FR2821127A1 - Control valve for variable displacement compressor for automotive vehicle air-conditioning system, is in equilibrium between belows force and force of electromagnetic solenoid, and diverse pressure emanating from exhaust chamber - Google Patents

Abstract

The valve is in equilibrium between the bellows force and the force of the electromagnetic solenoid (13), and diverse pressures emanating from the exhaust chamber (42), from the engine casing (33) and the suction chamber (41), pressing on the control valve (1). The equilibrium is obtained by the action of a first rod pushed by the bellows and which pushes a valve body in the direction for opening the valve orifice, and by the action of a second rod pushed by the piston and which pushes the body of the valve in the opposed direction for closing the valve orifice.

Description

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VARIABLE EQUIPE D'UNE TELLE SOUPAPE. CONTROL VALVE AND DISPLACEMENT COMPRESSOR

VARIABLE EQUIPPED WITH SUCH A VALVE.

BACKGROUND OF THE INVENTION
The present invention relates to a variable displacement compressor for use in an air conditioning device for a vehicle. More particularly, the present invention relates to a variable displacement compressor having a control valve which can operate practically only by the force of an electromagnetic solenoid and by the force of a bellows.

DESCRIPTION OF THE PRIOR ART
In a refrigeration circuit of an air conditioning device for a vehicle, a variable displacement compressor is often used, for example a compressor of the swash plate type or a compressor of the nutation plate type. In these compressors, the amplitude of the displacement depends on the length of the piston stroke, this length depending in turn on the angle of inclination of the swash plate or the nutation disc relative to the axis of a shaft . This angle in turn depends on the pressure of the refrigerant which is introduced into the compressor crankcase. Thus, the movement of these compressors can be controlled by adjusting the pressure of the crankcase. Generally, these compressors are equipped with a control valve which controls the amount of refrigerant introduction from a discharge chamber to the crankcase. The general structure of the control valve is as follows.

 A control valve mainly comprises a bellows chamber housing a bellows, a valve chamber housing a valve body, and a piston chamber housing a piston. The piston chamber is in fluid communication with a suction chamber of the compressor so that the bellows stretches or contracts in response to the pressure of the suction chamber. When the bellows stretches, it excites the valve body in one direction via a rod. When an electromagnetic solenoid surrounding the piston is activated, the piston energizes the valve body to the opposite direction via another rod. Thanks to a balance between the strength of the

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 bellows and the strength of the electromagnet, the critical point of opening and closing of the valve is given.

 When the valve is open, refrigerant is then introduced from the discharge chamber to the crankcase via the valve chamber to increase the pressure in the crankcase.

As the crankcase pressure increases, the tilt angle of the swash plate decreases, and therefore the piston stroke and the displacement of the compressor decrease.

 Conversely, when the valve is closed, the introduction of the refrigerant from the discharge chamber to the crankcase via the valve chamber is stopped. Because the coolant in the crankcase then spontaneously flows through various parts towards lower pressure parts, the crankcase pressure decreases and therefore the tilt angle of the swash plate increases. As a result, the piston stroke and the displacement of the compressor increase.

 By adjusting the amplitude of the electric current flowing through the electromagnetic solenoid, the opening / closing point of the valve can be moved at will, and therefore, the movement of the compressor can also be controlled at will.

 In a control valve explained above, it is not preferable that the pressure of the discharge chamber or the pressure of the crankcase or the pressure of the suction chamber directly affects the movement of the valve body. These pressures vary at all times and cause the opening / closing point of the valve body to fluctuate. The design of the valve body only takes into account the balance of the bellows force and the force of the electromagnetic solenoid.

 A control valve described in Japanese patent publication 2000-18420 aims to solve this problem. By using the structure of the control valve described in this reference, it is supposed to be possible to reduce the direct effects of the pressure of the exhaust chamber and the pressure of the crankcase on the point of opening / closing of the valve. However, according to an analysis of this structure by the author of the present invention, although it is possible to reduce the effect of the pressure of the exhaust chamber, the net effect of the pressure of the crankcase n is still not

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 neutralized. When the valve is closed, a residual pressure net of the crankcase pressure affects the movement of the valve body and the solenoid rod, and due to the fluctuation of the crankcase pressure, the movement control d The opening / closing of the valve body is hampered.

SUMMARY OF THE INVENTION
A first object of the invention is to provide a control valve whose valve body does not undergo the direct effects of the pressure of the discharge chamber, the pressure of the crankcase and the pressure of the chamber d suction.

 A second object of the present invention is to provide a variable displacement compressor equipped with this control valve.

 A control valve according to the present invention has a first rod which is excited by a bellows towards the opening direction of the valve body, a second rod which is excited by an electromagnetic solenoid towards the closing direction of the valve body, and a passage which puts in fluid communication a bellows chamber and a piston chamber. The first stem has a neck portion at the end of which the valve body is integrally formed. The cross-sectional areas of effective pressure reception in the upper part and in the lower part of the neck part are designed to have substantially equal value. Consequently, the upward and downward force acting on this cross-sectional area for receiving the upper effective pressure and this cross-sectional area for receiving the lower effective pressure due to the refrigerant gas introduced into a space around the part neck of the first rod from the discharge chamber of the compressor, cancel each other. Thus, the direct effect on the movement of the valve body due to the fluctuation of the pressure of the discharge chamber can be eliminated.

 Projecting inside a valve chamber into which the crankcase pressure is introduced, a flat-bottom end of the second rod, the overall shape of which is a straight cylinder, comes into contact with the upper surface of the body valve. Because the second rod has a straight cylindrical shape, it does not have

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 cross sectional area receiving substantial effective pressure over which pressure from the crankcase can exert a net force in the valve chamber. Consequently, the pressure of the motor housing which fills the space formed by the wall of the valve chamber and the cylindrical surface of the second rod cannot exert substantial force on the second rod in its sliding direction. Thus, the direct effect on the movement of the valve body due to the fluctuation of the crankcase pressure can also be eliminated.

 The passage which places the bellows chamber and the piston chamber in fluid communication brings the pressure from the pressure chamber introduced into the bellows chamber further into the piston chamber. The force due to the pressure in the bellows chamber and the force due to the pressure in the piston chamber are confronted to each other via the first rod and the valve body and the second rod. Since the pressures in the bellows chamber and the piston chamber balance each other by means of the passage, the upward force acting on the first rod and the downward force acting on the second rod cancel each other out. 'one another. Thus, the direct effect on the movement of the valve body due to the fluctuation of the pressure of the suction chamber can also be eliminated.

 Thus, all the effects of the pressure of the discharge chamber, the pressure of the crankcase and the pressure of the suction chamber on the movement of the valve body can be eliminated as far as possible.

 Other objects, characteristics and advantages of this invention will be understood from the following description of preferred embodiments with reference to the drawings in which: BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a cross-sectional view of a compressor variable displacement equipped with a control valve according to a first embodiment of the present invention; Figure 2 is an enlarged cross-sectional view of the control valve of Figure 1; Figure 3 is an enlarged cross-sectional view of the neck portion of the first rod of Figure 2; and

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 Figure 4 is a cross-sectional view of a control valve according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In Figure 1, a variable displacement compressor 100 of the swash plate type equipped with a control valve 1 according to a first embodiment of the present invention is shown. The compressor 100 comprises a front housing 22, a casing 21 formed integrally with a cylinder block 26, and a rear housing 24. These parts are fixed to each other by means of bolts 25. A drive shaft 27 is provided for so as to pass through the center of the front housing 22 and of the cylinder block 26. The drive shaft 27 is rotatably supported by the front housing 22 and the cylinder block 26 via bearings 50 and 51. In the bloccylindres 26, a plurality of cylinder bores 38 are provided equianglely about an axis of the drive shaft 27. In each of the cylinder bores 38, a piston 37 is slidably mounted. The pistons 37 are capable of reciprocating movements along the direction parallel to the axis of the drive shaft 27.

 At the drive shaft 27, a rotor 34 is fixed so as to rotate together with it. The rotor 34 has an arm 34a at the end of which is formed a pin 35 directed in a direction perpendicular to the axis of the drive shaft 27 (perpendicular to the sheet). The front housing 22 and the housing 21 cooperatively define a motor housing 33. Inside the motor housing 33 is housed a swash plate 36 having a penetration hole 36c at its central part, through which penetrates the drive shaft 27. On a surface of the front housing side of the swash plate 36, an arm 36a at the end of which an oblong hole 36h is provided is formed. The spindle 35 of the rotor 34 engages the oblong hole 36h of the swash plate 36 so as to allow a change in the angle of inclination of the swash plate 36 relative to the axis of the drive shaft 27. The circumferential part of the swash plate 36 has the shape of a ring and is slidably connected to the tail parts of the pistons 37 via pairs of shoes 53.

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 Around a cylindrical part 22a of the front housing 22, a pulley 28 is rotatably attached via a bearing 54. In the front housing 22, an electromagnet 32 is fixed, and occupies a hollow space in the pulley 28. At the end of the drive shaft 27 is fixed a hub 55. A frame 31 which is attracted towards the pulley 28 when the electromagnet 32 is energized, is fixed to the hub 55 via an elastic element 29. When the electromagnet 32 does not is not excited, an air space is formed between the frame 31 and the pulley 28, which corresponds to a disconnected state of the pulley 28 and the frame 31.

 The pulley 28 is always rotated by an external drive source (not shown) via a belt. If the electromagnet 32 is energized, the armature 31 is attracted towards the pulley 28, the latter connecting and rotating together. The driving force of the external drive source is then transmitted to the drive shaft 27 via the pulley 28, the armature 31, the elastic element 29 and the hub 55.

 When the drive shaft 27 is driven by the external power source, it drives with it the rotor 34 in rotation about the axis of the drive shaft 27. The swash plate 36 is also rotated by the rotor 34 via the connection mechanism comprising the arm 34a, the pin 35 of the rotor 34, the oblong hole 36h and the arm 36a of the swash plate 36. During the rotation of the swash plate 36, its circumferential part exhibits a nutation movement . Only one component of this movement in the axial direction is transferred to the pistons 37 via the sliding shoes 53. Consequently, the pistons 37 are driven in reciprocating motion inside each cylinder bore 38.

 The reciprocating movement of the piston 37 can be divided into suction stroke and evacuation stroke. During the suction stroke, the refrigerant from an external refrigeration circuit (not shown) is drawn into the compression chamber 56 which is defined by the rear face of the piston 37, the cylinder bore 28, and a valve plate 23, via a suction chamber 41 and a suction hole 43 which is provided in the valve plate 23. During the discharge stroke, the refrigerant is compressed inside the compression 56 and discharged to the refrigeration circuit

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 outside via the evacuation hole 44 which is provided in the valve plate 23 and an evacuation chamber 42.

 The control valve 1 according to the first embodiment of the present invention is fixed to the rear housing 24 by means of a bolt 57. A passage 47 which penetrates in the axial direction through the cylinder block 26 and the rear housing 24 is planned. The passage 47 is in fluid communication with a passage 1b which is provided in the control valve 1. The motor housing 33 and the interior of the control valve 1 are in fluid communication with one another via the passage 47 and passage lb. In the rear housing 24, another passage 46 is also provided. The passage 46 is in fluid communication with a passage 1a which is provided in the control valve 1. The discharge chamber 42 and the interior of the control valve 1 are in fluid communication with each other via the passage 46 and passage la. In addition, a passage 48 is provided in the rear housing 24. In addition, several holes 49 are bored on the surface of the lower part of the control valve 1. The suction chamber 41 and the bellows chamber of the valve control 1 are in fluid communication with each other via the passage 48 and the holes 49.

 In Figure 2, the detailed structure of the control valve 1 is shown. The control valve 1 comprises an electromagnet 14 and a casing 2.

 The electromagnet 14 comprises an electromagnetic solenoid 13, a piston 12, a stator 11 and a second rod 10. The piston 12 is housed in a piston chamber 16 which is delimited by an inner surface of the electromagnetic solenoid 13, and can slide in the ascending and descending directions. Under the piston 12 is a stator 11 which is fixed to the electromagnetic solenoid 13. A distance 16a is provided between a lateral side surface of the stator 11 and the interior surface of the piston chamber 16. In the stator 11, a through hole vertical 1 la is provided, in which the second rod 10 is slidably mounted. The upper end of the second rod 10 is in contact with the bottom of the piston 12.

 In the casing 2, a valve chamber 9 and a bellows chamber 17 are provided. A vertical through hole 7 is drilled in the casing 2, from the valve chamber 9 through the

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 bellows 17 and a passage lb perpendicular to the axis of the casing 2 is provided for putting the motor casing 33 and the valve chamber 9 into fluid communication. In addition, in the casing 2, another passage perpendicular to the axis of the casing 2 is provided for putting the evacuation chamber 42 and the through hole in fluid communication 7. In the casing 2, holes 49 surrounding the bellows chamber 17 are provided for putting the suction chamber 41 in fluid communication and the bellows chamber 17.

 In the bellows chamber 17, a bellows 3 is housed. The bottom of the bellows 3 is fixed to a guide element 4. The bellows 3 together with the guide 4 are excited in an upward direction by a spring 5.

 In the through hole 7, a first rod 6 is slidably mounted. At the upper end of the first rod 6 is integrally formed a valve body 19. Under the valve body 19, a neck portion 6b is formed in the upper part of the first rod 6 to have a diameter narrower than the diameter of the main part 6a of the lower part of the first rod 6. The cylindrical space around the neck part 6b is defined as a valve hole 8. The valve hole 8 is in fluid communication with the passage there. The lower end of the first rod 6 is in contact with the upper end of the bellows 3.

The upper surface of the valve body 19 is in contact with the lower end of the second rod 10. Thus, the bellows 3 excites both the first rod 6, the valve body 19 and the second rod 10 in an upward direction when it stretches. Conversely, the piston 12 excites both the second rod 10, the valve body 19 and the first rod 6 in a downward direction when the electromagnetic solenoid is excited. Consequently, when the stretching force of the bellows 3 exceeds the force of the piston 12, the valve body 19 moves in an upward direction, and the valve hole 8 is thus opened. In other words, the refrigerant can flow from passage la to passage 1 b. When an introduction of refrigerant from the discharge chamber 42 into the crankcase 33 begins, the pressure of the crankcase begins to increase, and the amplitude of movement of the compressor will decrease. Conversely, when the force of the piston 12 exceeds the stretching force of the bellows 3, the body of

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 valve 19 is moved down, and the valve hole 8 is thus closed. In other words, the flow of refrigerant from passage 1a to passage 1b is inhibited. The refrigerant begins to flow from the crankcase 33 to the lower pressure portions, the crankcase pressure begins to decrease, and the displacement range of the compressor will increase.

 By adjusting the amplitude of the electric current exciting the electromagnetic solenoid 13, the critical opening / closing transition point of the valve body 19 and consequently the amplitude of the displacement of the compressor can be controlled.

 In Figure 3, the first feature of the invention is shown. The pressure of the evacuation chamber is introduced via the passage 1a towards the valve hole 8 around the neck portion 6b of the first rod 6. The pressure of the evacuation chamber exerts forces on the cross-sectional areas receiving the effective pressure 8a and 6c which are located at the upper part and the lower part of the neck part 6b respectively. In the present invention, since the through hole 7 is formed as a straight hole, the cross-sectional areas for receiving the effective pressure 8a and 6c are substantially identical. Consequently, due to the fact that the forces acting on these cross-sectional areas of receiving effective pressure in opposite directions cancel each other out, the pressure of the discharge chamber does not exert a net force on the first rod 6. Thus, in this way, the direct effect on the valve body 19 from the pressure of the discharge chamber can be eliminated.

 Referring again to Figure 2, the second feature of the present invention can be seen from the figure. The second rod 10, the flat lower end of which projects into the valve chamber 9, has a straight cylindrical shape.

The diameter of the second rod 10 and the diameter of the valve body 19 differ somewhat. As a result, the cross-sectional area of receiving the effective pressure over which the crankcase pressure introduced into the valve chamber 9 can exert a net force is reduced. The pressure of the engine casing therefore exerts no net force on the second rod 10. Thus, in this way, the direct effect

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 pressure from the crankcase on the second rod 10 can also be eliminated.

 The third feature of the present invention is as follows. In the casing 2, a passage 15 is further provided in order to put the gap 16a in the piston chamber 16 and the bellows chamber 17 in fluid communication. Thanks to the function of this passage 15, the piston chamber 16 and the bellows chamber 17 are both filled with refrigerant at the same pressure, that is to say the pressure of the suction chamber. And according to the present invention, the cross-sectional areas of the main body 6a of the first rod 6 and of the second rod 10 are designed to have the same value.

The refrigerant introduced into the piston chamber 16 exerts a downward force on the second rod 10 via the upper part of the second rod 10. The refrigerant introduced into the bellows chamber 17 exerts an ascending force on the first rod 6 via the part of bottom of the first rod 6. Because the cross-sectional areas of the rods 6, and 10 on which the forces mentioned above act are identical, these forces cancel each other out. Thus, the direct effect of the pressure of the suction chamber on the first rod 6, the valve body 19 and the second rod 10 can also be eliminated.

 Thus, a variable displacement compressor 100 using the control valve 1 described so far, during the opening / closing operation to control the amplitude of the displacement, does not undergo the influences of all the variations in the pressure of the exhaust chamber, crankcase pressure and suction chamber pressure.

 In Figure 4, the second embodiment of the present invention is shown. In this embodiment, the first rod 6 and the valve body 19 as well as the second rod 10 are all formed integrally.

 Although the explanation of the present invention has been given in the case of a swash plate type compressor, the control valve according to the present invention can also be used with other types of compressors, for example the compressor of the nutation tray type. Those skilled in the art will understand that variations and modifications can be made without departing from the scope of the invention.

Claims (10)

1. Control valve (1) for a variable displacement compressor comprising: an electromagnetic solenoid (13); a piston (12) housed inside a piston chamber (16) which is defined in said electromagnetic solenoid (13); a stator (11) housed inside said piston chamber (16); a second rod (10) slidably mounted in a through hole (11a) which is drilled vertically in said stator (11); a housing (2); a bellows chamber (17) provided inside said casing (2); a bellows (3) whose lower end is fixed to the bottom of

 said bellows chamber (17) via a guide (4) and a spring (5); a valve chamber (9) provided in said housing (2); a valve body (19) housed in said valve chamber (9); a passage (lb) for introducing pressure from the crankcase of the compressor to said valve chamber (9); a through hole (7) reamed in said housing (2) from said valve chamber (9) through said bellows chamber (17); a first rod (6) slidably mounted in said through hole (7) having a neck portion (6b); a valve hole (8) defined by an inner surface of said through hole (7) and a surface of said neck portion (6b) of said first rod (6); a passage (la) for introducing pressure from the discharge chamber of said compressor to said valve hole (8); characterized in that: a passage (15) placing said bellows chamber (17) and said piston chamber (16) in fluid communication is further provided in said casing (2).  2. The control valve of claim 1, further characterized in that said valve body (19) is integrally formed with said first rod (6).  3. Control valve according to claim 1, further characterized in that cross-sectional areas for receiving the effective pressure (8a) and (6c) located at the top and <Desc / Clms Page number 12>  of the lower part of said neck part (6b) are substantially identical.  4. The control valve of claim 1, further characterized in that the lower end of said second rod (10) projects into said valve chamber (9), and said second rod (10) has a straight cylindrical shape and a flat bottom end.  5. Control valve according to claim 1, further characterized in that cross-sectional areas of said first rod (6) and said second rod (10) are identical.  6. Variable displacement compressor of the swash plate type equipped with said control valve (1) according to claim 1.  7. Variable displacement compressor of the nutation plate type equipped with said control valve (1) of claim 1.  8. The control valve of claim 1, further characterized in that said first rod (6) and said valve body (19) as well as said second rod (10) are integrally formed.  9. A variable displacement compressor of the swash plate type equipped with said control valve (1) according to claim 8.  10. Variable displacement compressor of the nutation plate type equipped with said control valve (1) according to claim 8.