Abstract:
A variable displacement axial piston pump is typically used to receive fluid from a tank and supply pressurized fluid through a control valve to move an actuator. The present variable displacement axial piston pump has a swashplate arrangement that is capable of being angled in two different directions to control the pressure transitions between the low pressure inlet port passage and the higher pressure outlet port passage as cylinder bores in a barrel of a rotating group rotate through trapped volume regions situated between inlet and outlet port passages of the axial piston pump. Movement of the swashplate arrangement in two different directions provides smooth pressure transitions and increases the operating efficiency of the variable displacement axial piston pump.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates generally to an axial piston pump and more specifically to a swashplate arrangement for an axial piston pump.  
         BACKGROUND  
         [0002]    Variable displacement axial piston pumps are well known in the art and typically include a barrel having a plurality of piston assemblies slideably disposed in respective bores within the barrel and a swashplate that is in mating contact with the piston assemblies so that the piston assemblies are forced to reciprocate within the bores of the barrel to receive fluid therein and discharge fluid therefrom. The swashplate is secured to the housing of the pump and is selectively pivotable relative to the barrel so that the volume of fluid being discharged therefrom may be controlled. There has been many attempts to control the pressure transition between the point at which all of the fluid has been discharged from the respective bores and the point at which the respective bores are opened to receive more fluid. Likewise, there has been many attempts to control the pressure transition between the point at which the respective bores are full and the point at which respective bores are opended to discharge fluid. In most of these attempts, special slots or holes are provided to controllably interconnect the high pressure side of the pump to the low pressure side and vice-versa to make the pressure transition as smooth as possible. Even with the special slots or holes, energy is wasted during the respective pressure transitions.  
           [0003]    Another example of an axial piston pump attempts to provide a new neutral control of the swashplate. In this arrangement, the swashplate assembly has a primary swashplate that is rotated in a well known manner and a thrust plate is permitted to freely pivot in a 360 degree arc relative to the primary swashplate for a small, predefined distance. This permits the pump to rely on its internal swivel forces to move the thrust plate to a non-fluid discharging mode anytime the swashplate is near its zero position. Such an arrangement is set forth in U.S. Pat. No. 4,825,753, issued May 2, 1989 and assigned to Kayaba Industry Co.  
           [0004]    The present invention is directed to overcoming one or more of the problems as set forth above.  
         SUMMARY OF THE INVENTION  
         [0005]    In one aspect of the present invention, a variable displacement axial piston pump is adapted for use in a fluid system. The variable displacement axial piston pump includes a housing, a rotating group, and a swashplate arrangement. The housing has a body portion and a head portion with an inlet port passage and an outlet port passage. The rotating group is disposed in the body portion and has an axis of rotation. The rotating group includes a barrel having a plurality of cylinder bores and a plurality of piston assemblies with each of the plurality of piston assemblies having a piston slideably disposed within one of the cylinder bores and a shoe pivotably attached to and extending from the piston. The barrel of the rotating group is in fluid communication with the inlet and outlet port passages of the housing head portion. The swashplate arrangement is disposed in the body portion and is pivotable in a first arcuate direction relative to the axis of rotation of the barrel and pivotable in a second arcuate direction in response to various system parameters.  
           [0006]    In another aspect of the subject invention, a method of controlling pressure transitions is provided within a variable displacement axial piston pump between its inlet passage and its outlet passage. The method includes providing a rotating group having an axis of rotation, providing a swashplate arrangement pivotable in a first arcuate direction relative to the axis of rotation of the rotating group and pivotable in a second arcuate direction in response to various system parameters. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a partial schematic and partial diagrammatic representation of a fluid pump and a fluid system incorporating an embodiment of the present invention;  
         [0008]    [0008]FIG. 2 is a partial schematic and partial diagrammatic representation of a section  2 - 2  taken from FIG. 1;  
         [0009]    [0009]FIG. 3 is a diagrammatic representation of the porting of the fluid within the head of the pump or the port plate taken along the line  3 - 3  from FIG. 1;  
         [0010]    FIGS.  4 A-C are plots illustrating the relationship of different differential pressures within the fluid system at a fixed primary swashplate angle relative to a secondary angle of the swashplate;  
         [0011]    FIGS.  5 A-C are plots illustrating the relationship of different primary swashplate angles at a fixed differential pressure within the fluid system relative to a secondary angle of the swashplate;  
         [0012]    FIGS.  6 A-C are plots illustrating the power savings of the subject invention with the primary angle of the swashplate being held at various fixed positions; and  
         [0013]    FIGS.  7 A-B are plots illustrating how, during operation, the top and bottom dead center positions effectively move when the secondary angle of the swashplate is changed. 
     
    
     DETAILED DESCRIPTION  
       [0014]    Referring now to the drawings and more particularly to FIGS.  1 - 3 , a fluid system  10  is illustrated and includes a variable displacement axial piston pump  12  that receives fluid from a tank  14  via a conduit  16  and delivers pressurized fluid via a supply conduit  18  to a fluid control valve  20  and selectively through work conduits  22 ,  24  to a fluid actuator  26 . In the subject arrangement, the variable displacement axial piston pump  12  is a unidirectional pump that rotates in a counterclockwise direction as driven by a power input shaft  27 .  
         [0015]    The fluid system  10  also includes first and second pressure sensors  28 ,  30  respectively connected to the tank conduit  16  and the supply conduit  18 . The pressure sensors  28 ,  30  are operative to sense the pressure in the respective lines and deliver an electrical signal to a controller  32  through electrical lines  34 ,  36 . A position sensor  40  is mounted on the variable displacement axial piston pump  12  and operative to sense the displacement of the pump and deliver a signal representative thereof to the controller  32  via an electrical line  42 .  
         [0016]    Various other components could be used in the subject fluid system  10  without departing from the essence of the subject invention. For example, several control valves  20  and associated fluid actuators  26  could be used. Likewise, other sensors of various types and styles could be used.  
         [0017]    The variable displacement axial piston pump  12  includes a housing  44  having a head portion  46  and a body portion  48 . The head portion  46  defines an inlet port passage  50  that is connected to the conduit  16  and an outlet port passage  52  that is connected to the supply conduit  18 . In the subject arrangement, a port plate  54  is disposed between the head portion  46  and the body portion  48 . The construction of the porting within the port plate  54  is more clearly illustrated in FIG. 3 and will be discussed more fully below. It is recognized that the porting illustrated in FIG. 3 could be made within the head portion  46  without departing from the essence of the subject invention.  
         [0018]    A rotating group  56  is disposed within the body portion  48  and includes a barrel  58  having a plurality of cylinder bores  59  defined therein spaced from one another around an axis of rotation  60  of the barrel  58 . Each of the cylinder bores  59  is oriented within the barrel  58  parallel with the axis of rotation  60 . A plurality of piston assemblies  62  are operatively associated with the barrel  58  and each one of the plurality of piston assemblies  62  includes a piston  64  slideably disposed in the respective ones of the plurality of cylinder bores  59 . Each one of the plurality of piston assemblies  62  also has a shoe  66  pivotably attached to one end of each piston  64  in a conventional manner.  
         [0019]    The barrel  58  has an end surface  68  that is in mating, sealing contact with the port plate  54  to provide communication between the cylinder bores  58  and the respective inlet and outlet port passages  50 ,  52  of the head portion  46 . A closed chamber  70  is defined in each cylinder bore  59  of the barrel  58  between the end of the piston  64  and the end surface  68  thereof.  
         [0020]    Referring to FIG. 3, the porting between the barrel  58  and inlet and outlet port passages  50 ,  52  of the head portion  46  is more clearly illustrated. For explanation purposes only, the “270” degree position illustrated in FIG. 3 relates to a position on the right side of the drawing of FIG. 1 and the “0” degree position illustrated in FIG. 3 relates to a position on the right side of the drawing of FIG. 2. An arcuate slot  72  is defined in the port plate  54  and provides communication between the plurality of closed chambers  70  and the inlet port passage  50 . A plurality of slots  74  are defined in the port plate  54  circumferentially spaced from the arcuate slot  72  and provides communication between the plurality of closed chambers  70  and the outlet port passage  52 . The “0” and the “180” degree positions represent a neutral axis which will be more fully described hereinafter. The “90” degree position, commonly referred to as the Top Dead Center (TDC) position, represents the point at which the respective closed chambers  70  are at their smallest volume for a given displacement of the variable displacement axial piston pump  12 . The “270” degree position, commonly referred to as the Bottom Dead Center (BDC) position, represents the point at which the respective closed chambers  70  are at their largest volume for a given displacement. The arcuate distances ‘delta’ TDC and ‘delta’ BDC represent the distance that the barrel  58  travels during use in which a trapped volume of fluid within respective closed chambers  70  are being subjected to changing pressures depending on the direction of movement of the respective pistons  64  within their associated cylinder bores  59 .  
         [0021]    Referring again to FIGS. 1 and 2, a swashplate arrangement  76  is pivotably disposed within the body portion  48 . As viewed in FIG. 1, the swashplate arrangement  76  is pivoted in a first arcuate, clockwise direction relative to the axis of rotation  60  of the rotating group  56 . The swashplate arrangement  76  of the subject embodiment includes a primary member  78 , a secondary member  80 , and an actuating mechanism  82 . The primary member  78  is mounted within the body portion  48  on a pair of arcuate bearing assemblies  84  in a known manner. An operating lever  86  extends from the primary member  78  and is operative in response to an external command (not shown) to change the angular position of the primary member  78  relative to the axis of rotation of the rotating group  56 . The primary member  78  has a concave spherical surface  88  on one side thereof between the pair of bearing assemblies  84 .  
         [0022]    The secondary member  80  is pivotably disposed on the primary member  78  and has a convex spherical surface  90  on one side thereof that is of a size and shape sufficient to mate with the concave spherical surface  88  of the primary member  78 . As viewed in FIG. 2, the secondary member  80  rotates in a counterclockwise direction. The pivot direction of the secondary member  80  is oriented at an angle about the axis of rotation  60  of the rotating group  56  relative to the pivot direction of the primary member  78  and could be in the range of 80 to 100 degrees. In the subject embodiment, the angle is at 90 degrees. A flat surface  92  is disposed on the other side of the secondary member  80  and mates, in a well known sliding relationship, with the respective shoes  66  of the plurality of piston assemblies  62  of the rotating group  56 .  
         [0023]    In FIG. 2, the actuating mechanism  82  is shown broken out from the sectional view. As can be understood from FIG. 1, the actuating mechanism  82 , when viewed in FIG. 2, would be located behind the power input shaft  27 . In order to more clearly illustrate the actuating mechanism  82 , it is being shown as a broken out portion. The actuating mechanism  82  includes a link  94  having a first portion  96  and a second portion  98 . The first portion  96  is disposed in a slot  100  of the primary member  78  and rotated about a pin  102  disposed thereacross. The first portion  96  also includes a lever arm  104  at the end thereof away from the second portion  98 . An abutment shoulder  106  is disposed within the slot  100  at the bottom thereof and the lever arm  104  is in operative contact with the abutment shoulder  106 . A biasing member  108 , such as a spring, is disposed in the slot  100  and is operative to bias the lever arm  104  against the abutment shoulder  106  thus holding the secondary member  80  in its “ 0 ” angle position relative to the primary member  78 .  
         [0024]    The second portion  98  of the link  94  extends into a slot  110  defined within the secondary member  80 . A slot  112  is defined at the end of the second portion  98  and a reaction member  114  is disposed across the slot  110  of the secondary member  80  and through the slot  112  of the second portion  98  of the link  94 .  
         [0025]    A remotely controlled actuating mechanism  116  is mounted on the housing  48  and is connected to the controller  32  via a signal line  118 . The actuating mechanism  116  includes an actuator  120  having an output member  122  in continuous operative contact with a force member  124  that is disposed within the primary member  78  and in contact with the lever arm  104  of the link  94  and acts against the bias of the biasing member  108 .  
         [0026]    FIGS.  4 A-C relates to one representative example, each plot refers to the relationship of the differential pressure between the inlet and outlet port passages  50 ,  52  and the magnitude of movement needed in the secondary member  80 , with the primary angle at a fixed location, to provide a smooth pressure transition between the inlet and outlet port passages  50 ,  52  as each cylinder bore  59  of the barrel  58  moves through the top and bottom dead center positions (TDC, BDC). The plot line  126  in FIG. 4A illustrates the above noted relationship when the primary member  78  is fixed at  3  degrees. The plot line  128  in FIG. 4B illustrates the same relationship when the primary member  78  is fixed at 7 degrees while the plot line  130  in FIG. 4C illustrates the same relationship when the primary member  78  is fixed at 13 degrees.  
         [0027]    FIGS.  5 A-C relates to the same representative working example as that of FIGS.  4 A-C. Each plot of FIGS.  5 A-C relates to the relationship of the angle of the primary member  78  and the magnitude of movement needed for the angle of the secondary member  80  when the differential pressure between the inlet and outlet port passages  50 ,  52  is maintained at a fixed level to provide a smooth pressure transition between the inlet and outlet port passages  50 ,  52  as each cylinder bore  59  of the barrel  58  moves through the top and bottom dead center positions (TDC, BDC). The plot line  132  of FIG. 5A illustrates the above noted relationship when the differential pressure between the inlet and outlet port passages  50 ,  52  is maintained at 10,350 kPa (approx. 1500 psi). The plot line  134  of FIG. 5B illustrates the same relationship when the differential pressure is maintained at 20,700 kPa (approx. 3000 psi) while the plot line  136  of FIG. 5C illustrates the same relationship when the differential pressure is maintained at 31,050 (approx. 4500 psi).  
         [0028]    FIGS.  6 A-C relates to the same representative working example set forth with respect to FIGS.  4 A-C and FIGS.  5 A-C. The plots of FIGS.  6 A-C illustrate the relationship of power saved with the subject invention when the subject variable displacement axial piston pump  12  is being worked within a range of differential pressures with the primary member  78  being maintained at different fixed angles. The plot line  138  of FIG. 6A illustrates the power savings for a range of differential pressures when the primary member  78  is being maintained at 3 degrees. The plot line  140  of FIG. 6B illustrates the power savings for a range of differential pressures when the primary member  78  is being maintained at 7 degrees while the plot line  142  of FIG. 6C illustrates the power savings for a range of differential pressures when the primary member  78  is being maintained at 13 degrees.  
         [0029]    FIGS.  7 A-B generally illustrates how the TDC and BDC positions are effectively moved, during use, when the angle of the secondary member  80  is changed relative to the primary member  78 . The representative face surface  144  of the plot of FIG. 7A generally illustrates the flat surface  92  of the secondary member  80  with the primary member  78  rotated to its maximum position about its neutral axis, i.e., a line from the “0” degree point to the “180” degree point, with the secondary member  80  at its zero angle position. The outline  146  of the representative face surface  144  illustrates one of the closed cylinder chambers  70  makes a complete revolution. As previously noted, at the “90” degree point, the volume of the closed cylinder chamber  70  is at its smallest volume during the rotation of the barrel  58 . As the cylinder chamber  70  rotates counterclockwise from the “90” degree point on to the “270” degree point, the cylinder chamber  70  is increasing in volume and reaches its largest volume at the “270” degree point or BDC position. As it continues to rotate from the “270” degree point to the “90” degree point, the volume in the closed chamber  70  decreases.  
         [0030]    [0030]FIG. 7B illustrates the representative flat surface  144  with both the primary member  78  and the secondary member  80  angled to their maximum positions. As seen from this representation, the TDC position has shifted from the “90” degree position towards the “0” degree position and the BDC position has shifted from the “270” degree position towards the “ 180 ” degree position. Consequently, the respective closed cylinder chambers  70  reach their minimum effective volume at a location less than  90  degrees and each of the closed cylinder chambers  70  reach their maximum effective volume at a location less than 270 degrees of rotation of the barrel  58 .  
       Industrial Applicability  
       [0031]    During the operation of the subject fluid system  10  incorporating the subject variable displacement axial piston pump  12 , the operator initiates an input to the fluid control valve  20  to direct pressurized fluid to one end of the fluid actuator  26  moving it in the desired direction. The fluid being exhausted from the other end of the fluid actuator  26  returns to the tank  14  across the control valve  20  in a conventional manner. The operator&#39;s input results in a simultaneous command, based on the load requirements, being delivered to the operating lever to pivot the primary member  78  to a flow producing angle. In the subject piston pump  12 , the angle ranges from 0 degrees to 15 degrees. It is recognized that the magnitude of the angle range could be more or less without departing from the subject invention. An input command to the actuating lever  86  acts to rotate the primary member  78  in a clockwise direction as viewed in FIG. 1. Once the primary member  78  is pivoted to a desired angular position, the respective pistons  64  of the plurality of piston assemblies  62  begin to reciprocate within the respective cylinder bores  59  of the barrel  58 . With reference to FIG. 3, a closed chamber  70  is illustrated as being at the TDC position, in which the volume of fluid within the closed chamber  70  is at its smallest level. As the barrel  58  rotates in a counterclockwise direction, the piston  64  begins to withdraw from the cylindrical bore  59  due to the fact that the shoe  66  is following the flat surface  92  of the secondary member  80  that is still at its “0” degree position relative to the primary member  78 . Since the flat surface  92  is at an angle with respect to the axis of rotation  60 , the distance between the flat surface  92  and the end surface  68  of the barrel  58  is increasing. The movement of the piston  64  results in the volumetric space within the closed chamber  70  increasing. As illustrated in FIG. 3, an arcuate distance is defined in which the closed chamber  70  is not in communication with either the outlet port passage  52  through the slots  74  or with the inlet port passage  50  through the slot  72 . Consequently, there is a trapped volume of fluid within the closed chamber  70  that is expanding since the volumetric size of the closed chamber is increasing. Once the closed chamber  70  reaches the slot  72 , fluid from the tank  14  begins to enter the closed chamber  70  to fill it with low pressure fluid. It should be recognized that at the TDC position of the closed chamber  70 , the fluid within the closed chamber  70  was still pressurized since it had just left communication with the pressurized slots  74 . Naturally, the pressurized fluid at TDC is transformed to tank pressure by the time that the closed chamber  70  enters the slot  72 . This is referred to as ‘the pressure transition’.  
         [0032]    Once the closed chamber  70  reaches the BDC position, the closed chamber is totally filled with fluid at tank pressure, which in the subject arrangement is atmospheric pressure. At the BDC position, the closed chamber  70  is at its largest volumetric value. As the rotation of the barrel  58  moves the closed chamber  70  past the BDC position, the piston  64  begins to retracts into the cylinder bore  59  which reduces the volume of the closed chamber  70 . From the time the closed chamber  70  leaves the BDC position, the fluid within the closed chamber  70  is trapped from both the tank and the pressure port. During this movement from BDC, the fluid is being compressed. Once the closed chamber  70  reaches the high pressure slots  74 , the fluid in the closed chamber  70  enters the slots  74  and forced at the high pressure to the fluid actuator  26  to do work in a conventional manner. From the time that the closed chamber  70  leaves the BDC position, the fluid therein goes from zero pressure to the pressure level within the slots  74  which as noted above is referred to as ‘the pressure transition’. As the closed chamber  70  continues to move towards the TDC position, the fluid therein is continually being expelled therefrom at the system operating pressure.  
         [0033]    In order to smooth out the respective pressure transitions and improve system operating efficiencies, the volume of trapped fluid at the TDC and BDC positions are controlled. It is believed that the magnitude of fluid compression needed at the TDC and BDC position are very similar. Consequently, the subject invention uses an average of the TDC and BDC fluid compression requirement for both TDC and BDC pressure transition control for each set of system parameters. It should be recognized that the fluid compression requirements change as the system parameters change.  
         [0034]    In the subject arrangement, the pressures of the fluid in the tank inlet conduit  16  and the supply conduit  18  are being sensed by pressure sensors  28 ,  30  and representative signals delivered to the controller  32  to establish a deferential pressure between the inlet port passage  50  and the outlet port passage  52 . Likewise, the position of the primary member  78  is being sensed by the position sensor  40  and the representative signal delivered to the controller  32 . These system parameters are then being used to determine what position to pivot the secondary member  80 . Based on the relationships set forth in the plots illustrated in FIGS.  4 A-C and  5 A-C, a series of maps would be provided in the controller  32 . Consequently, for any differential pressure between the inlet and outlet passages  50 ,  52  and any angular position of the primary member  78 , the controller  32  would generate a signal to move the secondary member  80  to a desired angular position in the range of 0-10 degrees. The secondary member  80  is pivoted, as viewed in FIG. 2, in a counterclockwise direction in response to receipt of the signal from the controller  32  being directed to the remotely controlled actuating mechanism. The output member  122  acts on the force member  124  causing the link  94  to pivot about the pin  102 . The link  94  acts on the reaction member  114  to move the secondary member  80  in proportion to the signal from the controller  32 .  
         [0035]    As clearly indicated in FIG. 7B, any combined movement of both the primary member  78  and the secondary member  80  results in the location of TDC and BDC positions changing from the positions set forth in FIG. 7A that represent angular movement of only the primary member  78 . It should be recognized that the representation illustrated in FIG. 7B applies to one example in which both the primary member  78  and the secondary member  80  are at their extreme angular positions. From the illustration of FIG. 7B, it should be noted that the closed chamber  70  reaches the indicated TDC position prior to the barrel  58  reaching the 90 degree position. Consequently, further rotation of the barrel  58  towards the 90 degree position does not change the pressure of the fluid in the closed chamber  70 . The pressure within the closed chamber  70  only begins to gradually decrease when the closed chamber  70  reaches the 90 degree position. From a review of FIG. 3 it is noted that the closed chamber  70  is still in communication with the pressure slots  74  at a location less than  90  degrees but due to the change in location of the TDC position, the volume of the closed chamber  70  is at its smallest volume and is slightly increasing as is noted from the outline  146  that represents the path of the piston  64 . The volume within the closed chamber  70  is beginning to slightly increase. However, the pressure of the fluid in the fluid system  10  remains the same. As the closed chamber  70  moves from the 90 degree position, communication with the pressure slots  74  is interrupted. As the closed chamber  70  moves through the delta TDC arc, the pressure within the closed chamber  70  is being reduced at a more gradual rate and once it opens into the tank slot  72  the pressure therein has been effectively transformed.  
         [0036]    Likewise, once the closed chamber  70 , reaches the new BDC position as indicated in FIG. 7B, the volume of the fluid within the closed chamber  70  has reached its largest value. As noted from FIG. 3, the closed chamber  70  is still in communication with the tank through the slot  72 . As the closed chamber  70  moves towards the ‘270’ position, the volume of the fluid in the closed chamber  70  is being slightly reduced while it is still in communication with the low pressure slot  72 . As the closed chamber  70  moves through the delta BDC arc, the trapped volume of fluid is compressed. Thus the pressure transition between the low pressure slot  72  and the high pressure slots  74  is made smoother by compressing the fluid in the closed chamber  70  while the closed chamber  70  rotates through the trapped region near BDC.  
         [0037]    From the above, it is noted that the pressure change within the piston chamber is a function of the volume change that the piston chamber undergoes as the piston passes through the trapped volume region (delta TDC/delta BDC). Naturally, the amount of trap distance required at TDC and BDC will be different for any given angle of the primary member  78  because the amount of fluid in the closed chamber  70  at TDC is less than the amount of fluid in the closed chamber at BDC.  
         [0038]    As recognized from a review of FIGS.  6 A-C, there is significant power savings of the subject arrangement over conventional systems where the swashplate has only one degree of movement. The plots illustrated are for example only. It is recognized that operation of a different axial piston pump would result in different power savings. Likewise, operation of the subject embodiment would result in different power savings for different angles of the primary member  78 .  
         [0039]    From the foregoing, it is readily apparent that the subject variable displacement axial piston pump  12  provides smooth pressure transitions between the inlet port passage  50  and the outlet port passage  52  at both TDC and BDC positions. By controlling the pressure transitions, the efficiency of the variable pump is increased.  
         [0040]    Other aspects, objects and advantages of the subject invention can be obtained from a study of the drawings, the disclosure and the appended claims.