JP2000230481A - Crank pressure control mechanism of variable capacity comperssor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent crank pressure from increasing more than necessary in advance and to eliminate wasting of high-pressure coolant gas generated by the compressor even when letting a compressor of swash plane type rapidly shift to the minimum capacity operation by increasing the crank pressure in a short period. SOLUTION: In the middle of an intake passage 28 coupling a discharge chamber 22 of a variable capacity compressor of swash plane type and a crank chamber 5, a valve portion 51 in the intake side of an electromagnetic switch valve and gas flow adjusting mechanism 80 are provided in series. The valve portion 51 in the intake side opens and closes the intake passage 28 by external control. The gas flow adjusting mechanism 80 chronologically changes the quantity of passing gas in response to gas supplied from the discharge chamber 22 by an opening operation of the valve 51 in the intake side to adjust the quantity of gas flowing into the crank chamber 5 as time goes by.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crank pressure control mechanism for a variable displacement compressor capable of changing a tilt angle of a swash plate based on control of an internal pressure of a crank chamber to adjust a displacement.

[0002]

2. Description of the Related Art Generally, the discharge capacity of a variable displacement type swash plate type compressor is adjusted by changing the inclination angle of a swash plate based on the internal pressure control of a crank chamber. One of the control methods of the crank chamber pressure (crank pressure Pc) is an inlet control. This is because a part of the high-pressure refrigerant gas discharged into the discharge chamber of the compressor is appropriately introduced into the crank chamber through the inlet-side control valve, and the crank pressure Pc is increased to reduce the inclination angle of the swash plate and reduce the discharge capacity. This is a control method of lowering. In the conventional inlet-side control, for example, in order to immediately reduce the discharge capacity of the compressor from the maximum capacity (maximum tilt angle) to the minimum capacity (minimum tilt angle), and to maintain the minimum capacity operation thereafter, the input-side control in the valve-closed state is required. The valve had to be fully opened and then kept fully open.

However, if the fully open state of the inlet control valve is maintained, the crank pressure Pc increases more than necessary and adversely affects the internal mechanism of the compressor. For example, an excessive increase in the crank pressure Pc may cause a problem (a so-called piston top contact) in which the compression end face of the piston that has reached the top dead center position collides with a valve plate that defines one end face of the cylinder bore. In order to prevent such a problem beforehand, even when the inlet control valve is opened, the diameter of the bleed passage for discharging the gas in the crank chamber to the suction chamber is set to be slightly larger so that the crank pressure Pc does not increase more than necessary. A safety design is often adopted in which a fixed throttle is disposed and pressure is constantly released from the crank chamber to the suction chamber. However, in such a design, in order to maintain the minimum capacity operation, it is necessary to continue to supply the high pressure refrigerant gas from the discharge chamber to the crank chamber from the discharge chamber in an amount exceeding the amount of gas released from the crank chamber via the bleed passage, This implies that the high-pressure refrigerant gas flows down the discharge chamber → the crank chamber → the suction chamber. In this case, the refrigerant gas compressed by the compressor is wasted, and a decrease in the efficiency of the compressor is inevitable.

On the other hand, it is desirable to maintain good responsiveness when switching the discharge capacity of the compressor from the maximum capacity to the minimum capacity (that is, changing the swash plate from the maximum tilt angle to the minimum tilt angle), that is, the rapidity of the change. There is a demand that. Therefore, at least until the crank pressure Pc reaches the minimum high pressure state necessary for shifting the swash plate from the low pressure state corresponding to the maximum tilt state to the minimum tilt state, the inlet control valve is kept fully open. Is preferred.

It is an object of the present invention to increase the crank pressure Pc in a short time so that the compressor can be quickly shifted to the minimum capacity operation, and even in such a case, the crank pressure Pc is prevented from rising more than necessary. To provide a crank pressure control mechanism for a variable displacement compressor capable of causing the compressor to operate at its original efficiency without wasting high pressure gas produced by the compressor. is there.

[0006]

A first aspect of the present invention is a crank pressure control mechanism in a variable displacement compressor capable of adjusting a discharge angle by changing a tilt angle of a swash plate based on control of an internal pressure of a crank chamber. An inlet side opening / closing valve which is provided in an air supply passage connecting the discharge pressure region of the compressor to the crank chamber, and which can open and close the air supply passage by external control; and The gas supply amount is provided in the air supply passage so as to intervene, and the gas passage amount changes with time in response to gas supply from the discharge pressure region due to the opening operation of the inlet-side on-off valve, and gas flows into the crank chamber. This is a crank pressure control mechanism of a variable displacement compressor including a gas inflow adjusting mechanism for adjusting the amount with time.

According to this configuration, when the inlet-side on-off valve is opened by external control, high-pressure gas corresponding to the discharge pressure is supplied from the discharge pressure region of the compressor to the gas inflow adjusting mechanism. Then, in response to the gas supply, the gas inflow adjusting mechanism changes the gas passage amount with time to adjust the gas inflow amount to the crank chamber with time. By interposing a gas inflow adjusting mechanism having such a function between the inlet-side on-off valve and the crank chamber, the minimum amount of high-pressure gas necessary for raising the crank pressure Pc to the target pressure is automatically measured. , Can flow into the crankcase in a short time.
Therefore, if the crank pressure control mechanism of the first aspect is used, not only can the crank pressure Pc be increased in a short time to quickly shift the compressor to the minimum displacement operation, but also in that case, the crank pressure Pc is required. It is possible to prevent the above-mentioned rise from occurring beforehand, and to make the compressor operate at the original efficiency without wasting the high-pressure gas produced by the compressor.

According to a second aspect of the present invention, in the crank pressure control mechanism for the variable displacement compressor according to the first aspect, the gas inflow adjusting mechanism allows the gas to pass for a predetermined time immediately after the inlet-side on-off valve is opened. It is characterized in that the gas passage amount is narrowed down after the predetermined time elapses while the amount is kept large.

According to this configuration, a (minimum) amount of high-pressure gas required to raise the crank pressure Pc to the target pressure is sent into the crank chamber within a predetermined time immediately after the opening of the inlet-side on-off valve, and the crank pressure is increased. After Pc reaches the target pressure, only the minimum amount of high-pressure gas required to maintain the target pressure can be continuously supplied to the crank chamber. Therefore, by using the crank pressure control mechanism according to the second aspect, it is possible to simultaneously increase the crank pressure quickly, avoid excessive crank pressure, and prevent waste of high-pressure gas.

According to a third aspect of the present invention, in the crank pressure control mechanism for a variable displacement compressor according to the first or second aspect, the gas inflow adjusting mechanism is a movable wall provided reciprocally in the room. A spool valve element, an introduction chamber and a pressure regulation chamber partitioned in the room by the spool valve element, and a connection between the introduction chamber and the crank chamber and opening / closing as the spool valve element reciprocates. An outlet passage, a throttle that communicates the introduction chamber with the pressure regulation chamber, and the spool valve element is supplied with gas from the discharge pressure region to the introduction chamber by the opening operation of the inlet-side on-off valve. While moving forward from the original position to open the lead-out passage, and after a predetermined period of time, when the pressure in the introduction chamber and the pressure regulating chamber is equalized via the throttle, the spool valve body returns to the original position and returns to the original position. To block the exit passage And butterflies.

According to this structure, the lead-out passage connecting the introduction chamber and the crank chamber can be opened for a predetermined time required for the reciprocating operation of the spool valve body. The discharge chamber and the crank chamber can be directly connected via the introduction chamber and the outlet passage. The opening time of the outlet passage corresponds to the time required for equalizing the pressure in the introduction chamber and the pressure regulating chamber via the throttle. Therefore, by appropriately changing the size of the throttle and the volume of the pressure regulation chamber,
It is possible to optimally set the opening time of the lead-out passage.

According to a fourth aspect of the present invention, in the crank pressure control mechanism for a variable displacement compressor according to the first or second aspect, the gas inflow adjusting mechanism is provided between the forward position and the backward position in the room. A spool valve body as a movable wall provided so as to be able to reciprocate, a biasing spring for biasing the spool valve body toward a forward position, and a partition defined in the room by the spool valve body and An introduction chamber connected to a side opening / closing valve, a pressure regulation chamber partitioned into the room by the spool valve body and communicating with the crank chamber via a pressure guiding passage, and the introduction chamber and the crank chamber. An outlet passage that is connected and closed when the spool valve element is at a forward position and opened when the spool valve element is at a retracted position; and the introduction chamber formed inside or around the spool valve element. A first throttle that communicates with the pressure regulating chamber; and a second throttle that is provided in the pressure guiding passage that communicates the pressure regulating chamber with the crank chamber. The gas passage amount is smaller than the gas passage amount of the first throttle.

[0013] Claim 4 specifies the most preferable configuration of the gas inflow adjusting mechanism. The operation and effect based on this configuration will be clarified in an embodiment of the invention described later, and thus will not be described repeatedly.

According to a fifth aspect of the present invention, in the crank pressure control mechanism for a variable displacement compressor according to any one of the first to fourth aspects, the inlet opening / closing valve and the gas inflow adjusting mechanism are integrated. This constitutes a single valve mechanism (see FIGS. 6 and 7). According to this configuration, the crank pressure control mechanism becomes compact, which is convenient for incorporation into an actual machine (compressor).

According to a sixth aspect of the present invention, in the crank pressure control mechanism for a variable displacement compressor according to any one of the first to fifth aspects, a bleed passage that connects a crank chamber of the compressor to a suction pressure region. And a withdrawal opening / closing valve capable of opening and closing the bleed passage by external control, wherein one of the withdrawal opening / closing valve and the input-side opening / closing valve is open when one is in a valve-open state. The interlocking control is performed so that the valve is closed.

According to this configuration, when the inlet-side on-off valve is opened to increase the crank pressure Pc by external control, the drain-side on-off valve is closed.
Therefore, the communication between the crank chamber and the suction pressure region does not occur during the operation of increasing the crank pressure, and the high-pressure gas does not drool at all as a disadvantage of the prior art. Therefore, wasteful use of the high-pressure gas is prevented, and the operating efficiency of the compressor can be improved.

According to a seventh aspect of the present invention, in the crank pressure control mechanism for a variable displacement compressor according to the sixth aspect, the inlet-side on-off valve, the discharge-side on-off valve, and the gas inflow adjusting mechanism are integrated. (See FIGS. 6 and 7). According to this configuration,
The crank pressure control mechanism becomes compact, which is convenient for incorporation into an actual machine (compressor).

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a variable displacement swash plate type compressor with a clutch will be described below with reference to FIGS.
This will be described with reference to FIG.

(Outline of Compressor Body) As shown in FIG. 1, the swash plate type compressor has a cylinder block 1, a front housing 2 joined to a front end thereof, and a valve forming body 3 at a rear end of the cylinder block 1. Rear housing 4 joined via
And These 1, 2, 3, and 4 are joined and fixed to each other by a plurality of through bolts (not shown) to form a compressor housing. A crank chamber 5 is defined in a region surrounded by the cylinder block 1 and the front housing 2. A drive shaft 6 is rotatably supported in the crank chamber 5 by a plurality of radial bearings provided in the housing. A coil spring 7 and a rear thrust bearing 8 are provided in a central concave portion of the cylinder block 1. On the other hand, a rotary support 11 is fixed on the drive shaft 6 in the crank chamber 5 so as to be integrally rotatable, and a front thrust bearing 9 is disposed between the rotary support 11 and the inner surface of the front housing 2. I have. The drive shaft 6 is thrust supported by a rear bearing 8 and a front bearing 9 urged forward by a spring 7.

The front end of the drive shaft 6 is operatively connected to a vehicle engine E as an external drive source via an electromagnetic clutch 40. The electromagnetic clutch 40 is connected to the front housing 2
A pulley 42 rotatably supported by a bearing 41 on a front cylindrical portion of the drive shaft 6, an annular solenoid coil 43, and a front end region of the drive shaft 6 are slidably moved forward and backward while being urged by a leaf spring 44. Armature 45 provided.
FIG. 1 shows the armature 4 against the urging force of the leaf spring 44.
5 shows a state in which 5 is joined to the end face of the pulley 42. When the armature 45 is attracted and joined to the end face of the pulley 42 by electromagnetic force generated by energizing the coil 43, the driving force of the engine E is transmitted to the drive shaft 6 via the power transmission belt 46, the pulley 42 and the armature 45. You. If the electromagnetic force disappears due to the stoppage of the current supply to the coil 43, the armature 45 is separated from the pulley 42 by the urging force of the leaf spring 44, and the power transmission is cut off. As described above, the engine power is selectively transmitted to the drive shaft 6 based on the control of energizing the coil 43.

Further, a swash plate 12 serving as a cam plate is accommodated in the crank chamber 5. The swash plate 12 has a through hole formed in the center thereof, and the drive shaft 6 is inserted through the through hole. The swash plate 12 is operatively connected to the rotation support 11 and the drive shaft 6 via a hinge mechanism 13 as a connection guide mechanism. The hinge mechanism 13 includes a support arm 14 having a guide hole protruding from a rear surface of the rotary support 11 and a swash plate 1.
2 and a guide pin 15 with a spherical head protruding from the front surface of the second. Then, by the linkage between the support arm 14 and the guide pin 15 constituting the hinge mechanism 13 and the contact with the drive shaft 6 in the central insertion hole of the swash plate 12,
The swash plate 12 is rotatable in synchronization with the drive shaft 6 and is capable of tilting with respect to the drive shaft 6 while sliding the drive shaft 6 in the axial direction.

A coil-shaped inclination-reducing spring 16 is provided on the drive shaft 6 between the rotary support 11 and the swash plate 12. The spring 16 urges the swash plate 12 in a direction approaching the cylinder block 1 (that is, a direction in which the inclination angle decreases). A circlip 17 is fixed on the drive shaft 6 behind the swash plate 12, and the circlip 17 restricts the swash plate 12 from retreating further, thereby reducing the minimum inclination angle of the swash plate 12 (for example, 3 to 3).
5 °). On the other hand, the maximum inclination angle of the swash plate 12 is determined when the counterweight portion 12a of the swash plate 12 abuts on the regulating portion 11a of the rotary support 11 (see FIG. 1).

As shown in FIG. 1, the cylinder block 1 has a plurality of cylinder bores 1a surrounding the drive shaft 6.
A single-headed piston 18 is reciprocally accommodated in each cylinder bore 1a.
The end of each piston 18 is moored to the outer periphery of the swash plate 12 via a pair of shoes 19, and the piston 18 and the swash plate 12 are operatively connected via the shoes 19. Further, between the valve forming body 3 and the rear housing 4, a suction chamber 21 located in a central region and a discharge chamber 22 surrounding the suction chamber 21 are defined. In the valve forming body 3, corresponding to each cylinder bore 1a,
Suction port 23 and suction valve 2 for opening and closing the port 23
4, and a discharge port 25 and a discharge valve 26 for opening and closing the port 25 are formed. The suction chamber 21 communicates with each cylinder bore 1 a via the suction port 23, and the cylinder bore 1 a communicates with the discharge chamber 22 via the discharge port 25.

In the swash plate type compressor shown in FIG. 1, when the drive shaft 6 is rotated by the power supply from the engine E, the swash plate 12 inclined at a predetermined angle is rotated. Then, each piston 18 is reciprocated at a stroke corresponding to the inclination angle of the swash plate, and in each cylinder bore 1a, the suction chamber 21 (suction pressure P
s area), suction and compression of the refrigerant gas from the
The discharge of the compressed refrigerant gas to the (area of the discharge pressure Pd) is sequentially repeated.

The tilt angle of the swash plate 12 of the compressor is determined by the moment of the rotational motion based on the centrifugal force at the time of rotation of the swash plate, the moment by the spring force based on the biasing action of the tilt reducing spring 16, and the gas pressure. There are three moments.
The product of inertia of the swash plate 12 is set such that the moment of the rotational motion always acts in the direction of increasing the tilt angle. On the other hand, the moment due to the gas pressure is the mutual reaction between the compression reaction force acting on the piston of the cylinder bore in the compression stroke, the internal pressure of the cylinder bore in the suction stroke, and the internal pressure of the crank chamber 5 (crank pressure Pc) which corresponds to the piston back pressure. This is a moment generated based on the relationship, and acts in the direction of decreasing the tilt angle. In the present embodiment, by maintaining the crank pressure Pc at a high level, the sum of the moment due to the gas pressure and the moment due to the spring force of the inclination reducing spring 16 exceeds the moment in the inclination increasing direction due to the rotational motion, and the swash plate 12 Is designed to be set to the minimum inclination. Also, the crank pressure P
By adjusting c, the sum of the moment due to the gas pressure and the moment due to the spring force is balanced with the moment of the rotational motion, and the inclination angle of the swash plate 12 is set to an arbitrary angle between the minimum inclination angle and the maximum inclination angle. You can also. Thus, the inclination of the swash plate 12 is determined based on the control of the crank pressure Pc, and the stroke of each piston 18, that is, the displacement of the compressor is variably adjusted according to the inclination.

As shown in FIGS. 1 to 5, the crank pressure Pc
The crank pressure control mechanism for controlling the pressure is provided in the inlet / outlet side interlocking electromagnetic on-off valve 50 (see FIGS. 2 and 3), the gas inflow adjusting mechanism 80 (see FIG. 5), and the compressor housing. It is constituted by an air supply passage 28 and a bleed passage 29. The air supply passage 28 connects the discharge chamber 22 and the crank chamber 5. In the middle of the air supply passage 28, an inlet-side valve portion (that is, an inlet-side on-off valve) 51 of an interlocking electromagnetic on-off valve 50 and a gas inflow An adjustment mechanism 80 is provided. The bleed passage 29 connects the crank chamber 5 and the suction chamber 21, and in the middle of the bleed passage 29, a removal valve portion (ie, a removal opening / closing valve) 52 of the interlocking electromagnetic on-off valve 50 is provided. . The components of the crank pressure control mechanism will be described later.

(Electronic Control Structure of External Refrigerant Circuit and Compressor) As shown in FIG.
1 is connected via an external refrigerant circuit 30. The external refrigerant circuit 30 forms a cooling circuit of the vehicle air conditioner together with the compressor. The external refrigerant circuit 30 includes a condenser (condenser) 31, a temperature-type expansion valve 32, and an evaporator (evaporator) 33. The opening degree of the expansion valve 32 is feedback-controlled based on the detected temperature and the evaporation pressure of a temperature-sensitive cylinder provided on the outlet side of the evaporator 33, and the expansion valve 32 supplies the liquid refrigerant corresponding to the heat load to the evaporator 33.
To adjust the refrigerant flow rate in the external refrigerant circuit 30.

Further, as shown in FIG. 2, a temperature sensor 34 is provided near the evaporator 33. The temperature sensor 34 detects the temperature of the evaporator 33 and provides the evaporator temperature information to the control computer C. The control computer C manages all controls related to cooling and heating of the vehicle air conditioner. A temperature sensor 3 is provided on the input side of the control computer C.
4, a room temperature sensor 35 for detecting a vehicle indoor temperature, a room temperature setting device 36 for setting the vehicle indoor temperature, an air conditioner operation switch 37, and an electronic control unit ECU of the engine E are connected. On the other hand, on the output side of the control computer C, a drive circuit 38 that controls the energization of the solenoid coil 43 of the electromagnetic clutch 40 described above,
The drive circuit 39 for controlling the energization of the coil 74 of the electromagnetic on-off valve 50 is connected. The control computer C controls the evaporator temperature obtained from the temperature sensor 34, the vehicle interior temperature obtained from the room temperature sensor 35, the desired room temperature set by the room temperature setting device 36, and the ON / OFF state of the air conditioner operation switch 37.
The electromagnetic clutch 40 and the electromagnetic on-off valve 50 are controlled on the basis of the OFF setting status and external information such as information on starting / stopping of the engine E and the engine speed from the ECU.

(Structure and Basic Operation of Electromagnetic On / Off Valve 50) As shown in FIG.
0 is an air supply passage 28 connecting the discharge chamber 22 and the crank chamber 5.
-Side valve section 51 as an inlet-side on-off valve for controlling the opening and closing of the valve
A withdrawal-side valve portion 52 as a withdrawal-side on-off valve for controlling the opening and closing of the bleed passage 29 connecting the crank chamber 5 and the suction chamber 21;
A solenoid unit 53 for driving the two valve units 51 and 52 is provided. These 51, 52, and 53 are incorporated in a valve housing 54 that forms the outer shell of the main body of the electromagnetic on-off valve 50.

The inlet valve portion 51 includes a valve housing 54.
An inlet-side valve chamber 55 is defined therein, and an inlet-side communication passage 56 which is a valve hole and is provided vertically in a ceiling area of the valve chamber. The inlet valve chamber 55 is connected to the first port 57 and the air supply passage 28.
The pressure (discharge pressure Pd) of the discharge chamber 22 is guided to the valve chamber 55 through the upstream portion of the discharge chamber 22. The inlet communication passage 56 communicates with the gas inflow adjusting mechanism 80 and the crank chamber 5 via the second port 58 and a downstream portion of the air supply passage 28. The first port 57, the inlet valve chamber 55, the inlet communication passage 56, and the second port 58 form a part of the air supply passage 28 in the electromagnetic on-off valve 50.

An inlet valve body 60 is provided in the inlet valve chamber 55 so as to be movable in a vertical direction (axial direction of the valve 50). The main body of the inlet valve body 60 moves with the valve hole 5
Open and close 6. From the lower end of the valve body 60, the first rod 6
A second rod 62 extends vertically from the upper end of the valve body 60, and the tip of each rod penetrates the partition wall of the valve housing 54 to reach the outside of the inlet valve chamber 55. I have. The integrated entry-side valve body 60 and the first and second rods 61 and 62 have an upper limit position at which the valve body 60 closes the valve hole 56 (see FIG. 2) and a lower limit at which the valve body 60 opens the valve hole 56. It can move up and down between two positions (see FIG. 3).

The extraction valve portion 52 includes a valve housing 54.
The valve-side valve chamber 63 is defined therein, and a valve-side communication passage 64 which is a valve hole and is provided vertically in a bottom region of the valve chamber.
The extraction side communication passage 64 is connected to the third port 65 and the bleed passage 29.
Communicates with the crankcase 5 through the upstream portion of the crankcase. The extraction side valve chamber 63 communicates with the suction chamber 21 via the fourth port 66 and a downstream portion of the bleed passage 29, and the pressure (suction pressure Ps) of the suction chamber 21 is guided to the valve chamber 63. Note that the third port 6
The extraction side communication passage 64, the extraction side valve chamber 63, and the fourth port 66 form a part of the bleed passage 29 in the electromagnetic on-off valve 50.

A pull-out valve body 67 is provided in the pull-out valve chamber 63 so as to be movable in the vertical direction (axial direction of the valve 50), and opens and closes the valve hole 64 with the movement. That is, the valve body 67 can be switched and arranged between an open position (see FIG. 2) where the valve body 64 opens the valve hole 64 and a closed position (see FIG. 3) where the valve hole 64 is closed. A closing spring 68 is provided in the pull-out valve chamber 63, and the closing spring 68 is
7 is urged in the closing direction of the valve hole 64. Further, the upper end (tip) of the second rod 62 disposed in the two communication passages 56 and 64 can be in contact with the lower end surface of the extraction valve body 67. Inlet valve body 60 and second rod 62
Is disposed at the upper limit position (see FIG. 2), the second rod 62 separates the extraction side valve body 67 from the valve hole 64 against the downward urging force of the closing spring 68 to open the valve hole 64. . On the other hand, when the inlet side valve body 60 and the second rod 62 are arranged at the lower limit position (see FIG. 3), the second rod 62 does not press the pull-out side valve body 67 upward, and the valve body 67 is closed in principle. The valve hole 64 is closed by the downward biasing force of the spring 68.

The solenoid 53 is provided with the valve housing 5
4 is provided with a solenoid chamber 71 partitioned therein. A fixed iron core 72 is provided in a boundary area between the solenoid chamber 71 and the inlet valve chamber 55. The lower end (tip) of the first rod 61 enters the solenoid chamber 71 and the rod 6
A movable iron core 73 as a plunger is fixed to the distal end of the armature 1. An open spring 69 is interposed between the fixed iron core 72 corresponding to the ceiling of the solenoid chamber 71 and the movable iron core 73, and the open spring 69 is integrated with the movable iron core 73,
The inlet valve body 60 and the first and second rods 61 and 62 are urged downward. The valve housing 54 has two iron cores 7.
A coil 74 is mounted so as to surround the coils 2 and 73. The energization of the coil 74 is controlled by the computer C.
Electromagnetic attraction (ie, upward electromagnetic biasing force) acts between the three. When the coil 74 is energized with the minimum current value, the upward electromagnetic urging force exceeds the downward urging force of the springs 68 and 69, and the valve bodies 60 and 67 are arranged at the positions shown in FIG.

As described above, the inlet-side valve portion 51, the withdrawal-side valve portion 52, and the solenoid portion 53 are in an interlocking relationship with each other, and each of the valve portions 51, 5 depends on whether or not the coil 74 is energized.
2 is controlled alternatively. That is, when the coil 74 is energized, as shown in FIG.
Is closed, and the withdrawal valve portion 52 is opened. Conversely, when the energization of the coil 74 is stopped, as shown in FIG. 3, the inlet valve portion 51 is in the open state and the extraction valve portion 52 is in the closed state. Therefore, this solenoid on-off valve 50
Are controlled by the external control to the inlet valve portion 51 and the withdraw valve portion 5.
It can be considered as an ON / OFF valve of an interlocking type on / off side that selectively opens only one of the two.

As shown in FIG. 3, the pressure on the valve hole 64 side (that is, the crank pressure Pc) becomes excessive when the withdrawing valve 67 closes the valve hole 64, and the valve 67 is closed. The pressure difference (Pc-Ps) acting up and down (front and back) is determined by the closing spring 6.
8 may exceed the spring force. Then, as shown in FIG. 4, the valve body 67 momentarily moves upward against the urging force of the spring 68, and the gas flows from the crank chamber 5 to the suction chamber 21 via the extraction side communication passage 64 and the valve chamber 63. Drilling is performed. As described above, the valve body 67 and the second rod 62 are separated (that is, can be separated from and separated from each other), so that the extraction side valve portion 52 also functions as a differential pressure valve that autonomously adjusts the crank pressure Pc.

(Structure of Gas Inflow Control Mechanism 80) As shown in FIGS. 2 and 3, in the middle of the downstream portion of the air supply passage 28, that is, between the second port 58 of the electromagnetic on-off valve 50 and the crank chamber 5. Has a gas inflow adjusting mechanism 80 as shown in FIGS. 5 (A) and 5 (B). The adjusting mechanism 80 includes a spool valve element 83 housed in a room 82 formed by an apparatus housing 81. Spool valve element 83
Is provided as a movable wall capable of reciprocating between a first stopper portion 91 and a second stopper portion 92 provided on the inner wall of the room 82. That is, the spool valve element 83 is moved to the forward position or the original position (see FIG. 5A) where the advance of the valve element is regulated by the first stopper 91, and the second stopper 92.
(FIG. 5)
(See (B)). The room 82 is divided into an introduction chamber 84 and a pressure regulation chamber 85 by the spool valve element 83.

The introduction chamber 84 is connected to the second port 58 of the inlet side valve portion 51 of the electromagnetic on-off valve 50 via an introduction port 86, and communicates with the crank chamber 5 via an outlet port 87 and an outlet passage 88. It is possible. The introduction chamber 84 and the pressure regulating chamber 85 communicate with each other via a throttle (first throttle) 83 a formed in the spool valve element 83. The pressure regulating chamber 85 has a port 89 and a throttle (second throttle).
It is connected to the crank chamber 5 through a pressure guiding passage 90 with 90a. However, the diameter of the throttle 90a of the pressure guide passage is smaller than the diameter of the throttle 83a of the spool valve body, and the gas passage amount of the throttle 90a is set to be smaller than the gas passage amount of the throttle 83a. Further, an urging spring 93 is provided in the pressure adjusting chamber 85, and urges the spool valve element 83 from the retracted position toward the advanced position (original position). When the pressure in the introduction chamber 84 and the pressure adjustment chamber 85 is substantially equalized, FIG.
As shown in (A), the spool valve element 83 is arranged at the forward position by the action of the biasing spring 93, and the spool valve element 8
3, the outlet port 87 is closed.

(Operation) The operation of the variable displacement swash plate type compressor provided with the electromagnetic on-off valve 50 and the gas inflow adjusting mechanism 80 will be described. When the air conditioner operation switch 37 is turned off, the electromagnetic clutch 40 is in a disconnected state and the engine E
No power is supplied to the compressor from the compressor, and the compressor has stopped operating. In this case, the coil 74 of the solenoid on-off valve 50 is not energized, and therefore, the action of the springs 68 and 69 causes the inlet side valve part 51 to be in the open state and the extraction side valve part 52 to be in the closed state. You. If this operation stop state continues for a long time, the pressures in the respective chambers 5, 21, 22 of the compressor are equalized, and the swash plate 12 is maintained at the minimum inclination by the urging action of the inclination reducing spring 16. On the other hand, when the air conditioner operation switch 37 is turned on, the control computer C sends the solenoid coil 4 of the electromagnetic clutch 40
3 is energized, the engine E and the compressor are connected, and the compressor is operated.

When the cooling load is large, the outlet pressure of the evaporator 33 (that is, the suction pressure Ps) is large, and the room temperature sensor 3
The difference between the detected room temperature of No. 5 and the set temperature of the room temperature setting device 36 also increases. At this time, in order to secure the discharge capacity of the compressor enough to overcome the magnitude of the cooling load, the control computer C
Energizes the coil 74 of the solenoid on-off valve 50 to close the inlet valve portion 51 and open the withdraw valve portion 52 (see FIG. 2). Then, the supply of gas from the discharge chamber 22 to the crank chamber 5 is shut off, while the discharge valve portion 5
2, the crank chamber 5 and the suction chamber 21 communicate directly with each other, so that the crank pressure Pc decreases to near the suction pressure Ps.
In addition, when the inlet valve portion 51 is closed, the crank pressure Pc
Reaches the pressure adjustment chamber 85 and the introduction chamber 84 via the two throttles 90a and 83a of the gas inflow adjustment mechanism 80, and the three chambers of the crank chamber 5, the pressure adjustment chamber 85, and the introduction chamber 84 are almost equalized by the crank pressure Pc. The spool valve 83 is located at the forward position and the outlet port 87 is closed. In this situation, the crank pressure Pc decreases to near the suction pressure Ps, so that the moment due to the gas pressure is minimized, the inclination angle of the swash plate 12 is maximized, and the discharge capacity of the compressor is maximized.

When the cooling load decreases (ie, the outlet pressure Ps of the evaporator 33 decreases) due to an increase in the compressor discharge capacity, the detected temperature of the room temperature sensor 35 and the room temperature setting device 3
The difference from the set temperature of No. 6 also becomes small. At this time, in order to make the discharge capacity of the compressor appropriate for the small cooling load, the control computer C operates the coil 74 of the electromagnetic on-off valve 50.
The energization to the valve is stopped, the inlet valve portion 51 is opened, and the extraction valve portion 52 is closed (see FIG. 3).

Immediately after the inlet valve portion 51 is opened, the discharge pressure P
The high pressure refrigerant gas corresponding to d is introduced into the introduction chamber 84 of the gas inflow adjustment mechanism 80. Immediately before this gas introduction, outlet port 8
7 is closed by a spool valve element 83 (FIG. 5).
(Refer to (A)). Also, immediately after the gas introduction, the passage connecting the introduction chamber 84 and the pressure regulation chamber 85 is the throttle 83a. A differential pressure of Pc) occurs. Due to this differential pressure, the spool valve element 83 retreats at once from the forward position to the retreat position against the urging force of the urging spring 93, and the outlet port 87 is opened (see FIG. 5B). ). As a result, the introduction chamber 84 communicates with the crank chamber 5 via the outlet port 87 and the outlet passage 88, and direct introduction of the high-pressure refrigerant gas from the discharge chamber 22 to the crank chamber 5 is achieved.

However, this direct introduction is only temporary. That is, after a predetermined short time has elapsed after the spool valve element 83 has reached the retreat position, the pressure in the introduction chamber 84 and the pressure adjustment chamber 85 is equalized to the discharge pressure Pd via the throttle 83a. This is because the diameter of the throttle 90a on the outlet side of the pressure regulating chamber 85 is smaller than the diameter of the throttle 83a on the inlet side so that the pressure regulating chamber 85 easily falls into a state where the gas inflow from the introduction chamber 84 is excessive. It is. As the high-pressure gas gradually flows into the pressure regulating chamber 85 via the throttle 83a and the pressure difference between the two chambers 84, 85 decreases, the spool valve element 83 moves from the retracted position to the advanced position by the action of the biasing spring 93. Move (return). Then, it returns to the forward position (original position) shown in FIG. Thus, the spool valve element 83
The outlet port 87 is in the open state only while the actuator reciprocates once from the forward position to the backward position to the forward position. In other words, the high-pressure refrigerant gas having a flow rate corresponding to the time interval of one reciprocation of the spool valve element 83 is automatically measured by the gas inflow adjusting mechanism 80,
Only the high-pressure refrigerant gas measured in a short time during which the spool valve element 83 makes one reciprocation is supplied to the crank chamber 5. The time during which the spool valve element 83 reciprocates one time, that is, the opening time of the outlet port 87 and the outlet passage 88, is determined mainly by the volume of the pressure regulating chamber 85 and the flow rate difference per unit time by the two throttles 83a and 90a. Is done.

When the solenoid on-off valve 50 is in the state shown in FIG. 3, the discharge of gas from the crank chamber 5 to the suction chamber 21 is shut off, while the automatic metering is performed via the inlet valve 51 and the adjusting mechanism 80 as described above. The required minimum amount of the high-pressure refrigerant gas is introduced into the crank chamber 5 in a short time.
c quickly rises to near the discharge pressure Pd. as a result,
The moment due to the gas pressure is maximized, the inclination angle of the swash plate 12 is minimized, and the discharge capacity of the compressor is minimized.

Thereafter, the swash plate 12 is maintained at the minimum inclination angle as long as the extraction side valve portion 52 is maintained in the closed state. In addition,
Even after the spool valve element 83 of the adjusting mechanism 80 reciprocates and the outlet port 87 is reclosed, the pressure from the pressure regulating chamber 85 equalized to the discharge pressure Pd to the crank chamber 5 via the throttle 90a of the pressure guiding passage. The high-pressure gas equivalent to the discharge pressure Pd is supplied little by little, but this is to compensate for the unavoidable decrease in the crank pressure Pc, and is merely for maintaining the crank pressure Pc at the current high pressure state. Absent. If the crank pressure Pc becomes excessive, as shown in FIG.
Functions as a differential pressure valve (or a safety valve) to temporarily release gas from the crank chamber 5 to prevent the crank pressure Pc from becoming excessive.

When the cooling load increases again, the control computer C resumes the energization of the coil 74 of the solenoid on-off valve 50 to close the inlet valve portion 51 and open the outlet valve portion 52. (See FIG. 2), the inclination angle of the swash plate 12 is increased. In this case, since the gas escapes from the introduction chamber 84 and the pressure adjustment chamber 85 of the gas inflow adjustment mechanism 80 to the crank chamber 5 through the throttles 83a and 90a, the two chambers 8
The internal pressure of 4, 85 is gradually reduced from the discharge pressure Pd to the crank pressure Pc. However, the aperture 83 is smaller than the aperture of the aperture 90a.
Since the diameter of “a” is larger, no pressure difference is generated between the two chambers 84 and 85 even in the process of gradually reducing the pressure of the two chambers 84 and 85. For this reason, the spool valve element 83 is kept in the
(A) is held at the forward position, and the outlet port 87 is maintained in the closed state.

It should be noted that the state where the cooling load is almost negligible and the temperature detected by the temperature sensor 34 becomes equal to the set temperature (evaporator 33)
Temperature that reflects the situation where frost is likely to occur)
In the following cases, the control computer C
Power supply to the solenoid coil 43 is stopped, and the engine E
The power transmission from the compressor to the compressor is stopped to stop the operation of the compressor.

(Effects) According to the present embodiment, the following effects can be obtained. ○ During operation at the maximum discharge capacity (maximum swash plate inclination angle), the inlet side valve portion 51 of the solenoid on-off valve is set to the fully closed state to set the discharge chamber 22
Of the high-pressure refrigerant gas from the pump to the crank chamber 5 can be avoided. For this reason, almost all of the high-pressure refrigerant gas discharged into the discharge chamber 22 can be supplied to the external refrigerant circuit 30, and the performance of the compressor can be maximized.

In order to shift to the operation with the minimum discharge capacity (minimum swash plate inclination angle), the spool valve element 83 of the gas inflow adjusting mechanism 80 is immediately turned on as soon as the inlet side valve portion 51 of the electromagnetic on-off valve is switched to the fully open state. The outlet port 87 and the outlet passage 88 are opened. For this reason, the discharge chamber 2
The supply of the high-pressure refrigerant gas from 2 to the crank chamber 5 is speeded up, and the crank pressure Pc is quickly increased. As described above, the transition to the operation with the minimum discharge capacity is performed quickly, and the response to variable capacity is excellent.

Outgoing port 8 of gas inflow adjusting mechanism 80
7 and the outlet passage 88 are opened only while the spool valve element 83 makes one reciprocating movement. By this temporary opening operation, only the minimum amount of high-pressure refrigerant gas necessary to sufficiently increase the crank pressure Pc is released from the crank chamber. 5 can be sent. That is, the introduction of the extra high-pressure gas is avoided, and the amount of the high-pressure gas extracted from the discharge chamber 22 is suppressed to a necessary minimum. Therefore,
The operation efficiency of the compressor is improved as compared with the conventional case.

According to the gas inflow adjusting mechanism 80 of this embodiment, even when the opening / closing operation of the inlet valve section 51 is repeated in a short cycle, the spool valve element 83 is reciprocated each time, and the high-pressure refrigerant gas Automatic weighing can be repeated many times. For this reason, even when the cooling load repeatedly changes suddenly, it is possible to cope with any situation without impairing the followability of the discharge capacity control.

In the case where the pull-out valve body 67 of the pull-side valve portion 52 and the second rod 62 can be brought into contact with and separated from each other, and the crank pressure Pc tends to be excessive, the pull-out valve portion 52 is connected as shown in FIG. In addition, it can function as a differential pressure valve (or a safety valve) independent of the operation of the inlet valve section 51. Therefore, even in the event of an emergency, an excessive increase in the crank pressure Pc can be prevented.

(Another Example) The embodiment of the present invention may be modified as follows. In the above embodiment, the electromagnetic on-off valve 50 and the gas inflow adjusting mechanism 80 are configured as separate devices. However, as shown in FIGS. 6 and 7, the gas inflow adjusting mechanism 80 is provided in the valve housing 54 of the electromagnetic on-off valve. May be integrated to integrate them. That is, as shown in FIGS. 6 and 7, a room for the adjusting mechanism 80 is defined above the entry-side valve portion 51, and the spool valve element 83 is accommodated therein so as to be movable in the vertical direction. In this case, the second rod 62 passes through the center of the spool valve element 83 so as to be relatively slidable. An inlet chamber 84 is defined below the spool valve element 83, communicates the inlet chamber 84 with the inlet valve chamber 55 through the valve hole 56, and an outlet port 87 (also a second port) provided on the valve housing wall. ) Can be communicated with the crank chamber 5. Also, the spool valve element 8
A pressure regulating chamber 85 is defined on the upper side of 3, and communicates with the crank chamber 5 via a throttle 90a and a third port 65 formed in a partition wall on the ceiling. In addition, a point where the urging spring 93 is disposed in the pressure regulating chamber 85, a point where both chambers 84 and 85 are communicated by a throttle 83a (having a larger diameter than the throttle 90a) formed in the spool valve element 83, The spool valve element 83 is the first
When it is located at the forward position or the original position (see FIG. 6) in contact with the stopper 91, the outlet port 87 is closed,
When the spool valve element 83 is disposed at the retracted position (see FIG. 7) in contact with the second stopper 92, the point at which the outlet port 87 is opened is exactly the same as that of the gas inflow adjusting mechanism of FIG. is there. In this case, the downstream portion of the air supply passage 28 also serves as the outlet passage 88. When the electromagnetic on-off valve with the gas inflow adjusting mechanism as shown in FIGS. 6 and 7 is incorporated in the compressor of FIG. According to this configuration, the crank pressure control mechanism becomes more compact, which is convenient for incorporation into a compressor.

In the configuration shown in FIGS. 6 and 7, when the volume of the pressure regulating chamber 85 cannot be sufficiently secured in the valve housing 54, a communication port is formed in a housing wall which defines the pressure regulating chamber 85. A separate chamber for securing an additional volume may be provided inside the compressor via the communication port.

In FIG. 5, a throttle 8 is provided in the spool valve element 83.
3a, the side clearance is intentionally secured between the inner wall surface of the room 82 and the outer sliding surface of the spool valve element 83, and this side clearance may be made to function as a throttle (first throttle) 83a. Good.

In FIGS. 2, 3, 6 and 7, an open spring 69 for urging the integrated body of the inlet valve body 60, the rods 61, 62 and the plunger 73 downward is disposed in the solenoid chamber 71. As shown in FIG.
5 may be provided.

In the embodiment (FIGS. 1 to 5) and the other examples (FIGS. 6 to 8), an interlocking valve having an inlet valve portion 51 and a withdrawal valve portion 52 is used as an electromagnetic on-off valve. Used
The interlocking valve is not provided with the withdrawal-side valve portion 52, and the input-side valve portion 5 is not provided.
The solenoid valve may be replaced by a single-type solenoid on-off valve including the solenoid valve 1 and the solenoid 53 (see FIG. 9). In this case, the crankcase 5
A fixed throttle 100 is provided in a bleed passage 29 connecting the
Is preferably provided. The flow rate of the blow-by gas leaking from the cylinder bore 1a into the crank chamber 5 during the compression stroke is represented by fA, and the flow rate of the gas supplied from the discharge chamber 22 to the crank chamber 5 via the inlet valve portion 51 and the gas inflow adjusting mechanism 80. Assuming that the flow rate is fB and the flow rate of the gas discharged from the crank chamber 5 to the suction chamber 21 via the bleed passage 29 is fC, when the inlet valve section 51 is opened, fC <fA + fB. When the valve is closed, the aperture of the fixed throttle 100 may be set so that fC> fA.

The present invention is applied to a clutchless type variable displacement compressor (compressor of the type that directly transmits power from the external drive source E to the drive shaft 6 without interposing a clutch mechanism such as an electromagnetic clutch). May be applied.

(Other technical ideas other than those set forth in the claims) In the crank pressure control mechanism according to the sixth aspect, the extraction side on-off valve has a valve hole (a part of the bleed passage). 64), a withdrawal-side valve element (67) arranged on the suction pressure region side for opening and closing the valve hole, and a closing spring (68) for urging the valve element in a direction to close the valve hole. The release-side on-off valve is provided independently of the operation of the inlet-side on-off valve and resists the urging action of the closing spring based on the differential pressure between the crank pressure and the suction pressure acting on the valve element. That the valve can be opened. According to this configuration, the withdrawal-side on-off valve can function as a type of differential pressure valve, and an excessive rise in crank pressure can be effectively prevented.

[0060]

According to the crank pressure control mechanism of the variable displacement compressor described in each of the above claims, it is only possible to increase the crank pressure in a short time and quickly shift the compressor to the minimum displacement operation. In this case, the crank pressure can be prevented from rising more than necessary, and the compressor can be operated at the original efficiency without wasting the high-pressure gas produced by the compressor. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a sectional view of a variable displacement swash plate type compressor according to an embodiment.

FIG. 2 is a cross-sectional view of a solenoid-operated on-off / off-side electromagnetic on-off valve.

FIG. 3 is a cross-sectional view of a solenoid-operated on-off / off-side electromagnetic on-off valve.

FIG. 4 is a partial cross-sectional view when a part of an electromagnetic on-off valve functions as a differential pressure valve.

FIGS. 5A and 5B are cross-sectional views showing a gas inflow adjusting mechanism.

FIG. 6 is a sectional view showing an example of an electromagnetic on-off valve with a gas inflow adjusting mechanism.

FIG. 7 is a sectional view showing an example of an electromagnetic on-off valve with a gas inflow adjusting mechanism.

FIG. 8 is a partial cross-sectional view showing another example of the electromagnetic on-off valve.

FIG. 9 is a block diagram of another example in which a pull-out valve is not provided.

[Explanation of symbols]

5: crank chamber, 12: swash plate, 21: suction chamber (suction pressure area), 22: discharge chamber (discharge pressure area), 28: air supply passage,
29: bleed passage, 40: electromagnetic clutch, 50: electromagnetic on / off valve, 51: inlet side valve part (entrance side on / off valve), 52: extraction side valve part (extraction side on / off valve), 80: gas inflow adjusting mechanism, 82
... room, 83 ... spool valve element (movable wall), 83a ... restrictor (first restrictor), 84 ... introduction chamber, 85 ... pressure regulation chamber, 87 ...
Outgoing port, 88 ... Outgoing passage, 90 ... Pressure guiding passage, 90a
... throttle (second throttle), 93 ... biasing spring, E ... vehicle engine (external drive source).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Taku Yasutani 2-1-1 Toyota-cho, Kariya-shi, Aichi Pref. Inside Toyota Industries Corporation (72) Inventor Ryo Matsubara 2-1-1 Toyota-cho, Kariya-shi, Aichi Pref. F term in Toyota Industries Corporation (reference) 3H045 AA04 AA10 AA13 AA27 BA19 BA32 CA02 CA03 DA25 EA33 3H076 AA06 BB21 BB33 CC12 CC16 CC17 CC20 CC27 CC41 CC84 CC92 CC93

Claims (7)

[Claims] 1. A crank pressure control mechanism in a variable displacement compressor capable of adjusting a tilt angle of a swash plate and adjusting a discharge capacity based on control of an internal pressure of a crank chamber. An inlet-side open / close valve that is provided in an air supply passage that connects the air supply passage and that can open and close the air supply passage by external control; and is provided in the air supply passage so as to be interposed between the inlet-side open / close valve and the crank chamber. A gas inflow adjustment mechanism that changes the gas passage amount over time in response to gas supply from the discharge pressure region by the opening operation of the inlet side on-off valve, and adjusts the gas inflow amount to the crank chamber with time. Pressure control mechanism for a variable displacement compressor equipped with 2. The gas inflow adjusting mechanism is configured to secure a large gas passage amount only for a predetermined time immediately after the opening of the inlet-side on-off valve, and to narrow the gas passage amount after the predetermined time has elapsed. 2. The method according to claim 1, wherein
5. A crank pressure control mechanism for a variable displacement compressor according to claim 1. 3. The gas inflow adjusting mechanism includes: a spool valve body as a movable wall provided reciprocally in a room; an introduction chamber and a pressure regulation chamber partitioned in the room by the spool valve body. An outlet passage that connects the introduction chamber and the crank chamber and that opens and closes in accordance with the reciprocation of the spool valve body; and a throttle that communicates the introduction chamber and the pressure regulation chamber; With the supply of gas from the discharge pressure region to the introduction chamber by the valve opening operation, the spool valve body moves forward from the original position to open the lead-out passage, and passes through the throttle after a predetermined time thereafter. The crank of the variable displacement compressor according to claim 1, wherein when the pressure of the introduction chamber and the pressure adjustment chamber is equalized, the spool valve element returns to the original position and closes the outlet passage. 4. Pressure control mechanism. 4. A spool valve element as a movable wall provided reciprocally between a forward position and a retreat position in a room, wherein the gas inflow adjusting mechanism moves the spool valve element to a forward position. A biasing spring biased toward the inlet, an introduction chamber partitioned in the room by the spool valve body and connected to the inlet-side on-off valve, and guided and partitioned in the room by the spool valve body. A pressure regulating chamber communicating with the crank chamber through a pressure passage, connecting the introduction chamber and the crank chamber, and closing the spool valve element when the spool valve element is at a forward position; An outlet passage that is sometimes opened, a first throttle formed inside or around the spool valve body and communicating the introduction chamber and the pressure regulation chamber, and the pressure regulation chamber and the crank chamber. Before communicating And a second aperture provided in the pressure introducing passage, claim 1 in which the gas passage of the second diaphragm is characterized in that is smaller than the gas throughput of the first aperture
Or a crank pressure control mechanism of the variable displacement compressor according to 2. 5. The capacity according to claim 1, wherein the inlet-side on-off valve and the gas inflow adjusting mechanism are integrated to constitute one valve mechanism. Crank pressure control mechanism for variable compressor. 6. A vent opening / closing valve provided in a bleed passage connecting the crank chamber of the compressor and a suction pressure region and capable of opening / closing the bleed passage by external control. The valve and the inlet-side on-off valve,
The crank pressure control mechanism for a variable displacement compressor according to any one of claims 1 to 5, wherein the control is interlocked so that one of the valves is in an open state and the other is in a closed state. 7. The valve according to claim 6, wherein the inlet-side on-off valve, the withdrawal-side on-off valve, and the gas inflow adjusting mechanism are integrated to constitute one valve mechanism. Crank pressure control mechanism for variable displacement compressor.