Patent Abstract:
A piston pump assembly with a rotatingly driven swashplate in driving relationship with a rocker arm and piston engaged with one end of the rocker arm. A spring urges the rocker arm and piston into contact with an annular ring carried by a bearing in the swashplate. The spring may be a separate leaf spring or may be formed integrally with the rocker arm. The rocker arm engagement with the piston uses a spherical ball-joint-like surface. The contact between each of the rocker arm and piston and the annular ring utilize spherical surfaces on the rocker arm and piston, with an elongated footprint on the rocker arm and a circular footprint on the piston. The piston is allowed a slight radial play in operation.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   Reference is made to the following copending and commonly assigned United States Patent Applications by the same inventors, each of which was filed on the same day as the instant application, and each of which is hereby expressly incorporated by reference: 
   i) STRAINER AND VALVE RELEASE, Ser. No. 10/427,446; and 
   ii) FAN BAFFLE, Ser. No. 10/427,448. 
   FIELD OF THE INVENTION 
   This invention relates to the field of pumps for paint and related coating materials. 
   BACKGROUND OF THE INVENTION 
   In the past, various forms of pumps have been used to deliver paint (or other similar coating material) to a spray gun for atomization in airless spraying. Such pumps have included piston pumps, where the pistons have been driven using a variety of mechanisms, such as eccentric cams, scotch yokes, or cranks and connecting rods to convert rotary to linear motion. Each of these approaches have suffered from various drawbacks, both technical and economic. 
   The present invention overcomes shortcomings of the prior art by using a unique mechanism in an assembly which is both technically and economically efficient. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a paint pump apparatus useful in the practice of the present invention. 
       FIG. 2  is an exploded view of the apparatus of  FIG. 1 . 
       FIG. 3  is a side section elevation view of the apparatus of  FIG. 1 , taken along line  3 — 3  of  FIG. 4 . 
       FIG. 4  is an end section elevation view of the apparatus of  FIG. 1 , taken along line  4 — 4  of  FIG. 3 . 
       FIG. 5  is a free-body side elevation view of a swashplate assembly from  FIG. 3  to illustrate certain aspects of the present invention. 
       FIG. 6  is a perspective view of a rocker arm useful in the practice of the present invention. 
       FIG. 7  is a top plan view of the rocker arm of  FIG. 6 . 
       FIG. 8  is a side section elevation view of the rocker arm of  FIG. 6 , taken along line  8 — 8  of  FIG. 10 . 
       FIG. 9  is a bottom plan view of the rocker arm of  FIG. 6 . 
       FIG. 10  is an end section elevation view of the rocker arm of  FIG. 6 , taken along line  10 — 10  of  FIG. 7 . 
       FIG. 11  is an end elevation view of the rocker arm of  FIG. 6 , with a fragmentary section view taken along line  11 — 11  of  FIG. 7 . 
       FIG. 12  is a fragmentary section view of a socket of the rocker arm of  FIG. 6 , taken along line  12 — 12  of  FIG. 10 . 
       FIG. 13  is a fragmentary section view of a socket of the rocker arm of  FIG. 6 , taken along line  13 — 13  of  FIG. 10 . 
       FIG. 14  is a fragmentary section view of a socket of the rocker arm of  FIG. 6 , taken along line  14 — 14  of  FIG. 10 . 
       FIG. 15  is a perspective view of the rocker arm of  FIG. 6 , assembled together with a piston and useful in the practice of the present invention. 
       FIG. 16  is an end section view of the rocker arm and piston, taken along line  16 — 16  of  FIG. 15 . 
       FIG. 17  is a fragmentary section elevation view of a portion of  FIG. 3 , showing parts of the swashplate assembly with the piston at a bottom dead center position. 
       FIG. 18  is a fragmentary section elevation view of a portion of  FIG. 3 , showing parts of the swashplate assembly with the piston at a top dead center position. 
       FIG. 19  is a fragmentary section bottom plan view of a portion of  FIG. 3 , showing parts of the swashplate assembly with the piston at a mid stroke position. 
       FIG. 20  is an alternative embodiment for the rocker arm useful in the practice of the present invention. 
       FIG. 21  is a side view to illustrate certain features of a piston useful in the practice of the present invention. 
   

   DETAILED DESCRIPTION 
   Referring to the Figures, and most particularly to  FIGS. 1–4 , a paint pump apparatus  20  useful in the practice of the present invention may be seen. Apparatus  20  is intended to pump paint and similar coatings at high pressure to a spray gun (not shown) for application to a surface to be coated via airless spraying. As will be described infra, the apparatus  20  utilizes a swashplate action to drive a piston in a reciprocating manner without relying on return springs or paint back pressure on the piston to maintain contact between the piston and swashplate on the return stroke. 
   Apparatus  20  includes a paint reservoir  22  and a pump assembly  24  carried by a frame  26 . Reservoir  22  may have a cover  28 . Frame  26  preferably has a handle portion  30  and a pair of foot portions  32 ,  34 . Foot portions  32  and  34  are received in a base  36  which supports pump assembly  24 . It is to be understood that a high pressure hose (not shown) is connected to an outlet  38  of the pump assembly  24  after a cap  40  is removed. The high pressure hose is also connected to an airless spray gun (not shown) for delivering paint or other coating material to a surface (not shown) desired to be coated. An inlet  42  of the pump assembly  24  is in fluid communication with reservoir  22 , and sealed against leakage therebetween by one or more O-rings  44 . As may be seen most clearly in  FIG. 4 , paint is delivered by gravity from reservoir  22  to inlet  42  of the paint pump assembly  24 . As is conventional, a return tube  46  is provided from a pump and valve housing  48  containing inlet  42  and outlet  38 . Return tube  46  will return paint from the pump to the reservoir during a “priming” mode. A mechanical switch  50  enables transfer from the “priming” mode to a “run” mode wherein paint is delivered to the outlet  38  instead of the return tube  46 . An ON-OFF electrical switch  52  enables power from a power cord  54  (when connected to electrical supply, not shown) to be delivered to an electric motor  56 . Motor  56  (or another form of prime mover, such as a gasoline engine, not shown) provides mechanical power for pump assembly  24 . 
   Referring now most particularly to  FIGS. 3 and 5 , a gear box  58  couples motor  56  to a spider  60  which is journalled for rotation in pump assembly  24  by a bearing  62  and provides direct drive to a swashplate  64  via a shaft  66  on which the spider  60  and swashplate  64  are rigidly mounted. Referring now also to  FIGS. 17 and 18 , a distal end  68  of shaft  66  is journalled for rotation in a pump assembly housing  70  by a bushing  72 . 
   Referring again to  FIGS. 3 ,  17  and  18 , an inlet check valve  74  is positioned in inlet  42 . Similarly an outlet check valve  76  is positioned in outlet  38 . 
     FIG. 5  illustrates a swashplate assembly  80 , which includes the spider  60 , bearing  62  and swashplate  64  all mounted on shaft  66 . Assembly  80  also includes a rocker arm  82 , a piston  84 , a sleeve bearing or bushing  86 , a seal  88 , and a spring  90 . Additionally, assembly  80  includes an annular thrust plate  92 , thrust bearing  94  and an annular radial spacer  96  as part of the swashplate  64 , as may be seen most clearly in  FIGS. 17 ,  18  and  19 . Returning to  FIG. 5 , spring  90  is shown in solid lines  98  to illustrate the spring itself in a relaxed state and spaced apart from its operating position, and is shown in chain lines  100  in its operating position, where it is urging the rocker arm  82  towards the swashplate  64 . Spring  90  preferably applies at least a  10  pound force on rocker arm  82  in the embodiment shown. Rocker arm  82  has a keyhole shaped recess  102  which is engaged with a generally spherical head  104  of piston  84 , as may be most clearly seen in  FIGS. 15 and 16 . In operation, swashplate  64  is rotated by motor  56  acting through gear box  58  and spider  60  when pump assembly  24  is to be operated, since swashplate  64  is carried on shaft  66 . Rocker arm is constrained in a congruent cavity  106  (see  FIG. 19 ) in pump and valve housing  48 , but is free to oscillate in a rocking motion when driven by rotation of swashplate  64 . The piston  84  follows the motion of keyhole recess  102 , reciprocating in a substantially linear motion, since it is constrained by sleeve bearing  86  against side motion caused by side loads imposed on the head  104  of piston  84  as the swashplate  64  tilts with respect to the piston  84  during operation. Reciprocation of piston  84  will draw paint into a pumping chamber  119  through inlet  42  and deliver paint under pressure via outlet  83 . 
   Referring now to  FIGS. 6–14 , various details of the rocker arm  82  may be seen. Arm  82  is preferably molded of an acetal resin polymer such as is offered under the trademark Delrin by DuPont. Arm  82  has a pair of arched support legs  108  spanned by a first bridge  110  containing the key hole shaped recess  102 , and further spanned by a second bridge  112  having a dome  114  therein. Dome  114  preferably has a spherical radius of 0.75 inches and the recess  102  preferably has a spherical recess  103  with a radius of 0.25 inches in the embodiment shown. A pair of slightly raised shoulders or ramps  116  are located on the underside of bridge  110 , adjacent lateral sides of the key hole shaped recess  102  to limit the amount to which the piston  84  can pivot laterally up to an angle  118  (shown in  FIG. 16 ) of ±2 degrees. Details of shoulders  116  may be seen in  FIGS. 9 ,  13  and  14 . It is to be understood that the piston  84  is retained to the rocker arm  82  in a “snap fit” or detent arrangement wherein the socket end  110  of the rocker arm will temporarily deform to receive the piston, and thereafter retain the piston, while allowing a limited range of angular motion between the piston  84  and the rocker arm  82 . The range of angular motion permitted is sufficient to permit piston  84  to remain aligned with the sleeve bearing  86  as the rocker arm  82  pivots to follow the motion of swashplate  64 . Bearing  86  maintains piston  84  in substantially constant cylindrical alignment with the cylinder chamber  119  in housing  48  as piston  84  reciprocates to provide the pumping action from pump assembly  24 . It is to be understood, however that piston  84  preferably has a slight radial degree of freedom with respect to bearing  86 , preferably between about 0.0025 inches and 0.0005 inches, which has been found to improve the life of seal  88 . This is achieved in the embodiment shown and described by having a bore in the sleeve bearing  86  with a diameter of 0.439 +0.000 −0.001 inches with the piston diameter described infra. 
   Referring now most particularly to  FIG. 15 , dome  114  exhibits a characteristic elongated footprint  156 , corresponding to a wear pattern resulting from contact between dome  114  and plate  92  of swashplate assembly  80 . 
   Referring to  FIG. 17 , swashplate  64  has an axis of rotation  120 . A plane of a drive surface  122  of the swashplate  64  is indicated by line  124 . Line  126  represents a plane which is perpendicular to the axis of rotation  120 . The drive surface  122  of swashplate  64  is preferably predetermined to be a profile angle  128  of 8 degrees, as measured between planes  124  and  126 , keeping in mind that  FIG. 17  shows swashplate  64  at a bottom dead center position for piston  84 . 
   Referring now to  FIG. 21 , piston  84  is preferably formed of 440 C stainless steel, (preferably heat treated to Rc 56–58) and preferably has a head portion  130  and a main cylindrical body portion  132 . A diameter  152  of the main cylindrical portion  154  is preferably 0.437±0.0005 inches. The head portion  130  has a ball-joint-like surface  134  formed with a generally spherical radius profile indicated by radius  136 , which, in the embodiment shown, is preferably 0.25 inches. The head portion  130  has a convex end surface  138  with a generally spherical profile preferably having a radius  140  greater than radius  136 . In the embodiment shown, radius  140  is preferably 0.75 inches. A cylindrical surface  142  (of preferably 0.5 inches diameter) connects the convex end surface  138  and the ball-joint-like surface  134 . The main cylindrical body has a cone shaped surface  144  spaced apart from and facing the ball-joint-like surface  134 . Cone shaped surface  144  is connected to the ball-joint-like surface by a concave cylindrical neck portion  146  preferably having a 0.031 inch radius  148  for the embodiment shown. Cone shaped surface  144  preferably has a cone angle  150  substantially equal to the profile angle  128  of the swashplate  64 , which in this embodiment is preferably  8  degrees. The piston is preferably machined to a finish of  32  microinches, except for a distal end  152  which is preferably finished to 15 microinches for a distance  154  of 0.62 inches, which includes the “working” portion of the piston  84  in contact with seal  88 . Convex end surface  138  exhibits a characteristic circular or toroidal footprint  158 , corresponding to a wear pattern resulting from contact between the end surface  138  of head portion  130  of piston  84  and plate  92  of swashplate assembly  80 . Footprint  158  results from rotation of piston  84  in the pump assembly  24  during operation. 
   Referring now to  FIG. 20 , spring  90  may be replaced with one or more integrally formed cantilevered fingers  160 , preferably two pair of such fingers, with one pair of fingers located on each of opposite lateral sides of the rocker arm  82 ′. 
   In operation, it is to be understood that the piston pump assembly  24  operates from a source of rotary power such as electric motor  56  (or an alternative power source, not shown, such as an internal combustion engine). The rotary power source rotatingly drives a swashplate assembly  80  which in turn is in contact with a rocker arm  82 . The swashplate reciprocates the rocker arm, causing the piston to pump paint in a reciprocating motion by driving the piston in a first direction and by action of the rocker arm returning the piston in a second direction opposite to the first direction. This eliminates the need for a piston return spring commonly found in prior art swashplate pump designs. In the present invention, the rocker arm and piston contact the swashplate at diametrically opposite regions of the swashplate, more particularly contacting the annular thrust plate  92 . The needle bearing  94  is interposed between the thrust plate  92  and a backing plate  95 . The piston is guided by the sleeve bearing  86 , and cup seal  88  prevents paint from leaking past the piston out of the pumping chamber  119 . As the piston moves from the position shown in  FIG. 17  to the position shown in  FIG. 19 , paint is drawn from the reservoir  22  through the inlet check valve  74 . As the piston moves from the position shown in  FIG. 19  to the position shown in  FIG. 17  paint is moved out of the pumping chamber  119  past the outlet check valve  76  to be delivered to a spray gun (not shown). 
   It is to be understood that the numerical values for radii, angles and other parameters of the embodiment described may be varied from those stated, while still remaining within the scope of the present invention. 
   The invention is not to be taken as limited to all the details thereof as modifications and variations thereof may be made without departing from the spirit or scope of the invention.

Technology Classification (CPC): 8