EP1489304A1 - Displacement control mechanism of a variable displacement type compressor - Google Patents

Abstract

A displacement control mechanism controls displacement of a variabledisplacement type compressor that forms a refrigerant circulation circuit for an airconditioning apparatus. The displacement is decreased as a pressure in a crankchamber rises while being increased as the pressure in the crank chamber falls.The displacement control mechanism includes a bleed passage, a supplypassage, a first control valve and a second control valve. The second controlvalve includes a back pressure chamber, a valve chamber, a valve body, a springand a second valve portion. The second valve portion is provided with the backsurface of the valve body. The second valve portion closes an opening of anintroduction passage in the back pressure chamber when the first valve portionmaximizes the opening of the bleed passage.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a displacement control mechanism forcontrolling the displacement of a variable displacement type compressor thatforms a part of refrigerant circulation circuit of an air conditioning apparatus andthe displacement of which is decreased as a pressure in a crank chamber of thecompressor rises while being increased as the pressure in the crank chamberfalls.

There is known a displacement control mechanism shown in FIG. 7, inwhich the pressure in acrank chamber 153 or crank pressure Pc is adjusted bytechnique, what is called, a supply control.

Namely, in a variable displacement type swash plate compressor(hereinafter the compressor), thecrank chamber 153 communicates with asuction chamber 155 via ableed passage 154. Adischarge chamber 151 of thecompressor communicates with thecrank chamber 153 via asupply passage 152in which acontrol valve 156 is arranged. The amount of refrigerant gasintroduced into thecrank chamber 153 via thesupply passage 152 is controlled by adjusting the opening of thecontrol valve 156, and the crank pressure Pc isdetermined in accordance with the relation between the amounts of refrigerantgas introduced into and bleeding from thecrank chamber 153.

Afixed throttle 158 is arranged in thebleed passage 154 so that therefrigerant gas bleeds slowly from thecrank chamber 153 to thesuction chamber155. Thus, even when the amount of the refrigerant gas supplied from thedischarge chamber 151 to thecrank chamber 153 via thesupply passage 152 issmall, the crank pressure Pc is steadily increased. Therefore, when thecontrolvalve 156 increases the opening of thesupply passage 152, the crank pressurePc is rapidly increased. Consequently, appropriate response in decreasing thecompressor displacement is obtained.

Also, an amount of gas that blows from a cylinder bore 157 to thecrankchamber 153 and that leaks to thesuction chamber 155 via thebleed passage154, and an amount of the refrigerant gas that moves from thedischargechamber 151 to thesuction chamber 155 via thecrank chamber 153 asmentioned above, so-called, a kind of internal leakage, are reduced as much aspossible by the provision of thefixed throttle 158. Consequently, decrease inefficiency of the compressor caused by providing the displacement controlmechanism is prevented.

However, the arrangement of the fixedthrottle 158 on thebleed passage154 makes decrease in a pressure in thecrank chamber 153 slow. In other words,response in increasing the displacement of the compressor deteriorates.Especially, when the compressor is started, the crank pressure Pc tends to beexcessively increased since the liquid refrigerant accumulated in thecrankchamber 153 evaporates and the fixedthrottle 158 hampers smooth flow of therefrigerant gas from thecrank chamber 153. Therefore, even when thecontrolvalve 156 closes thesupply passage 152 so as to increase the displacement ofthe compressor in response to the requirement for cooling shortly after thecompressor is started, it takes time before the displacement of the compressor isactually increased, and starting performance of an air conditioning apparatusdeteriorates.

To solve such problems, it is proposed to provide asecond control valve161 for controlling the opening of thebleed passage 154 in addition to the controlvalve (first control valve) 156, as shown in FIG. 8. Please see JapaneseUnexamined Patent Publication No. 2002-21721 (pages 7 to 10, and Figures 1, 4and 5).

Specifically, in the proposed structure, a region K is provided in thesupplypassage 152 downstream of the position of the first control valve 156 (i.e. theposition of the valve opening adjustment) and upstream of afixed throttle 169, as shown in FIG. 8. Thesecond control valve 161 is a spool type valve that includesaspool 162 and aback pressure chamber 166 into which the pressure in theregion K is introduced. Avalve chamber 167 of thesecond control valve 161forms a part of thebleed passage 154 and communicates with thesuctionchamber 155. Thevalve chamber 167 also communicates with thecrankchamber 153 via avalve hole 168 that forms the upstream portion of thebleedpassage 154.

Thespool 162 is movably fitted in aspool supporting recess 164 that isformed in a compressor housing. Thespool 162 includes avalve portion 162athat is located in thevalve chamber 167 and aback surface 162b that is locatedin theback pressure chamber 166. Thespool 162 or thevalve portion 162a ispositioned by various forces applied thereto such as urging force of the pressurein theback pressure chamber 166 acting on theback surface 162b in thedirection to close the valve, urging force of aspring 165 acting in the valveopening direction and force of the crank pressure Pc that is applied in the valveopening direction.

When thefirst control valve 156 closes thesupply passage 152, apressure PdK in theback pressure chamber 166 of thesecond control valve 161becomes substantially the same as the crank pressure Pc and, therefore, thespool 162 of thesecond control valve 161 is positioned by thespring 165 where the opening of thevalve hole 168 is maximum. When thebleed passage 154 iswidely opened by thesecond control valve 161, flowing of the refrigerant from thecrank chamber 153 to thesuction chamber 155 is prompted. Therefore, when thefirst control valve 156 closes thesupply passage 152 so as to increase thedisplacement of the compressor shortly after the compressor is started, thedisplacement of the compressor is immediately increased, so that the startingperformance of the air conditioning apparatus is improved.

A spring having a small urging force is utilized as theurging spring 165.Thus, when thesupply passage 152 is opened even slightly by thefirst controlvalve 156 and the pressure PdK in the region K exceeds the crank pressure Pc,thespool 162 moves against theurging spring 165, and thevalve portion 162aminimizes the opening of thevalve hole 168 that is not zero. Therefore, when thevalve hole 168 is thus set at the minimum opening that is not zero, thesecondcontrol valve 161 functions similarly to the above-describedfixed throttle 158shown in FIG. 7, and the decrease in the efficiency of the compressor caused byproviding the displacement control mechanism is prevented.

However, thefirst control valve 156 leaks the refrigerant gas byperformance deterioration due to aged deterioration even in a state that thefirstcontrol valve 156 closes thesupply passage 152. Thus, the pressure Pdk in theback pressure chamber 166 of thesecond control valve 161 rises due to the refrigerant gas which leaks from thefirst control valve 156, and thesecondcontrol valve 161 may inappropriately set the opening of thebleed passage 154at the minimum opening. Therefore, the refrigerant gas is flowed slowly from thecrank chamber 153 to thesuction chamber 155 through thebleed passage 154,and the starting performance of the air conditioning apparatus is insufficient.

To solve such a problem, a spring having large urging force is adopted astheurging spring 165 so that thespool 162 or thevalve portion 162a maintainsthe maximum opening of thevalve hole 168 even if the pressure Pdk in thebackpressure chamber 166 is raised somewhat.

However, when the spring having large urging force is adopted as theurging spring 165, thesecond control valve 161 cannot set thebleed passage154 at the minimum opening unless thefirst control valve 156 widely opens thesupply passage 152 and the pressure Pdk in theback pressure chamber 166 isgreatly raised. Therefore, in a state that thefirst control valve 156 opens thesupply passage 152, such period that thesecond control valve 161 sets thebleedpassage 154 at an opening other than the minimum opening, in other words, suchperiod that thesecond control valve 161 cannot function similarly to thefixedthrottle 158 increases, and decrease in the efficiency of the compressor iscaused.

SUMMARY OF THE INVENTION

The present invention is directed to a displacement control mechanismthat prevents a second control valve from inappropriately operating even whenperformance of a first control valve deteriorates while preventing decrease inefficiency of a variable displacement type compressor.

According to the present invention, a displacement control mechanismcontrols displacement of a variable displacement type compressor that forms arefrigerant circulation circuit for an air conditioning apparatus. The displacementis decreased as a pressure in a crank chamber rises while being increased as thepressure in the crank chamber falls. The refrigerant circulation circuit has asuction pressure region and a discharge pressure region. The displacementcontrol mechanism includes a bleed passage, a supply passage, a first controlvalve and a second control valve. The bleed passage interconnects the crankchamber with the suction pressure region. The supply passage interconnects thecrank chamber with the discharge pressure region. The first control valve islocated on the supply passage for adjusting an opening of the supply passage ata position of valve opening adjustment. The second control valve includes a backpressure chamber, a valve chamber, a valve body, a spring and a second valveportion. A pressure on a downstream side of the position of valve openingadjustment of the first control valve in the supply passage is introduced to the back pressure chamber through an introduction passage. The valve chamberforms a part of the bleed passage. The valve body has a first valve portionlocated in the valve chamber and a back surface located in the back pressurechamber. The first valve portion decreases an opening of the bleed passage as apressure in the back pressure chamber which is applied to the back surface rises.The spring urges the valve body so that the first valve portion increases theopening of the bleed passage. The second valve portion is provided with the backsurface of the valve body. The second valve portion closes an opening of theintroduction passage in the back pressure chamber when the first valve portionmaximizes the opening of the bleed passage.

Other aspects and advantages of the invention will become apparentfrom the following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are setforth with particularity in the appended claims. The invention, together withobjects and advantages thereof, may best be understood by reference to thefollowing description of the presently preferred embodiments together with theaccompanying drawings in which:

FIG. 1 is a longitudinal sectional view illustrating a variable displacementtype swash plate compressor;

FIG. 2 is a longitudinal sectional view illustrating a first control valve;

FIG. 3 is a partially enlarged view illustrating a second control valve andits vicinity of FIG. 1;

FIG. 4 is a longitudinal sectional view illustrating operation of the secondcontrol valve;

FIG. 5 is an enlarged longitudinal sectional view illustrating anothersecond control valve and its vicinity;

FIG. 6 is an enlarged longitudinal sectional view illustrating yet anothersecond control valve and its vicinity;

FIG. 7 is a schematic view illustrating a prior art displacement controlmechanism; and

FIG. 8 is a longitudinal sectional view illustrating a prior art second control valve and its vicinity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe a preferred embodiment of the presentinvention. In the preferred embodiment, the present invention is applied to avariable displacement type swash plate compressor (hereinafter the compressor)that is used in a vehicle air conditioning apparatus for compressing refrigerantgas.

Referring to FIG. 1, the compressor includes acylinder block 11, afronthousing 12, avalve plate assembly 13 and arear housing 14. In FIG. 1, the leftside and the right side respectively correspond to the front side and the rear sideof the compressor. Thefront housing 12 is fixedly joined to the front end of thecylinder block 11, and therear housing 14 is fixedly joined to the rear end of thecylinder block 11 via thevalve plate assembly 13. Thecylinder block 11, thefronthousing 12 and therear housing 14 cooperate to form a compressor housing.

Acrank chamber 15 is defined by thecylinder block 11 and thefronthousing 12. Adrive shaft 16 is rotatably supported in thecrank chamber 15. Alugplate 17 is fixed to thedrive shaft 16 so as to be integrally rotated with the driveshaft.

The front end of thedrive shaft 16 is operatively connected to a vehicleengine E as an external drive source via a power transmission mechanism PTThe power transmission mechanism PT may be a clutch mechanism (e.g. anelectromagnetic clutch) that selectively transmits and blocks driving poweraccording to electric control from an external device, or a continuous transmissiontype clutchless mechanism (e.g. the combination of a belt and a pulley) thatdispenses with the above clutch mechanism. In the present preferredembodiment, the clutchless type power transmission mechanism PT is utilized.

Aswash plate 18 as a cam plate is accommodated in thecrank chamber15. Theswash plate 18 is slidably and inclinably supported by thedrive shaft 16.Ahinge mechanism 19 is interposed between thelug plate 17 and theswashplate 18. Thus, a hinge connection between thelug plate 17 and theswash plate18 via thehinge mechanism 19 and the support of theswash plate 18 by thedriveshaft 16 allow theswash plate 18 to rotate synchronously with thelug plate 17and thedrive shaft 16 as well as to incline with respect to an axis of thedrive shaft16 in accordance with the sliding movement of theswash plate 18 in the axialdirection of thedrive shaft 16.

A plurality of cylinder bores 11a is formed in thecylinder block 11extending axially through thecylinder block 11 and is arranged around thedrive shaft 16. In FIG. 1, only one cylinder bore is shown. A single-head piston 20 isaccommodated in each of the cylinder bores 11a for reciprocation therein. Thefront and rear openings of the cylinder bores 11a are respectively closed by thepistons 20 and thevalve plate assembly 13. Compression chambers are definedin the cylinder bores 11a, and the volumes of the compression chambers arevaried in accordance with the reciprocating movement of thepistons 20. Each ofthepistons 20 is engaged with the periphery of theswash plate 18 via a pair ofshoes 10, so that the rotation of theswash plate 18 with the drive shaft 6 isconverted into linear reciprocating movement of thepistons 20.

Asuction chamber 21 and adischarge chamber 22 are defined betweenthevalve plate assembly 13 and therear housing 14. Thesuction chamber 21 islocated in the middle region of therear housing 14 and is surrounded by thedischarge chamber 22. Asuction port 23 and asuction valve 24 are formed in thevalve plate assembly 13 for each of the cylinder bores 11 a. Thesuction valve 24is adapted to open and close thesuction port 23. Adischarge port 25 and adischarge valve 26 are also formed in thevalve plate assembly 13 for each of thecylinder bores 11a. Thesuction chamber 21 communicates with each of thecylinder bores 11 a via the correspondingsuction port 23, and each of the cylinderbores 11a communicates with thedischarge chamber 22 via thecorrespondingdischarge port 25.

As each of thepistons 20 moves from the top dead center toward thebottom dead center, the refrigerant gas is drawn into the corresponding cylinderbore 11 a via the associatedsuction port 23 pushing away the associatedsuctionvalve 24. As thepistons 20 move from the bottom dead center toward the topdead center, the refrigerant gas introduced into the cylinder bore 11a iscompressed to a predetermined pressure and is discharged into thedischargechamber 22 via the associateddischarge port 25 pushing away thedischargevalve 26.

An inclination angle of theswash pate 18, which is defined as an anglemade between theswash plate 18 and a plane perpendicular to the axis of thedrive shaft 16 is varied in accordance with the pressure in the crank chamber 5(or a crank pressure Pc) between the minimum inclination angle as indicated by asolid line in FIG. 1 and the maximum inclination angle as indicated by a two-dotchain line in FIG. 1.

A displacement control mechanism for controlling the crank pressure Pcwhich has bearing on control of the inclination angle of theswash plate 18includes afirst bleed passage 27, asecond bleed passage 28, asupply passage29, a first control valve CV1 and a second control valve CV2.

The first andsecond bleed passages 27 and 28 interconnect thecrank chamber 15 with thesuction chamber 21 as a suction pressure (Ps) region. Thesecond bleed passage 28 has a fixedthrottle 28a and extends through thecylinder block 11 and thevalve plate assembly 13. Thesupply passage 29interconnects thedischarge chamber 22 as a discharge pressure (Pd) region withthecrank chamber 15. The first control valve CV1 is arranged in thesupplypassage 29 for adjusting the opening of thesupply passage 29. It is noted thatthefirst bleed passage 27 and thesupply passage 29 are partially sharedtherebetween as will be later described.

The first control valve CV1 adjusts the opening of thesupply passage 29while the second control valve CV2 adjusts the opening of thesupply passage 29and thefirst bleed passage 27. By so doing, the balance between [an] the amountof high-pressure discharge gas introduced from thedischarge chamber 22 intothe crank chamber 5 via thesupply passage 29 and [an] the amount of therefrigerant gas flowing from the crank chamber 5 into thesuction chamber 21 viathe first andsecond bleed passages 27 and 28 is controlled, and the crankpressure Pc is determined, accordingly. Pressure difference between the crankpressure Pc and the internal pressure in the cylinder bores 11 a via thepistons 20is changed in accordance with the variation of the crank pressure Pc, and theinclination angle of theswash plate 12 is varied, accordingly. Consequently, thestroke ofpistons 20, that is, the displacement of the compressor is adjusted.

For example, when the first control valve CV1 reduces the opening of thesupply passage 29 and the crank pressure Pc is decreased, the inclination angleof theswash plate 18 is increased, and the displacement of the compressor isincreased. On the other hand, when the first control valve CV1 increases theopening of thesupply passage 29 and the crank pressure Pc is increased, theinclination angle of theswash plate 18 is decreased, and the displacement of thecompressor is decreased. It is note that the minimum displacement of thecompressor is set at zero or about zero

A refrigerant circulation circuit (or a refrigeration cycle) of the vehicle airconditioning apparatus includes the above-described compressor and an externalrefrigerant circuit 30. The externalrefrigerant circuit 30 includes acondenser 31,anexpansion valve 32 and anevaporator 33. Acirculation pipe 35 for therefrigerant is provided on the downstream side of the externalrefrigerant circuit30, interconnecting the outlet of theevaporator 33 with thesuction chamber 21 ofthe compressor. Acirculation pipe 36 for the refrigerant is provided on theupstream side of the externalrefrigerant circuit 30, interconnecting thedischargechamber 22 of the compressor with the inlet of thecondenser 31. Thecompressor draws and compresses therein the refrigerant gas which isintroduced from the downstream side of the externalrefrigerant circuit 30 into thesuction chamber 21, and then discharges the compressed refrigerant gas to thedischarge chamber 22 which interconnects with the upstream side of the externalrefrigerant circuit 30.

As shown in FIG. 2, the first control valve CV1 includes a valve portion inthe upper half thereof as seen on the drawing of FIG. 2 and asolenoid portion 60in the lower half. The valve portion adjusts the opening (a degree of throttle) ofthesupply passage 29 that interconnects thedischarge chamber 22 with thecrank chamber 15. Thesolenoid portion 60 is an actuator for controlling theoperation of avalve rod 40 arranged in the control valve CV1 in response to acontrol signal from an external device. Thevalve rod 40 is a rod-like member[and] which includes apartition portion 41 at the top of the rod, aconnectionportion 42, avalve body portion 43 at the middle and aguide rod portion 44 at thebase.

Avalve housing 45 for the first control valve CV1 includes avalve bodyhousing 45a [in] forming its upper part and anactuator housing 45b [in] forming itslower part. Avalve accommodating chamber 46, acommunication passage 47and apressure sensing chamber 48 are defined in thevalve body housing 45a.Thevalve rod 40 is arranged in thevalve accommodating chamber 46 and thecommunication passage 47 for axial movement, that is, movement in the verticaldirection [of] as seen in FIG. 2. Thepartition portion 41 of thevalve rod 40 isinserted [into] through thecommunication passage 47 thereby to shut off thecommunication between the pressure sensing chamber 48 [from] and thecommunication passage 47.

Ports 51 and 52 are formed through the peripheral wall of thevalve bodyhousing 45a. Theport 51 communicates with thevalve accommodating chamber46, and theport 52 communicates with thecommunication passage 47,respectively. Thevalve accommodating chamber 46 communicates with thedischarge chamber 22 of the compressor via theport 51 and the upstream part ofthesupply passage 29, or apassage 84. Thecommunication passage 47communicates with thecrank chamber 15 of the compressor via theport 52, thedownstream part of thesupply passage 29 or apassage 83, the second controlvalve CV2 and apassage 75. Thesupply passage 29 includes thepassage 84,theport 51, thevalve accommodating chamber 46, thecommunication passage47, theport 52, thepassage 83, the second control valve CV2 and thepassage75.

Thevalve body portion 43 of thevalve rod 40 is located in thevalveaccommodating chamber 46. Avalve seat 53 is formed at the stepped portionlocated between thevalve accommodating chamber 46 and thecommunicationpassage 47, and thecommunication passage 47 functions as a valve hole. Whenthevalve rod 40 moves upward from the position of FIG. 2, where thecommunication passage 47 (or the supply passage 29) is opened, to a positionwhere thevalve body portion 43 contacts thevalve seat 53, the communication passage 47 (the supply passage 29) is closed.

A bellows 50 is accommodated in thepressure sensing chamber 48. Theupper end of thebellows 50 is fixed to thevalve housing 45. The top of thepartition portion 41 of thevalve rod 40 is fitted into the lower end of thebellows 50.Thepressure sensing chamber 48 is divided into two chambers by thebellows 50,namely afirst pressure chamber 54 formed inside the bellows and asecondpressure chamber 55 formed outside the bellows50.

As shown in FIG. 1, athrottle 36a is formed on thecirculation pipe 36between thedischarge chamber 22 and the externalrefrigerant circuit 30.Referring back to FIG. 2, thefirst pressure chamber 54 communicates via a firstpressure introducing passage 37 with thedischarge chamber 22 at a firstpressure monitoring point P1 that is located on the upstream side of thethrottle36a. Thesecond pressure chamber 55 communicates via a secondpressureintroducing passage 38 with thecirculation pipe 36 at a second pressuremonitoring point P2 that is located on the downstream side of thethrottle 36a.Thus, a monitored pressure PdH at the first pressure monitoring point P1 isintroduced into thefirst pressure chamber 54, and a monitored pressure PdL atthe second pressure monitoring point P2 is introduced into thesecond pressurechamber 55.

The lower end of thebellows 50 vertically moves in accordance with thepressure difference (PdH - PdL) between the pressures on opposite sides of thethrottle 36a. Thus, the position of the valve rod 40 (or the valve body portion 43) isdetermined by varying the pressure difference. The pressure difference (PdH -PdL) between the pressures on opposite sides of thethrottle 36a variesdepending on the refrigerant flow rate in the refrigerant circulation circuit. Forexample, when the refrigerant flow rate is increased, the pressure difference(PdH - PdL) is increased. On the other hand, when the refrigerant flow rate isdecreased, the pressure difference (PdH - PdL) is decreased. The bellows 50operates thevalve body portion 43 such that the displacement of the compressoris changed so as to cancel the variation of the pressure difference (PdH - PdL)

Thesolenoid portion 60 of the first control valve CV1 has in the middle oftheactuator housing 45b anaccommodating cylinder 61 that has a cylindricalshape with a bottom. A fixedcore 62 of a column shape is fittingly fixed to theupper opening of theaccommodating cylinder 61. Thus, asolenoid chamber 63 isdefined in the lower portion of theaccommodating cylinder 61.

Amovable core 64 is axially movably accommodated in thesolenoidchamber 63. Aguide hole 65 extends through the center of the fixedcore 62 inthe axial direction of thevalve rod 40. Theguide rod portion 44 of thevalve rod 40is arranged in theguide hole 65 so as to move in the axial direction of thevalve rod 40. Theguide rod portion 44 is fittingly fixed to themovable core 64 of thesolenoid chamber 63. Thus, themovable core 64 and thevalve rod 40 verticallymove together.

Ahelical spring 66 is accommodated between the fixedcore 62 and themovable core 64 in thesolenoid chamber 63 for urging thevalve rod 40 in suchdirection that causes thevalve body portion 43 to move away from thevalve seat53.

Acoil 67 is wound around the outer periphery of theaccommodatingcylinder 61 over a range covering the fixedcore 62 and themovable core 64.Driving signal is transmitted from a drivingcircuit 68a to thecoil 67, based on thecommand from acontrol device 68 in accordance with air conditioning load. Withsuch driving signal transmitted to thecoil 67, electromagnetic force (orelectromagnetic attraction) is generated between the fixedcore 62 and themovable core 64, the magnitude of which electromagnetic force is determined byamount of electric power supplied to thecoil 67. The electromagnetic force istransmitted to the valve rod 40 (or the valve body portion 43) through themovablecore 64. Controlling energization of thecoil 67 is performed by adjusting thevoltage applied to thecoil 67, and duty cycle control is utilized in the presentpreferred embodiment.

Thesolenoid portion 60 of the first control valve CV1 varies theelectromagnetic force for application to thevalve body portion 43 in accordancewith the amount of the electric power supplied from an external device. In the firstcontrol valve CV1, therefore, control target (or set pressure difference) for thepressure difference (PdH - PdL) between the pressures on opposite sides of thethrottle 36a, that is, a standard for positioning thevalve body portion 43 by thebellows 50 is changed by varying the electromagnetic force for application to thevalve body portion 43. In other words, the first control valve CV1 is formed tointernally autonomously position the valve rod 40 (or the valve body portion 43) inaccordance with the variation of the pressure difference (PdH - PdL) between thefirst and second pressure monitoring points P1 and P2 such that the set pressuredifference determined by the amount of the electric power supplied to thecoil 67is maintained.

The set pressure difference of the first control valve CV1 is varied byadjusting the amount of the electric power supplied to thecoil 67 from theexternal device. For example, when the duty ratio that is commanded from thecontrol device 68 to thedriving circuit 68a is increased, electromagnetic urgingforce of thesolenoid portion 60 is increased, and the set pressure difference ofthe first control valve CV1 is increased, accordingly. With the set pressuredifference of the first control valve CV1 thus increased, the displacement of thecompressor is increased. On the other hand, when the duty ratio that is commanded from thecontrol device 68 to thedriving circuit 68a is decreased,electromagnetic urging force of thesolenoid portion 60 is decreased, and the setpressure difference of the first control valve CV1 is decreased. When the setpressure difference of the first control valve CV1 is decreased, the displacementof the compressor is decreased.

It is noted that the compressor of the present preferred embodiment iswhat is called a clutchless type compressor, and thedrive shaft 16 is continuouslyrotated while the engine E is driven. When the air conditioning is not needed,however, supplying the electric power to thecoil 67 is stopped by switching off theair conditioning apparatus, that is, the duty ratio is zero, and the swash plate isset at the minimum inclination angle. Thus, the displacement of the compressor isset at the minimum displacement, namely, zero or about zero by only onemeaning. Therefore, even when thedrive shaft 16 is rotated, supplying therefrigerant from the compressor to the externalrefrigerant circuit 30 issubstantially stopped, and the refrigeration cycle is stopped.

As shown in FIGS. 1, 3 and 4, anaccommodation hole 70 is formed in arear end surface of the rear housing 4 for accommodating therein the secondcontrol valve CV2. Avalve housing 71 is fittingly fixed to theaccommodation hole70. Thevalve housing 71 includes acylindrical portion 72 whose outsidediameter is smaller than that of theaccommodation hole 70 and afitting portion 73 that continues from thecylindrical portion 72 on the opening side ofaccommodation hole 70 and is fittingly fixed to theaccommodation hole 70. Thevalve housing 71 is pushed into theaccommodation hole 70 such that the distalend of thecylindrical portion 72 contacts aninner bottom surface 70a of theaccommodation hole 70.

Thecylindrical portion 72, theend surface 73a of thefitting portion 73 thatfaces the inside of thecylindrical portion 72, and theinner bottom surface 70a oftheaccommodation hole 70 define anaccommodation chamber 74 in thecylindrical portion 72. Acommunication space 79 is formed between the outerperipheral surface of thecylindrical portion 72 and the inner peripheral surface oftheaccommodation hole 70. Thecommunication space 79 communicates withthe crank chamber15 via apassage 75 arranged on the side of thecrankchamber 15.

In theaccommodation chamber 74, aspool 76 that serves as a valvebody is movably accommodated in the direction in which thecylindrical portion 72extends. Thespool 76 is slidable between the position at which thespool 76contacts theinner bottom surface 70a of theaccommodation hole 70 and theposition at which thespool 76 contacts theend surface 73a of thefitting portion73, and has a cylindrical shape with a bottom on the side of theend surface 73aof thefitting portion 73.

Thespool 76 divides theaccommodation chamber 74 into front and rearspaces, which are blocked by the contact between the outer peripheral surface ofthespool 76 and the inner peripheral surface of theaccommodation chamber 74.The blocked front and rear spaces are respectively defined as avalve chamber77 on the side of theinner bottom surface 70a of theaccommodation hole 70 andaback pressure chamber 78 on the side of theend surface 73a of thefittingportion 73. In thespool 76, the end surface on the opening side of thespool 76arranged in thevalve chamber 77 is defined as anend valve portion 76a and theouter bottom surface of thespool 76 arranged in theback pressure chamber 78 isdefined as aback surface 80. Thespool 76 contacts theinner bottom surface 70aof theaccommodation hole 70 with theend valve portion 76a.

Thecylindrical portion 72 of thevalve housing 71 forms a first gap-hole72a and a second gap-hole 72b therethrough. The first gap-hole 72acommunicates with the inside and the outside of thecylindrical portion 72. Thesecond gap-hole 72b is located nearer thefitting portion 73 than the first gap-hole72a, and communicates with the inside and the outside of thecylindrical portion72.

The first gap-hole 72a communicates with thevalve chamber 77 and thecommunication space 79 in a state that thespool 76 is in contact with theend surface 73a of thefitting portion 73 as shown in FIG. 4. The first gap-hole 72a isblocked by a region on the side of thevalve chamber 77 in the outer peripheralsurface of thespool 76, that is, a firstperipheral valve portion 76b in a state thatthespool 76 is in contact with theinner bottom surface 70a of theaccommodationhole 70. Thus, the communication between thevalve chamber 77 and thecommunication space 79 is blocked as shown in FIG. 3.

The second gap-hole 72b communicates with theback pressure chamber78 and thecommunication space 79 in a state that thespool 76 is in contact withtheinner bottom surface 70a of theaccommodation hole 70 as shown in FIG. 3.The second gap-hole 72b is blocked by a region on the side of theback pressurechamber 78 in the outer peripheral surface of thespool 76, that is, a secondperipheral valve portion 76c in a state that thespool 76 is in contact with theendsurface 73a of thefitting portion 73. Thus, the communication between thebackpressure chamber 78 and thecommunication space 79 is blocked as shown inFIG. 4.

Thevalve chamber 77 communicates with thesuction chamber 21 via apassage 81 formed in therear housing 14. Thepassage 81 is opened moreinwardly than an annular region or a sealed region in which theend valve portion76a of thespool 76 contacts theinner bottom surface 70a of theaccommodationhole 70.

Therefore, the communication of the inside and the outside of thevalvechamber 77 relative to the sealed region of theend valve portion 76a are blockedin a state that thespool 76 is in contact with theinner bottom surface 70a of theaccommodation hole 70. In addition, the first gap-hole 72a is blocked by the firstperipheral valve portion 76b. Thus, the communication between thepassage 81and the communication space 79 (or the passage 75) is blocked as shown in FIG.3. The communication of the inside and the outside of thevalve chamber 77relative to the sealed region of theend valve portion 76a are opened in a statethat thespool 76 is in contact with theend surface 73a of thefitting portion 73. Inaddition, the first gap-hole 72a is opened by the firstperipheral valve portion 76bof thespool 76. Thus, the communication between thepassage 81 and thecommunication space 79 (or the passage 75) is opened as shown in FIG. 4.

In the present preferred embodiment, thepassage 81, thevalve chamber77, the first gap-hole 72a, thecommunication space 79, and thepassage 75which is shared with thesupply passage 29 form thefirst bleed passage 27.Therefore, in thespool 76, theend valve portion 76a and the firstperipheral valveportion 76b which open and close the communication between thepassage 81and thecommunication space 79 are regarded as a first valve portion foradjusting the opening of thefirst bleed passage 27.

Theback pressure chamber 78 communicates with theport 52 of the firstcontrol valve CV1 via apassage 82 formed in thefitting portion 73 of thevalvehousing 71 and apassage 83 that forms thesupply passage 29. Thepassage 82is opened at anopening 82a formed at the center of theend surface 73a of thefitting portion 73 in theback pressure chamber 78. Therefore, the refrigerant gasflowed from thedischarge chamber 22 is introduced into theback pressurechamber 78 via apassage 84, the first control valve CV1 which is in a openingstate, thepassages 83 and 82. That is, a pressure Pdk on the downstream side ofthe position of the valve opening adjustment of the first control valve CV1, or thevalve seat portion 53, in thesupply passage 29 is applied to theback pressurechamber 78 via thepassage 82 that serves as an introduction passage.

The refrigerant gas introduced from thedischarge chamber 22 to theback pressure chamber 78 is flowed into thecrank chamber 15 via the secondgap-hole 72b, thecommunication space 79 and thepassage 75. That is, in thesecond control valve CV2, thepassage 82, theback pressure chamber 78, thesecond gap-hole 72b and thecommunication space 79 form thesupply passage29.

Thespool 76 is urged toward theinner bottom surface 70a of theaccommodation hole 70, that is, in such direction that theend valve portion 76aand the firstperipheral valve portion 76b of the first valve portion decrease the opening of thefirst bleed passage 27 by the force of the pressure Pdk in thebackpressure chamber 78 applied to theback surface 80. On the other hand, thespool 76 is urged toward theend surface 73a of thefitting portion 73, that is, insuch direction that theend valve portion 76a and the firstperipheral valve portion76b of the first valve portion increase the opening of thefirst bleed passage 27 bythe force of the suction pressure Ps which is applied to theend valve portion 76aand thevalve chamber 77.

Ahelical spring 85 is arranged in thespool 76 of thevalve chamber 77.Thespring 85 has a movable end and a fixed end on the opposite sides thereof.The movable end of thespring 85 is in contact with thespool 76 while the fixedend of thespring 85 is held and accommodated in anaccommodating groove 70bformed in theinner bottom surface 70a of theaccommodation hole 70. Thespring85 urges thespool 76 in such direction that theend valve portion 76a and the firstperipheral valve portion 76b of the first valve portion increase the opening of thefirst bleed passage 27.

That is, thespool 76 is positioned by the balance between the urgingforce in the valve closing direction of theend valve portion 76a and the firstperipheral valve portion 76b of the first valve portion caused by the force of thepressure Pdk in theback pressure chamber 78, the urging force in the valveopening direction of theend valve portion 76a and the firstperipheral valve portion 76b of the first valve portion caused by the force of the pressure Ps in thevalve chamber 77, and the urging force in the valve opening direction of theendvalve portion 76a and the firstperipheral valve portion 76b of the first valveportion caused by the force of the urgingforce 85.

Meanwhile, in the present embodiment, theback surface 80 of thespool76 forms thereon asecond valve portion 86 for opening and closing theopening82a of thepassage 82 in theback pressure chamber 78 in accordance with theposition of thespool 76. Thesecond valve portion 86 protrudes from the center oftheback surface 80 of thespool 76 so as to face theopening 82a of thepassage82. Thesecond valve portion 86 is shaped into a circular shape in a transversesection, and is tapered so that the distal end of thesecond valve portion 86becomes a minor diameter. The taper shape of thesecond valve portion 86 issuch shaped that the diameter of the proximal end thereof becomes larger thanthat of theopening 82a of thepassage 82 and the diameter of the distal endthereof becomes smaller than that of theopening 82a. Thesecond valve portion86 is made of resilient material such as synthetic rubber or synthetic resin.

As shown in FIG. 4, the movement of thespool 76 toward thefittingportion 73 is regulated by the contact of thesecond valve portion 86 with theendsurface 73a of thefitting portion 73. In such a state that the movement of thespool 76 is regulated by the contact with theend surface 73a of thefitting portion 73, that is, in a state that thefirst bleed passage 27 is fully opened by theendvalve portion 76a and the firstperipheral valve portion 76b of the first valveportion, the distal end of thesecond valve portion 86 enters the inside of thepassage 82 via theopening 82a while ataper surface 86a of thesecond valveportion 86 contacts at an annular region on the rim of theopening 82a of thepassage 82. Thus, the communication between theback pressure chamber 78and thepassage 82 is blocked. In addition, in such a state, the second gap-hole72b is blocked by the secondperipheral valve portion 76c of thespool 76. Thus,the communication between thepassage 83 and the communication space 79 (orthe passage 75) is blocked.

In contrast, as shown in FIG. 3, in a state that the movement of thespool76 is regulated by the contact with theinner bottom surface 70a of theaccommodation hole 70, that is, in a state that thefirst bleed passage 27 is fullyclosed by theend valve portion 76a and the firstperipheral valve portion 76b ofthe first valve portion, thesecond valve portion 86 is distanced from theendsurface 73a of thefitting portion 73 and theopening 82a of thepassage 82 isopened. In addition, in such a state, the second gap-hole 72b is opened by thesecondperipheral valve portion 76c of thespool 76. Thus, thepassage 83 andthe communication space 79 (or the passage 75) are interconnected with eachother.

The operating characteristics of the control valve CV2 will be nowdescribed. As shown in FIG. 3, in a state that theend valve portion 76a and thefirstperipheral valve portion 76b of the first valve portion of thespool 76 of thesecond control valve CV2 have decreased the opening of thefirst bleed passage27 from the fully opening state of thefirst bleed passage 27, thesecond valveportion 86 of thespool 76 opens the division of theback pressure chamber 78and thepassage 82 and the pressure Pdk in thepassage 82 is applied to theback pressure chamber 78. Therefore, in the second control valve CV2, if thecross sectional area of theback pressure chamber 78 that is perpendicular to theaxial direction of thespool 76 is represented as "SA", and the urging force of thespring 85 is represented as "f', condition expression (1) for increasing theopening of thefirst bleed passage 27 in the second control valve CV2 isexpressed as follows:(Pdk-Ps) • SA<f

As shown in FIG 4, in the second control valve CV2, in a state that thatthefirst bleed passage 27 is fully opened by theend valve portion 76a and thefirstperipheral valve portion 76b of the first valve portion of thespool 76, thesecond valve portion 86 of thespool 76 blocks the communication between theback pressure chamber 78 and thepassage 82. Thus, the pressure Pdk in thepassage 82 is not applied to theback pressure chamber 78. Therefore, the pressure Pdk in thepassage 82 is applied only to thesecond valve portion 86 oftheback surface 80 of thespool 76. If the cross sectional area at theopening 82aof thepassage 82 that is perpendicular to the axial direction of thepassage 82 isrepresented as "SB" (< "SA"), condition expression for decreasing the opening ofthefirst bleed passage 27 in the second control valve CV2 in a state that thefirstbleed passage 27 is fully opened is expressed as follows:(Pdk-Ps) • SB>f

When time has passed for more than a predetermined time after thevehicle engine E was stopped, the pressure in the refrigerant circulation circuit isequalized at a relatively small value, and thus the pressure Pdk and the suctionpressure Ps equalized to each other. Since the condition expression (1) iseffective and the condition expression (2) is not effective, as shown in FIG. 4, thespool 76 moves by thespring 85 and thesecond valve portion 86 blocks thesupply passage 29. At the same time, theend valve portion 76a and the firstperipheral valve portion 76b of the first valve portion fully opens thefirst bleedpassage 27.

In a conventional compressor for a vehicle air-conditioning apparatus,any liquid refrigerant existing on the low pressure side of the externalrefrigerantcircuit 30 with the vehicle engine E kept at a stop for a long time flows into thecrank chamber 15 via thesuction chamber 21 due to the fluid communicationbetween thecrank chamber 15 and thesuction chamber 21 via the first andsecond bleed passages 27 and 28. Especially, when the temperature in theengine room where the compressor is located is lower than that in the vehicleinterior, a large amount of the liquid refrigerant flows into thecrank chamber 15via thesuction chamber 21 and is accumulated in thecrank chamber 15.

Therefore, when the vehicle engine E is started and the compressor isalso started thereby through the clutchless type power transmission mechanismPT, the liquid refrigerant evaporates under the influence of heat generated by thevehicle engine E and also of the stirring effect of theswash plate 18, with theresult that the crank pressure Pc tends to be increased regardless the opening ofthe first control valve CV1.

For example, when the vehicle engine E is started while the vehicleinterior is hot, thecontrol device 68 is operated in response to the demand froman occupant to command maximum duty ratio to thedrive circuit 68a, and the setpressure difference of the first control valve CV1 is set at the maximum value,accordingly, for performing cooling as required from the occupant. For thispurpose, the first control valve CV1 closes thesupply passage 29, and no highpressure refrigerant gas is supplied from thedischarge chamber 22 to thebackpressure chamber 78 of the second control valve CV2 and thecrank chamber 15. Therefore, even if evaporation of the liquid refrigerant occurs in thecrankchamber 15, the state wherein the pressure difference between the crankpressure Pc and the suction pressure Ps does not exceed the urging force f, thatis, the state wherein the condition expression (2) is not effective, continues.

Consequently, thespool 76 of the second control valve CV2 ismaintained by the urging force f of thespring 85 in such a state that theend valveportion 76a and the firstperipheral valve portion 76b of the first valve portion fullyopens thefirst bleed passage 27, and the liquid refrigerant in thecrank chamber15, as well as the refrigerant gas evaporated from part of the liquid refrigerant, areimmediately flowed into thesuction chamber 21 via the fully-openedfirst bleedpassage 27. Thus, the crank pressure Pc is maintained at a low value since thefirst control valve CV1 closes thesupply passage 29, and the compressorincreases the inclination angle of theswash plate 18 thereby to increase thedisplacement of the compressor to its maximum.

If the first control valve CV1 still closes thesupply passage 29 even afterthe liquid refrigerant is flowed out of thecrank chamber 15, thefirst bleedpassage 27 is fully opened by theend valve portion 76a and the firstperipheralvalve portion 76b of the first valve portion of the second control valve CV2 asdescribed above. Thus, even if the amount of blow-by gas from the cylinder bores11a to the crankchamber 15 is increased from the amount initially designed, the blow-by gas is immediately flowed into thesuction chamber 21 via the first andsecond bleed passages 27 and 28. Therefore, the crank pressure Pc ismaintained at substantially the same level as the suction pressure Ps, and themaximum inclination angle of theswash plate 18, that is, the maximumdisplacement operation (100% displacement operation) of the compressor ismaintained.

When the vehicle interior is cooled to a certain extent due to the abovemaximum displacement operation of the compressor, thecontrol device 68reduces the duty ratio that is commanded to thedriving circuit 68a from themaximum. Accordingly, the first control valve CV1 opens thesupply passage 29so that the pressure Pdk in thepassage 82 exceeds the suction pressure Ps inthevalve chamber 77. Thus, the condition expression (2) is satisfied, so that thespool 76 moves against the urging force f of thespring 85 in the direction toreduce the valve opening of theend valve portion 76a and the firstperipheralvalve portion 76b of the first valve portion from the fully-opened state as shown inFIG. 3.

In the second control valve CV2, in a state that theend valve portion 76aand the firstperipheral valve portion 76b of the first valve portion of thespool 76decreases the opening of thefirst bleed passage 27 from the fully-opened state,thesecond valve portion 86 of thespool 76 opens the division of theback pressure chamber 78 and thepassage 82. Therefore, condition expression (3) fordecreasing the opening of thefirst bleed passage 27 in the second control valveCV2 in a state that thefirst bleed passage 27 is opened but is not fully opened isexpressed as follows:(Pdk-Ps) • SA>fThe condition expression (3) is effective due to the relation "SA>SB" as long asthe urging force f of thespring 85 is fixed, even if the pressure difference "Pdk-Ps"between the pressure Pdk in thepassage 82 and the pressure Ps in thevalvechamber 77 is smaller than the minimum value that satisfies the conditionexpression (2). Therefore, thespool 76 which has been distanced from thefully-opened state of thefirst bleed passage 27 by the formation of the conditionexpression (2) is moved in the direction to reduce the opening of thefirst bleedpassage 27 without stopping on the way by the formation of the conditionexpression (3). Since the urging force of thespring 85 is relatively small, thespool76 which has been distanced from the fully-opened state of thefirst bleedpassage 27 is immediately moved to the closed state of thefirst bleed passage27.

Thus, the crank pressure Pc is immediately raised by opening thesupplypassage 29 of the first control valve CV1 and closing thefirst bleed passage 27 of the second control valve CV2. Consequently, the compressor decreases theinclination angle of theswash plate 18 thereby to decrease the displacement ofthe compressor.

An amount of the compressed refrigerant gas that leaks from thedischarge chamber 22 to the crankchamber 15 further to thesuction chamber 21is reduced to the amount of compressed refrigerant gas which leaks only throughthesecond bleed passage 28 by closing thefirst bleed passage 27 in the secondcontrol valve CV2, so that a decrease in the efficiency of the compressor isprevented. Furthermore, although the refrigerant circulation circuit in the presentpreferred embodiment is formed such that the refrigerant circulation stops byoperating the compressor at the minimum displacement (so called an offoperation of the clutchless compressor), the off operation of the compressor isensured by closing thefirst bleed passage 27 in the second control valve CV2.

The present embodiment provides the following advantageous effects.

(1) If the performance of the first control valve CV1 deteriorates due to itsaged deterioration, the first control valve CV1 leaks the refrigerant gas even whenthe first control valve CV1 is operated on the maximum duty ratio. When the firstcontrol valve CV1 leaks the refrigerant gas, the pressure Pdk in thepassage 82 israised and the spool is urged in the direction to reduce the opening of thefirst bleed passage 27 in accordance with the pressure Pdk.However, thespool 76 of the second control valve CV2 provides with thesecond valve portion 86 which blocks theopening 82a of thepassage 82 in theback pressure chamber 78 in a state that the second control valve CV2 fullyopens thefirst bleed passage 27. Therefore, in theback surface 80 of thespool76, referring to the condition expression (2), the pressure Pdk in thepassage 82is applied only to thesecond valve portion 86, but is not applied to thebacksurface 80 other than thesecond valve portion 86. Thus, in the first control valveCV1 in a state that thesupply passage 29 is blocked, even if leakage of therefrigerant gas which is caused by the performance deterioration of the firstcontrol valve CV1 generates, the fully-opened state of thefirst bleed passage 27is maintained even by the spring having small urging force f, such thatmechanical error of the second control valve CV2 is prevented. Consequently, themaximum inclination angle of theswash plate 18, that is, the maximumdisplacement operation (100% displacement operation) of the compressor ismaintained.If thespring 85 whose urging force is relatively small is adopted, thesecond control valve CV2 can set thefirst bleed passage 27 at the minimumopening without increasing the pressure Pdk in theback pressure chamber 78 bywidely opening thesupply passage 29 in the first control valve CV1. Therefore, in a state that the first control valve CV1 opens thesupply passage 29, the period inwhich the second control valve CV2 sets thefirst bleed passage 27 at theopening other than the closed state is not increased. Thus, decrease in theefficiency of the compressor is prevented.

(2) Thesecond valve portion 86 of the second control valve CV2 is shaped ina protruding shape and a taper shape so as to enter thepassage 82. Therefore,theopening 82a of thepassage 82 is closed by thesecond valve portion 86.

(3) Theback pressure chamber 78 of the second control valve CV2 and thepassage 82 for introducing the refrigerant gas from thedischarge chamber 22 totheback pressure chamber 78 form a part of thesupply passage 29. That is, in astate that the first control valve CV1 closes thesupply passage 29, thesecondvalve portion 86 of the second control valve CV2 closes thesupply passage 29on the downstream side of the first control valve CV1. Therefore, in this state,even if the refrigerant gas leaks by the performance deterioration of the firstcontrol valve CV1, the leaked refrigerant gas is not supplied into thecrankchamber 15. Thus, the maximum inclination angle of theswash plate 18, that is,the maximum displacement operation of the compressor is maintained.

(4) The second control valve CV2 opens and closes thesupply passage 29at a plurality of places. In the present preferred embodiment, the second control valve CV2 opens and closes thesupply passage 29 at two places of the secondperipheral valve portion 76c and thesecond valve portion 86. Therefore, thesecond control valve CV2 surely closes thesupply passage 29 thereby furthereffectively preventing the refrigerant gas that leaks from the first control valveCV1 from being supplied into thecrank chamber 15.

(5) Thesecond valve portion 86 is made of resilient material. Therefore, theopening 82a of thepassage 82 is surely closed by thesecond valve portion 86 inresponse to the resilient deformation of thesecond valve portion 86.

(6) The first valve portion of the second control valve CV2 opens and closesthefirst bleed passage 27 at a plurality of places. In the present preferredembodiment, the first valve portion of the second control valve CV2 opens andcloses thefirst bleed passage 27 at two places of theend valve portion 76a andthe firstperipheral valve portion 76b. Therefore, the second control valve CV2surely closes thefirst bleed passage 27 thereby further effectively preventing thedecrease in the efficiency of the compressor.

The present invention is not limited to the above-described embodiment,but is modified as follows.

In the above-preferred embodiment, the second control valve CV2 is arranged on thesupply passage 29. In an alternative embodiment to the aboveembodiment, as shown in FIG. 5, the second gap-hole 72b of the second controlvalve CV2 is eliminated and thepassage 83 directly communicates with thecrankchamber 15. In addition, abranch passage 90 is branched off thepassage 83 andcommunicates with thepassage 82 of the second control valve CV2. In this case,thepassage 75 is exclusive for thefirst bleed passage 27.

In an alternative embodiment to the above embodiment, the aspect of FIG.5 is partially modified. The minimum opening of thefirst valve portion 76a and 76bis set to a value that is not zero by grooving thefirst valve portion 76a and 76b ofthe second control valve CV2 such that thefirst bleed passage 27 is continuouslyopened. Thesecond bleed passage 28 may be eliminated. In this case, thepassages of the displacement control mechanism are simply formed.

In an alternative embodiment to the above embodiment, the aspect of FIG.5 is partially modified. As shown in FIG. 6, positions at which thepassage 75 andthepassage 81 communicate with the second control valve CV2 are replaced byeach other. In addition, a fixedthrottle 83a is formed on thepassage 83. In thiscase, if thefirst bleed passage 27 is continuously opened by setting the minimumopening of thefirst valve portion 76a and 76b at a value that is not zero, andfurther if thesecond bleed passage 28 is eliminated, thesecond valve portion 86of the preferred embodiment of the present invention can be applied to the structure similar to the prior art control valve which is shown in FIG. 8.

In the above-described embodiments, thesecond valve portion 86 of thesecond control valve CV2 is shaped in a protruding shape on theback surface 80of thespool 76. In alternative embodiments to the above embodiments, thesecond valve portion 86 is eliminated from the above-described embodiments.Instead, theback surface 80 may be regarded as a flat second valve portion byadhering resilient coat such as rubber coat and resin coat on theback surface 80of thespool 76. In a technique other than adhering resilient coat on thebacksurface 80 of thespool 76 such that theback surface 80 of thespool 76 serves asa second valve portion, it is proposed that theback surface 80 and theendsurface 73a of thefitting portion 73 are polished in high accuracy.

In the above-described embodiments, the second control valve CV2opens and closes thesupply passage 29 at a plurality of places (at two places ofthe secondperipheral valve portion 76c and the second valve portion 86). Inalternative embodiments to the above embodiments, the second control valveCV2 opens and closes thesupply passage 29 at a singular place, or at thesecond valve portion 86.

In the above-described embodiments, thefirst valve portion 76a and 76bof the second control valve CV2 opens and closes thefirst bleed passage 27 at a plurality of places (at two places of theend valve portion 76a and the firstperipheral valve portion 76b). In alternative embodiments to the aboveembodiments, the first valve portion of the second control valve CV2 opens andcloses thefirst bleed passage 27 at a singular place such as theend valve portion76a or the firstperipheral valve portion 76b.

In the above-described embodiments, the spool 76 (a tubular body) isadopted as a valve body of the second control valve CV2. In alternativeembodiments to the above embodiments, a spherical body may be adopted asthe valve body. In this case, a hemispherical part of the spherical body on the sideof thevalve chamber 77 forms the first valve portion while the rest hemisphericalpart of the spherical body on the side of theback pressure chamber 78 forms theback surface and the second valve portion.

In the above-described embodiments, thespring 85 is a coil spring. In thepresent invention, however, the spring is not limited to the coil spring. Other typeof springs such as plate spring and torsion bar may be adopted.

In the above-described embodiments, the first control valve CV1 variesthe displacement of the compressor such that the pressure difference (PdH-PdL)between the pressures on opposite sides of thethrottle 36a is maintained at apredetermined target value (set pressure difference). Also, in the first control valve CV1, the set pressure difference is varied by external electric control. Inalternative embodiments to the above embodiments, the first control valve CV1 isoperated such that the pressure in the suction pressure region is maintained at apredetermined target value (set suction pressure) while the set suction pressureis varied by external electric control. In this case, the first control valve CV1 isso-called a control valve of variable set suction pressure type.

In the above-described embodiments, pressure sensing mechanism suchas thepressure sensing chamber 48 and thebellows 50 may be eliminated fromthe first control valve CV1, and the first control valve CV1 may be varied to asimple electromagnetic valve.

In the above-described embodiments, thesolenoid 60 may be eliminatedfrom the first control valve CV1, and the first control valve CV1 may be varied to asimple pressure sensing valve which does not provide with external controlfunction.

The present invention may be applied to a displacement control devicefor a variable displacement type compressor of a wobble type.

Therefore, the present examples and embodiments are to be consideredas illustrative and not restrictive and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.
   A displacement control mechanism controls displacement of a variabledisplacement type compressor that forms a refrigerant circulation circuit for an airconditioning apparatus. The displacement is decreased as a pressure in a crankchamber rises while being increased as the pressure in the crank chamber falls.The displacement control mechanism includes a bleed passage, a supplypassage, a first control valve and a second control valve. The second controlvalve includes a back pressure chamber, a valve chamber, a valve body, a springand a second valve portion. The second valve portion is provided with the backsurface of the valve body. The second valve portion closes an opening of anintroduction passage in the back pressure chamber when the first valve portionmaximizes the opening of the bleed passage.

Claims (7)

1. A displacement control mechanism for controlling displacement of avariable displacement type compressor that forms a refrigerant circulation circuitfor an air conditioning apparatus, the displacement being decreased as apressure in a crank chamber rises while being increased as the pressure in thecrank chamber falls, the refrigerant circulation circuit having a suction pressureregion and a discharge pressure region, the displacement control mechanismcomprising a bleed passage interconnecting the crank chamber with the suctionpressure region, a supply passage interconnecting the crank chamber with thedischarge pressure region, a first control valve located on the supply passage foradjusting an opening of the supply passage at a position of valve openingadjustment, and a second control valve including a back pressure chamber towhich a pressure on a downstream side of the position of valve openingadjustment of the first control valve in the supply passage is introduced throughan introduction passage, a valve chamber forming a part of the bleed passage, avalve body having a first valve portion located in the valve chamber and a backsurface located in the back pressure chamber, the first valve portion decreasingan opening of the bleed passage as a pressure in the back pressure chamberwhich is applied to the back surface rises, and a spring for urging the valve bodyso that the first valve portion increases the opening of the bleed passage,characterized in that a second valve portion is provided with the back surface of the valve body, andin that the second valve portion closes an opening of theintroduction passage in the back pressure chamber when the first valve portionmaximizes the opening of the bleed passage.
2. The displacement control mechanism according to claim 1, wherein thesecond valve portion is so shaped as to protrude and taper from the back surfacetoward the opening of the introduction passage, the second valve portion closingthe opening of the introduction passage by entering the introduction passage.
3. The displacement control mechanism according to claim 1 or 2, whereinthe introduction passage and the back pressure chamber form a part of thesupply passage.
4. The displacement control mechanism according to claim 3, wherein thesecond control valve opens and closes the supply passage at a plurality ofplaces.
5. The displacement control mechanism according to any one of claims 1through 3, wherein the second valve portion is made of resilient material.
6. The displacement control mechanism according to any one of claims 1through 5, wherein the first valve portion of the second control valve opens and closes the bleed passage at a plurality of places.
7. The displacement control mechanism according to any one of claims 1through 6, wherein the variable displacement type compressor is of a clutchlesstype, the variable displacement type compressor of clutchless type is such avariable displacement type compressor that continues to rotate a drive shaft in astate that a minimum inclination angle of a cam plate is maintained such that arefrigerant is not substantially flowed into an external refrigerant circuit while arefrigeration cycle stops.

Images