Patent Publication Number: US-6217289-B1

Title: Axial piston pump with auxiliary pump

Description:
This patent application is a continuation-in-part of application Ser. No. 09/553.285, filed on Apr. 20, 2000, pending and incorporated herein by reference. 
    
    
     This invention relates to axial piston pumps and more particularly to the combination of an axial piston pump with an auxiliary pump mounted thereto. 
     INCORPORATION BY REFERENCE 
     The parent patent application Ser. No. 09/553,285 is hereby incorporated by reference in its entirety both for the description of the axial piston pump disclosed therein, specifically the valving employed therein, and to which this invention is an improvement thereof and for the HEUI pump application disclosed therein because this invention has particular application for use in an HEUI system. 
     BACKGROUND 
     Conventional axial piston pumps (i.e., “Thoma” pump) are often used in high pressure applications. For example, in a hydraulically actuated electronically controlled united injector (HEUI) fuel control system, a high pressure, axial piston oil pump typically supplies the diesel injectors with 3,000-4,000 psi engine oil for hydraulic operation. This high pressure oil pump is charged with low pressurized fluid from another pump, typically the engine&#39;s oil pump. Conventionally, an auxiliary pump, the engine&#39;s fuel pump, is driven by the HEUI pump. The fuel pump transfers fluid from the fuel tank to the injectors for consumption by the engine and typically pumps at approximately 20-50 psi. 
     In many of these applications, the high pressure pump also drives a low pressure pump. A typical arrangement is illustrated in prior art FIG. 1 in which an input shaft  10  is splined to a rotatable cylinder  12  having circumferentially spaced bores containing pistons  13 . One end of each piston is ball shaped and received in a socket receptacle formed as a slipper  14  which, in turn, contacts an end face of a stationary swash plate  15 . Rotation of Input shaft  10  rotates cylinder  12  to cause pistons  13  to axially reciprocate in their bores by slipper contact with swash plate  15  while fluid intake and exhaust of pressurized fluid is through conventional kidney shaped intake/outtake ports  16 . Press fitted onto the tail end of input shaft  10  is a cam  18  which acts as an eccentric to drive a prime mover  19  of an auxiliary pump  20 . 
     In vehicular applications, space is at a premium and is often a determining factor in the OEM&#39;s selection process, especially for mature technologies such as that embodied in an axial piston pump. In the arrangement illustrated in FIG. 1, the addition of auxiliary pump  20  onto the tail end of input shaft  10  increases the length of the pump assembly. A more subtle point is that an eccentric lift is provided at a tail extension of the input shaft which requires that the input shaft be soundly journaled so as not only to unduly transmit loads to the high pressure pump but also to insure against any axial run out of the shaft which could potentially adversely affect the smoothness of the lift motion of prime mover  19 , especially if cam  18  wears. In the prior art pump of FIG. 1, front and rear ball bearings  21  journal input shaft  10  and internal and external retainer rings  22 ,  23  (lubricated) prevent shaft run out. The FIG. 1 arrangement has proven to be durable and commercially acceptable. Its length, however, is increased by auxiliary pump  20  and its cost must reflect the bearing arrangement. 
     In SAE Technical Paper 2000-01-0687, entitled “Development of a Variable-Displacement, Rail-Pressure Supply Pump for a Dimethyl Ether” by James C. McCandless, Ho Teng and Jeffrey B. Schneyer presented Mar. 6-9 2000, an axial piston pump is disclosed in which, like the parent application, a rotating swash plate/stationary cylinder is disclosed. In the pump disclosed in the SAE paper, the circumferential edge of the swash plate is used to control valving to the axial piston pump. Like FIG. 1, the input shaft of the SAE disclosed pump is journaled in ball bearings. Additionally, springs in the piston bores are used to maintain slippers in contact with the swash plate. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of the present invention to provided an axial piston pump configuration which allows for inclusion of an auxiliary pump without increasing axial pump length while minimizing cost of the pump. 
     This object along with other features of the invention is achieved in a pump assembly which includes an axial piston pump having a swash plate rotatable by an input shaft and a non-rotatable cylinder containing a plurality of axially movable pistons having spherical ends extending through the cylinder journaled in slipper assemblies that are in contact with the swash plate. A retainer plate in contact with the slipper assemblies is spring biased to urge the slippers against the swash plate to maintain the swash plate in fixed axial position and permit smooth swash plate rotation not withstanding varying force pulsations attributed to fluid pressure in the piston bores during pump operation. The swash plate has a cam shaped circumferential edge surface. An auxiliary pump having a prime mover in contact with the cam shaped edge of the swash plate is mounted between the axial ends of the piston pump whereby the length of the piston pump assembly is maintained constant. 
     In accordance with another aspect of the invention, the swash plate has one axial end generally perpendicular to the longitudinal centerline of the input shaft and an opposite swash end inclined at an angle to the longitudinal centerline with the cam edge extending between the swash plate ends. The piston pump has a housing containing a cylindrical shaft inlet passage at one axial end terminating in an intermediate or swash plate chamber containing the swash plate. The intersection of the intermediate chamber and the inlet passage defines an annular seat surface and a Teflon coated thrust plate between the annular seat surface and the axial end of the swash plate functions as a thrust bearing allowing swash plate rotation without grapping or seizing resulting in smooth operation of the secondary pump. The input shaft is only journaled within a similar, Teflon coated sleeve bearing pressed into the cylindrical shaft inlet passage thus eliminating bearing assemblies and retainer rings and the like. 
     It is thus an object of the present invention to provide an axial piston pump capable of driving an auxiliary pump without increasing the axial length of the pump. 
     It is another object of the invention to provide an axial piston pump which journals the input shaft and swash plate without the need for bearing assemblies, bearing races, retainer rings and the like. 
     It is another object of the invention to provide the combination of a high pressure axial piston pump and a low pressure pump ideally suited for HEUI and like applications. 
     It is yet another object of the invention to provide a low cost axial piston pump especially suited for driving an auxiliary pump. 
     These and other features, objects and advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the Detailed Description of the Invention set forth below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail and illustrated in the accompanying drawings which form a part hereof and wherein: 
     FIG. 1 is a longitudinally sectioned view of a prior art axial piston pump fitted with an auxiliary pump; 
     FIG. 2 is a sectioned side elevation view of the fixed displacement axial piston pump of the present invention shown with an auxiliary pump mounted thereto; and, 
     FIG. 3 is a sectioned elevation view of the pump of the present invention similar to that shown in FIG. 2 but through a section of the pump rotated about 90° to the pump section shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, there is shown in FIGS. 2 and 3 an axial piston pump  50  of the present invention. 
     Axial piston pump  50  includes an open ended pump housing  52 . In the preferred embodiment, pump housing  52  is a unitary casting but in accordance with the broader scope of the invention can comprise a composite assembly having the desired configuration. Pump housing  52  has at one axial end an inlet shaft passage  53 , at its opposite axial end a cylinder chamber  54  and interconnecting inlet shaft passage  53  with cylinder chamber  54  is an intermediate or swash plate chamber  55 . Inlet shaft passage  53 , cylinder chamber  54  and swash plate chamber  55  extend along and are generally concentric about longitudinal centerline  56 . Closing cylinder chamber  54  is an end plate  58  which in the preferred embodiment is a casting. End plate  58  has formed therein a pump outlet  59  which is in fluid communication with an annular pump discharge chamber  60 . 
     Disposed within cylinder chamber  54  is an annular cylinder  62  which is made non-rotatable in the preferred embodiment by the clamping force between end plate  58  and pump housing  52  exerted by cap screws  63  when the pump is assembled. Extending through the ring body of cylinder  62  is a plurality of circumferentially spaced piston bores  64  each of which contains a piston  65  axially movable therein. One end of each piston  65  extends through each piston bore  64  and is formed in the shape of a ball  66 . Each ball  66  is received within a socket formed in a slipper  68  so that the ball socket joint allows each slipper  68  to pivot omni-directionally. 
     Inserted within the central opening  69  of cylinder  62  is a cylindrical tail shaft  70  which has a cylindrical stem portion  71 . Stem portion  71  receives an annular spherical bearing  72  which has its outside diametrical surface formed as a sphere. A compression spring  74  fits over stem portion  71  and seats on tail shaft  70  as shown so that its biasing force tends to push spherical bearing  72  off tail shaft  70 . Spherical bearing  72  is maintained in its position by an annular retainer plate  75  having a plurality of circumferentially spaced slipper openings  76  which engage or fit within a stepped flange formed in slippers  68 . The central opening  77  of retainer plate  75  has a through diameter slightly less than the spherical diameter of spherical bearing  72  so that retainer plate  75  holds spherical bearing  72  at its axial position on stem portion  71  with the axial force of spring  74  transmitted to slippers  68 . The surface of central opening  77  is dished or curved at a spherical diameter equal to or greater than the spherical diameter of spherical bearing  72  so that retainer plate  75  can wobble or pivot about the outside spherical surface of spherical bearing  72  as pistons  65  axially move within piston bores  64 . 
     An inlet shaft  78  has an inlet shaft portion  79  within inlet shaft passage  53  and a swash plate portion  80  within swash plate chamber  55 . In the preferred embodiment inlet shaft  78  is a unitary structure having the shaft and swash plate portions as described but portions  79 ,  80  can be separate and integrally secured to one another. Pressed on to the end of inlet shaft portion  79  is a hub  81  (for a gear mount used in the preferred embodiment - not shown) for rotating inlet shaft  78  and sealed by a shaft seal  82 . Hub  81  is optional and inlet shaft  78  could be straight with shaft seal  82  riding directly on it or alternatively be a keyed or splined shaft. Shaft seal  82  is lubricated by a lubricating groove  83 . Inlet shaft portion  79  is journaled for rotation about a sleeve bearing  85  extending along a substantial portion of the length inlet shaft portion  79 . In the preferred embodiment, sleeve bearing  85  is a conventional sleeve bearing preferably a steel cylinder, the interior of which is coated with an annular lead/bronze composite wear metal and, the interior of the wear material, in turn, is coated with Teflon. Other conventional bearing materials may be used. 
     Pump housing  52  at the intersection of inlet shaft passage  53  with swash plate chamber  55  forms a flat annular seat surface  86 . Swash plate portion  80  at one axial end has an annular flat end surface  87  generally perpendicular to longitudinal centerline  56 , and at its opposite axial end has a swash plate surface  88  which is at an angle to longitudinal centerline  56 . In between housing annular seat surface  86  and swash plate end surface  87  is a non-rotatable, annular thrust bearing plate or washer  90 . In the preferred embodiment, thrust bearing  90  is an annular steel plate having one side seated against housing annular seat surface  86  and its other side coated with a composite lead/bronze metal which in turn is coated with Teflon against which swash plate end surface  87  seats. In the preferred embodiment, thrust bearing washer  90  is made non-rotatable by a discrete slit punched through thrust bearing washer  90  to form a tab  91  which fits in a tab recess formed in housing seat surface  86 . Alternatively, thrust bearing washer  90  could be made non-rotational by any number of arrangements such as dowel pin, screw, adhesive, etc. 
     The operation of pump  50  is opposite to that of a conventional Thoma pump. Rotation of inlet shaft  78  causes swash plate portion  80  to rotate axially moving swash plate surface  88  relative to piston bores  64  which are stationary. 
     Slippers  68  cause pistons  65  to axially move within piston bore  64 . Fluid form an inlet port  93  is drawn into piston bore  64  through a suction slot  94  during the suction stroke of piston  65 . When piston  65  axially travels forward in piston bore  64 , communication of suction slot  94  is cut off and compressed fluid exits piston bore  64  through a valved outlet shown, in the preferred embodiment, as a read-valve  95  into discharge chamber  60  and out through pump outlet  59 . Note that while most pumps can function as a motor, pressurizing inlet port  93  will not produce rotation of inlet shaft  78 . 
     It is to be noted that there are no ball bearings, tapered bearings, roller bearings and the like having bearing races etc. used in pump  50 . The entire arrangement is journaled at one point but the point extends a substantial length of inlet shaft  78  as a sleeve bearing ( 85 ) which works in combination with thrust bearing  90  to stably support the pump. That is, by making swash plate portion  80  integral with inlet shaft portion  79  and spring biasing swash plate portion  80  to contact housing annular seat surface  88 , axial runout is controlled without the need for bearing retainer rings and assembly of the pump is simplified. 
     It is to appreciated that the pressure within piston bores  64  during the compression stroke of the pump will generate a pulsating force on swash plate surface  88  which will rotate with the rotation of swash plate portion  80 . This pulsation stresses conventional bearings and could lead to shaft wobble. An obvious, conventional arrangement is to insert a compression spring in each piston bore such as shown in the SAE paper discussed above. However, while piston bore springs can be sized to exert a force on the swash plate during the suction stroke, a greater spring force will be exerted during the compression stroke increasing the pulsation force. The slipper/retainer plate/spring arrangement discussed above exerts a constant force about all of the slippers. By simply sizing spring  74 , uniform contact with thrust bearing washer  90  throughout the washer area is assured. Pulsations will still inevitably occur but they won&#39;t be enhanced or increased as a result of compression springs in piston bores  64 . A smoother pump operation will result and the bearing arrangement will be better stabilized. Shaft axial runout or shaft wobble is less likely to occur. 
     With stable rotation of swash plate portion  80  assured, the outer circumferential edge  98  of swash plate portion  80  between swash plate surface  88  and swash plate thrust bearing surface  87  can be formed as a cam surface (eccentric). A typical example of an auxiliary pump mounted to axial piston pump  50  is schematically illustrated in FIG.  2 . It is to be appreciated that the auxiliary pump can be used to pressurize any number of fluid systems, the fuel pump of a HEUI system being only one example. In fact the auxiliary pump can be used to supply low pressure fluid to inlet port  93 . The auxiliary pump may comprise a radial piston pump  100  in which the pump&#39;s prime mover or pumping element, in this case piston  101 , axially moves in a cylinder  102  to sequentially open and close an inlet port  103  to pump fluid through an outlet port  104 . Prime mover  101  is actuated by a crank  106  pivoted at one end to prime mover  102  and having a cam follower  107  at its opposite in contact with cam  98 . A spring  108  can be provided to assure cam follower contact with cam  98 . In each instance, the auxiliary pump would be actuated by a cam follower  107  providing a stroke to an appropriate linkage that would actuate or stroke the pump. Significantly, auxiliary pump  100  is between the axial ends of axial piston pump  50  thus minimizing the length of the pump arrangement. The journal/thrust bearing arrangement for the input shaft/swash plate in combination with the spring/retainer plate/slipper arrangement, while an inexpensive arrangement, produces a smoothly rotating swash plate minimizing the effects of axial pulsations on the rotation of swash plate and resulting in smooth performance of the auxiliary pump. 
     The invention has been described with reference to a preferred embodiment. Obviously, alterations and modifications will occur to those skilled in the art upon reading and understanding the Detailed Description of the Invention set forth herein. It is intended to include all such modifications and alterations insofar as they come within the scope of the present invention.