit temperature (16.degree.
C.) of the threshold temperature range (15-16.degree. C.) . If the
determination of step S111 is NO, the upper limit value DtMax
remains at 50%. On the contrary, if the determination of step S111
is YES, the upper limit value DtMax is changed from 50% to
100%.
[0059] FIG. 5 graphically shows the processes of steps S108-S112.
That is, if the temperature Te(t) detected by the evaporator air
temperature sensor 86 falls from a temperature greater than the
lower limit temperature (15.degree. C.) of the threshold
temperature range (15-16.degree. C.) to a temperature less than the
lower limit temperature (15.degree. C.), the computer 81 changes
the upper limit value DtMax of the duty ratio Dt from 100% to 50%.
In effect, this places an upper limit on the target differential
pressure .DELTA.Pd. If the temperature Te(t) detected by the
evaporator air temperature sensor 86 increases from a temperature
less than the upper limit temperature (16.degree. C.) of the
threshold temperature range (15-16.degree. C.) to a temperature
greater than the upper limit temperature (16.degree. C.), the
computer 81 changes the upper limit value DtMax of the duty ratio
Dt from 50% to 100%. In effect, this increases the upper limit of
the target differential pressure.
[0060] In other words, the computer 81 determines the need for
cooling by comparing the temperature Te(t) detected by the
evaporator air temperature sensor 86 with the target temperature
Te(set) and determines the degree of the cooling load by comparing
the detected temperature Te(t) to a limit of the threshold
temperature range (15-16.degree. C.) In addition, when the detected
temperature Te(t) is less than the lower limit of the threshold
temperature range (15-16.degree. C.), the computer determines that
there is little or no need for cooling and reduces the upper limit
value of the cooling capability. When the detected temperature
Te(t) is greater than the upper limit of the threshold temperature
range (15-16.degree. C.), the computer determines that the need for
cooling is large, and maximizes the cooling capability of the air
conditioner by changing the upper limit value of the cooling
capability.
[0061] In step S113, the computer 81 determines whether the duty
ratio Dt calculated by steps S104-S107 is less than 0%. If the
determination of step S113 is YES, the computer 81 corrects the
duty ratio Dt to 0% in step S114. Further, if the determination of
step S113 is NO, the computer 81 determines in step S115 whether
the duty ratio Dt calculated by steps S104-107 is greater than the
upper limit value DtMax, which may have been re-set by steps
S108-112. If the determination of step S115 is NO, the computer 81
sends the duty ratio Dt calculated by steps S104-S107 to the
driving circuit 82 in step S116. On the contrary, if the
determination of step S115 is YES, the computer 81 sends the upper
limit value DtMax to the driving circuit 82 in step S117.
[0062] When the upper limit value DtMax is set to 50%, step S115
monitors whether the target differential pressure, which is
calculated by steps S104-S107, in the form of the duty ratio, is
greater than the upper limit value. However, when the upper limit
value DtMax is set to 100%, step S115 monitors only whether the
duty ratio Dt is greater than the real range (0-100%) of the
driving signal output from the driving circuit 82. For example, if
a duty ratio Dt greater than 100% is sent to the driving circuit
82, the set differential pressure is set to the maximum value as
when the duty ratio is 100%. In spite of that, the calculation of a
duty ratio greater than 100% is not allowed because the set
differential pressure continuously remains at the maximum value
until the duty ratio falls below 100% if decrease the duty ratio Dt
is decreased under the condition that the duty ratio is greater
than 100%, thereby degrading the responsivity. This is similar to
the case that the duty ratio Dt is less than 0%. Accordingly, the
processes of the steps S113 and S114 are provided.
[0063] The effects of the illustrated embodiment are as
follows.
[0064] (1) The feedback control of the discharge capacity of the
compressor is done by using the differential pressure
.DELTA.Pd=PdH-PdL as the direct control target, without using the
suction pressure Ps, which is affected by the heat load.
Accordingly, regardless of the heat load circumstances, the control
of the discharge capacity and the responsiveness are improved.
[0065] (2) The operating efficiency of the compressor tends to
deteriorate when the piston speed is increased due to friction. The
piston speed is related to the rotating speed of the drive shaft
16. The compressor cannot change the rotating speed of the engine
Eg because the compressor is driven as an auxiliary unit of the
automotive engine Eg. Accordingly, to use the compressor
effectively and to improve the efficiency of the engine Eg, the
discharge capacity is normally not maximized when the rotating
speed of the automotive engine Eg is high. In terms of the
protection of the compressor, it is important that the compressor
not be in high load state. To protect the compressor, the control
valve 46 is designed such that the compressor has the maximum
discharge capacity, and the differential pressure between two
points (.DELTA.Pd=PdH-PdL) resulted from the region where the
rotating speed of the automotive engine Eg is less than the high
speed region is set to a maximum value of the set differential
pressure resulted when the duty ratio is 100%. Then, if the
rotating speed of the automative engine Eg enters the high speed
region, the differential pressure between two points .DELTA.Pd
becomes greater than the maximum value of the set differential
pressure in case that the discharge capacity becomes the maximum,
and then the compressor decreases internally the discharge capacity
from the maximum value.
[0066] However, in an initial state in which the compartment
temperature is high and the evaporator air temperature Te(t) is far
greater than the target temperature Te(set), it is necessary that
the air conditioner have the maximum cooling capability, regardless
of the rotating speed of the automotive engine Eg. Accordingly, the
control valve 46 is designed to have a high cooling performance
rather than high efficiency during those times. In other words, the
control valve 46 is designed such that the compressor has the
maximum discharge capacity and the differential pressure between
two points .DELTA.Pd resulted from the region where the rotating
speed of the automotive engine Eg is high is set to the maximum
value of the set differential pressure. By the above-mentioned
design, though the discharge capacity is the maximum value, the
differential pressure between two points (.DELTA.Pd=PdH-PdL) is not
greater than the maximum value of the set differential pressure
unless the rotating speed of the automotive engine Eg is pretty
large (actually, by the efficiency deterioration of the compressor,
when the rotating speed of the automotive engine Eg enters the high
speed region, the flow rate of the refrigerant is limited, and it
can be represented to "no matter how high the rotating speed of the
automotive engine Eg may be"). Accordingly, the discharge capacity
of the compressor must be the maximum if the duty ratio Dt becomes
100%. Therefore, the air conditioner can exhibit the maximum cool
capability at that time regardless of the rotating speed of the
automotive engine Eg, and can cope with the high cooling load
sufficiently.
[0067] If the automotive air conditioner of the present embodiment
did not performed steps S108-S117 to increase the cooling
performance, the following problem occurs. If the air temperature
at the evaporator Te(t) is less than the lower limit of the
threshold temperature range (15-16.degree. C.), the cooling load
decreases and the air temperature at the evaporator Te(t) is
decreased to the target temperature Te(set). Therefore, there is no
need for the maximum cooling capability at that time.
[0068] However, if steps S108-S112 are not performed, a duty ratio
Dt of 100% is always allowed. Accordingly, though the air
temperature at the evaporator Te(t) is decrease to the vicinity of
the target temperature Te(set) and the cooling load is small, there
is a problem that the duty ratio Dt may be set to 100% continuously
until the air temperature at the evaporator Te(t) is less than the
target temperature Te(set). If the duty ratio Dt is set to 100%,
when the rotating speed of the automotive engine Eg becomes very
high speed region, the discharge capacity of the compressor is
maximized by the control valve 46, and the cooling capability
continuously maximized. In other words, the compressor is
unnecessarily in a high load and inefficient state.
[0069] However, when steps S108-S112 are performed, if the air
temperature at the evaporator Te(t) is less than the lower limit of
the threshold temperature range (15-16.degree. C.), the cooling
load is determined to be small, and the duty ratio Dt is set to
50%, even though the air temperature of the evaporator Te(t) has
not reached the target temperature Te(set). Accordingly, when the
air temperature at the evaporator Te(t) is less than the lower
limit of the threshold temperature range (15-16.degree. C.), the
target differential pressure does not exceed an upper limit value
that corresponds to the duty ratio Dt of 50%. Also, when the set
differential pressure (the duty ratio)is set to the upper limit
value, if the rotating speed of the automotive engine Eg becomes
high, the differential pressure .DELTA.Pd will exceed the upper
limit value of the target differential pressure when the discharge
capacity reaches the maximum value that corresponds to the upper
limit value of 50%, and consequently the discharge capacity of the
compressor is automatically reduced by the control valve 46. As
mentioned, if the compressor avoids a low efficiency and high load
state, the operating efficiency of the automotive engine Eg is
improved, and fuel consumption is reduced. Also, the compressor can
be protected and used for a long time. Also, if, when the rotating
speed of the automotive engine Eg becomes very high, the discharge
capacity of the compressor (which is related to load torque) does
not reach the maximum value, the load of the compressor on the
engine Eg is reduced, and the traveling performance and the
acceleration performance of the vehicle are improved, and the heat
produced by the engine Eg is reduced. Therefore, the size of the
cooling unit for cooling the engine (particularly, the heat
exchanger) can be reduced.
[0070] (3) The present embodiment employs hysteresis such that the
air temperature at the evaporator Te(t) when the upper limit value
DtMax of the duty ratio Dt is changed from 100% to 50% is different
from that Te(t) when the upper limit value DtMax of the duty ratio
Dt is changed from 50% to 100%. This is accomplished with the
threshold temperature range (15-16.degree. C.). Therefore, by
avoiding hunting, which would occur if a single threshold
temperature were used, the discharge capacity control of the
compressor is stable. Such hunting would change the upper limit
value DtMax instantaneously and frequently.
[0071] (4) The computer 81 adjusts the target temperature Te(set)
of the evaporator air temperature Te(t) based on the temperature
indicated by temperature setting unit 85 or the compartment
temperature. In other words, the air conditioner can change the
cooling state of the evaporator 38 in accordance with the degree of
the need for cooling. For example, the air conditioner does not
comprise the internal air temperature sensor 84 or the temperature
setting unit 85, and can achieve the comfortableness improvement
(for instance, the change of the temperature flown into the
automotive room is suppressed) of the air conditioner or the
power-saving of the compressor in comparison with the composition
which the predetermined target temperature Te(set) is maintained.
In other words, in this comparative example, the target temperature
must be set to the low value to cope with the case that a demand
degree for the cooling is the largest (the case that an operator
demands the lowest room temperature). Accordingly, the evaporator
38 is unnecessarily cooled even when the demand cooling is small.
In addition, in this comparative example, when the demand degree
for the cooling is small, the air cooled by passing through the
evaporator 38 is reheated suitably by a heater (not shown) using
the heat generated by the operation of the automotive engine and
then flows into the passenger compartment.
[0072] (5) The compressor is a swash plate type variable
displacement compressor in which the stroke of the piston 21 can be
changed by controlling the pressure Pc of the crank chamber 15. The
control unit of the present embodiment is most suitable to capacity
control of a swash plate type variable displacement compressor.
[0073] In addition, the following are considered to be within the
scope of the present invention.
[0074] The threshold temperature may be a single temperature.
[0075] The temperature of a surface of the evaporator 38 may be
directly detected to indicate the cooling state of the evaporator
38.
[0076] The internal air temperature sensor 84 or the temperature
setting unit 85 may be omitted and the target temperature Te(set)
may be set to a fixed value.
[0077] The first pressure monitoring point P1 may be in the suction
pressure region between the evaporator 38 and the suction chamber
22, and the second pressure monitoring point P2 may be downstream
of the first pressure monitoring point P1 in the same suction
pressure region.
[0078] The first pressure monitoring point P1 may be in the
discharge pressure region between the discharge chamber 23 and the
condenser 36, and the second pressure monitoring point P2 may be in
the suction pressure region between the evaporator 38 and the
suction chamber 22.
[0079] The first pressure monitoring point P1 may be in the
discharge pressure region between the discharge chamber 23 and the
condenser 36, and the second pressure monitoring point P2 may be in
the crank chamber 15. Alternatively, the first pressure monitoring
point P1 may be in the crank chamber 15, and the second pressure
monitoring point P2 may be in the suction pressure region between
the evaporator 38 and the suction chamber 22. In other words, the
pressure monitoring points P1 and P2 are located in the
refrigeration circuit. The pressure monitoring points P1, P2 may be
in the high pressure region, the low pressure region, or the crank
chamber 15. In one embodiment, when the discharge capacity of the
compressor is increased, the differential pressure between the two
points (.DELTA.Pd=Pc-Ps) decreases (which is opposite to the manner
of the illustrated embodiment). Accordingly, if the evaporator air
temperature Te(t) is less than the lower limit of the threshold
temperature range (15-16.degree. C.), the lower limit value is set
to the differential pressure .DELTA.Pd between the two pressure
monitoring points as a limit value. In addition, the set
differential pressure determining means 81 compares the set
differential pressure calculated by the set differential pressure
calculating means with the lower limit value set by the limit value
setting means, deals with the set differential pressure in itself
if the set differential pressure is more than the lower limit
value, and deals with the lower limit value as new set differential
pressure if the set differential pressure is less than the lower
limit value.
[0080] For example, by using the control valve comprising only the
electric valve driving element, the pressures PdH, PdL of the two
pressure monitoring points P1, P2 are detected by the respective
pressure sensor. In this case, the pressure sensor for detecting
the pressures PdH, PdL of the each pressure monitoring points P1,
P2 forms the differential pressure sensing means.
[0081] The control valve may be the extracted side control valve
which adjusts the crank pressure Pc by adjusting the opening degree
of the charge passage 31, not by adjusting the opening degree of
the release passages 42, 44.
[0082] The control valve may be a three-way valve that adjusts the
crank pressure Pc by adjusting the opening degree of both sides of
the release passages 42, 44 and the charge passage 31.
[0083] The power transmitting mechanism may include an electronic
clutch.
[0084] The control apparatus of a wobble type variable displacement
compressor is concretized.
* * * * *