Abstract:
A Positive Fluid Displacement Device (PFDD) with single piece double-ended pistons connected to a crankpin for circular motion. Pistons are nested together to maintain all pistons in the same plane perpendicular to the axis of the crankshaft. Cylinders are driven in a reciprocating fashion by the pistons and are held loosely in a cylinder carriage along its axis with radial sealing engagement therebetween. Pliable members mount port plates within a housing such that there is no direct contact therebetween or with a two-layer manifold. A flat surface of the port plate is urged against the cylinder head by a pliable member which exerts a force on the center of the port plate. Grooves in the first layer of the manifold are sealed by the second layer to form fluid passageways. The cylinder head is guided in housing grooves with a pliable member. A sealing lip is integral with a piston head.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/204,951 filed May 17, 2000. This invention relates to improvements to the positive fluid displacement device (PFDD) with a removable fluid displacement module (FDM) which is the subject of U.S. Pat. No. 6,162,030 issued Dec. 19, 2000, incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to positive fluid displacement devices and more particularly to devices of the piston type for precision fluid delivery.  
         BACKGROUND OF THE INVENTION  
         [0003]    U.S. Pat. No. 6,162,030 describes a Positive Fluid Displacement Device (PFDD) which is the basis of the current invention. The object of the current invention is to improve the design of the patented device. The improved design described herein provides better performance, includes a broader range of applications, improves manufacturability, broadens tolerances, eliminates parts, eases assembly and lowers cost. However, the principles of operation of the PFDD are unchanged and since those principles are fully described in FIGS.  1 A- 1 D of the referenced patent, they are not repeated herein.  
           [0004]    The design has been improved by replacing separate metal parts with single parts using metal or plastic material. The coupling of some components has been modified to allow significantly greater variation in tolerances without reduction in accuracy of fluid delivery and performance of the PFDD. Pliable members are used to position parts with respect to each other for quieter operation, easier assembly and broadening of the tolerances. The configuration of the seals has been modified to eliminate metal parts and to allow the use of different sealing materials in order to meet chemical compatibility requirements with a minimum of changes.  
           [0005]    The use of glass and ceramic material as wetted parts in the device requires careful mounting since those parts cannot be made to the same degree of accuracy as can plastic and metal parts. Therefore, a design which allows significant tolerance in the dimensions of the wetted parts eliminates secondary machining or grinding, thus producing a lower cost device.  
           [0006]    Design improvements in the manifold permit variation in the internal configuration of the manifold passageways to meet different customer requirements, without change in the basic PFDD configuration. Improved mounts for motor connection permit different types of motors to be used, and provides improved rigidity in a minimum amount of space. The inclusion of an optional gearbox permits the use of a smaller motor by increasing the torque available from the motor.  
         SUMMARY OF THE INVENTION  
         [0007]    One aspect of this invention involves the replacement of the multi-part four-piston assembly of the Fluid Displacement Module (FDM) described in the referenced patent with two single parts, each acting as a double-headed piston. Each part is such that it can nest into another identical part, thus providing four pistons in the same plane but oriented approximately 90° apart. The two double-headed pistons are rotatably connected together in a plane perpendicular to the axis of the crankshaft. They are mounted concentrically around the crankpin, so the 90° separation of the pistons is not established by the pistons, but rather by the position of two cylinder carriages. The position of the carriages is defined by grooves in the housing of the PFDD.  
           [0008]    Each piston head also acts as a piston seal and each seal is secured directly to the end of the piston. The double-headed piston slides through the carriage for ease of assembly. Like the patented device, each one has a protrusion to fit inside the port in the cylinder head to reduce dead volume.  
           [0009]    A second aspect of this invention involves a cushioned support for holding the port plate that floats along an axis perpendicular to the axis of the crankshaft. The port plate is captivated to the housing by pliable members such as elastomeric cords which are embedded into the housing. This allows micromotion of the port plate inside the housing, without any part of the port plate directly in contact with the housing. This eliminates rubbing of the port plate directly against the housing, and provides for wide tolerance in the machining of the housing and the port plate. It also provides a spring action on the port plate against the manifold, thus insuring good sealing contact on seals located between the manifold and port plate without preventing the port plate from floating against the cylinder head.  
           [0010]    A third aspect of this invention also relates to cushioning the cylinder heads as they act against the manifold. The cylinder heads are slidably mounted on plastic rails that are also slidably mounted into grooves machined into the housing of the PFDD. Behind the rails, embedded inside the bottom of the grooves, is a pliable buffering member which acts as a spring pushing the cylinder heads against the manifold. The intimate and continuous contact of the cylinder heads against the manifold provides a silent operation without the need to machine the depth of the grooves and the width of the cylinder heads to high precision.  
           [0011]    A fourth aspect of this invention is to provide controlled pressure on the port plate toward the cylinder head in order to maintain zero leakage. This is accomplished by providing a resilient urging member between the housing and the port plate to urge the port plate against the cylinder head. The urging member, may be an elastomeric material or a spring. If a spring is used, the port plates are provided with a groove on the surface opposite the surface sliding against the cylinder head. The groove captivates a metal spring that applies pressure to the center of the port plate. The length and thickness of the spring precisely controls its force against the port plate. The two opposite ends of the spring react against the internal surface of the housing. This design reduces clearance between the top of the port plate and the external surface of the housing to near zero, thus reducing overall dimensions of the housing.  
           [0012]    A fifth aspect of this invention is to provide a cushioned mounting for essentially brittle ceramic or glass cylinders which are loosely mounted inside the cylinder head and the carriage. At the cylinder head, a compliant sealing member provides a seal between cylinder and the cylinder head that acts in a direction parallel to the sliding surface of the cylinder head, thereby avoiding pressure on the cylinder head in a direction perpendicular to the sliding surface. In that manner, distortion of the flatness of the sliding surface of the cylinder head is prevented since there is no contact pressure between the cylinder and the cylinder head, except through the sealing member. The sealing member, which may be an O-ring, also acts to center the cylinder inside the counterbore of the cylinder head. At the other end of the cylinder, a compliant washer, made of Teflon for example, is interposed between the cylinder and the carriage to prevent direct contact between the cylinder and the carriage, thereby avoiding stressing the glass or ceramic cylinder when the cylinder head is assembled to the carriage.  
           [0013]    Additionally, the area of the end surfaces of the carriage in contact with the cylinder head are reduced by providing recesses. The reduction of the contact surface area allows them to be machined and lapped to a flatness of better than two light bands.  
           [0014]    A sixth aspect of this invention is to provide a double-layer manifold that is fastened against the PFDD housing. A first layer of a two-layer manifold has a surface, opposite to the surface in contact with the housing, with fluid passageways grooved therein. The second layer of the two-layer manifold is pressed against the first layer and seals all the grooved passageways. Connection to the fluid supply and to devices using the PFDD is done through inlet and outlet ports on the second layer. The advantage of this design is the elimination of drilling long holes in the manifold and the use of smaller cross section passageways than can be done with a long hole design. The tightness of the fluid passageways is insured between the surfaces of the manifolds by lapping them to a flatness of better than two light bands.  
           [0015]    A seventh aspect of this invention is to directly mount the motor to the back of the PFDD, without couplings, and to have, as an option, a torque-increasing gearbox interposed between the motor and the PFDD.  
           [0016]    The above mentioned and other features and objects of this invention and the manner of obtaining them will become more apparent, and the invention itself will best be understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawing, a description of which follows. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0017]    [0017]FIG. 1 is an exploded view of a two piston fluid displacement module showing a double-ended single piece piston.  
         [0018]    [0018]FIG. 2 is an exploded view of a four piston fluid displacement device showing two fluid displacement modules each with a double-ended single piece piston which are designed to nest together in the PFDD.  
         [0019]    [0019]FIG. 3 shows two fluid displacement modules nested together in assembly.  
         [0020]    [0020]FIG. 4 is a cross-sectional view showing the seal configuration between the cylinder head and cylinder. It also shows the piston seal.  
         [0021]    [0021]FIG. 5 is a cross-sectional view showing the captivation of the port plate inside the PFDD housing in a plane perpendicular to the axis of the crankshaft.  
         [0022]    [0022]FIG. 6 is a cross-sectional view showing the captivation of the port plate inside the housing of the PFDD in a plane parallel to the axis of the crankshaft.  
         [0023]    [0023]FIG. 7 is a partial view of the cylinder carriage showing four contact surfaces which are machined and lapped for contact with the cylinder head.  
         [0024]    [0024]FIG. 8 is a cross-sectional view showing a metal spring located in a groove in a floating port plate to react with the housing and provide force on the floating port plate.  
         [0025]    [0025]FIG. 9 shows one piece of a two piece manifold with grooves and ports machined into the piece shown.  
         [0026]    [0026]FIG. 10 is a cross-sectional view of the two piece manifold.  
         [0027]    [0027]FIG. 11 is a cross-sectional view of the PFDD showing a motor mounted to the PFDD.  
         [0028]    [0028]FIG. 12 is an exploded view of a motor mounting with a torque increaser. 
     
    
     DETAILED DESCRIPTION  
       [0029]    When reference is made to the drawing, like numerals indicate like parts and structural features in the various figures.  
         [0030]    [0030]FIG. 1 is an exploded view of a fluid displacement module (FDM) showing a double-ended single piece piston  2 . Piston  2  has an end  9  having an opening  6  for holding a stem  8  of a single piece piston head  7 . A second piston head is held in the opposite end of piston  2 . In assembly, the piston heads are joined to the piston by pins  10 . Each piston head  7  has a protrusion  5  for filling openings  20  in cylinder heads  12  at top dead center. Hereafter, one piston/cylinder combination with associated elements is described since each combination is identical to the other in configuration although diameter of cylinders can vary.  
         [0031]    The piston and piston head assembly fits into a cylinder  11 . Cylinder  11  has a groove  15  on an end  16  providing for the location of a compliant sealing member  14  such as an O-ring. The end  16  of cylinder  11  fits into counterbore  13  of cylinder head  12 . In assembly with the cylinder head, the cylinder  11  is not pressed against the bottom  17  of counterbore  13  as shown in FIG. 4. In assembly, the bottom surface  25  of cylinder  11  is cushioned from contact with cylinder carriage  19  by a compliant washer  26  interposed between the two parts.  
         [0032]    Cylinder head  12  has a sliding surface  23  which is machined and lapped for sliding against a port plate, not shown in FIG. 1. Opposite surface  23  is a surface  18  of cylinder head  12  which mates with small contact surfaces  22  on cylinder carriage  19 . There are four contact surfaces  22  on each end of cylinder carriage  19  to mate with surface  18 . The four small contact surfaces are provided by locating four recesses  21  in the end of cylinder carriage  19 .  
         [0033]    A crankshaft, not shown, drives piston  2  through a bearing  3 .  
         [0034]    [0034]FIG. 2 is an exploded view of two fluid displacement modules showing how one can be nested in assembly with another around the crankshaft bearing  3 . Cylinder carriage  19  and cylinder carriage  19 A carry pistons  2  and  2 A, respectively, with bearing  3  passing through the openings  30  and  30 A in the pistons.  
         [0035]    [0035]FIG. 3 shows two fluid displacement modules  31  and  32  in assembly. When in assembly the device is a four-piston fluid displacement device and the two modules  31  and  32  are then sometimes referred to as one fluid displacement module.  
         [0036]    [0036]FIG. 4 is a cross-sectional view taken along line  4 - 4  of FIG. 3. It shows the cylinder, cylinder head, piston head and piston in assembly. Cylinder head  12  has an opening  20  which is emptied of fluid by protrusion  5  on piston head  7  at top dead center of piston travel. In assembly, cylinder  11  is spaced from cylinder head  12  by clearance space  24 . The bottom end of cylinder  11  is located on a compliant washer  26  which is interposed between cylinder  11  and cylinder carriage  19  and is intended to reduce clearance space  24  to near zero. Cylinder  11  is shown assembled within counterbore  13  with compliant sealing member  14  located between the cylinder and the cylinder head to provide sealing engagement therebetween. Piston  2  is assembled with piston head  7  through pin  10 . A seal between piston head  7  and cylinder  11  is provided by a sealing lip  4  which is integral with piston head  7 . Lip  4  is backed by an elastomeric element  27  which may be an O-ring.  
         [0037]    [0037]FIG. 5 is a partial cross-sectional view showing the assembly of floating port plate  33  with the cylinder/piston combination. An urging member  37 , which may be of elastomeric material, is interposed between the top surface of port plate  33  and the housing  34  of the PFDD. Pliable members  35  and  35 A, which may be made of elastomeric material, are interposed between the left and right surfaces of port plate  33  and the housing  34 .  
         [0038]    [0038]FIG. 5 shows displacement chamber  39  within cylinder  11 . Chamber  39  receives and discharges fluid through opening  20  in cylinder head  12 .  
         [0039]    [0039]FIG. 6 also shows the captivation of the port plate  33  within the housing  34  and shows another pliable buffering member  40  interposed between the back side of port plate  33  and the housing  34 . Together FIGS. 5 and 6 show that the port plate  33  does not come into direct mechanical contact with the housing  34 .  
         [0040]    Pliable seal  41 , which may be an O-ring, provides a seal between manifold  42  and port plate  33 . Rail  44  is located within a groove  43  in the housing  34  and provides support for the cylinder head  12  which slides within the rail  44 . A resilient member  45  is located between rail  44  and housing  34  providing compliance to the arrangement of rail and housing.  
         [0041]    [0041]FIG. 7 is a partial perspective view of cylinder carriage  19  and shows four recesses  21  in the end surface of cylinder  19 . Recesses  21  provide four small contact surfaces  22  which are machined and lapped to close tolerance for connection to cylinder head  12 . These four surfaces as well as surfaces  18  and  23  of cylinder head  12  (FIG. 4) are machined and lapped to a flatness of better than two light bands.  
         [0042]    [0042]FIG. 8 is a partial cross-sectional view showing the pliable member  37  as a spring  46  interposed between the housing  34  and port plate  33 . Spring  46  is located in a groove  47  in port plate  33  with the ends  48  of spring  46  bearing against the housing  34 . The spring applies pressure in the center of the port plate achieving superior control with a reduction in the clearance between the port plate and the housing compared to the elastomeric embodiment of FIG. 5.  
         [0043]    [0043]FIGS. 9 and 10 show a two-layer manifold with a first layer  42  directly adjacent to the port plate  33  and a second layer  49  on the opposite side of layer  42 . Layer  49  has inlet and outlet ports  50  and  51  to supply fluid to the PFDD and an outlet connection to components outside the PFDD. FIG. 9 shows layer  42  with grooves  61  and  63  cut into the surface of layer  42  extending from and to ports  60  and  62 . Grooves  61  and  63  are machined into the surface of layer  42  and are sealed by layer  49  when the manifold is assembled to create passageways for fluid to communicate with ports  60  and  62 . Ports  60 A and  62 A may be the inlet and outlet ports in communication with corresponding ports in the port plate of a first piston/cylinder assembly. Ports  60 B and  62 B are for a second piston/cylinder assembly, ports  60 C and  62 C are for a third such assembly, and ports  60 D and  62 D are for a fourth such assembly.  
         [0044]    [0044]FIG. 11 is a cross-sectional view of the PFDD in assembly with motor  64 . Drive shaft  70  is directly connected to crankshaft  67  through a pin  66 . Bearing  68  carries the crankshaft  67  and is interposed between adapter  69  and the housing  34  of the PFDD. Crankpin  65  is connected with a centerline offset from the centerline of crankshaft  67  in order to provide an orbital motion to piston  2  mounted on the crankpin. Diameter of piston movement is equal to twice the eccentricity of crankpin  65 . This design achieves a small PFDD/motor package and provides direct connection of the motor driveshaft to the PFDD crankshaft.  
         [0045]    [0045]FIG. 12 is an exploded view showing another motor  78  with its shaft modified to accommodate a pinion  76 . The pinion meshes with gear  72  to drive crankshaft  74  through disk  73  and achieve torque requirements. The pinion  76  is secured with the pin  77  to the motor driveshaft. Disk  73  is secured to crankshaft  74 . Location of the disk  73  is accurately controlled and provides precise meshing of the pinion and the ring gear. The motor is bolted to the adapter  69  via an eccentric ring  71  that provides support for the bearing  75 .  
         [0046]    In operation of the PFDD, and with respect to FIG. 4, fluid enters the displacement chamber  39  through opening  20  in the cylinder head and fills the displacement chamber. The fluid contacts piston seal  4  but never comes into contact with the piston  2 . The fluid is also dispelled from the displacement chamber through opening  20  and on through the port plate  33  and the passageways and ports in the manifold to using devices exterior to the PFDD.  
         [0047]    Note that the cylinder  11  fits inside the cylinder head  12  into the counterbore  13  with a seal which is a compliant sealing member  14 . The end  16  of cylinder  11  does not come into pressurized mechanical contact with the bottom  17  of the counterbore  13  and therefore axial forces are not placed on the cylinder (nor on the cylinder head.) The sealing pressure of member  14 , which may be an O-ring, is exerted radially in a plane parallel to the large surface  18  of the cylinder head. Sealing pressure from member  14  is along line A-A as shown in FIG. 4. The presence of the small clearance space  24  prevents any possibility of axial pressure on the cylinder head or the cylinder when the two are assembled. Note that the other end  25  of cylinder  11  is restrained on the cylinder carriage by a washer  26  made out of a semi-compliant material such as teflon. As a result the cylinder, which is often made of glass or ceramic material, is not stressed under axial forces when the PFDD is assembled and in use. Also, the arrangement avoids pressure on the cylinder head in a direction perpendicular to sliding surface  23  and therefore distortions of the surface sliding against the port plate are prevented.  
         [0048]    [0048]FIG. 2, an exploded view of fluid displacement modules, shows the construction which enables a nesting of the cylinder carriages within each other. It shows two double-ended pistons which are connected together around a bearing sleeve  3 . Since the pistons are connected around a bearing sleeve, the 90° angle between the two double-ended pistons is not defined by the pistons but rather by the position of the cylinder heads sliding within the rails  44 . Rails  44  are in turn held inside grooves  43  in the PFDD housing. As a consequence, no binding occurs and precision in establishing the angularity of the pistons is not required. Note that the carriages  19  and  19 A are of the same basic construction with the center of each carriage cut or milled out to allow the nesting of the carriages into each other. In that manner the axis of the two double-ended pistons are in the same plane, perpendicular to the axis of the crankshaft. FIG. 3 shows the two double-ended pistons and the carriages nested together to form a four piston fluid displacement module.  
         [0049]    As mentioned above, FIGS. 5 and 6 show that the port plate  33  does not come into direct mechanical contact with housing  34 . The port plate is urged against the cylinder head by pliable member  37  which may be, for example, an elastomer or a spring, and is held away from housing  34  by pliable members  35 ,  35 A,  37  and  40 . Forces exerted on the port plate by resilient members  40  are balanced by the pliable seal  41  located between the manifold  42  and the port plate. The port plate is never in direct mechanical contact with either the housing  34  or the manifold  42 , thus avoiding any abrasion which would be caused by micromotion of the hard material port plate (ceramic, sapphire, hardened steel, etc.) with the housing or manifold. The only direct contact of surfaces on the port plate with another part is the surface-to-surface contact with surface  23  of cylinder head  12 . Because of manufacturing tolerance, the cylinder head sliding in the rails  44  of the housing is not kept in a constant geometric location. Therefore, the surface of port plate  33  in contact with surface  23  of cylinder head  12 , which surface must always be in intimate contact with the cylinder head  12 , must be allowed to float and follow the geometric location of the cylinder head. As a result, a constant micromotion of the port plate results and can be very destructive to other surfaces of the port plate if they are in direct mechanical contact with the housing or manifold. The use of pliable members between those surfaces allows micromotion of the port plate to follow the cylinder head with no damage.  
         [0050]    [0050]FIG. 6 shows a groove  43  cut into the housing  34 . The purpose of the groove is to hold rail  34  along which the cylinder head slides. A resilient member  45  is located at the bottom of groove  43  and urges the cylinder head toward the manifold  42 . This arrangement eliminates clearance between the two large longitudinal sliding surfaces of the cylinder head, that is, surfaces which slide against the rail and the manifold. This assures a quiet operation and eliminates the requirement of precision manufacturing tolerances on the cylinder head and in the depth of the groove  43 .  
         [0051]    [0051]FIGS. 9 and 10 show the two-layer manifold which has grooves cut into the surface of the first manifold layer in order to provide communication between the ports  60  and  62 . The grooves may be cut in the same manufacturing setup in which the surface of manifold layer  42  is machined. The grooves are sealed by a second manifold layer  49  to provide passageways for conducting fluid through the manifold. The surfaces between the two layers are lapped to a flatness of better than two light bands to insure leak tightness without the need for using a gasket. Inlet and outlet ports on the second manifold layer  49  are connected to the passageways in the first manifold layer  42 . For applications where very low flow is required and minimum volume in the pump is a requirement, the passageways can be very small yet accessible and easy to clean.  
         [0052]    While the invention has been shown and described with reference to preferred embodiments thereof, it should be understood that changes in the form and details of the invention may be made therein without departing from the spirit and scope of the invention.