Compressor with oil separating structure

A compressor includes a compressing mechanism for compressing refrigerant gas and an oil separator for separating the oil from the gas. The separated oil is used to lubricate the compressor. The compressor has a discharge passage to permit refrigerant gas to flow out of the compressor, a recess located in the discharge passage, a plug press fitted in the recess and a supply passage for returning the separated oil to the compressor. The plug and the recess define a separation chamber having a circular cross-section and an annular chamber. The separation chamber is connected with the annular chamber by an outlet passage formed in the plug. The refrigerant gas swirls along the wall of the separation chamber, which separates the oil from the gas. Since the plug is press fitted in the recess, installation of the plug is facilitated. This structure also prevents the plug from loosening.

BACKGROUND OF THE INVENTION
 The present invention relates to a compressor. More specifically, the
 present invention pertains to oil separating structures for compressors
 that are used in vehicle air conditioners to separate atomized lubricant
 in refrigerant gas.
 Refrigerant gas in a compressor is compressed and circulated between the
 compressor and an external circuit to carry heat. Some compressors include
 an oil separating structure for collecting atomized oil. The collected oil
 is used for lubricating parts of the compressor. FIGS. 5(a) and 5(b) show
 such an oil separating structure. The compressor of FIGS. 5(a) and 5(b)
 includes a housing 101. The housing 101 accommodates a compressing
 mechanism (not shown). A discharge passage 102 is formed in the housing
 101 to conduct refrigerant from the compressing mechanism to an external
 refrigerant circuit. A recess 103 is defined in the housing 101 and
 located in the discharge passage 102. The recess 103 has a circular
 cross-section and extends in the axial direction of the compressor. A plug
 104 includes a first flange 105, second flange 106 and a cylinder 107,
 which connects the flanges 105, 106. The plug 104 is inserted into the
 recess 103 from the left, as viewed in FIG. 5(a). Specifically, the plug
 104 is press fitted in the recess 103 such that the first flange 105
 contacts a positioning step 103b defined on the inner wall 103a of the
 recess 103.
 An annular groove 103c is formed in the wall of the recess 103 at the open
 end. A snap ring 108 is engaged with the annular groove 103c.
 Specifically, the peripheral portion 108a of the snap ring 108 is fitted
 in the groove 103c. The cross section of the snap ring 108 is tapered such
 that its axial dimension decreases toward the periphery. The plug 104 is
 held between the snap ring 108 and the step 103b. The snap ring 108
 prevents the plug 104 from disengaging from the recess 103.
 Dimensional errors may vary the distance d between the groove 103c and the
 step 103b. However, the plug 104 is still securely held between the snap
 ring 108 and the step 103b, since the radial penetration of the peripheral
 portion 108a in the groove 103c can vary. This permits variation in the
 axial location of the plug 104. In FIG. 5(b), a solid line shows the
 position of the snap ring 108 when the distance d is shorter than the
 axial dimension h of the plug 104. A broken line shows the position of the
 snap ring 108 when the distance d is substantially the same as the axial
 dimension h of the plug 104.
 As shown in FIG. 5(a), a separation chamber 109 is defined at the right
 side of the plug 104 by the first flange 105. Also, the first and second
 flanges 105, 106 define the ends of an annular chamber 110. An outlet
 passage 111 is formed in the first flange 105 and the cylinder 107 to
 connect the separation chamber 109 with the annular chamber 110. The
 separation chamber 109 is exposed to the discharge pressure of the
 compressor. The separation chamber 109 is connected to a low pressure zone
 by an oil return passage 112 formed in the housing 101. The low pressure
 zone is an area where the pressure is lower than the discharge pressure.
 Refrigerant gas is discharged to the external circuit from the compressor
 via the discharge passage 102. Before being discharged, the gas flows
 along the inner wall 103a of the separation chamber 109. Centrifugal force
 separates atomized lubricant from the gas. The gas is then discharged to
 the external circuit via the outlet passage 111 and the annular chamber
 110. Due to the pressure difference between the separation chamber 109 and
 the low pressure zone, the separated oil is returned to the low pressure
 zone via the return passage 112. The oil is then supplied to parts in the
 compressor to lubricate and cool the parts.
 However, due to machining errors, the distance d between the groove 103c
 and the step 103b can be far shorter than the axial dimension h of the
 plug 104. In this case, the snap ring 108 cannot be fitted in the groove
 103c.
 Further, if the distance d is greater than the axial dimension h, the plug
 104 will not be firmly held between the snap ring 108 and the step 103b.
 In this case, the plug 104 can be rotated along with the flow of
 refrigerant gas in the separation chamber 109, which causes the
 circumferential surfaces 105a, 106a of the first and second flanges 105,
 106 to slide on the inner surface 103a of the recess 103, which wears the
 plug 104. Also, if loosely held, the plug 104 chatters in the recess 103,
 which produces vibration and noise.
 To solve this problem, the plug 104 is selected from plugs having different
 axial dimensions. When assembling the plug 104 in the chamber 103, the
 distance d between the groove 103c and the step 103b is measured, and a
 plug 104 having a corresponding axial dimension is selected. In this
 manner, dimensional errors due to machining accuracy are accommodated by
 the snap ring 108. Therefore, the assembly of the plug 104 into the recess
 103 is complicated.
 SUMMARY OF THE INVENTION
 Accordingly, it is an objective of the present invention to provide an oil
 separating structure for compressors that facilitates the installation of
 a plug in a recess.
 To achieve the foregoing and other objectives and in accordance with the
 purpose of the present invention, a compressor is provided. The compressor
 includes a housing, a compressing mechanism, a discharge passage and an
 oil separator. The compressing mechanism is housed by the housing, for
 compressing refrigerant gas. Lubricating oil is mixed in the gas. The
 discharge passage permits refrigerant to flow out of the compressor. The
 oil separator separates the lubricating oil from the gas. The separator
 includes a recess, a plug and a supply passage. The plug is securely
 press-fitted in the recess. The plug and the recess form a separation
 chamber located in the flow passage. The plug includes an outlet passage
 leading downstream from the separation chamber. The refrigerant gas enters
 the separation chamber, flows along the wall of the separation chamber and
 exits from the separation chamber, which separates the oil from the gas.
 The supply passage connects the separation chamber to the compressing
 mechanism to supply lubricant to the compressing mechanism.
 Other aspects and advantages of the present invention will become apparent
 from the following description, taken in conjunction with the accompanying
 drawings, illustrating by way of example the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 An oil separating structure according to one embodiment will now be
 described. The mechanism is used in variable displacement compressors for
 vehicle air conditioners.
 The construction of the compressor will first be described.
 As shown in FIG. 1, a front housing 11 is secured to the front end face of
 a cylinder block 12. A rear housing 13 is secured to the rear end face of
 the cylinder block 12. A valve plate 14 is located between the rear
 housing 13 and the rear end face. A crank chamber 15 is defined by the
 inner walls of the front housing 11 and the front end face of the cylinder
 block 12. The front housing 11, the cylinder block 12 and the rear housing
 13 are made of aluminum or aluminum alloy and constitute the compressor
 housing. Compared to a compressor housing made of iron alloy, a compressor
 housing made of aluminum or aluminum alloy reduces the weight of the
 compressor.
 A drive shaft 16 extends through the crank chamber 15 and is rotatably
 supported by the front housing 11 and the cylinder block 12. The drive
 shaft 16 is operably coupled to an engine by an electromagnetic clutch
 (not shown). When the engine is running, the clutch selectively transmits
 the drive power of the engine to the drive shaft 16.
 A lug plate 19 is fixed to the drive shaft 16 in the crank chamber 15. A
 swash plate 20 is supported by the drive shaft 16 in the crank chamber 15
 to slide along the surface of and to tilt with respect to the axis of the
 shaft 16. Part of the lug plate 19 and part of the swash plate 20
 constitute a hinge mechanism 21. The hinge mechanism 21 permits the swash
 plate 20 to incline with respect to the drive shaft 16 and to rotate
 integrally with the drive shaft 16. When the central portion of the swash
 plate 20 moves toward the cylinder block 12, the inclination of the swash
 plate 20 decreases. When the central portion of the swash plate 20 moves
 toward the lug plate 19, the inclination of the swash plate 20 increases.
 Cylinder bores 12a are formed in the cylinder block 12. Each cylinder bore
 12a houses a single-headed piston 22. Specifically, one end of each piston
 22 is located in the associated cylinder bore 12a and the other end of the
 piston 22 is coupled to the periphery of the swash plate 20 by shoes 23.
 The pistons 22 are reciprocated in the cylinder bores 12a by rotation of
 the swash plate 20.
 A suction chamber 24 and a discharge chamber 25 are defined in the rear
 housing 13. Suction ports 26, suction valve flaps 27, discharge ports 28
 and discharge valve flaps 29 are formed in the valve plate 14. Refrigerant
 gas is drawn to the suction chamber 24 from the external refrigerant
 circuit. Then, as each piston 22 moves from the top dead center to the
 bottom dead center in the associated cylinder bore 12a, refrigerant gas in
 the suction chamber 24 is drawn into the cylinder bore 12a through the
 associated suction port 26 and the associated suction valve flap 27. As
 the piston 22 moves from the bottom dead center to the top dead center in
 the cylinder bore 12a, the gas in the cylinder bore 12a is compressed to a
 predetermined pressure. The gas is then discharged to the discharge
 chamber 25 through the associated discharge port 28 and the associated
 valve flap 29.
 An expansion muffler 17 is formed to straddle the cylinder block 12 and the
 rear housing 13. A muffler chamber 17a is defined in the muffler 17. The
 muffler chamber 17a is connected to an external refrigerant circuit. A
 discharge passage 18 is formed in the rear housing 13 to connect the
 discharge chamber 25 with the muffler chamber 17a. Refrigerant gas in the
 discharge chamber 25 is discharged to the external circuit via the
 discharge passage 18 and the muffler chamber 17a. The muffler 17
 suppresses pressure pulsation of the refrigerant gas.
 A bleeding passage 30 includes a passage 30a formed in the drive shaft 16
 along its axis and a passage 30b formed in the cylinder block 12 and the
 valve plate 14. The bleeding passage 30 connects the crank chamber 15 with
 the suction chamber 24. A supply passage 31 connects a discharge pressure
 zone (a separation chamber 49, which will be described later) with the
 crank chamber 15, which is a low pressure zone. The pressure of the low
 pressure zone is lower than the discharge pressure.
 A displacement control valve 32 is accommodated in the rear housing 13 to
 regulate the supply passage 31. The control valve 32 is an electromagnetic
 valve and includes a solenoid 32a and a valve body 32b. Excitation and
 de-excitation of the solenoid 32a causes the valve body 32b to open and
 close the supply passage 31. The control valve 32 is connected to a
 computer (not shown). The computer excites and de-excites the solenoid 32a
 to move the valve body 32b in accordance with the need for air
 conditioning. Accordingly, the control valve 32 regulates the flow of
 refrigerant gas from the discharge chamber 25 to the crank chamber 15,
 which controls the difference between the pressure of the crank chamber 15
 and the pressure of the cylinder bores 12a. That is, the control valve 32
 changes the difference between the pressures acting on the front and rear
 ends of each piston 22. The inclination of the swash plate 20 is altered
 in accordance with changes in the pressure difference. This alters the
 stroke of the pistons 22 and varies the displacement of the compressor.
 When de-excited, the solenoid 32a causes the valve body 32b to open the
 supply passage 31, which connects the separation chamber 49 (discharge
 pressure zone) with the crank chamber 15. Accordingly, the highly
 pressurized gas in the chamber 49 is supplied to the crank chamber 15
 through the supply passage 31, which increases pressure of the crank
 chamber 15. An increase in the crank chamber pressure minimizes the
 inclination of the swash plate 20. This shortens the stroke of each piston
 22 and decreases the displacement of the compressor. When excited, the
 solenoid 32a causes the valve body 32b to close the supply passage 31,
 which releases the gas of the crank chamber 15 through the bleeding
 passage 30 thereby lowering the pressure of the crank chamber 15. A
 decrease in the crank chamber pressure maximizes the inclination of the
 swash plate 20. This lengthens the stroke of each piston 22 and maximizes
 the displacement.
 The oil separating structure of the above described compressor will now be
 described.
 As shown in FIGS. 2 and 3, a recess 41 is formed in the discharge chamber
 25 and located in the discharge passage 18. The recess 41 opens at the
 inner wall 25a of the discharge chamber 25. The open end 41a of the
 chamber 41 is tapered by chamfering. The diameter of the open end 41a
 increases toward the discharge chamber 25. The recess 41 has a circular
 cross-section. The inner wall 41b of the recess 41 includes a large
 diameter portion 42 adjacent to the open end 41a and a small diameter
 portion 43. A step 41c is defined between the large diameter portion 42
 and the small diameter portion 43.
 A plug 44 is made of the same material as that of the rear housing 13. That
 is, the plug 44 is made of aluminum or aluminum alloy. The plug 44 is made
 by casting or forging and includes a first flange 45, a second flange 46
 and a cylinder 47, which connects the first and second flanges 45, 46. The
 first flange 45 includes a stopper 52 and a distal portion 48. The distal
 portion 48 is formed on the opposite side of the stopper 52 from the
 cylinder 47. The outer diameter of the stopper 52 and the outer diameter
 of the second flange 46 are substantially the same as that of the large
 diameter portion 42 of the recess 41. A step 45a is defined between the
 stopper 52 and the distal portion 48. The step 45a of the stopper 52
 engages with the step 41c of the recess 41.
 As illustrated in FIG. 4(a), the entire surface of the plug 44, which
 includes the circumferential surfaces 52a, 48a of the stopper 52 and the
 distal portion 48 and the circumferential surface 46a of the second flange
 46, is roughened by shot blasting. FIG. 4(a) illustrates shots, or
 particles, striking the surface of the plug 44.
 As shown in FIG. 4(c), the roughened surface of the plug 44 is coated with
 a solid lubricant coating 47a. The coating 47a is formed by immersion
 coating. That is, the plug 44 is immersed in a solution in which the solid
 lubricant is dissolved. Then, the plug 44 is dried to remove the solution,
 which forms the coating of solid lubricant. The solid lubricant includes
 fluorocarbon resin such as molybdenum disulfide and
 polytetrafluoroethylene.
 As shown in FIG. 4(d), the coated plug 44 is inserted in the recess 41, and
 the distal portion 48 of the first flange 45 enters first. The plug 44 is
 pushed by a jig J until the step 45a of the first flange 45 engages with
 the step 41c. The outer diameter of the distal portion 48 is greater than
 the diameter of the small diameter portion 43. Thus, press fitting the
 distal portion 48 into the small diameter portion 43 causes the plug 44 to
 be supported by a predetermined contact area.
 The first flange 45 of the plug 44 defines a circular separation chamber 49
 in the right portion of the recess 41. An annular chamber 50 is defined by
 the first and second flanges 45, 46 at the left of the separation chamber
 49. An outlet passage 51 is formed in the first flange 45 and the cylinder
 47 to connect the separation chamber 49 with the annular chamber 50. The
 outlet passage 51 has an entrance in the distal portion 48 and is coaxial
 with the separation chamber 49. A transverse bore forms a pair of exits
 for the outlet passage 51 to the annular chamber 50. The diameter of the
 separation chamber 49 is greater than the diameter of the entrance to the
 outlet passage 51.
 As illustrated in FIG. 3, an introduction passage 18a forms an upstream
 portion of the discharge passage 18 and connects the discharge chamber 25
 with the separation chamber 49. The introduction passage 18a is connected
 to the separation chamber 49 such that, as viewed in the axial direction,
 the passage 18a is tangential to the inner wall 41b of the separation
 chamber 49 as shown in FIG. 3. An outlet passage 18b, which is connected
 to the muffler chamber 17a, forms the downstream portion of the discharge
 passage 18. The outlet passage 18b connects the annular chamber 50 with
 the muffler chamber 17a.
 Refrigerant gas in the discharge chamber 25 is led to the separation
 chamber 49 by the introduction passage 18a. The gas then rotates along the
 inner wall 41b of the separation chamber 49. The centrifugal force of the
 gas rotation separates atomized oil from the refrigerant gas. Gas located
 near the center axis of the separation chamber 49 contains less oil than
 gas located at the periphery of the chamber 49. The outlet passage 51 and
 the separation chamber 49 are coaxial, and the diameter of entrance to the
 outlet passage 51 is smaller than the diameter of the separation chamber
 49. Therefore, gas located at the center, which contains little oil, is
 discharged from the communication passage 50. The gas is then discharged
 to the external refrigerant circuit via the outlet passage 51, the annular
 chamber 50, the outlet passage 18b and the muffler chamber 17a. The
 pressure in the crank chamber 15 is lower than the discharge pressure,
 which acts on the separation chamber 49. The gas in the separation chamber
 49 is conducted to the crank chamber 15 by the pressure difference to
 control the compressor displacement. When gas is conducted to the crank
 chamber 15, the separated oil in the separation chamber 49 is drawn to the
 crank chamber 15 through the supply passage 31. The oil is then delivered
 between the pistons 22 and the shoes 23 and between the shoes 23 and the
 swash plate 20. The oil lubricates and cools the engaging surfaces.
 The illustrated embodiment has the following advantages.
 (1) The plug 44 is press fitted in the recess 41. In other words, the plug
 44 is easily assembled with the compressor by inserting the plug 44 into
 the recess 41, which significantly shortens the manufacturing time
 compared to the prior art.
 (2) The rear housing 13 and the plug 44 are made of the same material,
 which have the same coefficient of thermal expansion. Thus, the distal
 portion 48 of the plug 44 is prevented from being disengaged from the
 small diameter portion 43 of the recess 41 due to the influence of heat.
 That is, the plug 44 is firmly fixed in the recess 41 (the rear housing
 13) regardless of temperature changes.
 (3) The solid lubricant coating is formed on the surface of the plug 44.
 Particularly, the coating formed on the surfaces 52a, 48a of the stopper
 52 and the distal portion 48 of the first flange 45 allows the plug 44 to
 be smoothly inserted into the recess 41.
 If a liquid lubricant such as oil is applied on the surface of the plug 44,
 the liquid lubricant would be removed from the surface of the distal
 portion 48 when the distal portion 48 is pressed into the small diameter
 portion 43, since the distal portion 48 of the plug 44 and the small
 diameter portion 43 of the recess 41 are accurately machined. This
 prevents the plug 44 from being smoothly inserted into the recess 41.
 In the illustrated embodiment, the coating between the rear housing 13 (the
 small diameter portion 43) and the plug 44 (the distal portion 48) is made
 of a different material than the material of the rear housing 13 and the
 plug 44. The coating eliminates galling of the plug 44 and the recess 41,
 which prevents shavings of the rear housing 13 and the plug 44 from being
 mixed in the oil. Therefore, the supply passage 31 is not clogged with the
 shavings.
 (4) The surface of the plug 44 is roughened prior to forming of the coating
 47a. This allows the surface of the plug 44 to hold the solid lubricant,
 thereby strengthening the coating 47a.
 (5) The surface of the plug 44 is roughened by shot blasting. Compared to a
 method using chemical substance to roughen the surface of the plug 44,
 shot blasting allows the roughness to be easily controlled. Also, shot
 blasting improves the working environment for workers.
 (6) The outlet passage 51 opens to the separation chamber 49 and is coaxial
 with the recess 41. Therefore, the gas located in the center of the
 rotation is led to the annular chamber 50 by the outlet passage 51. In
 other words, gas from which oil has been removed by the centrifugal force
 flows to the annular chamber 50 through the outlet passage 51. This
 reduces the amount of oil drawn to the annular chamber 50 by the gas flow.
 That is, the structure reduces the amount of oil discharged to the
 external refrigerant circuit, which improves the oil recovery efficiency.
 (7) The plug 44 includes the first and second flanges 45, 46, which are
 integrated by the cylinder 47. This structure facilitates the installation
 of the plug 44 into the recess 41.
 (8) The open end 41a of the recess 41 is tapered. That is, the diameter of
 the open end 41a increases toward the discharge chamber 25. This allows
 the plug 44 to be smoothly inserted into the recess 41.
 (9) The positioning step 41c is formed in the recess 41. The plug 44 is
 pressed until it contacts the step 41c, which forms the separation chamber
 49 having a predetermined volume without measuring the pressing distance.
 Therefore, this construction reduces the variation of the oil separation
 ability of the separation chamber 49.
 (10) The positioning step 41c is tapered. This structure allows the distal
 portion 48 to be smoothly inserted into the small diameter portion 43.
 (11) The supply passage 31 controls the displacement of the compressor and
 also functions as an oil return passage for the oil separating structure.
 This structure eliminates the necessity for a passage exclusively designed
 for returning oil, which simplifies the compressor structure.
 It should be apparent to those skilled in the art that the present
 invention may be embodied in many other specific forms without departing
 from the spirit or scope of the invention. Particularly, it should be
 understood that the invention may be embodied in the following forms.
 The plug 44 may be made of brass or brass alloy. That is, the plug 44 may
 be made of different type of metal from that of the rear housing 13.
 Forming the rear housing 13 and the plug 44 with metals of different types
 prevents galling, which, would occur if the housing 13 and the plug 44 are
 made of the same type of metal, absent a proper solid lubricant. Compared
 to iron alloys, the coefficient of thermal expansion of brass and brass
 alloy is close to that of aluminum alloy. Therefore, the engagement
 between the recess 41 and the plug 44 is not loosened significantly by
 temperature changes.
 In the preferred embodiment, the rear housing 13 and the plug 44 are made
 of the same material. That is, the materials used for the rear housing 13
 and the plug 44 are of the same type and include the same ratios of
 components. While using the same type of materials for the rear housing 13
 and the plug 44, the components and their ratios may be changed. For
 example, when using aluminum alloys for the rear housing 13 and the plug
 44, one of the rear housing 13 and the plug 44 may be made of an aluminum
 alloy containing hard silicon particles while forming the other with an
 aluminum alloy containing no hard silicon particles. Alternatively, the
 rear housing 13 and the plug 44 may be made of materials containing hard
 particles. In this case, the ratio of the hard particles to the other
 components in the materials may be different.
 The plug 44 may be made of a synthetic resin, which facilitates forming of
 the plug 44 and reduces the weight.
 The oil separating structure may be constructed such that oil in the
 refrigerant gas is separated from the gas by inertial separation. In this
 case, the plug 44 may only have the first flange 45 and the outlet passage
 18b may be directly connected to the separation chamber 49.
 The first flange 45, the second flange 46 and the cylinder 47 may be
 separately formed and integrated by adhesive or welding to form the plug
 44. This simplifies the shape of each component of the plug 44 thereby
 facilitating the forming of the components. Further, the components are
 integrated to form the plug 44, which facilitates the installing of the
 plug 44 into the recess 41.
 The discharge chamber 25 may be connected to the crank chamber 15 by the
 supply passage 31, and the separation chamber 49 may be communicated with
 the crank chamber 15 by an oil return passage formed separately from the
 supply passage 31.
 The surface of the plug 44 may be roughened by a method other than shot
 blasting such as liquid honing.
 The solution to form the coating 47a may be applied to the plug 44 by
 spraying.
 The coating on the plug 44 may be formed by plating such as tin plating.
 Therefore, the present examples and embodiments are to be considered as
 illustrative and not restrictive and the invention is not to be limited to
 the details given herein, but may be modified within the scope and
 equivalence of the appended claims.