Abstract:
Variable displacement pistons are produced wherein hollow piston bodies are integrally formed with associated actuator arms to ensure proper alignment of the bodies and rods. The process utilizes a two-axis press to first form a pair of actuator arms by working a blank of metallic material along a first axis between opposing members of a die assembly. With the die assembly still closed after formation of the actuator arms, a pair of hollow piston bodies are formed by extruding the remainder of the blank of metallic material along a second axis. The hollow piston bodies are axially aligned and integrally formed with respective ones of the actuator arms. A piston head is welded to the end of each hollow piston body which is then machined. By separating the actuator arms from one another, a pair of variable displacement compressor pistons having hollow piston bodies axially aligned and integrally formed with respective actuator arms are thus formed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates in general to a variable displacement compressor piston, and, more particularly, to a variable displacement compressor piston having a hollow piston body axially aligned and integral with an actuator rod. 
     Variable displacement compressor pistons are used in a variety of applications including, for example, compressors used in automobile air conditioning systems. One method of producing such a piston involves forging a solid piston body with an accompanying integral actuator arm. A piston ring is added to the solid piston body to maintain sufficient air compression as the piston slides in a bore in a reciprocal fashion during compressor operation. The two components of such a piston must be manufactured separately and be later assembled thereby increasing production time and cost. Further, the solid piston body has a relatively large mass which increases reciprocating inertia in the system, and thus, reduces efficiency of the piston. 
     Another method of producing a variable displacement piston involves manufacturing a hollow piston body, typically by extrusion, and welding the hollow piston body to an actuator arm, which is typically formed by forging. The outer surface of the hollow piston body is machined along its length such that a piston ring is not required to maintain sufficient air compression during piston strokes. However, two parts still must be manufactured and assembled. Further, the piston body and actuator arm require machining to produce an appropriate surface at the joint where the two parts are welded together. The machining operation requires that the piston body and the actuator arm be precisely aligned during welding which is difficult. Improper alignment, due to lack of straightness, concentricity, perpendicularity and runout can result in unusable pistons once the machining operation is performed. 
     Accordingly, there is a need for a process of producing variable displacement compressor pistons which can be machined with little or no possibility of rendering the pistons unusable due to the machining operations. Preferably, such a process would produce pistons having relatively little mass and requiring no piston rings. Further, to improve manufacturing efficiency and accordingly expense, the process should require fewer and/or more simplified manufacturing steps. 
     SUMMARY OF THE INVENTION 
     The present invention meets this need by providing a process for producing variable displacement compressor pistons more efficiently and wherein hollow piston bodies are integrally formed with associated actuator arms to ensure proper alignment of the bodies and rods and thereby substantially eliminate machining problems associated with prior art pistons. The process utilizes a two-axis press to first form a pair of actuator arms by working a blank of metallic material along a first axis between opposing members of a die assembly. With the die assembly still closed after formation of the actuator arms, a pair of hollow piston bodies are formed by extruding the remainder of the blank of metallic material along a second axis. The hollow piston bodies are axially aligned and integrally formed with respective ones of the actuator arms. A piston head is welded to the end of each hollow piston body which is then machined and the actuator arms are separated from each other. A pair of variable displacement compressor pistons having hollow piston bodies axially aligned and integrally formed with respective actuator arms are thus formed. 
     According to a first aspect of the present invention, a process for forming a piston having an integral actuator arm comprises providing a blank of metallic material. The blank of metallic material is worked along a first axis so as to form at least one actuator arm. The blank of metallic material is also worked along a second axis so as to form at least one hollow piston body axially aligned with and integrally formed with the one actuator arm. 
     The step of working the blank of metallic material along a first axis so as to form at least one actuator arm may comprise the step of working the blank of metallic material along the first axis so as to form interconnected first and second actuator arms while the step of working the blank of metallic material along a second axis so as to form at least one hollow piston body axially aligned with and integrally formed with the at least one actuator arm may comprise the step of working the blank of metallic material along the second axis so as to form a first hollow piston body axially aligned with and integrally formed with the first actuator arm and a second hollow piston body axially aligned with and integrally formed with the second actuator arm. The process may further comprise coupling a first piston head to the first hollow piston body and coupling a second piston head to the second hollow piston body. The step of coupling a first piston head to the first hollow piston body may comprise the step of welding the first piston head to the first hollow piston body and the step of coupling a second piston head to the second hollow piston body may comprise the step of welding the second piston head to the second hollow piston body. The process may further comprise the step of separating the first and second interconnected actuator arms. The step of separating the first and second interconnected actuator arms may comprise the step of severing the blank of metallic material between the first and second interconnected actuator arms. 
     The step of working the blank of metallic material along a first axis so as to form at least one actuator arm may comprise positioning the blank of metallic material in a first stationary portion of a split die assembly. A second portion of the split die assembly is positioned over the first portion of the split die assembly with the first and second portions of the split die assembly forming a cavity. A first portion of the cavity has a shape corresponding to the shape of the at least one actuator arm. Pressure is applied to the second portion of the split die assembly along the first axis thereby forcing the second portion of the split die assembly towards the first portion of the split die assembly and working the blank of metallic material between the first and second portions of the split die assembly. 
     The step of working the blank of metallic material along a second axis so as to form at least one hollow piston body axially aligned with and integrally formed with the at least one actuator arm may comprise inserting at least one punch through a second portion of the cavity of the split die assembly positioned substantially adjacent the first portion of the cavity and having a diameter corresponding to an outer diameter of the first hollow piston body. The punch has a diameter corresponding to an inner diameter of the hollow piston body. Pressure is applied with the punch along the second axis to the blank of metallic material thereby back extruding the hollow piston body over the punch. The step of inserting at least one punch through the second portion of the cavity of the split die assembly and applying pressure with the punch along the second axis to the metallic material are preferably carried out with the second portion of the split die assembly engaging the first portion of the split die assembly. 
     The step of providing a blank of metallic material may comprise providing a block of metallic material having first and second surfaces forming planes that are generally perpendicular to the first axis and third and fourth surfaces forming planes that are generally perpendicular to the second axis. A portion of the block of metallic material is removed from the first side along a central portion of the block of metallic material. The step of removing a portion of the block of metallic material along a central portion of the block of metallic from the first side of the block of metallic material may comprise the step of forming a plurality of notches thereby forming at least a pair of generally symmetrical ribs. Preferably, the blank of metallic material comprises aluminum. 
     According to another aspect of the present invention, a process for forming a pair of pistons having integral actuator arms comprises providing a blank of metallic material. The blank of metallic material is worked along a first axis so as to form interconnected first and second actuator arms. The blank of metallic material is also worked along a second axis so as to form a first hollow piston body axially aligned and integral with the first actuator arm and a second hollow piston body axially aligned and integral with the second actuator arm. A first piston head is coupled to the first hollow piston body and a second piston head is coupled to the second hollow piston body. The first and second interconnected actuator arms are separated thereby forming a first piston having the first hollow piston body axially aligned and integral with the first actuator arm and a second piston having the second hollow piston body axially aligned and integral with the second actuator arm. 
     The step of coupling a first piston head to the first hollow piston body may comprise the step of welding the first piston head to the first hollow piston body and the step of coupling a second piston head to the second hollow piston body may comprise the step of welding the second piston head to the second hollow piston body. The step of separating the first and second interconnected actuator arms may comprise the step of sawing the blank of metallic material between the first and second interconnected actuator arms. The step of separating the first and second interconnected actuator arms may be performed prior to coupling a first piston head to the first hollow piston body and coupling a second piston head to the second hollow piston body. 
     The step of working the blank of metallic material along the first axis thereby forming interconnected first and second actuator arms may comprise positioning the blank of metallic material in a first stationary portion of a split die assembly. A second portion of the split die assembly is positioned over the first portion of the split die assembly with the first and second portions of the split die assembly forming a cavity. A first portion of the cavity has a shape corresponding to a shape of the interconnected first and second actuator arms. Pressure is applied to the second portion of the split die assembly along the first axis thereby forcing the second portion of the split die assembly towards the first portion of the split die assembly and working the blank of metallic material between the first and second portions of the split die assembly. 
     The step of working the blank of metallic material along the second axis thereby forming a first hollow piston body and a second hollow piston body may comprise inserting first and second punches through second and third portions of the cavity of the split die assembly. The second and third portions of the cavity are positioned substantially adjacent opposing ends of the first portion of the cavity and have diameters corresponding to the outer diameter of the first and second hollow piston bodies, respectively, while the first and second punches have a diameter corresponding to the inner diameter of the first and second hollow piston bodies. Pressure is applied with the first and second punches along the second axis to the blank of metallic material thereby back extruding the first and second hollow piston bodies over the first and second punches, respectively. The steps of inserting first and second punches through second and third portions of the cavity of the split die assembly and applying pressure with the first and second punches along the second axis to the third and fourth ends of the blank of metallic material are preferably carried out with the second portion of the split die assembly engaging the first portion of the split die assembly. 
     The step of providing a blank of metallic material may comprise providing a block of metallic material having first and second surfaces forming planes that are generally perpendicular to the first axis and third and fourth surfaces generally perpendicular to the second axis. A central portion of the block of metallic material is removed from the first side of the block of metallic material. The step of removing a central portion of the block of metallic material from the first side of the block of metallic may comprise the step of forming a plurality of notches thereby forming at least a pair of generally symmetrical ribs. Preferably, the blank of metallic material comprises aluminum. 
     Accordingly, it is an object of the present invention to provide a process for producing a variable displacement compressor piston more efficiently. It is another object of the present invention to provide a process for producing a variable displacement compressor piston wherein a hollow body is properly aligned with an associated actuator rod so that machining of the piston does not destroy the piston. It is yet another object of the present invention to provide a process that produces a piston having relatively little mass and no piston ring. It is still another object of the present invention to provide a process that produces a piston using fewer and/or more simplified steps. 
    
    
     Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 1A are a side view and a perspective view, respectively, of a variable displacement compressor piston manufactured according to the present invention; 
     FIG. 2 is a side view of a blank of metallic material used to form the piston of FIG. 1; 
     FIG. 3 is a side view of a block of metallic material used to form the blank of FIG. 2; 
     FIG. 3A is a bottom view of the block of metallic material of FIG.  3 . 
     FIG. 4 is a cross-sectional view of a two-axis press used to form the piston of FIG. 1; 
     FIG. 5 is a cross-sectional view of the two-axis press of FIG. 4 with the blank of metallic material positioned therein; 
     FIG. 6 is a cross-sectional view of the two-axis press of FIG. 4 with the blank of metallic material worked along a first axis; 
     FIG. 7 is a cross-sectional view of the two-axis press of FIG. 4 with the blank of metallic material worked along a second axis; 
     FIG. 8 is a side view of interconnected pistons formed using the two-axis press of FIG. 4; and 
     FIG. 9 is a cross-sectional view of a piston head covering a hollow piston body of the piston of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the present invention is applicable in general to the formation of pistons having hollow piston bodies axially aligned and integral with actuator arms, it will be described herein with reference to a piston for use with a variable displacement compressor in an automobile air conditioning system for which it is particularly attractive and in which it is initially being utilized. One such piston  10  is illustrated in FIGS. 1 and 1A and comprises a hollow piston body  12 , an actuator arm  14 , a piston head  16  and a connection rod  17 . As illustrated, the hollow piston body  12  is integrally formed and axially aligned with the actuator arm  14  along an axis A. By ensuring proper alignment of the hollow piston body  12  with the remainder of the piston, the piston  10  can be machined without destruction of the integrity of the piston which occurred in prior art pistons whenever the piston body was misaligned which, unfortunately, could be frequent. 
     In the illustrated embodiment, the hollow piston body  12  and the actuator arm  14  are integrally formed from a preformed blank  18  of metallic material shown in FIG.  2 . The blank  18  of metallic material is formed from a generally rectangular block  20  of metallic material shown in FIG.  3 . The block  20  comprises first and second surfaces  20 A,  20 B forming planes  22 ,  24  extending into the drawing and are generally perpendicular to a first axis  26 . The block  20  also comprises third and fourth surfaces  20 C,  20 D forming planes  28 ,  30  extending into the drawing and are generally perpendicular to a second axis  32 . In the illustrated embodiment, the first axis  26  is substantially perpendicular to the second axis  32 . The blank  18  is formed by removing a central portion  20 E from the block  20  through the first side  20 A. 
     As shown in FIG. 2, upon removal of the central portion  20 E from the first side  20 A of the block  20 , a cavity  34  is formed with a pair of ribs  36 ,  38  extending therein. The ribs  36 ,  38  are spaced and sized to aid in the formation of a corresponding pair of connector rods  17  as described herein. For descriptive purposes, the blank  18  includes first and second surfaces  18 A,  18 B forming the planes  22 ,  24  and third and forth surfaces  18 C,  18 D forming the planes  28 ,  30 . It should be apparent from the ensuing description that the hollow piston body  12  and the actuator arm  14  may be formed from other blanks of metallic material having a variety of shapes and configurations. In the illustrated embodiment, the blank  18  of metallic material comprises 4000 series aluminum. It will be appreciated by those skilled in the art that the blank  18  may also comprise other suitable metals and alloys as required for given applications. 
     Referring now to FIGS. 4-8, a pair of interconnected first and second pistons  10 ′,  10 ″, see FIG. 8, are formed using a split die assembly  40  and working the blank  18  of metallic material along the first axis  30  and then working the blank  18  along the second axis  32 . As shown in FIG. 8, the pair of interconnected first and second pistons  10 ′,  10 ″ comprise interconnected first and second actuator arms  14 ′,  14 ″, first and second hollow piston bodies,  12 ′,  12 ″, first and second piston heads  16 ′,  16 ″ and first and connection rods  17 ′,  17 ″. For descriptive purposes, the first and second axes  30 ,  32  referenced in FIGS. 2 and 3 correspond to the axes of working of the blank  18  within the die assembly  40  illustrated in FIGS. 4-7. 
     Referring again to FIGS. 4-7, the split die assembly  40  comprises a first stationary portion  42 , a second moveable portion  44 , a first punch  46  and a second punch  48 . The second portion  44  of the die assembly  40  moves relative to the first portion  42  along the first axis  30  while the first and second punches  46 ,  48  move towards each other along the second axis  32 . The first portion  42  of the die assembly  40  includes a first die block  52  and the second portion  44  of the die assembly  40  includes a second die block  54 . The first and second die blocks  52 ,  54  are aligned with each other and together form a cavity (not referenced) having a shape corresponding to the shape of the interconnected first and second actuator arms  14 ′,  14 ″. The first die block  52  is centered within the first portion  42  of the die assembly  40  and positioned between third and fourth die blocks  56 ,  58 . Similarly, the second die block  54  is centered within the second portion  44  of the die assembly  40  and positioned between fifth and sixth die blocks  60 ,  62 . As shown in FIG. 6, the third and fifth die blocks  56 ,  60  are aligned with each other and together form a cavity  64  having a diameter corresponding to an outer diameter of the first hollow piston body  12 ′. Similarly, the fourth and sixth die blocks  58 ,  60  are aligned with each other and together form a cavity  66  having a diameter corresponding to an outer diameter of the second hollow piston body  12 ″. 
     As shown in FIG. 5, the blank  18  is positioned over the first die block  52  within the first portion  42  of the die assembly  40 . Referring to FIG. 6, the second portion  44  of the die assembly  40  is aligned with the first portion  42  by a pair of guide posts (not shown) and moved towards the first portion  42  along the first axis  30  by a hydraulic press (not shown) thereby working the blank  18  between the first, second, third, fourth, fifth and sixth die blocks  52 ,  54 ,  56 ,  58 ,  60 ,  62 . The interconnected first and second actuator arms  14 ′,  14 ″ are thus formed between the first and second die blocks  52 ,  54 . The first and second hollow piston bodies  12 ′,  12 ″ are also partially formed within the cavities  64 ,  66  as portions of the blank  18  within the cavities  64 ,  66  are slightly rounded between the third, fourth, fifth and sixth die blocks  56 ,  58 ,  60 ,  62 . However, it will be appreciated by those skilled in the art that the first and second hollow piston bodies  12 ′,  12 ″ can be formed without partially rounding or otherwise processing the portions of the blank  18  within the cavities  64 ,  66  as the blank  18  is worked along the first axis  30 . 
     Referring now to FIG. 7, the first and second punches  46 ,  48  are inserted into the cavities  64 ,  66  and engage respective portions of the blank  18 . As illustrated in FIG. 7, the first and second punches  46 ,  48  are inserted into the cavities  64 ,  66  with the second portion  44  of the die assembly  40  fully engaged with the first portion  42  (i.e., with the die assembly  40  closed). The first and second punches  46 ,  48  are driven towards each other along the second axis  32  by hydraulic presses (not shown). The first and second punches  46 ,  48  work the respective portions of the blank  46 ,  48  thereby causing the first and second hollow piston bodies  12 ′,  12 ″ to be back extruded over the punches  46 ,  48 . A first portion  46 A of the first punch  46  has a diameter corresponding to the inner diameter of the first hollow piston body  12 ′ while a first portion  48 A of the second punch  48  has a diameter corresponding to the inner diameter of the second hollow piston body  12 ″. A second portion  46 B of the first punch  46  and a second portion  48 B of the second punch  48  each have a diameter corresponding to the diameter of each respective cavity  64 ,  66  so as to maintain the proper position of each punch  46 ,  48  within the die assembly  40  during the back extrusion process. It should be apparent that the thickness of the first and second hollow piston bodies  12 ′,  12 ″ is controlled by the diameters of the cavities  64 ,  66  and the diameters of the first portions  46 A,  48 A of the first and second punches  46 ,  48 . 
     As illustrated in FIG. 7, the first and second hollow piston bodies  12 ′,  12 ″ are completely formed once the first and second punches  46 ,  48  are fully extended within the cavities  64 ,  66 . As formed, the first actuator arm  14 ′ is axially aligned and integral with the first hollow piston body  12 ′ while the second actuator arm  14 ″ is axially aligned and integral with the second hollow piston body  12 ″ as the actuator arms  14 ′,  14 ″ and the piston bodies  12 ′,  12 ″ are formed from the same blank  18  of metallic material. The first and second punches  46 ,  48  are removed from the cavities  64 ,  66  and the second portion  44  of the die assembly  40  is disengaged from the first portion  42  exposing the interconnected first and second pistons  10 ′,  10 ″. The interconnected first and second pistons  10 ′,  10 ″ are forced out of the first portion  42  by pins  68 . 
     The interconnected first and second pistons  10 ′,  10 ″ are separated from each other, for example by sawing the actuator arms  14 ′,  14 ″ between the connection rods  17 ′,  17 ″. The piston heads  16 ′,  16 ″ are then welded to the first and second hollow piston bodies  12 ′,  12 ″, respectively thereby forming two separate pistons. 
     As shown in FIG. 9, the piston head  16  includes a base portion  70  having a button portion  72  extending from a first surface  16 A thereof and an annular ring  74  extending from a second surface  16 B thereof. A shoulder  16 C is formed between the annular ring  72  and the base portion  70 . The base portion  70  has a diameter corresponding to the outer diameter of the hollow piston body  12  while the annular ring  72  has an outer diameter corresponding the inner diameter of hollow piston body  12 . The shoulder  16 C of the piston head  16  thus engages the hollow piston body  12  with the annular ring  74  maintaining the orientation of the piston head  16  within the hollow piston body  12  prior to welding. The pistons are then machined as required. 
     It will be appreciated by those skilled in the art that the piston head  16  may be attached to the hollow piston body  12  using other suitable methods. In the illustrated embodiment, the piston head  16  comprises 6000 series aluminum. However, it will be appreciated by those skilled in the art that the piston head  16  may also comprise other suitable metals and alloys as required for a given application. 
     Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.