Abstract:
A pump/compressor that utilizes a wedge at a fixed angle to operate the pump&#39;s pistons at a fixed stroke. Alternatively the wedge can be moved axially to increase or decrease the clearance volume. Variable fluid flow at any clearance volume is achieved by rotating the wedge with respect to the port plate thereby changing the timing of the pistons with respect to the fixed port plate which changes the timing of the intake and output cycles. This results in a portion of the intake charge being breathed back into the intake port and a portion of the output charge being breathed back from the outlet port. This causes the pistons to not take in a full charge from the inlet port and to not pump out a full charge into the outlet port. Thus, fluid flow is varied. The design results in a smaller pump as the wedge is supported by the pump housing rather than a mechanical linkage required of prior adjustable angle swashplate designs.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a multi-piston axial machine that operates as a pump or compressor. Throughout this application the terms axial pump, axial pump/compressor or pump will refer to and include both an axial pump and an axial compressor.  
       DESCRIPTION OF THE PRIOR ART  
       [0002]     Axial pumps for liquids or gases employ a plurality of cylinders and reciprocating pistons that are aligned parallel to and disposed around a central axis. The pistons reciprocate successively within the cylinders with their strokes overlapping in time to provide continuous pumping of the working fluid. The distance a piston travels within the cylinder, i.e., travel, controls the amount of working fluid taken in and expelled in one complete cycle of a piston. The greater the distance traveled, the greater the amount of fluid pumped in one cycle. The product of the distance a piston travels in one-half of the cycle, the area of the cylinder and the number of cylinders equals the displacement of the pump. One or more valves allow flow of the working fluid in to and out of each cylinder on the intake and output strokes, respectively.  
         [0003]     One method and means of actuating the pistons in an axial pump is to provide a plate, typically a swash or wobble plate, which is tilted relative to the pump axis. The plate engages the pistons so as to actuate each piston successively as rotation takes place. Depending on the design of the axial pump, either the plate or the cylinders and pistons are rotated such that there is relative rotation between the plate and the cylinders.  
         [0004]     In an axial pump with a wobble plate, the plate rotates while the cylinders are stationary. In this type of pump, travel is typically fixed. Because travel is fixed, output from each cylinder is also typically fixed. A wobble plate axial pump typically has at least two valves allowing flow of the working fluid, one for intake and the other for output.  
         [0005]     In an axial pump with a swash plate, the plate does not rotate while the cylinders and pistons rotate around the axis of the pump. However, in this type of pump it is possible to change the angle of the tilt to the swash plate. As the tilt of the swash plate is changed the travel of the piston, and therefore the amount of fluid pumped with each stroke, is changed. A swash plate axial pump typically has a port plate in contact with the top of the cylinder barrel that allows separate intake and output of the working fluid.  
         [0006]     The port plate typically has at least two kidney-shaped openings, one that is open to each cylinder in which the piston is being retracted from the cylinder during rotation of the cylinder barrel, i.e., the intake stroke, and the other that is open to each cylinder in which the piston is being pushed into the cylinder during rotation of the cylinder barrel, i.e., the output stroke. Each end of the intake opening is separated from each end of the output opening by a distance equal to the diameter of a cylinder. One such separation, or “blocked bridge,” is at top-dead-center, or “TDC;” the other is at bottom-dead-center, or “BDC.” At TDC, a piston has finished the output stroke and is beginning the intake stroke. At BDC, a piston has finished the intake stroke and is beginning the output stroke. At TDC of the swash plate, and any output greater than zero, the distance between the swash plate surface and the top of the cylinder is at its shortest. At BDC of the swash plate, and any output greater than zero, the distance between the swash plate surface and the top of the cylinder is at its longest.  
         [0007]     In a swash plate axial pump, TDC for the port plate and the swash plate are typically the same and fixed, i.e., the swash plate and port plate are “on time”. The output of the pump is controlled by changing the distance a piston travels during a cycle, i.e., by changing the tilt angle of the swash plate. If the swash plate is rotated about the axis, the dead-center positions for the swash plate and port plate are no longer the same, i.e., they are “off time”. This means that at TDC of the port plate a piston is either continuing its input stroke or is in the middle of its output stroke, depending on the direction of rotation of the swash plate.  
         [0008]     One example of a swash plate that has its angled driving surface tilted to adjust the flow rate is in U.S. Pat. No. 4,455,920 issued Jun. 26, 1984 to Shaw. This patent discloses a conventional axial pump with an adjustable angle swash plate. Another is U.S. Pat. No. 5,724,879 issued Mar. 10, 1998 to Hugelman. This patent discloses a mechanism to vary the flow rate by using a double wedge system that rotates the wedges with respect to each other to vary the flow rate by increasing or decreasing the travel of the pistons while not altering the TDC positions of the swash plate and port plate.  
         [0009]     Typical adjustable swash plate designs for axial pumps generally make use of a tilt platform with a pin-ended bearing support along the tilt axis. An external mechanism is then used to rotate the pin-ended platform. This configuration requires the tilt platform and pin-ended bearing structures to support the full pump thrust loads. Under high pressures the pivoting assembly will flex between the bearings so that at short stroke and high pressures the degree of flexure may be of the same order of magnitude as the stroke itself. As a result, stroke adjustment becomes unstable. For these reasons high pressure hydraulic pumps are only adjustable over a limited range. Structural rigidity and dynamic performance are compromised with an accompanying increase in pump vibration, noise, and small stroke dynamic stability. Furthermore the flexing of the swash plate support contributes to the noise of a working pump. An unnecessarily large pump housing is required to accommodate this approach adding to pump cost and size while further exacerbating rigidity and noise problems. These large pump housings often dwarf the size of the actual working parts of the pump. The pumps continue increasing in size as the need for higher pressures continues putting increasing demands on the pumps.  
         [0010]     In a conventional pivoting swash plate axial pump, reducing the stroke extracts the piston assembly from the cylinder barrel reducing the piston/cylinder contact length and increasing clearance volume. To correct for this reduced contact length, the pistons are lengthened to maintain sufficient contact length at the shortest stroke. As a result, the cylinders and pistons are longer than necessary which adds to pump size, weight and cost.  
       SUMMARY OF THE INVENTION  
       [0011]     Applicant&#39;s axial pump is configured as a multi-piston pump with a rotating cylinder barrel where the pistons are actuated by a tilted swash plate. In this it is similar to and uses basic parts common to conventional pumps. However, applicant&#39;s pump differs in how the swash plate is supported and how variable output is achieved.  
         [0012]     Applicant&#39;s axial pump uses a single solid wedge as a swash plate with the base of the wedge buttressed against the pump housing or case. The tilt angle of the wedge is fixed. Thus there is no pin-ended bearing support to flex. This design provides for a very compact design tightly wrapped around the internal working parts resulting in low noise and increased pressure capacity.  
         [0013]     The output is controlled and varied by rotation of the wedge. The rotation puts the pump “off time” relative to the fixed port plate. This rotation changes the timing of the piston strokes with respect to TDC and BDC of the fixed port plate so that a portion of the intake charge is breathed back up stream through the intake port and a portion of the output charge is breathed back up stream through the output port. The net result is that pistons do not pull in a full charge nor pump out a full charge. The greater the degree of rotation of the wedge, the more of the charge in each cycle is breathed back into its respective port. At 90 degrees rotation of the wedge, one half of each cycle is breathed back. That is, the same amount of fluid is taken in and breathed back out on the input side of the pump. Likewise, the same amount of fluid is pushed out and breathed back in on the output side of the pump. The net result is zero fluid flow into and out of the pump. Thus rotation of the wedge varies the flow rate of the pump.  
         [0014]     In one embodiment the wedge is a solid wedge maintained in one axial position with respect to the cylinder barrel so that the clearance volume remains constant. In a second embodiment the wedge, although still solid, is allowed to move axially so that the clearance volume can be varied. In this way, the compression ratio of a gas compressor can be varied independently of piston travel distance in the compressor.  
       OBJECTS AND ADVANTAGES  
       [0015]     It is an object to provide an axial pump that is smaller in size yet delivers the same or higher pump capacity than previous designed axial pumps that used a pivoting swash plate to vary the flow rate.  
         [0016]     It is another object to eliminate the pivoting swash plate of prior art axial pumps that was used to vary the flow rate and use a wedge that maintains the same tilt angle with respect to the pistons.  
         [0017]     It is another object to eliminate the pin-ended large bearing supported swash plate of the prior art axial pumps and instead use a solid wedge that is supported by the pump case or housing. An advantage of using a solid wedge supported by the housing is that it results in a smaller size pump for the same volume of fluid flow.  
         [0018]     It is still another object of this invention to provide an axial pump that provides a variable flow rate by means of breathing portions of the intake and output charges back into their respective ports resulting in a reduced charge delivered from the output. A related object is to vary the flow rate of a fluid from an axial pump by rotating the wedge to change the timing of the pistons with respect to the inlet and outlet ports, thus varying the amount of fluid drawn into the cylinder from the inlet port and the amount of fluid exhausted into the outlet port  
         [0019]     These and other objects and advantages will be apparent from the following Description of the Drawings and Description of the Preferred Embodiment. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a perspective view with portions of the housing removed of the inventive pump.  
         [0021]      FIG. 2  is an enlarged perspective view with portions removed of the cylinder, piston and swash plate. For clarity, only one of the pistons is shown in a cylinder.  
         [0022]      FIG. 3  is an enlarged perspective view of the intake and exhaust openings in the cylinder barrel.  
         [0023]      FIG. 4  is a cross sectional view with portions removed of the axial pump.  
         [0024]      FIG. 5  is a perspective view of the port plate.  
         [0025]      FIG. 6  is a top schematic view of the orientation of the rotating cylinders during the intake and exhaust cycles.  
         [0026]      FIG. 7  is a top schematic view of the orientation of the port plate and the inlet and outlet ports.  
         [0027]      FIGS. 8   a - 8   d  are schematic views of the orientation of the rotating cylinders to the port plate during rotation of the wedge from 0° to 90°.  
         [0028]      FIG. 9  is a graph of the displacement curve of the inventive pump as the wedge is rotated from 0° to 90°.  
         [0029]      FIG. 10  is a graph of Cycled Breathing Volume which shows the volume percentage that is breathed back into a port as a function of wedge rotation.  
         [0030]      FIG. 11  is a graph of Trapped Displacement Volume which shows the volume percentage “trapped” as the piston port rotates across the blocked bridge between the inlet and outlet ports.  
         [0031]      FIG. 12  is a graph of the compression ratio verses wedge axial movement. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]     Turning to  FIGS. 1-2 , there is illustrated an axial pump/compressor  10  of the present design. The pump  10  is contained within a front housing  12  attached to a main housing or case  14  by means of long case bolts  16 . A drive shaft  18  spins a cylinder barrel  20  containing a plurality of cylinders  22 . There is a piston assembly  24  having a piston foot  25  at one end and a piston  26  at the other end extending into each of the cylinders  22 . The pistons  26  cycle as the cylinder barrel  20  is spun by the drive shaft  18 . There is a wedge  28  near a foot end  30  of the cylinder barrel  20  that causes the pistons  26  to reciprocate as the cylinder barrel  20  is spun. The term “wedge” used throughout this application is meant to include a wobble plate, wedge swashplate and swashplate. Near a head end  32  of the cylinder barrel  20  is a fixed port plate  33  ( FIG. 4 ) with fixed inlet ports  34  and fixed outlet ports  36  ( FIG. 5 ). There are piston cylinder openings  38  ( FIG. 3 ) in the head end  32  of the rotating cylinder barrel  20  that pass over the fixed inlet and outlet ports  34 ,  36 . During operation of the pump, a low pressure charge is drawn in through the inlet port  34  and a high pressure charge is delivered at the outlet port  36 . The port plate  33  and inlet and outlet ports  34 ,  36  are fixed in position relative to the front housing  12  and main housing  14  while the wedge  28  can be rotated around the axis of the drive shaft  18  or pump axis. A worm drive assembly  40  mounted on the front housing  12  drives a worm gear  42  that in turn rotates the wedge  28  about the axis of the drive shaft  18 .  
         [0033]      FIG. 4  illustrates in greater detail the components of the axial pump  10 . The stationary components will be addressed first. There is a main bearing  44  press fitted into the front housing  12 . The bearing  44  is secured with a snap ring  46  and a drive shaft seal  50  is secured with snap ring  48 . A drive shaft oil seal  50  is press fitted into the housing  12  around the drive shaft  18 . There is a Teflon® thrust bearing  52  fitted into the inner face of the front housing  12 . The worm gear  42  is attached to a wedge thrust collar  54 . A needle bearing  56  is press fitted in the wedge  28  around the drive shaft  18 . The worm drive assembly  40  must drivingly engage the worm gear  42  so that when the worm drive assembly  40  is activated it rotates the worm gear  42  which in turn rotates the wedge  28 . The wedge  28  may have a smooth slipper plate  57  installed on its angled face.  
         [0034]     The rotating components will now be discussed also with reference to  FIG. 4 . Cylinder barrel spacers  58 , spring  60  and snap ring  62  are all installed into the cylinder barrel  20 . Dowel thrust pins  64  are installed into holes in the foot end  30  of the cylinder barrel  20 . A ball seat  66  is mounted on the foot end of the cylinder barrel  20 . One piston  26  is inserted into each cylinder  22  through the piston cylinder opening  38  in the foot end  30  of the cylinder barrel  20 . In the preferred embodiment there are nine piston assemblies equally positioned around the cylinder barrel  20 . The dowel thrust pins  64  compress the spring  60  holding the head end of the cylinder barrel and its cylinder face against the port plate  33 . The piston foot  25  is held firmly against the slipper plate  57  which in turn is pressed against the wedge  28  and against the thrust bearing  52 .  
         [0035]     The drive shaft  18  is retained within needle bearings  68  in an inner end cap  70 . There is an outer end cap  71  disposed at the rear of the pump  10  that is bolted to the case or main housing  14 . The port plate  33 , inner end cap  70 , outer end cap  71  and main housing  14  are all properly positioned by O-rings  72  and lock pins  74 . The case bolts  16  secure the front housing  12 , main housing  14 , inner end cap  70  and outer end cap  71 , with all internal components securely fastened or positioned within.  
         [0036]     The pistons  26  move through one intake and one exhaust stroke with one complete rotation of the of the cylinder barrel  20 . The pistons  26  move out of cylinders  22  from a top dead center point to a bottom dead center point and into cylinders  22  from a bottom dead center point to a top dead center point. Unlike prior devices the flow control is not controlled by adjusting the angle of a swashplate which in turn varies the distance a piston travels.  
         [0037]     Rather, the flow rate in Applicant&#39;s invention is controlled by rotation of the wedge  28 . Rotating the wedge  28  by means of the worm drive assembly  40  and worm gear  42  changes the timing, or travel, of the pistons  26  with respect to the fixed port plate  33  and the inlet and outlet ports  34 ,  36 . As seen in  FIG. 5 , the inlet port  34  and the outlet port  36  are elongated slots each having a beginning portion  35 , a middle portion  37  and an end portion  39 . As will be more fully described below portions of the intake and output charges are breathed back through the inlet port  34  and outlet port  36 , respectively. The rotation of the wedge  28  puts the pump “off time” relative to the fixed port plate  33 . The pistons  26  do not pump out a full charge from bottom dead center (“BDC”) to top dead center (“TDC”) nor pull in a full charge from TDC to BDC. Rather, since the pistons are now “off time” with respect to the fixed port plate  33 , a portion of the intake charge taken in through the inlet port  34  will be breathed, or discharged, back out through the inlet port  34 . Likewise, a portion of the output charge pumped out through the outlet port  36  will be breathed back in through the outlet port  36 . The net result is that less fluid is taken into, and discharged from the pump. Thus the degree of rotation of the wedge  28  determines the cycled breathing volume and varies the flow rate of the pump.  
         [0038]      FIG. 6  illustrates the orientation of the nine piston cylinder openings  38  in the head end of the cylinder barrel  32 . The cylinder barrel rotates one-half revolution (180°) during the intake cycle and one-half revolution (180°) during the output, or “exhaust” cycle.  FIG. 7  illustrates the orientation of the fixed port plate  33  [not numbered] and the inlet and outlet ports  34 ,  36 . There is a bridge  75  between the inlet and outlet ports  34 ,  36 . The bridge  75  causes a volume of trapped fluid as the piston cylinder opening  38  rotates and passes over the blocked bridge  75 . With the wedge  28  at 0°, the cylinders are oriented as seen in  FIG. 8   a . The cylinders are superimposed over the port plate  33 . This illustrates optimum timing and 100% or full fluid flow with the piston  26  drawing in fluid from the beginning of the inlet port  35  to the end of the inlet port  39 . During the cylinder&#39;s half rotation representing the intake cycle, the cylinder is positioned over the inlet port  34  for the full intake cycle or movement from TDC to BDC and draws in a full charge. The piston cylinder opening is likewise positioned over the outlet port  36  from the beginning of the slot  35  to the end of the slot  39  representing the movement of the piston  26  during the exhaust cycle from BDC to TDC and discharges a full charge.  
         [0039]      FIG. 8   b  illustrates the wedge  28  rotated 30° from top dead center. TDC and BDC of the piston intake and exhaust cycles are shifted 30° while the beginnings and ends of the inlet and outlet ports  34 ,  36  have remained stationary. This causes the piston to delay its ending of the exhaust cycle and beginning of the intake cycle by 30°. The result is that part of the exhaust cycle is breathed back into the inlet port  34  and the start of the intake stroke is delayed causing less fluid to be drawn in from the inlet port  34 . Likewise, part of the intake cycle is breathed back into the cylinder through the outlet port  36  and the start of the exhaust cycle is delayed causing less fluid to be pumped out of the outlet port  36 . This “off timing” wedge position results in decreased fluid flow from the outlet of the pump.  FIG. 8   c  illustrates the wedge  28  rotated 60°. TDC and BDC of the intake and exhaust cycles are shifted 60°. This causes the piston to delay its ending of the exhaust cycle and the beginning of the intake cycle by 60°. The result is that compared to the 30° shift in the cycle as illustrated in  FIG. 8   b , more of the exhaust cycle is breathed back into the inlet port  34  and there is less fluid drawn through the inlet port  34  into the cylinder during the intake cycle. Also, more fluid is breathed back into the cylinders from the outlet port  36  during the exhaust cycle. This increased “off time” wedge position results in substantially decreased fluid flow to the outlet port.  
         [0040]      FIG. 8   d  illustrates the wedge rotated 90°. Here fully half of the exhaust cycle is breathed back into the inlet port  34  and half of the intake cycle is breathed back from the outlet port  36 . The net result is that there is no fluid flow to the pump&#39;s outlet even though the cylinder barrel  20  is still rotating at the same speed as it was during full fluid flow.  
         [0041]     Although the preferred embodiment describes the invention as using a rotatable wedge to vary and control the timing to thereby control the fluid, the invention can also be used when the wedge remains stationary and the port plate and a portion of the end cap are rotated as a unit with respect to the wedge. This results in varying the timing as described in the preferred embodiment. The invention can also be used in a pump/compressor where the cylinder barrel is held stationary and the wedge is spun and a portion of the end cap is rotated as a unit with respect to TDC and BDC of the cylinder barrel.  
         [0042]     The output flow rate as a function of wedge rotation is illustrated in  FIG. 9 . The flow rate starts at its maximum flow rate at 0° wedge rotation and is reduced to zero flow rate at 90° wedge rotation.  
         [0043]      FIG. 10  is a graph of Cycled Breathing Volume. This is actually the inverse of the graph of  FIG. 9  but shows the volume percentage which is breathed back into and out of the pump as the wedge rotation angle is increased from 0° to 90°.  
         [0044]      FIG. 11  is the Trapped Displacement Volume. This shows the volume percentage “trapped” as the piston cylinder opening  38  rotates and passes across the blocked bridge  75  between the inlet and outlet port  34 ,  36  of the port plate  33 . This is important as during the transition period the piston contents are trapped with nowhere to go. The result is hydraulic lock for a hydraulic pump, but there is no effect upon a gas compressor. To prevent hydraulic lock damage, relief grooves must be cut along the track to allow the fluid trapped over the bridge to bleed back. The question arose as to whether the “off time” breathing would exacerbate the hydraulic locking problem common to all axial hydraulic pumps but as  FIG. 11  illustrates, the percentage of trapped displacement actually decreases with wedge rotation and breathing.  
         [0045]     As described, the wedge  28  is rotated by means of the worm drive assembly  40 . However, this can be replaced with a hydraulic or pneumatic cylinder with a piston operatively connected to the wedge  28  for rotation of the wedge  28 .  
         [0046]     In the inventive pump  10  the compression ratio is physically fixed since there is no change in wedge angle of axial position. However, in an alternate embodiment, the compression ratio can be changed by moving the wedge  28  and its driven piston assembly  24  axially. A plot of “Compression Ratio vs. Wedge Axial Movement” is seen in  FIG. 12  for this added feature. One method of adjusting the compression ration is illustrated in U.S. Pat. No. 6,629,488 incorporated herein by reference.  
         [0047]     Thus there has been provided an axial pump/compressor that fully satisfies the objects set forth above. While the invention has been described in conjunction with a specific embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.