[0001] The invention relates to a control valve according to the preamble of claim 1, for
a variable displacement compressor particularly in a refrigeration cycle of an automotive
air conditioner.
[0002] Variable displacement compressors capable of varying the refrigerant compression
capacity are employed in automotive air conditioners so as to obtain an adequate cooling
capacity without being constrained by the rotational speed of the engine driving the
compressor. In a known compressor a wobble plate on a shaft driven by the engine drives
compression pistons. By varying the wobble plate inclination angle the piston stroke
is varied to vary the refrigerant discharge amount. The inclination angle is continuously
changed by controlling the pressure in a crankcase, and by changing the balance of
pressures acting on opposite ends of each piston.
[0003] A known control valve (JP-2001-132650 A) is disposed either between the discharge
chamber and the crankcase, or between the crankcase and the suction chamber of the
compressor. The control valve adjusts the pressure in the crankcase by controlling
the flow rate between the discharge chamber and the crankcase, or between the crankcase
and the suction chamber, respectively. The control valve comprises a valve section
in a refrigerant passage between the discharge chamber and the crankcase. A path extends
between the discharge chamber and the suction chamber via an orifice between the crankcase
and the suction chamber. A valve element in the valve section receives discharge pressure
Pd in valve-opening direction. A piston rod integral with the valve element has approximately
the same diameter as a valve hole. An end face of the piston rod receives the suction
pressure Ps and the load of a solenoid in valve-closing direction for setting the
discharge capacity of the compressor by an external signal. Hence, the discharge pressure
Pd and the suction pressure Ps act on the opposite ends of the valve element and piston
rod on equal effective pressure-receiving areas. The differential pressure (Pd - Ps)
causes opening/closing operations of the valve element to control the flow rate between
the discharge chamber and the crankcase.
[0004] As the rotational speed of the compressor increases with increasing engine speed
the discharge capacity of the compressor is increased" i.e. the discharge pressure
Pd increases and the suction pressure Ps decreases to increase the differential pressure
(Pd - Ps). The valve lift increases depending on the value of the differential pressure
(Pd - Ps). The control valve increases the flow rate into the crankcase to increase
the pressure Pc and to decrease the discharge capacity. The value of the of the differential
pressure (Pd - Ps) decreases as well. In short, the control valve controls the flow
rate to the crankcase such that the differential pressure (Pd - Ps) is held at a predetermined
value which can be set by the value of electric current supplied to the solenoid.
[0005] Any changes of the discharge capacity change the value of the differential pressure
(Pd - Ps) to change the pressure Pc in the crankcase, whereby the wobble plate inclination
angle is changed to vary the discharge capacity between the maximum and minimum capacities.
For example, when the differential pressure (Pd - Ps) is zero as at the start of the
compressor, the compressor operates with maximum capacity. When the differential pressure
(Pd - Ps) reaches a certain value, the capacity starts to be varied. However, each
variable displacement compressor has an individual character, and the other differential
pressure (Pc - Ps) between the pressure Pc in the crankcase and the suction pressure
Ps at the start of varying the discharge capacity has a range of values varying depending
on the compressor. This is caused e.g. by individual fluctuations of the mobility
of the wobble plate, that is, by differences of sensitivity or response behaviour
among a series of compressors. A high-sensitivity compressor has the problem of reacting
sensitively to rapid changes in the discharge pressure Pd and the suction pressure
Ps caused by a sudden change of the engine speed, resulting in hunting.
[0006] It is an object of the invention to provide a control valve for a variable displacement
compressor, which is capable of controlling even a high sensitivity compressor stably
without causing hunting, i.e. when a rapid pressure change is caused by a sudden change
of the engine speed.
[0007] This object is achieved by the features of claim 1.
[0008] When a pressure change results from a gentle speed change of the compressor, the
pressure-sensing section remains insensitive to the pressure change, and performs
the same operation as the conventional compressor. However, when a pressure change
results from a rapid speed change of the compressor, the pressure-sensing section
senses and responds to this pressure change, and makes the motion of the valve section
slower (retarding effect) by interfering with action of the valve section in a direction
opposite to the valve-opening or valve-closing direction. This motion is retarded
by a value, which is proportional to the degree of the occurring pressure change.
[0009] Even a high-sensitivity compressor promptly restores a predetermined discharge capacity
without overshooting the carried out pressure change even when a rapid speed change
of the compressor occurs.
[0010] This enables the control valve to perform stable displacement control without any
hunting even when the high-sensitivity compressor undergoes a rapid speed change.
[0011] Embodiments of the invention will be described with reference to the drawings.
- Fig. 1
- is a longitudinal section view of a first embodiment of a control valve for a variable
displacement compressor,
- Fig. 2
- is a diagram explaining the operation of the control valve when the rotational compressor
speed rapidly increases,
- Fig. 3
- is a longitudinal section of a second embodiment of the control valve,
- Fig. 4
- is a longitudinal section of a fourth embodiment of the control valve,
- Fig. 6
- is a longitudinal section of a fifth embodiment of the control valve,
- Fig. 7
- is a longitudinal section of a sixth embodiment of the control valve,
- Fig. 8
- is a longitudinal section of a seventh embodiment of the control valve, and
- Fig. 9
- is a longitudinal section of an eighth embodiment of the control valve.
[0012] A control valve 11 in Fig. 1 comprises a pressure-sensing section 12 for exclusively
sensing rapid changes in a discharge pressure Pd, a valve section 13 for sensing the
differential pressure (Pd - Ps) between the discharge pressure Pd and suction pressure
Ps to control the refrigerant flow rate between a discharge chamber and a crankcase,
and a solenoid 14 for setting a predetermined value to which the differential pressure
(Pd - Ps) is to be controlled by the control valve, from outside. These sections are
arranged on the same axis.
[0013] A body 15 containing the pressure-sensing section 12 and the valve section 13 has
a cylinder in an upper part. An upper end opening is closed by a lid 17. A high-pressure
port 18 communicating with the discharge chamber of the variable displacement compressor
is provided in the body 15 at a location below the cylinder 16. A pressure-sensing
piston 19 is axially movably disposed within the cylinder 16. A space for a pressure-adjusting
chamber 20 is defined by an upper portion of the cylinder 16, by the body 15 and by
the lid 17. The pressure-adjusting chamber 20 communicates with the high-pressure
port 18 via a predetermined clearance between the cylinder 16 and the pressure-sensing
piston 19. A hole is formed in the centre of a bottom of the cylinder 16. A hollow
cylindrical valve seat-forming member 21 is press-fitted in the hole. The valve seat-forming
member 21 has a passage axially extending therethrough, i.e. a valve hole, and a lower
end forming a valve seat 21 a of the valve section 13. A shaft 22 extends through
the valve hole of the valve seat-forming member 21. One end of the shaft 22 is fixed
to the pressure-sensing piston 19.
[0014] A valve element 23 is movably disposed opposed to the valve seat 21 a. The valve
element 2 at one side is integrally formed with the shaft 22 and with a piston rod
24 at the other side. The piston rod 24 is movably guided in a hole of the body 15.
The outer diameter of the piston rod 24 is equal to the inner diameter of the valve
hole of the valve seat-forming member 21. The piston rod 24 is urged by a spring 25
in valve opening direction. A space accommodating the valve element 23 communicates
with a medium-pressure port 26 for supplying pressure Pc to the crankcase of the compressor.
A space accommodating the spring 25 communicates with a low-pressure port 27 for receiving
the suction pressure Ps from a suction chamber.
[0015] A hole is formed in the centre of a lower part of the body 15. The rim of an opening
of a bottomed sleeve 28 is tightly connected to the hole. The bottomed sleeve 28 contains
a core 29 and a plunger 30 of the solenoid 14. The core 29 is fixed to the hole in
the centre of the lower part of the body 15 and the bottomed sleeve 28 by press-fitting.
The plunger 30 is axially slidably disposed in the bottomed sleeve 28, and is fixed
to one end of a shaft 31 which axially extends through the core 29. The plunger 30
is urged toward the core 29 by a spring 32 such that the other end of the shaft 31
is brought into abutment with a lower end face of the piston rod 24. A coil 33 surrounds
the bottomed sleeve 28. A harness 34 leads from the coil 33 to the outside.
[0016] The force of the spring 25 is stronger than the force of the spring 32. When the
solenoid 14 is de-energized, the valve element 23 is kept away from the valve seat
21 a, the valve section 13 is fully open. High-pressure refrigerant (discharge pressure
Pd) passes from the high-pressure port 18 through the open valve section 13 and flows
from the medium-pressure port 26 into the crankcase. The pressure Pc in the crankcase
is close to the discharge pressure Pd. The compressor operates with minimum discharge
capacity.
[0017] When the automotive air conditioner is started or when the cooling load is maximum,
the value of electric control current supplied to the solenoid 14 is maximum. The
plunger 30 is attracted with the maximum attractive force by the core 29. The piston
rod 24 is pushed by the shaft 31 fixed to the plunger 30, in valve-closing direction
against the force of the spring 25. The valve element 23 is seated on the valve seat
21a. The valve section 13 is fully closed. The high-pressure refrigerant (discharge
pressure Pd) is blocked by the valve section 13. The pressure Pc in the crankcase
is close to the suction pressure Ps. The compressor operates with maximum discharge
capacity.
[0018] When the value of the electric current supplied to the solenoid 14 is set to a predetermined
value, the valve element 23 will stop at a valve lift position where the load of the
spring 25, the load of the solenoid 14, the force of the discharge pressure Pd, and
the force of the suction pressure Ps are balanced.
[0019] In the above balanced state, when the compressor speed is increased e.g. by an increase
of the engine speed, in order to increase the discharge capacity of the compressor,
the discharge pressure Pd increases and the suction pressure Ps decreases so that
the differential pressure (Pd - Ps) increases. This action causes a force in valve-opening
direction on the valve element 23 and the piston rod 24. The valve element 23 is lifted
further from the balanced position. Refrigerant flows from the discharge chamber into
the crankcase at an increased flow rate. The pressure Pc in the crankcase is increased
to adjust the compressor to operate in a direction reducing the discharge capacity,
and such that the differential pressure (Pd - Ps) is controlled to the predetermined
value set by the solenoid 14.
[0020] When, however, the engine speed has decreased, the control valve operates inversely
and the compressor is controlled such that the differential pressure (Pd - Ps) again
becomes equal to the predetermined value set by the solenoid 14.
[0021] When the compressor speed changes only gently as in the case where the automotive
vehicle is cruising at an approximately constant speed, the pressure-sensing section
12 will remain insensitive, and will perform like the conventional control valve.
This is due to the fact that then a piston driving differential pressure does not
occur, because the gentle pressure change is also directly transmitted into the pressure-adjusting
chamber 23.
[0022] Next, the operation will be described when the compressor speed rapidly changes when
the automotive vehicle i.e. the engine suddenly accelerates or decelerates.
[0023] When the compressor in Fig. 2 first has been stably operating e.g. at a speed of
800 rpm, and then the speed has increased suddenly up to a rotational speed of 2000
rpm, the valve lift is increased due to the rising discharge pressure Pd and the dropping
suction pressure Ps. The control valve 11 increases the pressure Pc in the crankcase.
At this time, in the compressor with higher sensitivity, as indicated by broken lines
in Fig. 2, overshooting of the valve lift, of the discharge pressure Pd, of the pressure
Pc in the crankcase, and of the suction pressure Ps tend to occur, causing a hunting
phenomenon.
[0024] When the overshooting tendency occurs, the pressure-sensing section 12 receives the
rapidly increased discharge pressure Pd at the pressure-sensing piston 19 in a sufficiently
larger pressure-receiving area than that of the valve element 23. In contrast, in
the pressure-adjusting chamber 20, pressure Pd(av), which is an average pressure remaining
from the discharge pressure Pd before it has rapidly increased, is maintained. The
differential pressure (Pd - Pd(av)) now generates a force on the pressure-sensing
piston 19 in valve opening direction. This force is transmitted via the shaft 22 to
the valve element 23, namely a force obtained by subtracting the differential pressure
(Pd - Pd(av)) acting on the pressure-sensing section 12 from the rapidly increased
discharge pressure Pd. As a result, as indicated by solid lines in FIG. 2, the valve
lift is increased more slowly or the valve element movement is retarded, respectively,
so that the control valve 11 increases the pressure Pc in the crankcase more slowly.
After that, in the pressure-sensing section 12, the rapidly increased discharge pressure
Pd promptly also reaches the pressure-adjusting chamber 20 via the clearance between
the cylinder 16 and the pressure-sensing piston 19. Now the differential pressure
(Pd - Pd(av)) becomes equal to zero. At this time, the retarding servo-function of
the pressure-sensing section 12 has been lost, meaning that the pressure-sensing section
12 has the function of sensing and responding to a rapid increase in the discharge
pressure Pd only, to temporarily make the motion of the valve section 13 in valve-opening
direction slower by a value proportional to the degree of the rapid pressure change.
The control valve 11 promptly restores the compressor to the predetermined discharge
capacity without causing any hunting.
[0025] The control valve 11 operates similarly but in quite an opposite way when the compressor
speed is rapidly decreased. Then, the differential pressure (Pd(av) - Pd) acting on
the pressure-sensing section 12 serves as a force for moving the pressure-sensing
piston 19 toward the valve section 13 and for temporarily urging the valve element
23, which is about to move in valve-closing direction, in the valve-opening direction,
i.e. retarding the valve element movement.
[0026] The pressure-sensing piston 19 optionally may be provided with flow rate-adjusting
means, such as a piston ring, which has a circumferentially cut out portion of a predetermined
length, to adjust the size of a passage via which refrigerant flows into or out of
the pressure-adjusting chamber 20 to thereby control the response characteristics
of the pressure-sensing section 12.
[0027] Distinct from the control valve 11 in Fig. 1, the control valve 11a in Fig. 3 (second
embodiment) is configured to sense and respond to a rapid change of the pressure Pc
instead as supplied to the crankcase when controlling the valve lift of the valve
section 13.
[0028] The pressure-sensing section 12 is disposed in a space communicating with the medium-pressure
port 26, and the pressure-sensing piston 19 receiving the pressure Pc is fixed to
the piston rod 24 which is integrally formed with the valve element 23. The valve
seat-forming member 21 has a flange portion that is fitted in an opening formed in
an upper end of the body 15. The pressure-sensing piston 19 is loosely, i.e. axially
movably, fitted in the body 15 at a location below the valve seat-forming member 21.
An annular space of the pressure-adjusting chamber 20 is defined by the body 15 and
the flange portion of the valve seat-forming member 21. The pressure-sensing piston
19 has an upper central recess 19a. The recess 19a is formed with a communication
hole 19b through the bottom of the piston 19 such that the recess 19a communicates
with the space communicating with the medium-pressure port 26 via the communication
hole 19b.
[0029] When the control valve 11 a controls the compressor at a predetermined valve lift,
if the discharge pressure Pd rapidly increases, and the suction pressure Ps rapidly
decreases, the differential pressure (Pd - Ps) between the opposite ends of the valve
element 23 and the piston rod 24 increases, whereby the valve lift is about to increase.
This causes the pressure Pc on the downstream side of the valve section 13 as well
to rapidly increase. Since the pressure-sensing piston 19 has a sufficiently larger
pressure-receiving area than the valve element 23, an upwardly acting force is generated
on the pressure-sensing piston 19. The force causes the piston rod 24 fixed to the
pressure-sensing piston 19 to act in valve-closing direction also on the valve element
23, which was about to move in valve-opening direction by the increased differential
pressure (Pd - Ps), and hence the valve lift increases more slowly or in retarded
fashion. The discharge pressure Pd and the pressure Pc in the crankcase also increase
slowly in accordance with the slowed down increase in the valve lift. After a short
time, when the pressure in the pressure-adjusting chamber 20 becomes equal to the
pressure Pc in the crankcase, the discharge pressure Pd, the pressure Pc in the crankcase,
the suction pressure Ps, and the valve lift promptly return to their original states,
however, without showing any overshooting tendency. Of course, similarly, also when
the compressor speed rapidly decreases, the control valve 11 a operates with retardation
to promptly restore the compressor to the predetermined discharge capacity.
[0030] The control valve 11 b in Fig. 4 (third embodiment) is configured to sense and to
respond to a rapid change of the suction pressure Ps instead when controlling the
valve lift of the valve section 13.
[0031] The pressure-sensing piston 19 separates a space accommodating the spring 25 and
communicating with the low-pressure port 27 from a space communicating with the solenoid
14. The pressure-sensing piston 19 is fixed to the piston rod 24 which is integral
with the valve element 23. In the control valve 11 b, a space defined by the body
15, by the pressure-sensing piston 19, by the piston rod 24, by the core 29, and by
the shaft 31 forms the pressure-adjusting chamber 20.
[0032] When the control valve 11b controls the compressor at a predetermined valve lift,
if the discharge pressure Pd rapidly increases, and the suction pressure Ps rapidly
decreases, the differential pressure (Pd - Ps) between the opposite ends of the valve
element 23 and the piston rod 24 increases, whereby the valve lift increases. This
causes the suction pressure Ps to rapidly decrease. At this time, since the pressure-sensing
piston 19 of the pressure-sensing section 12 has a sufficiently larger pressure-receiving
area than the valve element 23, an upwardly acting force is generated on the pressure-sensing
piston 19. The force causes the piston rod 24 fixed to the pressure-sensing piston
19 to act in valve-closing direction on the valve element 23, i.e. opposite to the
direction of the lift of the valve element 23. The valve lift then only slowly increases,
to cause the discharge pressure Pd and the pressure Pc in the crankcase to also only
slowly increase. In a short time, however, after the pressure in the pressure-adjusting
chamber 20 has become equal to the suction pressure Ps, the discharge pressure Pd,
the pressure Pc in the crankcase, the suction pressure Ps, and the valve lift promptly
return to their original states without causing overshooting tendencies. Of course,
similarly, also when the compressor speed rapidly decreases, the control valve 11
b will operate slowly to restore the compressor to the predetermined discharge capacity.
[0033] The control valve 11c in Fig. 5 (fourth embodiment) has a pressure-sensing section
12 which does not sense or respond to a rapid change in the discharge pressure Pd
in increasing direction but sensitively senses and responds to a rapid change in the
discharge pressure Pd in decreasing direction only for controlling of the valve lift
of the valve section 13.
[0034] The pressure-sensing piston 19 as a component of the pressure-sensing section 12
is equipped with a check valve mechanism (sensitivity-switching means) for switching
the response sensitivity between when a rapid change occurs in the discharge pressure
Pd in increasing direction and when a rapid change occurs in decreasing direction.
The check valve mechanism comprises a passage 19c with a stepped portion in the pressure-sensing
piston 19 for communication between the high-pressure port 18 and the pressure-adjusting
chamber 20, further a ball-shaped valve element 41 in a large-diameter passage part
19b facing the pressure-adjusting chamber 20, and a leaf spring 42 in an open end
of the passage 19b facing the pressure-adjusting chamber 20 to prevent the valve element
41 from falling out.
[0035] When the control valve 11 c controls the compressor at a predetermined valve lift,
if the discharge pressure Pd rapidly increases, the check valve mechanism immediately
opens by the differential pressure between the discharge pressure Pd and the pressure
in the pressure-adjusting chamber 20, to thereby reduce the differential pressure
to zero. As a result, the pressure-sensing section 12 is placed in an insensitive
state. The valve section 13 acts rapidly in the valve-opening direction in a manner
sensitively responsive to the rapid increase in the discharge pressure Pd, thereby
causing the pressure Pc in the crankcase to rise more promptly such that the discharge
capacity of the compressor is promptly controlled in the decreasing direction.
[0036] Inversely, if the discharge pressure Pd has rapidly decreased, the check valve mechanism
closes by the differential pressure between the rapidly-lowered discharge pressure
Pd and the pressure Pd(av) in the pressure-adjusting chamber 20, which is an average
pressure remaining from the discharge pressure Pd before it has rapidly decreased.
The pressure-sensing piston 19 having a larger pressure-receiving area than the valve
element 23 sensitively detects and responds to the change in the rapidly-lowered discharge
pressure Pd. Although the valve element 23 attempts to act in valve-closing direction
in response to the rapid decrease in the discharge pressure Pd, since the pressure-sensing
piston 19 instantaneously responds in valve-opening direction due to the rapid change
in the discharge pressure Pd, the valve element 23 is made slower in its action in
valve-closing direction. The control valve 11 c then has asymmetric valve-opening
characteristics, i.e. operates with high sensitivity in case of a rapid change in
the discharge pressure Pd in increasing direction, but operates with low sensitivity
in case of a rapid change in the discharge pressure Pd in decreasing direction. Therefore,
e.g. even if the compressor excessively tends to respond to a rapid change in the
discharge pressure Pd in increasing direction to cause the discharge pressure Pd to
rapidly change in decreasing direction, the compressor is hindered from excessively
responding to a rapid change in the discharge pressure Pd in decreasing direction.
This prevents the occurrence of a hunting phenomenon.
[0037] In the control valve I1d in Fig. 6 (fifth embodiment), the check valve mechanism
of the pressure-sensing section 12 is provided in the lid 17. The valve element 41
of the check valve is a poppet valve body.
[0038] The check valve mechanism comprises a passage 17a with a stepped portion in the lid
17 communicating between a space receiving the discharge pressure Pd and the pressure-adjusting
chamber 20, the valve element 41 in the form of a mushroom or a poppet valve body
in a large-diameter passage part facing toward the pressure-adjusting chamber 20,
and a fixed leaf spring 42 in the open end of the passage 17a facing the pressure-adjusting
chamber 20 to prevent the valve element 41 falling into the pressure-adjusting chamber
20. A weak spring 43 between the lid 17 and the pressure sensing piston 19 urges the
pressure-sensing piston 19 away from the lid 17.
[0039] The operation of the control valve 11d is the same as the operation of the control
valve 11 c in Fig. 5.
[0040] In a further not shown alternative of the control valve the check valve mechanism
instead may be provided in the body 15 for isolating the pressure-adjusting chamber
20 from a side exposed to the discharge pressure Pd.
[0041] The control valve 11e in Fig. 7 (sixth embodiment) includes a sensitivity-switching
mechanism for switching the response sensitivity between when the discharge pressure
Pd rapidly increases and when the same rapidly decreases.
[0042] The sensitivity-switching mechanism in the pressure-sensing section 12 in Fig. 7
switches the ease of flow into or out of the pressure-adjusting chamber 20. The peripheral
shape of the pressure-sensing piston 19 is tapered, such that the outer diameter of
the pressure-sensing piston progressively increases from the side of the high-pressure
port 18 to the pressure-adjusting chamber 20. A gap 19c formed between the periphery
of the pressure-sensing piston 19 and the cylindrical wall of the body 15 has a narrowest
restriction at an upper end in the pressure-adjusting chamber 20. The gap 19c progressively
increases in passage cross-sectional area from the restriction to a lower space communicating
with the high-pressure port 18. Assuming that the cross-sectional area of the refrigerant
passage is hugely expanded on the high-pressure port side of the restriction in the
gap 19c, and refrigerant flows through the restriction into the hugely-expanded portion,
a contracted flow will be produced there. Insofar as the differential pressure between
pressure in the high-pressure port 18 and the pressure in the pressure-adjusting chamber
20 is the same, the pressure-sensing section 12 has a characteristic that the flow
rate is smaller when refrigerant flows from the pressure-adjusting chamber 20 to the
high-pressure port 18 after being abruptly restricted in flow by the restriction than
when refrigerant flows from the high-pressure port 18 flows into the pressure-adjusting
chamber 20 through the restriction after being progressively restricted in flow.
[0043] When the compressor speed is rapidly increased to thereby rapidly increase the discharge
pressure Pd, refrigerant is about to flow from the high-pressure port 18 into the
pressure-adjusting chamber 20 through the gap 19c, i.e. by the difference in pressure
between the increased pressure in the high-pressure port 18 and the still lower pressure
in the pressure-adjusting chamber 20. Inversely, when the compressor speed is rapidly
decreased to rapidly lower the discharge pressure Pd, refrigerant is about to flow
through the gap 19c from the pressure-adjusting chamber 20 toward the high-pressure
port 18. In this regard, there is a difference in the flow rate through the gap 19c
between when the discharge pressure Pd has rapidly increased and when the same has
rapidly decreased. When the discharge pressure Pd has rapidly increased, it takes
a short time until the pressure in the pressure-adjusting chamber 20 becomes equal
to the rapidly increased discharge pressure Pd. When the discharge pressure Pd has
rapidly decreased, it takes a longer time until the pressure in the pressure-adjusting
chamber 20 becomes equal to the rapidly decreased discharge pressure Pd. The force
exerted by the pressure-sensing piston 19 on the valve element 23 in valve-closing
direction when the discharge pressure Pd has rapidly increased is smaller than the
force exerted by the pressure-sensing piston 19 on the valve element 23 in valve-opening
direction when the discharge pressure Pd has rapidly decreased. That is, when the
discharge pressure Pd has rapidly increased, the pressure-sensing section 12 becomes
less sensitive, whereby the sensitivity of the valve section 13 is not much lowered.
On the other hand, during a transition period over which the discharge pressure Pd
rapidly decreases, the pressure-sensing piston 19 easily moves in valve-opening direction,
and hence the pressure-sensing section 12 becomes more sensitive. Since the differential
pressure between the discharge pressure Pd and the suction pressure Ps becomes smaller,
a force trying to operate the valve section 13 in valve-closing direction is instantaneously
cancelled by a force trying to operate the pressure-sensing section 12 in valve-opening
direction. As a result, the movement of the valve element 23 of the valve section
13 in valve-closing direction is suppressed or retarded, and the valve section 13
is inhibited from performing an excessive response in the direction in which the discharge
pressure Pd is rapidly decreased. This prevents a high-sensitivity compressor from
causing a hunting phenomenon due to a rapid change in the discharge pressure Pd.
[0044] In the control valve 11f in Fig. 8 (seventh embodiment), the pressure-sensing section
12 does not sense or respond to a rapid change in the pressure Pc supplied to the
crankcase in increasing direction but sensitively detects and responds to only a rapid
change in the pressure Pc in decreasing direction for controlling or retarding the
valve lift of the valve section 13.
[0045] The pressure-sensing piston 19 contains a check valve mechanism for switching the
response sensitivity between when a rapid change occurs in the pressure Pc supplied
to the crankcase in increasing direction and when a rapid change occurs in decreasing
direction. The check valve mechanism comprises a passage 19b with a stepped portion
in the pressure-sensing piston 19 for communication between the medium-pressure port
26 and the pressure-adjusting chamber 20 the ball-shaped valve element 41 in a large-diameter
passage part facing the pressure-adjusting chamber 20, and a valve element stopper
44 fitted into an open end of the passage toward the pressure-adjusting chamber 20.
[0046] When the control valve 11f in Fig. 8 controls the compressor at a predetermined valve
lift, if a rapid increase in the discharge pressure Pd causes the valve section 13
to operate in valve-opening direction to thereby rapidly increase the pressure Pc
supplied to the crankcase, the check valve mechanism immediately opens by the differential
pressure between the pressure Pc in the crankcase and the pressure in the pressure-adjusting
chamber 20. The pressure-sensing section 12 does not adversely affect the operation
of the valve section 13, such that the valve section 13 promptly operates in valve-opening
direction in response to the rapid increase in the pressure Pc to increase the pressure
Pc in the crankcase more promptly, thereby promptly controlling the discharge capacity
of the compressor in the decreasing direction.
[0047] Inversely, if the pressure Pc supplied to the crankcase has rapidly decreased, the
pressure Pc in the medium-pressure port 26 becomes lower than a pressure Pc(av) in
the pressure-adjusting chamber 20, which is an average pressure remaining from the
pressure Pc before it has rapidly decreased. Then the check valve mechanism is closed.
As a result, the pressure-sensing piston 19 having a larger pressure-receiving area
than the valve element 23 sensitively detects the rapid decrease in the pressure Pc,
and the differential pressure between the discharge pressure Pd and the suction pressure
Ps becomes smaller, so that the operation of the valve section 13 in valve-closing
direction is instantaneously suppressed or retarded by the pressure-sensing section
12 sensitively acting in valve-opening direction.
[0048] The control valve 11f in Fig. 8 has asymmetric valve-opening characteristics, namely
a high sensitivity to a rapid change in the pressure Pc supplied to the crankcase
in increasing direction, but a low sensitivity to a rapid change in the pressure Pc
in decreasing direction. This prevents occurrence of control hunting even if the pressure
Pc is rapidly changed due to the rapid change in the discharge pressure Pd.
[0049] In the control valve 11 g in Fig. 9 (eighth embodiment), the pressure-sensing section
12 does not sense a rapid change in the suction pressure Ps in decreasing direction
but sensitively detects only a rapid change in the suction pressure Ps in increasing
direction for controlling the valve lift of the valve section 13.
[0050] The pressure-sensing piston 19 contains a check valve mechanism for switching the
response sensitivity between when a rapid change occurs in the suction pressure Ps
in increasing direction and when a rapid change occurs in decreasing direction. The
check valve mechanism comprises a passage 19b with a stepped portion in the pressure-sensing
piston 19 for communication between the low-pressure port 27 and the pressure-adjusting
chamber 20, the ball-shaped valve element 41 in a large-diameter passage part facing
the low-pressure port 27, and the valve element stopper 44 in an open end of the passage
19b facing the low-pressure port 27.
[0051] When the control valve 11 g controls the compressor at a predetermined valve lift,
if a rapid increase in the discharge pressure Pd causes a rapid decrease in the suction
pressure Ps, the check valve mechanism opens by the differential pressure between
the suction pressure Ps and the pressure in the pressure-adjusting chamber 20. The
pressure-sensing section 12 then does not adversely affect the operation of the valve
section 13, so that the valve section 13 promptly opens in response to the rapid increase
in the discharge pressure Pd to increase the pressure Pc in the crankcase more promptly,
and promptly adjusts the compressor to decrease the discharge capacity.
[0052] Inversely, if a rapid decrease in the discharge pressure Pd causes a rapid increase
in the suction pressure Ps, the suction pressure Ps in the low-pressure port 27 becomes
higher than the pressure Ps(av) in the pressure-adjusting chamber 20, which is an
average pressure remaining from the suction pressure Ps before it has rapidly increased.
The check valve mechanism closes. As a result, the pressure-sensing piston 19 sensitively
detects the rapid increase in the suction pressure Ps, and the operation of the valve
section 13 in the valve-closing direction is instantaneously suppressed or retarded
by the pressure-sensing section 12 which sensitively acts in the valve-opening direction.
[0053] The control valve 11 g in Fig. 9 has asymmetric valve-opening characteristics, namely
high sensitivity for a rapid change in the suction pressure Ps in decreasing direction,
and low sensitivity for a rapid change in the pressure Pc in increasing direction.
This prevents occurrence of hunting.
1. A control valve for a variable displacement compressor, the control valve (11, 11a,
11b, 11c, 11d, 11e, 11f, 11g) sensing the differential pressure (Pd-Ps) between the
discharge pressure (Pd) in a compressor discharge chamber and the suction pressure
(Ps) in a compressor suction chamber, and controlling the refrigerant flow rate between
the discharge chamber and a crankcase to thereby change the refrigerant discharge
capacity,
characterised by:
a pressure-sensing section (13) in the control valve for sensing pressure changes
caused by a rapid change of the rotational compressor speed and for retarding a valve
section motion in valve-opening/closing direction by a value which is proportional
to a degree of the respective pressure change.
2. The control valve according to claim 1, characterised in that the pressure-sensing section (13) comprises a pressure-sensing piston (19) in a high-pressure
port (18), for receiving the discharge pressure (Pd) at a larger pressure-receiving
area than the pressure receiving area of a valve element (23), that a shaft (22) transmits
an axial motion or force of the pressure sensing piston (19) generated by the differential
pressure (Pd-Pd(av)) between the discharge pressure (Pd) and a pressure (Pd(av)) in
a pressure-adjusting chamber (20) which is bounded by the pressure-sensing piston
(19) to the valve element (23).
3. The control valve according to claim 2, characterised in that the shaft (22) is integral with the valve element (23), that the valve element (23)
receives the discharge pressure (Pd) at one end face, that a piston rod (24) is integral
with the valve element (23), and that the piston rod (24) receives the suction pressure
(Ps) at an end face opposite to the other end face.
4. The control valve according to claim 2, characterised in that the pressure-sensing section (12) further comprises sensitivity-switching means for
making the force of the pressure-sensing piston (19) on the valve element (23) smaller
when the discharge pressure (Pd) is rapidly increased than when the discharge pressure
(Pd) is rapidly decreased.
5. The control valve according to claim 4, characterised in that the sensitivity-switching means is a check valve disposed in a passage (19b) in the
pressure-sensing piston (19) between a high-pressure port side and the pressure-adjusting
chamber (20), for allowing flow from the high-pressure port side into the pressure-adjusting
chamber (20), and blocking flow from the pressure-adjusting chamber (20) to the high-pressure
port side.
6. The control valve according to claim 4, characterised in that the sensitivity-switching means is a check valve provided in a passage (17a) in a
member (17) jointly defining the pressure-adjusting chamber (20) together with the
pressure-sensing piston (19), the passage (17a) communicating between a discharge
pressure side and the pressure-adjusting chamber (20), for blocking flow from the
discharge pressure side to the pressure-adjusting chamber (20), and allowing flow
from the pressure-adjusting chamber (20) to the discharge pressure side.
7. The control valve according to claim 4, characterised in that the sensitivity-switching means is formed by a tapered periphery of the pressure-sensing
piston (19) such that a gap (19c) formed with the wall of a cylinder accommodating
the pressure sensing piston (19), and that the gap (19c) progressively decreases in
cross-sectional area from the high-pressure port side to the pressure-adjusting chamber
(20).
8. The control valve according to claim 1, characterised in that the pressure-sensing section (12) has a pressure-sensing piston (19) disposed in
communication with a medium-pressure port (26) through which control pressure (Pc)
controlled by the valve section (13) is delivered to the crankcase, that the pressure
sensing piston (19) receives the control pressure at a pressure-receiving area larger
than that of a valve element (23), and that the pressure-sensing piston (19) is configured
to transmit an axial motion or force generated by the differential pressure (Pc-Pc(av))
between the control pressure (Pc) and a pressure (Pc(av)) in a pressure-adjusting
chamber (20) which is bounded by the pressure-sensing piston (19) to the valve element
(23).
9. The control valve according to claim 8, characterised in that the pressure-sensing section (12) further comprises sensitivity-switching means for
making the force transmitted by the pressure-sensing piston (19) on the valve element
(23) smaller when the control pressure (Pc) rapidly increases than when the control
pressure (Pc) rapidly decreases.
10. The control valve according to claim 9, characterised in that the sensitivity-switching means is a check valve provided in a passage (19c) through
the pressure-sensing piston (19) between a first a side communicating with the medium-pressure
port (26) and the pressure-adjusting chamber (20), for allowing flow from the first
side to the pressure-adjusting chamber (20), and blocking flow from the pressure-adjusting
chamber (20) to the first side.
11. The control valve according to claim 1, characterised in that the pressure-sensing section (12) has a pressure-sensing piston (19) disposed adjacent
to a low-pressure port (27) through which the suction pressure (Ps) is introduced,
that the pressure sensing piston (19) receives the suction pressure at a pressure-receiving
area larger than that of a valve element (23), and that the pressure-sensing piston
(19) is configured to transmit an axial motion or force generated by the differential
pressure (Ps-Ps(av)) between the suction pressure (Ps) and the pressure (Ps(av)) in
a pressure-adjusting chamber (20) which is bounded by the pressure-sensing piston
(19) to the valve element (23).
12. The control valve according to claim 11, characterised in that the pressure-sensing section (12) further comprises sensitivity-switching means for
making the force transmitted by the pressure-sensing piston (19) on the valve element
(23 larger when the suction pressure (Ps) rapidly increases than when the suction
pressure (Ps) rapidly decreases.
13. The control valve according to claim 12, characterised in that the sensitivity-switching means is a check valve disposed in a passage through the
pressure-sensing piston (19) between a side toward the low-pressure port (27) and
the pressure-adjusting chamber (20), for allowing flow from the side toward the low-pressure
port (27) into the pressure-adjusting chamber (20), and blocking flow from the pressure-adjusting
chamber (20) to the side toward the low-pressure port (27).