Single-headed piston for swash plate type compressor wherein head portion has a curved surface at axial end

Information

  • Patent Grant
  • 6575080
  • Patent Number
    6,575,080
  • Date Filed
    Friday, September 22, 2000
    24 years ago
  • Date Issued
    Tuesday, June 10, 2003
    21 years ago
Abstract
A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor, characterized in that; the outer circumferential surface of the head portion includes a cylindrical surface and a curved surface which is formed adjacent to at least one of opposite axial ends of the cylindrical surface, so as to smoothly extend from at least one circumferential part of the cylindrical surface, the curved surface being formed such that a radial distance between a centerline of the cylindrical surface and the curved surface gradually decreases in an axial direction of the cylindrical surface from the corresponding axial end of the cylindrical surface toward the corresponding axial end of the piston, and such that a radius of curvature of a cross sectional shape of the curved surface taken in a plane which includes the centerline of the cylindrical surface is larger than a diameter of the inner circumferential surface of the cylinder bore.
Description




This application is based on Japanese Patent Application No. 11-270355 filed Sep. 24, 1999, the contents of which are incorporated hereinto by reference.




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates in general to a method of producing a body member for a piston for a awash plate type compressor, and more particularly to a method of producing, by die-casting, such a body member having a hollow cylindrical head portion.




2. Discussion of the Related Art




A swash plate type compressor is adapted to compress a gas by a plurality of pistons which are reciprocated by a rotary movement of a swash plate. In general, the piston includes a head portion slidably fitted in a cylinder bore formed in a cylinder block of the compressor, and an engaging portion which sidably engages the swash plate. For reducing the weight of the piston, it has been proposed to form the piston with a hollow cylindrical head section. As one example of the method of producing such a piston, the assignee of the present invention proposed in JP-A-11-152239 a method of producing a blank for the piston, comprising the steps of preparing a body member including a hollow head section which is closed at one of its opposite ends and is open at the other end, and an engaging section which is formed integrally with the head section; and fixing a closing member prepared separately from the body member, to the body member so as to close the open end of the head section. While the closing member may be produced by any method, the body member is preferably produced by die-casting.




SUMMARY OF THE INVENTION




The present invention was made in the light of the background art described above. It is an object of the present invention to provide a single-headed piston for a swash plate type compressor, which has a reduced operating noise.




The object indicated above may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depend from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.




(1) A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor, characterized in that: the outer circumferential surface of the head portion includes a cylindrical surface and a curved surface which is formed adjacent to at least one of opposite axial ends of the cylindrical surface, so as to smoothly extend from at least one circumferential part of the cylindrical surface, the curved surface being formed such that a radial distance between a centerline of the cylindrical surface and the curved surface gradually decreases in an axial direction of the cylindrical surface from the corresponding axial end of the cylindrical surface toward the corresponding axial end of the piston, and such that a radius of curvature of a cross sectional shape of the curved surface taken in a plane which includes the centerline of the cylindrical surface is larger than a diameter of the inner circumferential surface of the cylinder bore.




The curved surface formed adjacent to at least one of axially opposite ends of the cylindrical surface of the head portion of the single-headed piston is effective to reduce the noise generated by the awash plate type compressor during its operation. The presence of the curved surface permits the head portion of the piston to smoothly slide on the inner circumferential surface of the cylinder bore.




(2) A single-headed piston according to the above mode (1), the curved surface is formed at at least one of an axial end of the cylindrical surface nearer to the engaging portion so as to extend from a first circumferential part of the cylindrical surface which is nearer to an axis of rotation of the swash plate, and an axial end of the cylindrical surface remote from the engaging portion so as to extend from a second circumferential part of the cylindrical surface which is more distant from the axis of rotation of the swash plate than the first circumferential part.




The above-indicated first and second circumferential parts of the cylindrical surface of the head portion of the piston generally suffer from a particularly large contacting surface pressure when the head portion of the piston contacts the inner circumferential surface of the cylinder bore during operation of the swash plate type compressor. By forming the curved surfaces in these circumferential parts, the piston can be smoothly reciprocated within the cylinder bore.




(3) A single-headed piston according to the above mode (2), wherein the curved surface is formed at the axial end of the cylindrical surface which is remote from the engaging portion and extends over an entire circumference of the cylindrical surface.




It is confirmed that the curved surface formed at the axial end of the head portion of the piston which is remote from the engaging portion is particularly advantageous. In general, the axial end face of the head portion remote from the engaging portion has a simple circular configuration. Since the cylindrical surface and the circular end face intersect each other so as to define a simple circle, it is easy to form the curved surface which extends over the entire circumference of the cylindrical surface of the head portion at the axial end which is remote from the engaging portion.




(4) A single-headed piston according to the above mode (2) or (3), wherein the curved surface is formed at one of opposite axial ends of the head portion which is nearer to the engaging portion and extends over an entire circumference of the axial end of the head portion.




Where the single-headed piston has a hollow cylindrical head portion, the axial end of the outer circumferential surface of the head portion which is nearer to the engaging portion has a simple circular shape. Accordingly, it is easy to form the curved surface which extends over the entire circumference of the outer circumferential surface at that axial end. However, the curved surface which extends over the entire circumference of the outer circumferential surface may be formed at that axial end portion whose configuration is not a simple circle.




(5) A single-headed piston according to any one of the above modes (1)-(4), wherein the cross sectional shape of the curved surface taken in the plane which includes the centerline of the cylindrical surface is an arc.




The cross sectional shape of the curved surface may be suitably determined, provided it has a smooth convex curve. For instance, the cross sectional shape of the curved surface may be a plurality of arcs having respective different radii of curvature, an ellipse, or a part of a hyperbola. If the cross sectional shape of the curved surface is a simple arc, the piston can be economically manufactured.




(6) A single-headed piston according to any one of the above modes (1)-(5), wherein a dimension r


1


between a surface of extension of the cylindrical surface and a straight line which is parallel to the surface of extension and which passes one of opposite ends of the curved surface which is remote from the cylindrical surface is not greater than 15 μm.




When the dimension r


1


is excessively large, the lubricant oil adhering to the inner circumferential surface of the cylinder bore is less likely to be introduced into a wedge-shaped gap which is formed between the inner circumferential surface of the cylinder bore and the outer circumferential surface of the head portion of the piston. In this case, the effect of the formed curved surface is reduced. In view of this, the above-indicated dimension r


1


is generally not greater than 15 μm, preferably not greater than 10 μm, and more preferably not greater than 5 μm. On the contrary, if the dimension r


1


is excessively small, the lubricant oil is less likely to be introduced into the wedge-shaped gap. Accordingly, the dimension r


1


is preferably not smaller than 1 μm, and more preferably not smaller than 2 μm.




(7) A single-headed piston according to any one of the above modes (1)-(6), wherein a quotient obtained by dividing a dimension r


1


between a surface of extension of the cylindrical surface and the straight line which is parallel to the surface of extension and which passes one of opposite ends of the curved surface which is remote from the cylindrical surface, by an axial dimension l


1


of the curved surface as measured in a direction parallel to the centerline of the cylindrical surface, is substantially equal to a quotient obtained by dividing a clearance r


2


between the outer circumferential surface of the head portion of the piston and the inner circumferential surface of the cylinder bore when the piston is fitted in the cylinder bore, by an axial dimension l


2


of the cylindrical surface, the clearance r


2


being a difference between a diameter of the outer circumferential surface of the head portion and a diameter of the inner circumferential surface of the cylinder bore.




When the piston is inclined within the cylinder bore due to a side force which is applied from the swash plate to the piston in a direction perpendicular to its centerline, an intermediate portion of the curved surface of the head portion as seen in a direction parallel to the centerline of the cylindrical surface contacts the inner circumferential surface of the cylinder bore. Accordingly, the present arrangement assures a smooth sliding of the outer circumferential surface of the head portion of the piston on the inner circumferential surface of the cylinder bore. The above-indicated axial dimension l


2


of the cylindrical surface is an axial distance between a boundary of the cylindrical surface and the curved surface which contacts the inner circumferential surface of the cylinder bore when the piston is inclined within the cylinder bore due to the above-indicated side force, and one of opposite axial ends of the cylindrical surface which is spaced from the above-indicated boundary in the diametric direction of the head portion of the piston and which is remote from the boundary in the axial direction of the head portion. The angle of inclination of the head portion of the piston is determined depending upon the axial dimension l


2


of the cylindrical surface of the head portion and the clearance between the outer circumferential surface of the head portion of the piston and the inner circumferential surface of the cylinder bore when the head portion of the piston is fitted in the cylinder bore. This clearance will be hereinafter referred to as a “fitting clearance”. Further, the angle of inclination of the head portion of the piston within the cylinder bore determined as described above determines the manner in which the curved surface contacts the inner circumferential surface of the cylinder bore. In essence, the axial dimension l


2


of the cylindrical surface is determined such that a wedge-shaped gap, which has a suitable size for facilitating introduction of the lubricant oil thereinto, is formed between the curved surface and the inner circumferential surface of the cylinder bore when the head portion of the piston is inclined in the cylinder bore.




As described above, the axial dimension l


2


of the cylindrical surface determines the angle of inclination of the head portion of the piston in the cylinder bore. Even when the cylindrical surface has an opening or openings or is not continuously formed between its opposite axial ends, the axial dimension l


2


of the cylindrical surface is an axial distance between the opposite axial ends.




(8) A single-headed piston according to any one of the above modes (1)-(7), wherein the axial dimension l


1


of the curved surface which is parallel to its centerline is not larger than ⅕ of the axial dimension l


2


of the cylindrical surface.




The axial dimension l


2


of the cylindrical surface decreases and the angle of inclination of the head portion within the cylinder bore increases with an increase of the axial dimension l


1


of the curved surface. Accordingly, it is not desirable that the axial dimension l


1


of the curved surface is too large. In view of this, the axial dimension l


1


of the curved surface is preferably not larger than ⅕, not larger than ⅛, or not larger than {fraction (1/15)} of the axial dimension l


2


of the cylindrical surface. It is not desirable, however, that the axial dimension l


1


of the curved surface is too small. In view of this, the axial dimension l


1


of the curved surface is preferably not smaller than {fraction (1/100)} of the axial dimension l


2


of the cylindrical surface.




(9) A single-headed piston according to any one of the above modes (1)-(8), wherein the outer circumferential surface of the head portion includes a tapered surface which smoothly extends from one of opposite ends of the curved surface which is remote from the cylindrical surface such that the tapered surface has a diameter which gradually and linearly reduces in an axial direction of the cylindrical surface from the curved surface toward the corresponding axial end of the piston, the tapered surface being formed such that a difference between a radius of its large-diameter end and a radius of its small-diameter end is selected within a range between 1 μm and 15 μm.




The tapered surface cooperates with the curved surface to define the wedge-shaped gap which facilitates introduction of the lubricant oil thereinto. Accordingly, the taper angle of the tapered surface is considerably smaller than that of a chamfer formed adjacent to the tapered surface. Accordingly, the tapered surface is formed such that the difference between the radius of the large-diameter end and the radius of the small-diameter end, in other words, a half of a difference between a diameter D


1


of the large-diameter end a diameter D


2


of the small-diameter end, is generally in a range between 1 μm and 15 μm, and more preferably in a range between 2 μm and 5 μm.




(10) A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor, characterized in that: the outer circumferential surface of the head portion includes a cylindrical surface, and a tapered surface which is formed adjacent to at least one of axially opposite ends of the cylindrical surface so as to extend from at least one circumferential part of the cylindrical surface, the tapered surface being formed such that a difference between a radius of its large-diameter end and a radius of its small-diameter end is selected within a range between 1 μm and 15 μm.




The tapered surface which is formed adjacent to at least one of opposite ends of the cylindrical surface of the head portion of the piston is effective to reduce the noise of the compressor during its operation since the head portion of the piston smoothly slides within the cylinder bore owing to the tapered surface. The reduction of the operating noise of the compressor is achieved even when an area of boundary between the tapered surface and the cylindrical surface is not substantially rounded, as well as when the area of boundary is substantially rounded. This is because an angle between the tapered surface and the cylindrical surface is considerably close to 180°. Further, the introduction of the lubricant oil into the wedge-shaped gap formed between the tapered surface and the inner circumferential surface of the cylinder bore prevents contact of a line of intersection of the tapered surface and the cylindrical surface, with the inner circumferential surface of the cylinder bore, or reduces the contacting surface pressure between the tapered surface and the cylindrical surface.




(11) A single-headed piston according to any one of the above modes (1)-(10), wherein the head portion of the piston has a hollow cylindrical shape.




When the head portion of the piston has a hollow cylindrical shape, the weight of the piston can be easily reduced, resulting in reduction of the operating noise of the compressor. Further, the curved surface can be easily formed over the entire circumference at each of the opposite ends of the cylindrical surface, since the hollow cylindrical head portion has at its opposite axial ends a simple circular shape in transverse cross section.




(12) A single-headed piston according to any one of the above modes (1)-(10), wherein the head portion of the piston includes a sealing section having a circular cross sectional shape, and two auxiliary sliding surfaces which are located between the engaging portion of the piston and the sealing section and which consist of an inner auxiliary sliding surface which is nearer to an axis of rotation of the swash plate, and an outer auxiliary sliding surface which is remote from the axis of rotation of the swash plate, the two auxiliary sliding surfaces are flush with an outer circumferential surface of the sealing section.




In the piston according to this arrangement, the auxiliary sliding surfaces cooperate with the outer circumferential surface of the sealing section to form the outer circumferential surface of the head portion of the piston. Accordingly, when the curved surface is formed at one of opposite ends of the outer circumferential surface of the head portion on the side of the engaging portion, the curved surface is formed at one of opposite ends of each of the auxiliary sliding surfaces, which is located on the side of the engaging portion.




(13) A swash plate type compressor comprising: a housing having a plurality of cylinder bores, a rotary drive shaft which is rotatably supported by the housing, a swash plate which is prevented from rotating relative to the rotary drive shaft and which is inclined with respect to an axis of the rotary drive shaft; and a piston including a head portion slidably fitted in each of the cylinder bores, and an engaging portion slidably engaging the swash plate through a pair of shoes which are held in contact with opposite surfaces of the swash plate at a radially outer portion of the swash plate, and wherein the piston has a structure as defined in any one of the above modes (1)-(l


2


).




(14) A swash plate type compressor according to the above mode (14), further comprising a swash plate angle adjusting device for adjusting an angle of inclination of the swash plate with respect to the axis of the rotary drive shaft.




A swash plate type compressor wherein the angle of inclination of the swash plate is variable, in particular, a variable capacity type swash plate compressor having the above-indicated swash plate angle adjusting device which is adapted to control the inclination angle of the swash plate by controlling the pressure in the crank chamber, suffers from a serious problem of the operating noise. The piston constructed according to the present invention described above is effective to solve such a problem when applied to the above-described variable capacity type awash plate compressor having the inclination angle adjusting device.











BRIEF DESCRIPTION OF THE DRAWINGS




The above and optional objects, features, advantages and technical and industrial significance of the present invention will be better understood and appreciated by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which:





FIG. 1

is a front elevational view in cross section of a swash plate type compressor equipped with a single-headed piston constructed according to one embodiment of the present invention;





FIG. 2

is a perspective view of a single-headed piston included in the swash plate type compressor of

FIG. 1

;





FIG. 3

is a front elevational view of the piston of

FIG. 2

;





FIG. 4

is an enlarged front elevational view showing a portion of the piston of

FIG. 2

;





FIGS. 5A and 5B

are views each showing the piston which is inclined within the cylinder bore of the cylinder block of the compressor;





FIG. 6

is a fragmentary enlarged view in cross section showing the piston which contacts at its curved surface with the inner circumferential surface of the cylinder bore in

FIG. 5A

;





FIG. 7

is an enlarged front elevational view showing a portion of a piston constructed according to another embodiment of the present invention; and





FIG. 8

is a front elevational view showing a single-headed piston constructed according to still another embodiment of the present invention.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




Referring to the accompanying drawings, there will be described presently preferred embodiments of the present invention as applied to a single-headed piston for a swash plate type compressor used for an air conditioning system of an automotive vehicle.




Referring first to

FIG. 1

, there is shown a compressor of swash plate type incorporating a plurality of single-headed pistons (hereinafter referred to simply as “pistons”) each constructed according to one embodiment of the present invention.




In

FIG. 1

, reference numeral


10


denotes a cylinder block having a plurality of cylinder bores


12


formed so as to extend in its axial direction such that the cylinder bores


12


are arranged along a circle whose center lies on a centerline M of the cylinder block


10


. The piston generally indicated at


14


is reciprocably received in each of the cylinder bores


12


. To one of the axially opposite end faces of the cylinder block


10


, (the left end face as seen in

FIG. 1

, which will be referred to as “front end face”), there is attached a front housing


16


. To the other end face (the right end face as seen in

FIG. 1

, which will be referred to as “rear end face”), there is attached a rear housing


18


through a valve plate


20


. The front housing


16


, rear housing


18


and cylinder block


10


cooperate to constitute a housing assembly of the swash plate type compressor.




The rear housing


18


and the valve plate


20


cooperate to define a suction chamber


22


and a discharge chamber


24


, which are connected to a refrigerating circuit (not shown) through an inlet


26


and an outlet


28


, respectively. The valve plate


20


has suction ports


40


, suction valves


42


, discharge ports


46


and discharge valves


48


.




A rotary drive shaft


50


is disposed in the cylinder block


10


and the front housing


16


such that the axis of rotation of the drive shaft


50


is aligned with the centerline M of the cylinder block


10


. The drive shaft


50


is supported at its opposite end portions by the front housing


16


and the cylinder block


10


, respectively, via respective bearings. The cylinder block


10


has a central bearing hole


56


formed in a central portion thereof, and the bearing is disposed in this central bearing hole


56


, for supporting the drive shaft


50


at its rear end portion. The front end portion of the drive shaft


50


is connected, through a clutch mechanism such as an electromagnetic clutch, to an external drive source (not shown) in the form of an engine of an automotive vehicle. In operation of the compressor, the drive shaft


50


is connected through the clutch mechanism to the vehicle engine in operation so that the drive shaft


50


is rotated about its axis.




The rotary drive shaft


50


carries a swash plate


60


such that the swash plate


60


is axially movable and tiltable relative to the drive shaft


50


. To the drive shaft


50


, there is fixed a rotary member


62


as a torque transmitting member, which is held in engagement with the front housing


16


through a thrust bearing


66


. The swash plate


60


is rotated with the drive shaft


50


by a hinge mechanism


68


during rotation of the drive shaft


50


The hinge mechanism


68


guides the swash plate


60


for its axial and tilting motions. The hinge mechanism


68


includes a pair of support arms


70


fixed to the rotary member


62


, guide pins


72


which are formed on the swash plate


60


and which slidably engage guide holes


74


formed in the support arms


70


.




The piston


14


indicated above includes as an engaging portion in the form of a neck portion


80


engaging the swash plate


60


, a head portion


82


fitted in the corresponding cylinder bore


12


, and a connecting portion


83


which connects the neck portion


80


and the head portion


82


. The neck portion


80


has a groove


84


formed therein, and the swash plate


60


is held in engagement with the groove


84


through a pair of hemispherical shoes


86


. The hemispherical shoes


86


are held in the groove


84


such that the shoes


86


slidably engage the neck portion


80


at their hemispherical surfaces and such that the shoes


86


slidably engage the radially outer portions of the opposite surfaces of the swash plate


60


at their flat surfaces. The configuration of the piston


14


will be described in detail.




A rotary motion of the swash plate


60


is converted into a reciprocating linear motion of the piston


14


through the shoes


86


. A refrigerant gas in the suction chamber


22


is sucked into the pressurizing chamber


79


through the suction port


40


and the suction valve


42


, when the piston


14


is moved from its upper dead point to its lower dead point, that is, when the piston


14


is in the suction stroke. The refrigerant gas in the pressurizing chamber


79


is pressurized by the piston


14


when the piston


14


is moved from its lower dead point to its upper dead point, that is, when the piston


14


is in the compression stroke. The pressurized refrigerant gas is discharged into the discharge chamber


24


through the discharge port


46


and the discharge valve


48


. A reaction force acts on the piston


14


in the axial direction as a result of compression of the refrigerant gas in the pressurizing chamber


79


. This compression reaction force is received by the front housing


16


through the piston


14


, swash plate


60


, rotary member


62


and thrust bearing


66


.




As shown in

FIG. 2

, the neck portion


80


of the piston


14


has an integrally formed rotation preventive part


88


, which is arranged to contact the inner circumferential surface of the front housing


16


, for thereby preventing a rotary motion of the piston


14


about its centerline N.




The cylinder block


10


has a supply passage


94


formed therethrough for communication between the discharge chamber


24


and a crank chamber


96


which is defined between the front housing


16


and the cylinder block


10


. The supply passage


94


is connected to a solenoid-operated control valve


100


provided to control the pressure in the crank chamber


96


. The solenoid-operated control valve


100


includes a solenoid coil


102


, and a shut-off valve


104


which is selectively closed and opened by energization and de-energization of the solenoid coil


102


. Namely, the shut-off valve


104


is placed in its closed state when the solenoid coil


102


is energized, and is placed in its open state when the coil


102


is de-energized.




The rotary drive shaft


50


has a bleeding passage


110


formed therethrough The bleeding passage


110


is open at one of its opposite ends to the central bearing hole


56


, and is open to the crank chamber


96


at the other end. The central bearing hole


56


communicates at its bottom with the suction chamber


22


through a communication port


114


.




When the solenoid coil


102


of the solenoid-operated control valve


100


is energized, the supply passage


94


is closed, so that the pressurized refrigerant gas in the discharge chamber


24


is not delivered into the crank chamber


96


. In this condition, the refrigerant gas in the crank chamber


96


flows into the suction chamber


22


through the bleeding passage


110


and the communication port


114


, so that the pressure in the crank chamber


96


is lowered, to thereby increase the angle of inclination of the swash plate


60


with respect to a plane perpendicular to the axis M of rotation of the drive shaft


50


. The reciprocating stroke of the piston


14


which is reciprocated by rotation of the swash plate


60


increases with an increase of the angle of inclination of the swash plate


60


, so as to increase an amount of change of the volume of the pressurizing chamber


79


, whereby the discharge capacity of the compressor is increased. When the solenoid coil


102


is de-energized, the supply passage


94


is opened, permitting the pressurized refrigerant gas to be delivered from the discharge chamber


24


into the crank chamber


96


, resulting in an increase in the pressure in the crank chamber


96


, and the angle of inclination of the swash plate


60


is reduced, so that the discharge capacity of the compressor is accordingly reduced.




The maximum angle of inclination of the swash plate


60


is limited by abutting contact of a stop


62


formed on the swash plate


60


, with the rotary member


62


, while the minimum angle of inclination of the swash plate


60


is limited by abutting contact of the swash plate


60


with a stop


122


in the form of a ring fixedly fitted on the drive shaft


50


.




As described above, the pressure in the crank chamber


96


is controlled by controlling the solenoid-operated control valve


100


to selectively connect and disconnect the crank chamber


96


to and from the discharge chamber


24


. By controlling the pressure in the crank chamber


96


by utilizing a difference between the pressure in the discharge chamber


24


as a high-pressure source and the pressure in the suction chamber


22


as a low pressure source, a difference between the pressure in the crank chamber


96


which acts on the front sides of the piston


14


and the pressure in the pressurizing chamber


79


is regulated to change the angle of inclination of the swash plate


60


with respect to a plane perpendicular to the axis M of rotation of the drive shaft


50


, for thereby changing the reciprocating stroke (suction and compression strokes) of the piston


14


, whereby the discharge capacity of the compressor can be adjusted.




The solenoid coil


102


of the solenoid-operated control valve


100


is controlled by a control device not shown depending upon a load acting on the air conditioning system including the present compressor. The control device is principally constituted by a computer. The swash plate type compressor of the present embodiment is variable capacity type In the present embodiment, the supply passage


94


, the crank chamber


96


, the solenoid-operated control valve


100


, the bleeding passage


110


, the communication port


114


, and the control device for the control valve


100


cooperate to constitute a major portion of an angle adjusting device for controlling the angle of inclination of the swash plate


60


depending upon the pressure in the crank chamber


86


.




The cylinder block


10


and each piston


14


are formed of an aluminum alloy. The piston


14


is coated at its outer circumferential surface with a fluoro resin film which prevents a direct contact of the aluminum alloy of the piston


14


with the aluminum alloy of the cylinder block


10


, and makes it possible to minimize the amount of clearance between the piston


14


and the cylinder bore


12


. The cylinder block


10


and the piston


14


may also be formed of an aluminum silicon alloy. Other materials may be used for the cylinder block


10


, the piston


14


, and the coating film.




There will next be described the configuration of the piston


14


.




As shown in

FIGS. 2 and 3

, the head portion


82


portion of the


14


includes a boby portion


124


, an outer sliding portion


126


and an inner sliding portion


128


which correspond to respective radially outer and inner portions of the cylinder block


10


. The radially outer portion of the cylinder block


10


is more distant from the centerline M than the radially inner portion of the cylinder block


10


. The body portion


124


has a circular shape in cross section. The outer and inner sliding sections


126


,


128


project towards the neck portion


80


from respective circumferential parts of the circular body portion


124


, which parts correspond to the radially outer and inner portions of the cylinder block


10


. An outer circumferential surface


130


of the body portion


124


and a part-circumferential surface


132


of the outer sliding section


126


, and a part-circumferential surface


134


of the inner sliding section


128


are contiguous to or flush with one another. The outer and inner sliding sections


126


,


128


are adapted to slide on the respective circumferential portions of the inner circumferential surface of the cylinder bore


12


, which portions correspond to the radially outer and inner portions of the cylinder block


10


. The connecting portion


83


of the piston


14


includes a rib


137


connecting the outer sliding section


126


and the neck portion


80


, and a rib


138


connecting the inner sliding section


128


and the neck portion


80


.




In the present embodiment, a total length L


1


of the body portion


124


and the inner sliding section


138


(referred to as “head inner length which is a length of the head portion


82


as measured at the inner sliding section


138


) is made larger than a total length L


2


of the body portion


124


and the outer sliding section


137


(referred to as “outer head length”, which is a length of the head portion


82


as measured at the outer sliding section


137


). In other words, the length L


1


from an end face


136


of the body portion


124


(which is remote from the neck portion


80


) to the end of the inner sliding section


128


which is remote from the end face


136


is made larger than the length L


2


from the end face


136


to the end of the outer sliding section


137


. By increasing the length of the inner sliding section


128


, the sliding surface pressure in the inner sliding section


128


at the end of the compression stroke of the piston can be lowered, resulting in an improved durability of the piston


14


. Namely, the wear and the removal of the fluoro resin coating of the piston


14


can be prevented. However, an increase in the head inner length L


1


will result in an increase in the weight of the piston


14


. It is noted that the piston


14


has a given operating stroke. Therefore, the head inner length L


1


is desirably determined with those factors taken into account. It is noted that the piston


14


may be formed by either joining together the head portion


82


, neck portion


80


and connection portion


83


which have been formed as separate members, or forming these portions


82


,


80


,


83


integrally with each other.




As shown in

FIG. 2

, the configuration of the inner sliding section


128


in transverse cross section is not uniform in the axial direction. That is, the circumferential dimension of the inner sliding section


128


as represented by a central angle (between two lines which connect the centerline of the body portion


124


and circumferentially opposite ends of the inner sliding section


128


as seen in the circumferential direction of the body portion


124


) is made smaller at a distal part of the inner sliding section


128


nearer to the neck portion


80


than at a proximal part nearer to the body portion


124


. According to this arrangement, the amount of increase in the weight of the piston


14


can be made smaller than in an arrangement wherein these distal and proximal parts of the inner sliding section


128


have the same central angle or circumferential dimension. Although the sliding surface pressure of the inner sliding section


126


at its distal part decreases with an increase in the central angle, the weight of the piston


14


increases with the central angle. Therefore, the central angles at the distal and proximal parts of the inner sliding section


128


are desirably determined with those factors taken into account.




The respective outer circumferential surfaces


130


,


132


,


134


of the body portion


124


, outer sliding portion


126


, and inner sliding portion


128


cooperate with one another to provide a cylindrical surface


152


and curved surfaces


146


,


148


,


150


. The curved surface


146


smoothly and continuously (in a mathematical sense) extends from one of the opposite axial ends of the cylindrical surface


152


while the curved surfaces


148


,


150


smoothly and continuously extend from the other axial end. The expression “smoothly and continuously” is interpreted to mean a manner of connection of the curved surfaces


146


,


148


,


150


to the cylindrical surface


152


such that there is not any bend or any abrupt change of angle between the cylindrical surface


152


and the curved surfaces


146


,


148


,


150


. The cylindrical surface


152


is part-cylindrical at its circumferential portions corresponding to the outer sliding portion


126


and the inner sliding portion


128


, respectively. Chamfers


140


,


142


,


144


are formed at one of opposite ends of the respective curved surfaces


146


,


148


,


150


on the side remote from the cylindrical surface


152


. As shown in an enlarged view of

FIG. 4

which shows the curved surface


146


formed at one axial end of the cylindrical surface


152


on the side of the body portion


124


, by way of example, the curved surface


146


is formed such that a radial distance between the curved surface


146


and the centerline of the cylindrical surface


162


gradually decreases in an axial direction of the cylindrical surface


162


from the corresponding axial end of the cylindrical surface


152


toward the end face


136


, and such that a cross sectional shape of the curved surface


146


taken in a plane that includes the centerline of the cylindrical surface


152


is an arc having a constant radius of curvature. The radius of curvature of the arc is larger than the diameter of the inner circumferential surface of the cylinder bore


12


, and is about 1000 mm in the present embodiment. The cylindrical surface


152


, and the curved surfaces


146


,


148


,


150


cooperate with one another to provide an outer circumferential surface of the head portion


82


of the piston


14


.




Each of the curved surfaces


146


,


148


,


150


is formed such that a quotient r


1


/l


1


is substantially equal to a quotient r


2


/l


2


, wherein r


1


is a dimension of each curved surface


146


,


148


,


150


between a surface of extension of the cylindrical surface


152


and a straight line which is parallel to the surface of extension and which passes one of opposite ends of each curved surface which is remote from the cylindrical surface


152


, l


1


is an axial dimension of each curved surface


146


,


148


,


150


as measured in a direction parallel to the centerline of the cylindrical surface


152


, r


2


is a clearance which is a difference between a diameter d


1


of the inner circumferential surface of the cylinder bore


12


and a diameter d


2


of the cylindrical surface


152


of the head portion


82


of the piston


14


. This clearance will hereinafter be referred to as a “fitting clearance”, and l


2


is an axial dimension of the cylindrical surface


152


.




In the present embodiment, the above-indicated axial dimension l


2


of the cylindrical surface


152


is an axial distance between (1) a boundary between the cylindrical surface


152


and each curved surface


146


,


148


,


150


which contacts the inner circumferential surface of the cylinder bore


12


when the head portion


82


of the piston


14


is inclined within the cylinder bore


12


due to the side force applied from the swash plate


60


to the piston


14


in its radial direction, and (2) one of the opposite axial ends of the cylindrical surface


152


which is spaced from the above-indicated boundary in the diametric direction of the head portion


82


of the piston


14


and which is remote from the boundary in the axial direction of the head portion


82


.




In the present embodiment wherein the head inner length L


1


(i.e., the length of the head portion


82


as measured at the inner sliding section


128


) is made larger than the head outer length L


2


(i.e., the length of the head portion


82


as measured at the outer sliding section


126


) as described above, the axial dimension l


2


of the cylindrical surface


152


when the piston


14


is inclined within the cylinder bore


12


such that the axial end of the head portion


82


on the side of the end face


136


of the piston


14


(which partially defines the pressurizing chamber


79


) contacts a radially outer portion of the inner circumferential surface of the cylinder bore


12


, as shown in

FIG. 5A

, is different from that when the piston


14


is inclined within the cylinder bore


12


such that the above-indicated axial end of the head portion


82


contacts a radially inner portion of the inner circumferential surface of the cylinder bore


12


, as shown in FIG.


5


B. For easier understanding, only the head portion


82


of the piston


14


is schematically shown in

FIGS. 5A and 5B

without indicating the chamfers


140


,


142


,


144


, and the inclination of the head portion


82


is exaggerated.




When the piston


14


is inclined within the cylinder bore


12


such that the axial end of the head portion


82


on the side of the end face


136


of the piston


14


contacts the radially outer portion of the inner circumferential surface of the cylinder bore


12


, as shown in

FIG. 5A

, the axial dimension l


2


of the cylindrical surface


152


is an axial distance between (1) a boundary between the cylindrical surface


152


and the curved surface


146


which is held in contact with the radially outer portion of the inner circumferential surface of the cylinder bore


12


of the cylinder block


10


, and (2) a boundary between the cylindrical surface


152


and the curved surface


150


which is formed on the side of the inner sliding portion


128


and which is held in contact with the radially inner portion of the inner circumferential surface of the cylinder bore


12


of the cylinder block


10


.




When the piston


14


is inclined within the cylinder bore


12


such that the above-indicated axial end of the head portion


82


contacts a radially inner portion of the inner circumferential surface of the cylinder bore


12


, as shown in

FIG. 5B

, the axial dimension l


2


of the cylindrical surface


152


is an axial distance between (1) a boundary between cylindrical surface


152


and the curved surface


146


which is held in contact with the radially inner portion of the inner circumferential surface of the cylinder bore


12


, and (2) a boundary between the cylindrical surface


152


and the curved surface


148


which is formed on the side of the outer sliding portion


126


and which is held in contact with the radially outer portion of the inner circumferential surface of the cylinder bore


12


.




Referring next to

FIG. 6

, there will be described a significance of the quotient r


1


/l


1


which is made substantially equal to the quotient r


2


/l


2


.

FIG. 6

schematically shows a portion of the body portion


124


of the head portion


82


in an exaggerated manner. For easier understanding, there is established an imaginary tapered surface


156


(indicated by a two-dot chain line in

FIG. 6

) instead of the curved surface


146


. The imaginary tapered surface


156


has the same dimensions r


1


and l


1


as the curved surface


146


. The r


2


/l


2


obtained by dividing the fitting clearance r


2


by the axial dimension l


2


of the cylindrical surface


152


is equal to an inclination angle


81


of the head portion


82


within the cylinder bore


12


. The quotient r


1


/l


1


obtained by dividing the dimension r


1


of the imaginary tapered surface


156


(i.e., a dimension between the surface of extension of the cylindrical surface


152


and one of opposite ends of the imaginary tapered surface


156


which is remote from the cylindrical surface


152


), by the axial dimension l


1


of the imaginary tapered surface


156


(i.e., an axial dimension of the imaginary tapered surface


156


as measured in the direction parallel to the centerline of the cylindrical surface


152


) is equal to an inclination angle


82


of the imaginary tapered surface


156


with respect to the surface of extension of the cylindrical surface


152


. The fact that the inclination angles


81


and


82


are made equal to each other indicates that the imaginary tapered surface


156


is parallel to and held in close contact with the inner circumferential surface of the cylinder bore


12


when the head portion


82


of the piston


14


is inclined within the cylinder bore


12


at the angle


81


. Actually, the curved surface


146


rather than the imaginary tapered surface


156


is brought into contact with the inner circumferential surface of the cylinder bore


12


. The actual inclination angle of the head portion


82


indicated by a solid line in

FIG. 6

is smaller than the angle of inclination of the head portion


82


as indicated by the two-dot chain line since the curved surface


146


is located radially outwardly of the imaginary tapered surface


156


. Accordingly, the curved surface


146


is held in contact with the inner circumferential surface of the cylinder bore


12


at its axially intermediate portion, to thereby form a wedge-shaped gap between the curved surface


146


and the inner circumferential surface of the cylinder bore


12


. The effect of the wedge-shaped gap will be described in greater detail. The above explanation is true for the curved surface


146


of the body portion


124


which is held in contact with the radially inner portion of the inner circumferential surface of the cylinder bore


12


of the cylinder block


10


, and the curved surfaces


148


,


150


. It is desirable to determine the various dimensions described above such that each curved surface


146


,


148


,


150


is held in contact with the inner circumferential surface of the cylinder bore


12


at its axial portion which is nearer to the boundary between the cylindrical surface


152


and the end of the curved surface, than its axially intermediate portion. In the present embodiment, the dimension r


1


of each curved surface


146


,


148


,


150


is in a range of 2-4 μm, while the axial dimension l


1


of the curved surface is in a range of 1.8˜2.8 mm. The axial dimension l


1


is ⅛˜{fraction (1/13)} of the axial dimension l


2


of the cylindrical surface


152


. The wedge-shaped gap which is formed when the axially intermediate portion of each curved surface


146


,


148


,


150


is held in contact with the inner circumferential surface of the cylinder bore


12


as a result of inclination of the head portion


82


of the piston within the cylinder bore


12


, has a dimension of 2˜8 μm as measured in the direction of r


1


. In other words, the above-indicated dimension of the wedge-shaped gap is a distance between the inner circumferential surface of the cylinder bore


12


and one of opposite ends of each curved surface


146


,


148


,


150


which is remote from the cylindrical surface


152


, which one end is a boundary between each curved surface


146


,


148


,


150


and the corresponding chamfer


140


,


142


,


144


.




When the thus constructed piston


14


is used for the swash plate type compressor, it was confirmed by the following experiment that the noise of the compressor during its operation was reduced. In the experiment, there were used two variable capacity type swash plate compressors having seven cylinder bores in each of which a single-headed piston


14


having a diameter of 32 mm was fitted. The single-headed piston used for one of the swash plate type compressors does not have the curved surfaces as described above, whereas the single-headed piston


14


used for the other swash plate type compressor has the curved surfaces


146


,


148


,


150


according to the present invention. Under the same circulating condition of the refrigerant gas, the two swash plate type compressors were operated at 1000 rpm and at a discharge pressure of 1.5 Mpa, so that the levels of the noise generated by the two compressors were compared with each other. The comparison revealed that the noise generated by the swash plate type compressor which was equipped with the single-headed pistons having the curved surfaces


146


,


148


,


150


was smaller by 3-4 dB than that generated by the swash plate type compressor equipped with the single-headed pistons without the curved surfaces


146


,


148


,


150


.




It is considered that the reduction of the noise in the swash plate type compressor equipped with the single-headed pistons having the curved surfaces


146


,


148


,


150


is owing to a reduced sliding resistance of the piston


14


during its reciprocating movement within the cylinder bore


12


. When the head portion


82


of the piston


14


is slidably moved in the cylinder bore


12


, the piston


14


is inclined in the cylinder bore


12


by a rotary moment based on the side force applied from the swash plate


60


to the piston


14


. In the compression stroke of the piston


14


, in particular, the circumferential portion of the body portion


124


which corresponds to the radially outer portion of the cylinder block


10


, and the inner sliding portion


128


are brought into contact with the inner circumferential surface of the cylinder bore


12


at a large contacting pressure, as shown in FIG.


5


A. In the present embodiment, the surface pressure of contact of the head portion


82


of the piston


14


with the inner circumferential surface of the cylinder bore


12


is reduced owing to the curved surfaces


146


,


148


,


150


. Namely, the head portion


82


of the piston


14


is dimensioned such that the head portion


82


is brought into contact with the inner circumferential surface of the cylinder bore


12


at the curved surfaces


146


,


158


,


150


when the head portion


82


of the piston


14


is inclined in the cylinder bore


12


, so that the surface pressure of contact with the head portion


82


of the piston


14


with the inner circumferential surface of the cylinder bore


12


is reduced. If the outer circumferential surface of the head portion


82


were a complete cylindrical surface without the curved surfaces


146


,


148


,


150


provided according to the present invention, the head portion


82


would be pressed at its periphery onto the inner circumferential surface of the cylinder bore


12


at a large contacting pressure even when the piston


14


is slightly inclined. In this case, a film of a lubricant oil adhering to the inner circumferential surface of the cylinder bore


12


is undesirably scraped off by the peripheral edge of the head portion


82


, causing seizure between the head portion


82


and the inner circumferential surface of the cylinder bore


12


. In contrast, the piston


14


of the present invention having the curved surfaces


146


,


148


,


150


does not suffer from such a problem, owing to a reduced sliding resistance of the piston


14


. In the present embodiment, the curved surfaces


146


,


148


,


160


and the inner circumferential surface of the cylinder bore


12


cooperate with one another to form the wedge-shaped gap therebetween such that an angle between the inner circumferential surface of the cylinder bore


12


and each curved surface


146


,


148


,


150


smoothly decreases in a direction toward the contact point of each curved surface


146


,


148


,


150


with the inner circumferential surface of the cylinder bore


12


. Accordingly, when the piston


14


is slidably moved in the cylinder bore


12


, the lubricant oil adhering to the inner circumferential surface of the cylinder bore


12


and the lubricant oil dispersed in the form of a mist in the refrigerant gas is introduced into the wedge-shaped gap, with a result of formation of an oil film between the curved surfaces


146


,


148


,


150


and the inner circumferential surface of the cylinder bore


12


, permitting fluid lubrication to prevent a direct contact of the curved surfaces


146


,


148


,


150


and the inner circumferential surface of the cylinder bore


12


. Accordingly, the piston


14


can be smoothly moved in the cylinder bore


12


since the piston


14


is prevented from directly contacting the inner circumferential surface of the cylinder bore


12


, or the contacting surface pressure therebetween is reduced.




When the piston


14


suffers from a rotary moment as shown in

FIG. 5A

, the piston


14


is permitted to rotate by a small angle. With this rotation of the piston


14


, the curved surfaces


146


,


148


,


150


approach the inner circumferential surface of the cylinder bore


12


, and the size of the wedge-shaped gap formed therebetween is reduced. Since the size of the wedge-shaped gap is small enough to inhibit the lubricant oil from flowing out of the gap, there is generated a relatively high pressure of the oil film between the curved surfaces


146


,


148


.


150


and the inner circumferential surfaces of the cylinder bore


12


when the piston


14


is rotated. The high pressure of the oil film is effective to prevent further inclination of the piston


14


. In particular when the piston


14


is moved toward its upper dead point (in the rightward direction as seen in

FIG. 5A

) while the piston


14


is inclined, a relatively large oil pressure is generated between the curved surface


146


and the inner circumferential surface of the cylinder bore


12


owing to a wedge effect, so that the curved surface


146


is pressed away from the inner circumferential surface of the cylinder bore


12


by the high oil pressure. Accordingly, the aluminum alloy of the piston


14


is prevented from directly contacting the aluminum alloy of the cylinder block


10


, thereby reducing the sliding resistance of the head portion


82


of the piston


14


in the cylinder bore


12


.




In the present swash plate type compressor wherein the inclination of the piston


14


in the cylinder bore


12


is restricted or limited and the piston


14


is smoothly movable in the cylinder bore


12


, local wearing and removal of the fluoro resin coating on the outer circumferential surface of the head portion


82


of the piston


14


can be minimized.




Since the end face of the body portion


124


partially defining the pressurizing chamber


79


has a simple circular configuration, the curved surface


146


can be easily formed over the entire circumference of the end face of the body portion


82


.




In the present embodiment, the body portion


124


provides a sealing portion, and the outer circumferential surfaces


132


,


134


of the outer and inner sliding portions


126


,


128


provide auxiliary sliding surfaces. The curved surfaces may be formed only at the circumferential part of the body portion


124


corresponding to the radially outer portion of the cylinder block


10


, and at the inner sliding portion


128


, in view of the fact that the above-indicated circumferential part of the body portion


124


and the inner sliding portion


128


tend to be held in a pressing contact with the inner circumferential surface of the cylinder bore


12


in the compression stroke of the piston


14


due to the side force applied from the swash plate


60


to the piston


14


. Alternatively, the curved surface may be formed at the outer circumferential surface of the end portion of at least one of the body portion


124


, inner sliding portion


128


and outer sliding portion


126


. Further, the curved surface may be formed at only a part of the outer circumferential surface of each of those portions


124


,


128


,


126


, which part is held in contact with the inner circumferential surface of the cylinder bore


12


, or only at the above-indicated part contacting the inner circumferential surface of the cylinder bore


12


and a portion adjacent thereto.




The cross sectional shape of the curved surface is not limited to an arcuate shape having a constant radius of curvature in the present embodiment, but may be any other configuration having a smooth convex curve. For instance, the cross sectional shape of the curved surface may be constituted by a plurality of arcs whose radii of curvature gradually decrease in a longitudinal direction of the piston


14


away from the cylindrical surface.




Referring next to

FIG. 7

, there is shown a piston constructed according to another embodiment, wherein the outer circumferential surface of the head portion


82


of the piston is shaped differently from that of the piston in the preceding embodiment of

FIGS. 1-6

. In

FIG. 7

, the same reference numerals as used in the embodiment of

FIGS. 1-6

are used to identify the corresponding components, and a detailed explanation of which is dispensed with. As shown in

FIG. 7

, the outer circumferential surface of the head portion


82


on the side of the body portion


124


includes the cylindrical surface


152


, a curved surface


200


which smoothly and continuously (in a mathematical sense) extends from the cylindrical surface


152


, and a tapered surface


202


which smoothly and continuously extends from one of opposite ends of the curved surface


200


on the side remote from the cylindrical surface


152


. The expression “smoothly and continuously” is interpreted in the same manner as explained above with respect to the cylindrical surface


152


and the curved surfaces


146


,


148


,


150


. The curved surface


200


and the tapered surface


202


are formed over the entire circumference of the body proton


124


. In

FIG. 7

, a circumferential portion of the body portion


124


which corresponds to the radially outer portion of the cylinder block


10


is shown. Like the curved surface


146


in the preceding embodiment of

FIGS. 1-6

, the curved surface


200


of this embodiment is formed such that a radial distance from the centerline of the cylindrical surface


152


gradually decreases in a longitudinal direction of the piston


14


away from the cylindrical surface


152


, and such that the cross sectional shape of the curved surface


200


taken in a plane which includes the centerline of the cylindrical surface


152


is an arc having a constant radius of curvature. The tapered surface


202


has a diameter which linearly decreases in the axial direction of the cylindrical surface


152


from the curved surface


200


toward the end face


136


. The chamfer


140


is formed adjacent to at one of opposite ends of the tapered surface


202


which is remote from the curved surface


200


. The taper angle of the tapered surface


202


is smaller than that of the chamfer


140


. The tapered surface


202


is formed such that a difference A (

FIG. 7

) between a radius of its large-diameter end and a radius of its small-diameter end is preferably in a range of 1 μm˜15 μm. Owing to a wedge effect of a wedge-shaped gap formed between the tapered surface


202


and the inner circumferential surface of the cylinder bore


12


, the lubricant oil adhering to the inner circumferential surface of the cylinder bore


12


and the mist-form lubricant oil dispersed in the refrigerant gas is effectively introduced into the wedge-shaped gap. As for the outer circumferential surfaces of the outer and inner sliding portions


126


,


128


, the tapered surface may be formed so as to smoothly extend from one of opposite ends of the curved surface


200


as described above. When the head portion


82


of the piston


14


is adapted to be held in contact with the inner circumferential surface of the cylinder bore


12


at its curved surface


200


as in the preceding embodiment, the contacting surface pressure therebetween can be reduced. Accordingly, the head portion


82


of the piston


14


is prevented from contacting directly the inner circumferential surface of the cylinder bore


12


, or the contacting surface pressure between the outer circumferential surface of the head portion


82


and the inner circumferential surface of the cylinder bore


12


is reduced, so that the sliding resistance of the piston


14


is reduced.




The outer circumferential surface of the head portion


82


may consist of a cylindrical surface and a tapered surface which extends from one of opposite ends of the cylindrical surface. Like the tapered surface


202


of

FIG. 7

, this tapered surface has a diameter which linearly decreases in the axial direction of the cylindrical surface


152


from this surface


152


toward the axial end face


136


. The taper angle of this tapered surface is smaller than that of the chamber formed adjacent thereto. The tapered surface is formed such that a difference between a radius of its large-diameter end and a radius of its small-diameter end is preferably in a range of 1˜15 μm. The operating noise generated by the compressor is reduced owing to the wedge effect formed between the tapered surface and the inner circumferential surface of the cylinder bore. For advantageously enjoying the wedge effect, the dimensions of the cylindrical surface, the tapered surface, and the clearance with respect to the cylinder bore


12


are preferably determined such that such that the wedge-shaped gap has a dimension of 1˜5 μm even when the head portion


82


of the piston is inclined in the cylinder bore


12


to a maximum extent. The above-indicated dimension of the wedge-shaped gap is a distance between the small-diameter end of the tapered surface and the inner circumferential surface of the cylinder bore


12


.




The configuration of the piston


14


is not particularly limited to that of the illustrated embodiment. For instance, the connection portion


83


need not include both of the ribs


137


,


138


, but may consist of only one of these two ribs


137


,


138


. Similarly, the configuration and size of the distal sliding part of each of the outer and inner sliding portions


126


,


128


(which is on the side of the neck portion


80


) are not limited to the details described above with respect to the illustrated embodiment. The distal sliding part of each outer and inner sliding portions


126


,


128


may have any configuration and size, provided that the configuration and size assure an improvement in the durability of the piston


14


. For instance, the distal sliding part of the inner sliding portion


128


may have a circumferential dimension and a center angle (between two straight lines which connect the centerline of the body portion


124


and circumferentially opposite ends of the inner sliding section


128


as seen in the circumferential direction of the body portion


124


) which continuously and smoothly decrease as the distal sliding part of the inner sliding portion


128


extends in the longitudinal direction of the piston


14


from the body portion


124


toward the neck portion


80


. In this case, the curved surface


150


may be formed so as to entirely extend between the appropriate end of the cylindrical surface


152


and the chamfer


144


. Alternatively, the curved surface


150


may be formed so as to partially extend between the cylindrical surface


152


and the chamfer


144


, i.e., at a portion which contacts the inner circumferential surface of the cylinder bore


12


. The configurations of the outer and inner sliding portions


126


,


128


may be either symmetrical or asymmetrical with respect to a plane which passes the centerline N of the piston


14


and the centerline M of the cylinder block


10


. The piston


14


may have various other configurations, such as a configuration as disclosed in Japanese Patent Application No. 11-150448 filed by the assignee of the present invention.




The pistons of the illustrated embodiments has a through-hole formed through its circumferentially intermediate portion, for thereby reducing the weight of the piston. In this respect, it is noted that the outer circumferential surface of head portion of the piston suffers from a particularly high sliding surface pressure at its circumferential parts corresponding to the respective radially outer and inner portions of the cylinder block


10


, and that the other circumferential parts (between the outer and inner sliding portions


137


,


138


) do not suffer from a high sliding surface pressure. Accordingly, the through-hole can be formed at the circumferentially intermediate portion of the piston to reduce its weight.




The weight of the piston can be reduced by forming the piston with a hollow cylindrical head portion.

FIG. 8

shows a single-headed piston


300


constructed according to another embodiment of the invention. The structure of the swash plate type compressor which uses the piston


300


is the same as that of the compressor in the embodiment of

FIGS. 1-6

, and a detailed explanation of which is dispensed with. The piston


300


includes a head portion


302


and an engaging portion in the form of a neck portion


304


which is integrally formed with the head portion


302


. The head portion


302


includes a hollow cylindrical body portion


306


which has an open end on the side remote from the neck portion


304


, and a closure member


308


which is fixed to the body portion


306


and which closes the open end of the body portion


306


. The head portion


306


has an inner circumferential surface


310


having a constant diameter over the entire axial length thereof. The closure member


308


includes a circular plate portion


312


, and an annular fitting protrusion


314


which protrudes from an inner end face of the plate portion


312


and which has a diameter smaller than the circular plate portion


312


. A shoulder


316


is formed between the circular plate portion


312


and the annular fitting protrusion


314


. The closure member


308


is fitted in the body portion


306


such that the fitting protrusion


314


of the closure member


308


engages the inner circumferential surface


310


of the body portion


306


, and such that the shoulder


316


of the closure member


308


is held in abutting contact with an end face


318


of the body portion


306


at its open end. With the closure member


308


being fitted in the body portion


306


, these two members are fixed to each other by welding, for instance.




The outer circumferential surface of the head portion


302


of the piston


300


includes a cylindrical surface


324


, and curved surfaces


326


,


328


which smoothly extend from the axially opposite ends of the cylindrical surface


324


, respectively. Chamfers


330


,


332


are formed at one of opposite ends of the respective curved surfaces


326


,


328


, which end is remote from the cylindrical surface


324


. Each of the curved surfaces


326


,


328


is formed such that a radial distance from the centerline of the cylindrical surface


324


gradually decreases in a direction away from the cylindrical surface


324


, and such that the cross sectional shape of each curved surface


326


,


328


cut along a plane which includes the centerline of the cylindrical surface


324


is an arc having a constant radius of curvature. The curved surfaces


326


,


328


are formed over the entire circumference at opposite ends of the body portion


306


, respectively. The dimensions and the configurations of the curved surfaces


326


,


328


are the same as those of the curved surfaces


146


,


148


,


150


of the preceding embodiment, and a detailed explanation of which is dispensed with. In the present embodiment, however, the axial dimension


12


of the cylindrical surface


324


when the head portion


302


of the piston


300


is inclined in the cylinder bore


12


toward the radially outer portion of the cylinder block


10


, is not different from that when the head portion


302


is inclined in the cylinder bore


12


toward the radially inner portion of the cylinder block


10


. The dimensions of the curved surfaces


326


.


328


are determined with the above-indicated fact taken into account, As in the swash plate type compressor equipped with the piston


14


according to the preceding embodiment, the sliding resistance of the piston


300


of the present embodiment during its reciprocating movement in the cylinder bore


12


can be reduced, and the operation noise of the compressor can be reduced. Owing to the curved surface


328


formed at one of the opposite ends of the head portion


302


, which end is on the side of the neck portion


304


, the contacting surface pressure between the head portion


302


of the piston


300


and the inner circumferential surface of the cylinder bore


12


when the piston


300


is inclined in the cylinder bore


12


can be reduced, so that the piston


300


exhibits an excellent durability. Since the opposite ends of the cylindrical surface of the head portion


302


has a simple circular configuration, it is easy to form the curved surfaces


326


,


328


over the entire circumference at the opposite ends of the head portion


302


. As in the preceding embodiment shown in

FIGS. 1-6

, the curved surface may be formed at only one of opposite axial ends of the head portion


302


. Further, the curved surface may be formed at a selected circumferential part of the opposite ends of the head portion


302


without extending over the entire circumference. A tapered surface similar to the tapered surface


202


of

FIG. 7

may be formed so as to smoothly extend from each curved surface


326


,


328


. The curved surfaces


326


,


328


may have any cross sectional shape which has a smooth convex curve.




The construction of the swash plate type compressor for which the pistons


14


,


300


are incorporated is not limited to that of FIG.


1


. For instance, the solenoid-operated control valve


100


is not essential, and the compressor may use a shut-off valve which is mechanically opened and closed depending upon a difference between the pressures in the crank chamber


96


and the discharge chamber


24


. In place of or in addition to the solenoid-operated control valve


100


, a solenoid-operated control valve similar to the control valve


100


may be provided in the bleeding passage


110


. Alternatively, a shut-off valve may be provided, which is mechanically opened or closed depending upon a difference between the pressures in the crank chamber


96


and the suction chamber


22


. The pistons of the present invention may be used for a fixed capacity type swash plate compressor wherein the angle of inclination of the swash plate is fixed.




While some presently preferred embodiments of this invention have been described above, for illustrative purpose only, it is to be understood that the present invention may be embodied with various changes and improvements such as those described in the SUMMARY OF THE INVENTION, which may occur to those skilled in the art.



Claims
  • 1. A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor,wherein said outer circumferential surface of said head portion includes a cylindrical surface and a curved surface which is formed adjacent to at least one of opposite axial ends of said cylindrical surface, so as to smoothly extend from at least one circumferential part of said cylindrical surface, said curved surface being formed such that a radial distance between a centerline of said cylindrical surface and said curved surface gradually decreases in an axial direction of said cylindrical surface from the corresponding axial end of said cylindrical surface toward the corresponding axial end of said piston, and such that a radius of curvature of a cross sectional shape of said curved surface taken in a plane which includes said centerline of said cylindrical surface is larger than a diameter of said inner circumferential surface of said cylinder bore, and a dimension (r1) between a surface of extension of said cylindrical surface and a straight line which is parallel to said surface of extension and which passes one of opposite ends of said curved surface which is remote from said cylindrical surface is not greater than 15 μm.
  • 2. A swash plate type compressor comprising:a housing having a plurality of cylinder bores, a rotary drive shaft which is rotatably supported by said housing, a swash plate which is prevented from rotating relative to said rotary drive shaft and which is inclined with respect to an axis of said rotary drive shaft; and a piston including a head portion slidably fitted in each of said cylinder bores, and an engaging portion slidably engaging said swash plate through a pair of shoes which are held in contact with opposite surfaces of said swash plate at a radially outer portion of said swash plate, and wherein said piston has a structure as defined in claim 1.
  • 3. A swash plate type compressor according to claim 2, further comprising a swash plate angle adjusting device for adjusting an angle of inclination of said swash plate with respect to said axis of said rotary drive shaft.
  • 4. A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor,wherein said outer circumferential surface of said head portion includes a cylindrical surface and a curved surface which is formed adjacent to at least one of opposite axial ends of said cylindrical surface, so as to smoothly extend from at least one circumferential part of said cylindrical surface, said curved surface being formed such that a radial distance between a centerline of said cylindrical surface and said curved surface gradually decreases in an axial direction of said cylindrical surface from the corresponding axial end of said cylindrical surface toward the corresponding axial end of said piston, and such that a radius of curvature of a cross sectional shape of said curved surface taken in a plane which includes said centerline of said cylindrical surface is larger than a diameter of said inner circumferential surface of said cylinder bore, and a quotient obtained by dividing a dimension (r1) between a surface of extension of said cylindrical surface and said straight line which is parallel to said surface of extension and which passes one of opposite ends of said curved surface which is remote from said cylindrical surface, by an axial dimension (l1) of said curved surface as measured in a direction parallel to said centerline of said cylindrical surface, is substantially equal to a quotient obtained by dividing a clearance (r2) between said outer circumferential surface of said head portion of the piston and said inner circumferential surface of said cylinder bore when the piston is fitted in said cylinder bore, by an axial dimension (l2) of said cylindrical surface, said clearance (r2) being a difference between a diameter of said outer circumferential surface of said head portion and said diameter of said inner circumferential surface of said cylinder bore.
  • 5. A single-headed piston according to claim 1, wherein said axial dimension (l1) of said curved surface which is parallel to its centerline is not larger than ⅕ of said axial dimension (l2) of said cylindrical surface.
  • 6. A swash plate type compressor comprising:a housing having a plurality of cylinder bores, a rotary drive shaft which is rotatably supported by said housing, a swash plate which is prevented from rotating relative to said rotary drive shaft and which is inclined with respect to an axis of said rotary drive shaft; and a piston including a head portion slidably fitted in each of said cylinder bores, and an engaging portion slidably engaging said swash plate through a pair of shoes which are held in contact with opposite surfaces of said swash plate at a radially outer portion of said swash plate, and wherein said piston has a structure as defined in claim 4.
  • 7. A swash plate type compressor according to claim 6, further comprising a swash plate angle adjusting device for adjusting an angle of inclination of said swash plate with respect to said axis of said rotary drive shaft.
  • 8. A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor,wherein said outer circumferential surface of said head portion includes a cylindrical surface and a curved surface-which is formed adjacent to at least one of opposite axial ends of said cylindrical surface, so as to smoothly extend from at least one circumferential part of said cylindrical surface, said curved surface being formed such that a radial distance between a centerline of said cylindrical surface and said curved surface gradually decreases in an axial direction of said cylindrical surface from the corresponding axial end of said cylindrical surface toward the corresponding axial end of said piston, and such that a radius of curvature of a cross sectional shape of said curved surface taken in a plane which includes said centerline of said cylindrical surface is larger than a diameter of said inner circumferential surface of said cylinder bore, and said outer circumferential surface of said head portion includes a tapered surface which smoothly extends from one of opposite ends of said curved surface which is remote from said cylindrical surface such that said tapered surface has a diameter which gradually and linearly reduces in an axial direction of said cylindrical surface from said curved surface toward the corresponding axial end of said piston, said tapered surface being formed such that a difference between a radius of its large-diameter end and a radius of its small-diameter end is selected within a range between 1 μm and 15 μm.
  • 9. A swash plate type compressor comprising:a housing having a plurality of cylinder bores, a rotary drive shaft which is rotatably supported by said housing, a swash plate which is prevented from rotating relative to said rotary drive shaft and which is inclined with respect to an axis of said rotary drive shaft; and a piston including a head portion slidably fitted in each of said cylinder bores, and an engaging portion slidably engaging said swash plate through a pair of shoes which are held in contact with opposite surfaces of said swash plate at a radially outer portion of said swash plate, and wherein said piston has a structure as defined in claim 8.
  • 10. A swash plate type compressor according to claim 9, further comprising a swash plate angle adjusting device for adjusting an angle of inclination of said swash plate with respect to said axis of said rotary drive shaft.
  • 11. A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor, characterized in that; said outer circumferential surface of said head portion includes a cylindrical surface, and a tapered surface which is formed adjacent to at least one of axially opposite ends of said cylindrical surface so as to extend from at least one circumferential part of said cylindrical surface, said tapered surface being formed such that a difference between a radius of its large-diameter end and a radius of its small-diameter end is selected within a range between 1 μm and 15 μm.
  • 12. A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor,wherein said outer circumferential surface of said head portion includes a cylindrical surface and a curved surface which is formed adjacent to at least one of opposite axial ends of said cylindrical surface, so as to smoothly extend from at least one circumferential part of said cylindrical surface, said curved surface being formed such that a radial distance between a centerline of said cylindrical surface and said curved surface gradually decreases in an axial direction of said cylindrical surface from the corresponding axial end of said cylindrical surface toward the corresponding axial end of said piston, and such that a radius of curvature of a cross sectional shape of said curved surface taken in a plane which includes said centerline of said cylindrical surface is larger than a diameter of said inner circumferential surface of said cylinder bore, and said head portion of the piston includes a sealing section having a circular cross sectional shape, and two auxiliary sliding surfaces which are located between said engaging portion of the piston and said sealing section and which consist of an inner auxiliary sliding surface which is nearer to an axis of rotation of said swash plate, and an outer auxiliary sliding surface which is remote from the axis of rotation of said swash plate, said two auxiliary sliding surfaces are flush with an outer circumferential surface of said sealing section.
Priority Claims (1)
Number Date Country Kind
11-270355 Sep 1999 JP
US Referenced Citations (5)
Number Name Date Kind
4191095 Heyl Mar 1980 A
5265331 Engel et al. Nov 1993 A
5630353 Mittlefehldt et al. May 1997 A
5970845 Beck Oct 1999 A
6010313 Kimura et al. Jan 2000 A
Foreign Referenced Citations (5)
Number Date Country
0 864 787 Sep 1998 EP
0 740 076 Oct 1996 JP
A-9-105380 Apr 1997 JP
A-9-177670 Jul 1997 JP
10 159 725 Jun 1998 JP
Non-Patent Literature Citations (1)
Entry
EP 00 12 0162 Search Report dated May 29, 2002.