Information
-
Patent Grant
-
6358016
-
Patent Number
6,358,016
-
Date Filed
Friday, July 14, 200024 years ago
-
Date Issued
Tuesday, March 19, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 062 2285
- 417 2222
- 417 269
- 417 270
- 417 271
-
International Classifications
-
Abstract
A controller normally supplies current the magnitude of which corresponds to a required cooling performance of a refrigeration circuit to a displacement control valve. As a result the compressor displacement is adjusted in accordance with the required cooling performance (usual displacement control). When a vehicle is quickly accelerated, the controller temporarily eliminates the current value to the control valve to minimize the compressor displacement (displacement limiting control). When the control is switched from the displacement limiting control to the usual In displacement control, the controller changes the current value from zero to a target value, which corresponds to the required cooling performance, taking a predetermined restoration time. For an initial period of the restoration period, the current value is set greater than a corresponding value on a direct proportional line, which represents a constant rate of change from zero to the target value. As a result, the control is smoothly and quickly switched from the displacement limiting control to the usual displacement control.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a variable displacement compressor used for vehicle air conditioners, and more specifically, to a device and a method for controlling the displacement of a compressor.
In a general variable displacement compressor used for vehicle air conditioners, the inclination angle of a swash plate provided in a crank chamber changes in accordance with the pressure in the crank chamber. The crank chamber is connected to a suction chamber through a bleed passage and also to a discharge chamber through a supply passage. In the bleed passage is provided a displacement control valve. A controller containing a computer controls a control valve to adjust the amount of refrigerant gas that flows out into the suction chamber from the crank chamber through the bleed passage. As a result, the amount of the refrigerant gas which flows out of the crank chamber changes relative to the amount of refrigerant gas which is supplied to the crank chamber from the discharge chamber through the supply passage so that the pressure in the crank chamber is adjusted.
The control valve is provided with, for example, a valve body, a pressure sensing mechanism for operating the valve body in accordance with the pressure in the suction chamber (suction pressure), and an electromagnetic actuator, which urges the valve body with a force corresponding to the value of electric current supplied from the controller. The force of the electromagnetic actuator to urge the valve body reflects the target suction pressure. The controller adjusts the value of electric current supplied to the electromagnetic actuator to change the target suction pressure.
The controller increases the value of electric current supplied to the electromagnetic actuator to decrease the target suction pressure, and decreases the value of electric current supplied to the electromagnetic actuator to increase the target suction pressure. When electric current is not supplied to the electromagnetic actuator, the target suction pressure becomes a maximum value.
When a suction pressure exceeds the target suction pressure, the pressure sensing mechanism operates the valve body so as to increase the opening size of the bleed passage. Therefore, the flow rate of refrigerant gas from the crank chamber to the suction chamber is increased and the pressure in the crank chamber is then reduced. This increases the inclination angle of the swash plate so that displacement of the compressor increases. When the displacement of the compressor increases, the cooling performance of a refrigeration circuit incorporating the compressor increases and a suction pressure decreases so that it is converged to the target suction pressure.
When the suction pressure is lower than the target suction pressure, the pressure sensing mechanism operates the valve body to decrease the opening size of the bleed passage. Therefore, the flow rate of refrigerant gas from the crank chamber to the suction chamber decreases and the pressure in the crank chamber then increases. This decreases the inclination angle of the swash plate so that the displacement of the compressor decreases. When the displacement of the compressor decreases, the cooling performance of refrigeration circuit is reduced and a suction pressure increases so that it is converged to the target suction pressure.
Thus, the pressure sensing mechanism operates the valve body in accordance with the suction pressure in order to maintain the suction pressure at the target suction pressure.
The load on a vehicle engine increases under abrupt acceleration of the vehicle. Since the compressor is driven by the vehicle engine, if the engine load is great, the displacement of the compressor is temporarily minimized to reduce the engine load. Such displacement limiting control under abrupt acceleration of the vehicle will be described with reference to time charts of FIGS.
6
(
a
) to
6
(
c
).
As shown in FIG.
6
(
a
), when a vehicle is abruptly to accelerated in a state where electric current of the predetermined value is supplied to an electromagnetic actuator of a displacement control valve, a controller sets the supplied current value for the electromagnetic actuator at zero to start the displacement limiting control. As a result, as shown in FIG.
6
(
b
), the target suction pressure Pst is set at a maximum value Pmax. Then, the pressure sensing mechanism of the displacement control valve closes the bleed passage with the valve body to bring an actual suction pressure Psa near to the maximum value Pmax. Thus, the pressure in the crank chamber increases and the inclination angle of the swash plate becomes minimum, whereby the displacement of the compressor becomes minimum as shown in FIG.
6
(
c
). In other words, the torque of the compressor becomes minimum so that the engine load is reduced.
When the target suction pressure Pst changes, some time is required for this change to be reflected in the change in the actual suction pressure Psa. Thus, when the target suction pressure Pst is rapidly changed to the maximum value Pmax as shown in FIG.
6
(
b
), the actual suction pressure Psa gradually increases toward the maximum value Pmax.
As shown in FIG.
6
(
a
), a displacement limiting control due to abrupt acceleration of a vehicle is completed after the lapse of the predetermined time S from its start. After that, the displacement limiting control is shifted to a usual displacement control in accordance with a cooling performance required for the refrigeration circuit. Specifically, the controller resumes the supply of current to the electromagnetic actuator after the lapse of the predetermined time S after setting the supplied current value for the electromagnetic actuator at zero. At this time, the controller obtains the target current value A
3
according to the cooling performance required for the refrigeration circuit, and gradually increases the supplied current value for the electromagnetic actuator from zero to the target current value A
3
for the predetermined time T (refer to the straight line H in FIG.
6
(
a
)). According to this increase, the target suction pressure Pst gradually decreases from the it maximum value Pmax to the value P
3
corresponding to the target current value A
3
for the predetermined time T as shown in FIG.
6
(
b
).
If the target suction pressure Pst rapidly decreases from the maximum value Pmax to the value P
3
, the actual suction pressure Psa, which is gradually increasing toward the maximum value Pmax, significantly exceeds the value P
3
temporarily. Then, the pressure sensing mechanism of the displacement control valve causes the valve body to abruptly open the bleed passage to decrease the actual suction pressure Psa to the value P
3
. This leads to an abrupt decrease in the pressure in the crank chamber and rapidly increases the displacement of the compressor. As a result, the torque of the compressor rapidly increases and the engine load rapidly increases, whereby the vehicle drivability is deteriorated. To avoid such problems, the target suction pressure Pst gradually decreases from the maximum value Pmax to the value P
3
for the predetermined time T.
As shown in FIG.
6
(
b
), the actual suction pressure Psa is always lower than the target suction pressure Pst set at the maximum value Pmax through the predetermined time S when the displacement limiting control is being executed. Further, since the target suction pressure Pst gradually decreases at the completion of the displacement limiting control, the actual suction pressure Psa is still lower than the target suction pressure Pst between the completion of the displacement limiting control and the end of time Ta. When the time Ta elapses after the completion of the displacement limiting control, the actual suction pressure Psa substantially becomes equal to the target suction pressure Pst. After that, the actual suction pressure Psa is gradually reduced to the value P
3
as the target suction pressure Pst is gradually reduced to the value P
3
.
When the actual suction pressure Psa is lower than the target suction pressure Pst, the pressure sensing mechanism of the displacement control valve causes the valve body to control the opening size of the bleed passage to increase the actual suction pressure Psa so as to bring it near the target suction pressure Pst. In other words, even if the displacement limiting control is completed, the pressure sensing mechanism does not execute an operation for decreasing the actual suction pressure Psa, that is an operation for increasing displacement of a compressor from the minimum state until the time Ta elapses after the completion.
In addition, the displacement control valve completely closes the bleed passage during execution of the displacement limiting control and the pressure in the crank chamber is excessively increased due to the high pressure gas supplied through the supply passage. Therefore, even if the control valve increases the opening size of the bleed passage to increase the displacement of the compressor after the lapse of the time Ta after the completion of the displacement limiting control, it takes much time to lower the pressure in the crank chamber to pressure by which the displacement of the compressor can shift from the minimum state to an increased state. Thus, as shown in FIG.
6
(
c
), the displacement of the compressor shifts from the minimum state to the increased state with a delay of a considerably long time Tb after the completion of the displacement limiting control. That is, the displacement of the compressor is maintained in the minimum state for a time longer than the execution time S of the displacement limiting control. This means that a cooling performance of the refrigeration circuit unnecessarily decreases for a long time. As a result, the passenger compartment temperature further becomes higher than before execution of the displacement limiting control, which gives discomfort to passengers in the vehicle.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide a displacement control device and a displacement control method for a variable displacement compressor which smoothly and rapidly shift a displacement limiting control to a usual displacement control.
To attain the above-mentioned object, the present invention provides a displacement control device for a compressor that changes the displacement in accordance with the pressure in a control pressure chamber. The control device includes a control valve, a detector and a controller. The control valve controls the pressure in the control pressure chamber. The control valve has a valve body and an electromagnetic actuator for actuating the valve body. The actuator urges the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator. The detector detects external conditions that are necessary for controlling the compressor displacement. The controller controls the value of current supplied to the actuator. The controller selects a control mode to be executed from a usual displacement control and a displacement limiting control based on the detected external conditions. When the usual displacement control is selected, the controller sets the current value to a target value, which corresponds to the detected external conditions. When the displacement limiting control is selected, the controller temporarily sets the current value to a specific value to minimize the compressor displacement. When the control mode is switched from the displacement limiting control to the usual displacement control, the controller changes the current value from the specific value to the target value taking a predetermined restoration period. For at least part of the restoration period, the controller sets the current value to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.
The present invention also provides a method for controlling the displacement of a compressor that changes the displacement in accordance with the pressure in a control pressure chamber. The method includes: controlling the pressure in the control pressure chamber by a control valve, wherein the control valve has a valve body and an electromagnetic actuator for actuating the valve body, wherein the actuator urges the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator; detecting external conditions that are necessary for controlling the compressor displacement; selecting a control mode to be executed from a usual displacement control and a displacement limiting control based on the detected external conditions; setting the current value to a target value, which corresponds to the detected external conditions, when the usual displacement control is selected; temporarily setting the current value to a specific value to minimize the compressor displacement when the displacement limiting control is selected; and changing the current value from the specific value to the target value taking a predetermined restoration period when the control mode is switched from the displacement limiting control to the usual displacement control. For at least part of the restoration period, the current value is set to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.
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
The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:
FIG. 1
is a cross-sectional view of a variable displacement compressor in one of the embodiments of the present invention;
FIG. 2
is a partially enlarged cross-sectional view showing the compressor of
FIG. 1
when it is being operated in the maximum displacement;
FIG. 3
is a partially enlarged cross-sectional view showing the compressor of
FIG. 1
when it is being operated in the minimum displacement;
FIGS.
4
(
a
) to
4
(
c
) are time charts showing operations during the displacement limiting control in the compressor of
FIG. 1
;
FIG. 5
is a time chart showing operations during a displacement limiting control in another embodiment; and
FIGS.
6
(
a
) to
6
(
c
) are time charts showing operations during a displacement limiting control in a conventional compressor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
One embodiment according to the present invention will be described with reference to FIG.
1
through FIG.
4
(
c
). First, the structure of a variable displacement compressor will be described. As shown in
FIG. 1
, a front housing member
11
is joined by the front end of a cylinder block
12
. A rear housing
13
is joined by the rear end of the cylinder block
12
through a valve plate assembly
14
. A control pressure chamber, which is a crank chamber
15
in this embodiment, is defined by the front housing member
11
and the cylinder block
12
.
A drive shaft
16
is rotatably supported by the front housing member
11
and the cylinder block
12
to extend through the crank chamber
15
. The drive shaft
16
is connected to a vehicle engine Eg, which functions as an external driving force, through a clutch mechanism C such as an electromagnetic clutch. The clutch mechanism C selectively transmits the driving force of the engine Eg to the drive shaft
16
.
A rotary support
17
is fixed to the drive shaft
16
in the crank chamber
15
. A drive plate, which is a swash plate
18
in this embodiment, is supported on the drive shaft
16
. The swash plate
18
slides along and inclines relative to the axis L. A hinge mechanism
19
is located between the rotary support
17
and the swash plate
18
. The swash plate
18
is connected to the rotary support
17
through the hinge mechanism
19
. The hinge mechanism
19
causes the swash plate
18
to rotate integrally with the rotary support
17
. Further, the hinge mechanism
19
guides the sliding and the inclination of the swash plate
18
with respect to the drive shaft
16
.
As the center portion of the swash plate
18
is moved toward the rotary shaft
17
, the inclination angle of the swash By plate
18
increases. On the other hand, as the center portion of the swash plate
18
is moved toward the cylinder block
12
, the inclination angle of the swash plate
18
decreases. A limit ring
20
is mounted on the drive shaft
16
between the swash plate
18
and the cylinder block
12
. As shown in
FIG. 1
, when the swash plate
18
contacts the rotary support
17
, the inclination angle of the swash plate
18
becomes maximum. As shown in
FIG. 3
, when the swash plate
18
contacts the limit ring
20
the inclination angle of the swash plate
18
becomes minimum.
Cylinder bores
21
(only one is shown in
FIG. 1
) extend through the cylinder block
12
to surround the drive shaft
16
. A single-headed piston
22
is accommodated in each cylinder bore
21
. Each piston
22
is coupled to the periphery of the swash plate
18
through a pair of shoes
23
. The swash plate
18
converts rotation of the drive shaft
16
to reciprocation of each piston
22
in the corresponding cylinder bore
21
.
A suction chamber
24
, which is a suction pressure zone, and a discharge chamber
25
, which is a discharge pressure zone, are formed in the rear housing member
13
. A suction port
26
, a suction valve flap
27
, a discharge port
28
and a discharge valve flap
29
are formed in the valve plate assembly
14
to correspond to each of the cylinder bores
21
.
When each piston
22
is moved from the top dead center position to the bottom dead center position, refrigerant gas is sucked to the corresponding cylinder bores
21
from the suction chamber
24
through the suction port
26
and the suction valve flap
27
. When each piston
22
is moved from the bottom dead center position to the top dead center position, the refrigerant gas is compressed to a predetermined pressure in the corresponding cylinder bore
21
and is then discharged to the discharge chamber
25
through the discharge port
28
and the discharge valve flap
29
. When the piston
22
compresses the refrigerant gas, a high pressure refrigerant gas escapes from the inside of the cylinder bore
21
to the crank chamber
15
through a slight gap between the piston
22
and the cylinder bore
21
. Such gas is referred to as blowby gas.
An external refrigerant circuit
61
connects the suction chamber
24
to the discharge chamber
25
. The external refrigerant circuit
61
includes a condenser
62
, an expansion valve
63
and an evaporator
64
. The compressor and the external refrigerant circuit
61
form a refrigeration circuit for a vehicle air-conditioner.
As shown in
FIG. 1
, a control passage, which is a bleed passage
30
, connects the crank chamber
15
to the suction chamber
24
. A displacement control valve
31
is accommodated in the rear housing
13
to regulate the bleed passage
30
. A supply passage
32
connects the discharge chamber
25
to the crank chamber
15
. The high pressure refrigerant gas in the discharge chamber
25
is supplied to the crank chamber
15
through the supply passage
32
.
A temperature adjuster
33
for setting the target value of a passenger compartment temperature, a passenger compartment temperature sensor
34
, a pedal position sensor
35
, the clutch mechanism C and the control valve
31
are connected to a controller X. The pedal position sensor
35
detects a degree of depression of the vehicle gas pedal, that is the position of the gas pedal. The degree of pedal depression represents the load on the engine Eg. The controller X contains a computer. Further, the controller X is connected to the control valve
31
through a drive circuit
36
. The temperature adjuster
33
, the temperature sensor
34
and the pedal position sensor
35
form an external state detecting means or an external state detector.
The control valve
31
will now be described. As shown in
FIGS. 2 and 3
, the control valve
31
has a valve housing
41
and a solenoid unit
42
, which are coupled to each other. A valve chamber
43
, which also serves as a pressure sensing chamber, is formed in the valve housing
41
. A valve body
44
is located in the valve chamber
43
. A valve hole
45
extends axially in the valve housing
41
. The valve hole
45
opens in the valve chamber
43
to face the valve body
44
. The valve chamber
43
is connected to the suction chamber
24
through the downstream portion of the bleed passage
30
.
A pressure sensing member, which is a bellows
46
in this embodiment, is housed in the valve chamber
43
. The top end of the bellows
46
is fixed to the ceiling wall of the valve chamber
43
and the lower end of the bellows
46
is connected to the valve body
44
. A setting spring
47
is located in the bellows
46
. The setting spring
47
sets the initial length of the bellows
46
. The valve chamber
43
, the bellows
46
and the setting spring
47
form a pressure sensing mechanism.
The solenoid unit
42
, or the electromagnetic actuator, has a plunger chamber
48
. To the upper opening of the plunger chamber
48
is fitted a fixed core
49
. A plunger
50
is housed in the plunger chamber
48
. A cylindrical coil
51
is located around the fixed core
49
and the plunger
50
. The drive circuit
36
is connected to the coil
51
. A follower spring
52
is located between the plunger
50
and the bottom wall of the plunger chamber
48
and urges the plunger
50
toward the fixed core
49
.
A guide hole
53
extends through the fixed core
49
to be coaxial with the valve hole
45
. A transmission rod
54
extends in the guide hole
53
and the valve hole
45
. The proximal end of the transmission rod
54
is fixed to the plunger
50
. The follower spring
52
urges the transmission rod
54
through the plunger
50
toward the valve body
44
, which causes the distal end of the transmission rod
54
to contact the valve body
44
. In other words, the plunger
50
and the valve body
44
are coupled to each other by the transmission rod
54
. The valve body
44
is urged in a direction to open the valve hole
45
by the follower spring
52
.
A port
55
is formed in the valve housing
41
between the valve chamber
43
and the plunger chamber
48
. The valve hole
45
is connected to the crank chamber
15
through the port
55
and the upstream portion of the bleed passage
30
. The valve chamber
43
, the valve hole
45
and the port
55
form a part of the bleed passage
30
.
Under operating conditions of the engine Eg, when an air-conditioner operating switch (not shown) is turned on and the passenger compartment temperature detected by the temperature sensor
34
exceeds the target temperature set by the temperature adjuster
33
, the controller X actuates the clutch mechanism C to drive the compressor.
The controller X normally determines a cooling performance required for the refrigeration circuit based on signals from the temperature adjuster
33
and the temperature sensor
34
. Accordingly, the controller X determines the value of current supplied to the coil
51
. The controller X supplies the current of the determined value to the coil
51
through the drive circuit
36
. Then, between the fixed core
49
and the plunger
50
is generated electromagnetic attraction force according to the supplied current value. The magnitude of the attraction force represents the target value of the pressure in the suction chamber
24
(target suction pressure) and urges the valve body
44
through the transmission rod in a direction increasing the opening size of the valve hole
45
.
On the other hand, the bellows
46
of the control valve
31
expands and contracts in accordance with the pressure in the valve chamber
43
. In other words, the bellows
46
applies a force the magnitude of which corresponds to the pressure in the valve chamber
43
to the valve body
44
. In this case the pressure (suction pressure) in the suction chamber
24
is introduced into the valve chamber
43
through the downstream portion of the bleed passage
30
. Therefore, the valve chamber
43
is exposed to the suction pressure.
The suction pressure in the valve chamber
43
urges the valve body
44
toward the valve hole
45
. Further, the valve body
44
is exposed to the pressure (crank pressure) in the crank chamber
15
through the upstream portion of the bleed passage
30
, the port
55
and the valve hole
45
. The crank. pressure urges the valve body,
44
away from the valve hole
45
. The crank pressure is than the suction pressure. Therefore, the valve body
44
is urged away from the valve hole
45
by the force corresponding to the difference between the crank pressure and the suction pressure.
Each of the forces that act on the valve body
44
determines the position of the valve body
44
with respect to the valve hole
45
, that is the degree of the opening of the valve hole
45
.
The higher the passenger compartment temperature is with respect to the target temperature, in other words, the greater the cooling performance required for the refrigeration circuit is, the controller X makes the supplied current value for the coil
51
greater. Accordingly, the attraction force between the fixed core
49
and the plunger
50
becomes stronger and the force which urges the valve body
44
away from the valve hole
45
increases. This means that the target suction pressure is set at a lower value. The bellows
46
causes the valve body
44
to adjust the opening size of the valve hole
45
such that the actual suction pressure is maintained to the lower target suction pressure. That is, the greatr the supplied current value to the coil
51
is, the control valve
31
adjusts the displacement of the compressor to maintain the lower suction pressure.
If the actual suction pressure is higher than the target suction pressure, the bellows
46
causes the valve body
44
to increase the opening size of the valve hole
45
. Then, the flow rate of the refrigerant gas discharged to the suction chamber
24
from the crank chamber
15
through the bleed passage
30
increases, and the pressure in the crank chamber
15
decreases. Thus, the inclination angle of the swash plate
18
increases and the displacement of the compressor increases. The increase in the compressor displacement increases the cooling performance of the refrigeration circuit and decreases the actual suction pressure so that the actual suction pressure is converged to the target suction pressure.
When the valve body
44
fully opens the valve hole
45
, a great amount of the refrigerant gas is discharged from the crank chamber
15
to the suction chamber
24
, whereby the pressure in the crank chamber
15
significantly decreases. Accordingly, the inclination angle of the swash plate
18
becomes maximum and the displacement of the compressor becomes maximum (see FIG.
2
).
The smaller the difference between the passenger compartment temperature and the target temperature is, in other words, the smaller the cooling performance required for the refrigeration circuit is, the controller X makes the supplied current value for the coil
51
smaller. Accordingly, the attraction force between the fixed core
49
and the plunger
50
becomes weaker and the force which urges the valve body
44
in a direction distant from the valve hole
45
decreases. This means that the target suction pressure is set at a higher value. The bellows
46
causes the valve body
44
to adjust the opening size of the valve hole
45
so that the actual suction pressure is maintained at the higher target suction pressure. That is, the smaller the supplied current value for the coil
51
is, the control valve
31
adjusts the displacement of the compressor to maintain the higher suction pressure.
If the actual suction pressure is lower than the target suction pressure, the bellows
46
causes the valve body
44
to decrease the opening size of the valve hole
45
. Then, the flow rate of the refrigerant gas discharged to the suction chamber
24
from the crank chamber
15
through the bleed passage
30
decreases, and the pressure in the crank chamber
15
increases. Thus, the inclination angle of the swash plate
18
becomes smaller and the displacement of the compressor decreases. The decrease in the compressor displacement decreases the cooling performance of the refrigeration circuit and increases an actual suction pressure so that the actual suction pressure may be converged to the target suction pressure.
When the valve body
44
fully closes the valve hole
45
, no refrigerant gas is discharged from the crank chamber
15
to the suction chamber
24
, which significantly increases the pressure in the crank chamber
15
. Accordingly, the inclination angle of the swash plate
18
becomes minimum and the displacement of the compressor becomes minimum (see FIG.
3
).
As described above, the displacement of the compressor is usually adjusted according to the cooling performance required for the refrigeration circuit. However, when the load on the engine Eg abruptly increases under an abrupt acceleration of the vehicle, a displacement limiting control for reducing the engine load is performed. The displacement limiting control temporarily minimizes the displacement of the compressor.
To reduce the engine load under abrupt acceleration of a vehicle, a clutch mechanism C may be turned off and the compressor may be temporarily separated from the engine Eg. However, to ensure the minimum cooling performance even under abrupt acceleration of the vehicle and to avoid shock that accompanies the turning on/off of the clutch mechanism, turning the clutch mechanism C off temporarily is not preferable.
Next, a displacement limiting control under abrupt acceleration of the vehicle will be described with reference to time charts of FIG.
4
(
a
) to FIG.
4
(
c
). As shown in FIG.
4
(
a
), when the degree of pedal depression detected by the pedal position sensor
35
reaches the predetermined value or greater under a state where the predetermined value of current was supplied to the coil
51
of the control valve
31
, the controller X determines the start of abrupt acceleration of a vehicle and starts the displacement limiting control. That is, the controller X commands the drive circuit
36
to make the supplied current value for the coil
51
change from a value corresponding to the required cooling performance to a specific value, or zero.
As a result, as shown in FIG.
4
(
b
), the target suction pressure Pst changes over from the value corresponding to the required cooling performance to the maximum value Pmax. Then, the bellows
46
causes the valve body
44
to close the valve hole
45
so that an actual suction pressure Psa approximates the maximum value Pmax. Therefore, the pressure in the crank chamber
15
increases and the displacement of the compressor becomes minimum as shown in FIG.
4
(
c
). In other words, the torque of the compressor becomes minimum, whereby the engine load is reduced. Thus, the vehicle is faborably abruptly accelerated.
As shown in FIG.
4
(
a
), after the predetermined time S (for-example one second) has passed from the start of the displacement limiting control, the controller X completes the displacement limiting control and shifts the displacement limiting control to a usual displacement control according to the cooling performance required for the refrigeration circuit. Specifically, the controller X increases the supplied current value for the coil
51
from zero to the target current value A
3
according to the required cooling performance for the predetermined time T. Accordingly, as shown in FIG.
4
(
b
), the target suction pressure Pst decreases from the maximum value Pmax to a value P
3
corresponding to the target current value A
3
for the predetermined time T.
The oblique line H shown by the two dotted and dash lines and the solid line in FIG.
4
(
a
) is a direct proportional increase line showing that the supplied current value for the coil
51
increases from zero to the target current value A
3
at a constant rate. During a period (the first term t
1
and the second term t
2
) in the predetermined time T, the values of current supplied to the coil
51
are set at values A
1
and A
2
, which are greatr than values in the corresponding period on the direct proportional increase line H.
Specifically, at the same time when the displacement limiting control has been completed, the supplied current value for the coil
51
is abruptly increased to the value A
1
from zero and the current value A
1
is maintained only during the first term t
1
. Subsequently, the supplied current value is abruptly lowered to the value A
2
, which is lower than the value A
1
, and the current value A
2
is maintained only during the second term t
2
. The second term t
2
is completed when the is current value A
2
agrees with a value on the direct proportional increase line H. In the subsequent third term t
3
, the supplied current value is gradually increased to the target current value A
3
in accordance with the direct proportional increase line H.
An oblique line H′ shown by two dotted and dash lines and a solid line in FIG.
4
(
b
) is a line corresponding to the direct proportional increase line H in FIG.
4
(
a
), which is a direct proportional decrease line showing that the target suction pressure Pst decreases from the maximum value Pmax to a value P
3
at a constant rate. During the first term t
1
and the second term t
2
, the target suction pressure Pst is set at values P
1
and P
2
. The values P
1
and P
2
correspond to the current values A
1
and A
2
and lower than values in the corresponding period on the direct proportional decrease line H′.
At the completion of the displacement limiting control, the current value A
1
in the first term t
1
sets the target suction pressure Pst to the value P
1
, which is significantly lower than the actual suction pressure Psa. Therefore, as shown in FIG.
4
(
b
), the actual suction pressure Psa is significantly higher than the value P
1
of the target suction pressure Pst immediately after the completion of the displacement limiting control. Then, the bellows
46
causes the valve body
44
to widely open the valve hole
45
to decrease the actual suction pressure Psa to the value P
1
immediately after the completion of the displacement limiting control. As a result, the pressure in the crank chamber
15
abruptly decreases so that the displacement of the compressor changes from the minimum state to an increased state with no substantial delay after the completion of the displacement limiting control, as shown in FIG.
4
(
c
).
As shown in FIG.
4
(
b
), in the second term t
2
, the target suction pressure Pst is set at a value P
2
, which is higher than the value P
1
and lower than the actual suction pressure Psa, when the supplied current value is changed to a value A
2
. In other words, in the second term t
2
, the target suction pressure Pst further increases to near the actual suction pressure Psa as compared with the case in the first term t
1
. Accordingly, the bellows
46
causes the valve body
44
to operate such that the opening size of the valve hole
45
is further reduced as compared with the case in the first term t
1
. As a result, an abrupt and excessive decrease in the pressure in the crank chamber
15
is prevented, which prevents an abrupt increase in the displacement and the torque of the compressor as shown in FIG.
4
(
c
).
As shown in FIG.
4
(
b
), the actual suction pressure Psa is substantially converged to the value P
2
of the target suction pressure Pst at the completion of the second term t
2
. In the subsequent third term t
3
, the target suction pressure Pst gradually decreases to the value P
3
in accordance with the direct proportional decrease line H′ as the supplied current value gradually increases in accordance with the direct proportional increase line H. The actual suction pressure Psa lowers in accordance with a gradual decrease of the target suction pressure Pst without deviating from the line showing the decrease in the target suction pressure Pst. Therefore, no abrupt change in the pressure in the crank chamber
15
occurs and the displacement and the torque of the compressor smoothly increase.
The present embodiment described above has the following advantages.
In returning to the usual displacement control from the displacement limiting control, the supplied current value for the coil
51
is changed to the target current value A
3
according to the required cooling performance from zero for the predetermined time T. Thus, the displacement of the compressor, in other words, the torque of the compressor gradually increases and an abrupt increase in the engine load is prevented, which improves the vehicle drivability.
In terms t
1
and t
2
just after the completion of the displacement limiting control, the supplied current values for the coil
51
are set at values A
1
and A
2
, which are nearer to the target current value A
3
than values in the corresponding period on the direct proportional increase line H shown in FIG.
4
(
a
). As a result, the pressure in the crank chamber
15
rapidly decreases and the displacement of the compressor changes from the minimum state to an increased state without substantial delay from the completion of the displacement limiting control. Thus, the compressor is operated at the minimum displacement only for a term substantially equal to the execution time S for the displacement limiting control, in other words, only for a necessary minimum time. Thus, the displacement limiting control does not significantly lower the cooling performance of the refrigeration circuit, and the passengers are not disturbed.
The supplied current value A
2
in the second term t
2
subsequent to the first term t
1
is made smaller than the supplied current value A
1
in the first term t
1
. As a result, the displacement of the compressor immediately increases after the completion of the displacement limiting control. However, an abrupt increase in displacement, which is accompanied with shock, is prevented. Therefore, the displacement limiting control is smoothly and rapidly changed to a usual displacement control.
The control valve
31
in the present embodiment has the solenoid unit
42
and the bellows
46
. The solenoid unit
42
sets the target suction pressure, which is used as the reference of operations of the bellows
46
, according to the supplied current value. The bellows
46
actuates the valve body
44
according to the actual suction pressure. As described in the background section, a change of the displacement of a compressor from the minimum state to an increased state delays after the displacement limiting control is completed. This problem is particularly likely to occur in the control valve
31
, which has the above described structure. Therefore, the application of the control system of the present embodiment to the control valve
31
is the most effective in overcoming the problem.
It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.
A current supply system for the coil
51
in the predetermined time T is not limited to the system shown in FIG.
4
(
a
). For example, as shown in
FIG. 5
, a supplied current value for the coil
51
may be immediately increased to the predetermined value (which is lower than the target current value A
3
) from zero immediately after the completion of the displacement limiting control and the value may be gradually increased to the target current value A
3
from the predetermined value at a constant ratio. In this case, the supplied current values for the coil
51
become greater than values in the corresponding period on the direct proportional increase line H in the entire predetermined time T.
Further, the supplied current values for the coil
51
may be maintained between the first term t
1
and the second term t
2
. Specifically, the supplied current value may be increased to the predetermined value (which is lower than the target current value A
3
) from zero after the completion of the displacement limiting control and the predetermined value may be then maintained until the required value agrees with a value on the direct proportional increase line H.
The periods of time in which the supplied current values for the coil
51
are made greater than the values on the direct proportional increase line H are not limited to the terms t
1
and t
2
shown in FIG.
4
(
a
). For example, the supplied current values may be greater than the values on the line H during a period after some time from the completion of the displacement limiting control.
The control valve to which the present invention is applied is not limited to that shown in
FIGS. 2 and 3
. For example, unlike the control valve
31
of
FIGS. 2 and 3
, the present invention may be applied to a control valve in which the target suction pressure is raised as the supplied current value to the coil is increased. As a pressure sensing member, a diaphragm may be used in place of the bellows
46
. Further, the pressure sensing member may be omitted, and the valve body
44
may be operated only by the solenoid unit
42
. Further, the present invention may be applied to a control valve located in the supply passage
32
.
The displacement limiting control may be started when the rate of change per unit time for a degree of pedal depression detected by the pedal position sensor
35
becomes the predetermined value or more.
Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.
Claims
- 1. A displacement control device for a compressor that changes the displacement in accordance with the pressure in a control pressure chamber, comprising:a control valve for controlling the pressure in the control pressure chamber, the control valve having a valve body and an electromagnetic actuator for actuating the valve body, wherein the actuator urges the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator; a detector for detecting external conditions that are necessary for controlling the compressor displacement; and a controller for controlling the value of current supplied to the actuator, wherein the controller selects a control mode to be executed from a usual displacement control and a displacement limiting control based on the detected external conditions, wherein, when the usual displacement control is selected, the controller sets the current value to a target value, which corresponds to the detected external conditions, wherein, when the displacement limiting control is selected, the controller temporarily sets the current value to a specific value to minimize the compressor displacement, wherein, when the control mode is switched from the displacement limiting control to the usual displacement control, the controller changes the current value from the specific value to the target value taking a predetermined restoration period, and wherein, for at least part of the restoration period, the controller sets the current value to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.
- 2. The control device according to claim 1, wherein the control valve includes a pressure sensing mechanism, and wherein the pressure sensing mechanism moves the valve body in accordance with a suction pressure, which is the pressure of refrigerant gas drawn into the compressor.
- 3. The control device according to claim 2, wherein the pressure sensing mechanism moves the valve body such that the suction pressure is maintained at a target suction pressure, and wherein the target suction pressure is determined by the current value supplied to the electromagnetic actuator.
- 4. The control device according to claim 1, wherein the part of the restoration period includes an initial period of the restoration period.
- 5. The control device according to claim 4, wherein, at substantially the same time as the displacement limiting control is finished, the controller instantaneously changes the current value to a first value, the first value being between the specific value and the target value.
- 6. The control device according to claim 5, wherein the controller maintains the current value to the first value for a predetermine first period after the displacement limiting control is finished, wherein, for a subsequent second period, the controller maintains the current value to a second value, which is closer to the specific value than the first value, and then gradually changes the current value from the second value to the target value along the direct proportional line.
- 7. The control device according to claim 5, wherein, during the restoration period, the controller gradually changes the current value at a constant rate from the first value to the target value.
- 8. The control device according to claim 1, wherein the specific value is zero.
- 9. The control device according to claim 1, wherein the compressor is installed in a refrigeration circuit and is driven by an external drive source, wherein the detector includes a first detector for detecting an external condition that represents the load on the external drive source and a second detector for detecting an external condition that represents a required cooling performance of the refrigeration circuit, wherein the controller selects the control mode to be executed based on the external condition detected by the first detector, and wherein, when the usual displacement control is selected, the controller determines the current value in accordance with the external condition detected by the second detector.
- 10. The control device according to claim 9, wherein the external drive source is a vehicle engine, and the first detector detects a depression degree of an acceleration pedal of the vehicle.
- 11. The control device according to claim 9, wherein the compressor is installed in a vehicle, wherein the second detector includes a temperature sensor for detecting the temperature of a passenger compartment and a temperature adjuster for setting a target value of the passenger compartment temperature, wherein, when the usual displacement control is selected, the controller determines the current value in accordance with the difference between the detected compartment temperature and the set target temperature.
- 12. A displacement control device for a compressor installed in a refrigeration circuit, wherein the compressor is driven by an external drive source and changes the displacement in accordance with the pressure in a control pressure chamber, the control device comprising:a control valve for controlling the pressure in the control pressure chamber, the control valve including: a valve body; a pressure sensing mechanism, wherein the pressure sensing mechanism moves the valve body in accordance with a suction pressure, which is the pressure of refrigerant gas drawn into the compressor, such that the suction pressure is maintained at a predetermined target suction pressure; and an electromagnetic actuator for urging the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator, wherein the current value determines the target suction pressure; a first detector for detecting an external condition that represents the load on the external drive source; a second detector for detecting an external condition that represents a required cooling performance of the refrigeration circuit; and a controller for controlling the value of current supplied to the actuator, wherein the controller selects a control mode to be executed from a usual displacement control and a displacement limiting control based on the external condition detected by the first detector, wherein, when the usual displacement control is selected, the controller sets the current value to a target value, which corresponds to the external condition detected by the second detector, wherein, when the displacement limiting control is selected, the controller temporarily sets the current value to a specific value to minimize the compressor displacement, wherein, when the control mode is switched from the displacement limiting control to the usual displacement control, the controller changes the current value from the specific value to the target value taking a predetermined restoration period, and wherein, for at least an initial period of the restoration period, the controller sets the current value to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.
- 13. The control device according to claim 12, wherein, at substantially the same time as the displacement limiting control is finished, the controller instantaneously changes the current value to a first value, the first value being between the specific value and the target value.
- 14. The control device according to claim 13, wherein the controller maintains the current value to the first value for a predetermine first period after the displacement limiting control is finished, wherein, for a subsequent second period, the controller maintains the current value to a second value, which is closer to the specific value than the first value, and then gradually changes the current value from the second value to the target value along the direct proportional line.
- 15. The control device according to claim 13, wherein, during the restoration period, the controller gradually changes the current value at a constant rate from the first value to the target value.
- 16. The control device according to claim 12, wherein the external drive source is a vehicle engine, and the first detector detects a depression degree of an acceleration pedal of the vehicle.
- 17. The control device according to claim 12, wherein the compressor is installed in a vehicle, wherein the second detector includes a temperature sensor for detecting the temperature of a passenger compartment and a temperature adjuster for setting a target value of the passenger compartment temperature, wherein, when the usual displacement control is selected, the controller determines the current value in accordance with the difference between the detected compartment temperature and the set target temperature.
- 18. A method for controlling the displacement of a compressor that changes the displacement in accordance with the pressure in a control pressure chamber, comprising:controlling the pressure in the control pressure chamber by a control valve, wherein the control valve has a valve body and an electromagnetic actuator for actuating the valve body, wherein the actuator urges the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator; detecting external conditions that are necessary for controlling the compressor displacement; selecting a control mode to be executed from a usual displacement control and a displacement limiting control based on the detected external conditions; setting the current value to a target value, which corresponds to the detected external conditions, when the usual displacement control is selected; temporarily setting the current value to a specific value to minimize the compressor displacement when the displacement limiting control is selected; and changing the current value from the specific value to the target value taking a predetermined restoration period when the control mode is switched from the displacement limiting control to the usual displacement control, wherein, for at least part of the restoration period, the current value is set to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.
- 19. The method according to claim 18, wherein the step changing the current value from the specific value to the target value includes instantaneously changing the current value to a first value at substantially the same time as the displacement limiting control is finished, wherein the first value is between the specific value and the target value.
- 20. The method according to claim 19, wherein the step of changing the current value from the specific value to the target value further includes:maintaining the current value to the first value for a predetermine first period after the displacement limiting control is finished; maintaining the current value to a second value, which is closer to the specific value than the first value, for a second period, which is subsequent to the first period; and gradually changing the current value from the second value to the target value along the direct proportional line after the second period.
Priority Claims (1)
Number |
Date |
Country |
Kind |
11-209357 |
Jul 1999 |
JP |
|
US Referenced Citations (9)
Foreign Referenced Citations (1)
Number |
Date |
Country |
0 814 262 |
Dec 1997 |
EP |