Patent Document

FIELD OF THE INVENTION 
   The present invention is directed toward a ceramic bore liner, a rotor body including a ceramic bore liner and a method of lining the bore of a rotor body with a ceramic liner, and, more specifically, toward a split ceramic bore liner configured to resist cracking during installation and operation, a rotor body having a split ceramic bore liner installed therein, and a method of installing a split ceramic bore liner in a rotor body to resist bore liner cracking during installation and operation. 
   BACKGROUND OF THE INVENTION 
   Fluid transfer devices are known that operate in a first direction as a pump and in a second direction as a motor. These devices may comprise a housing within which a rotor rotates with respect to a port plate and a cam plate angled with respect to the rotor&#39;s axis of rotation. The rotor includes one or more bores (generally an odd number) each for receiving a piston. One end of each piston held in contact with the cam plate. As the rotor rotates with respect to the housing, each piston moves axially with respect to the rotor and the port plate. 
   The port plate includes a fluid inlet through which a fluid enters the housing when a piston aligned with the fluid inlet moves away from the port plate and a fluid outlet through which fluid exits the housing when a piston aligned with the fluid outlet moves toward the port plate. When the rotor is connected to a source of motive power, the rotation of the rotor causes the pistons to draw fluid from the inlet and expel fluid through the outlet; when operated in this manner, the fluid transfer device is referred to as an axial piston pump. When fluid is applied under pressure to the fluid inlet and drawn from the fluid outlet at a lower pressure, the rotor is caused to turn by the pressure difference; when operated in this manner, the fluid transfer device is referred to as a hydraulic motor. Thus “axial piston pump” and “hydraulic motor” may refer to the same fluid transfer device, depending on the what is making the rotor turn. 
   It is known to provide rotor bores with a ceramic or metal liner to improve wear resistance and achieve satisfactory tribological performance. These liners may be thin-walled, right circularly cylindrical tubes that are shrink fitted into typically metallic rotors. A shrink fit, press fit, braze or similar type of connection is desirable to retain the liner in the bore under typical operation. Unfortunately, non-symmetrical stresses to the liner can be imparted during installation (or occur during use) and these stresses can crack the brittle ceramic bore liners. 
   SUMMARY OF THE INVENTION 
   These problems and others are addressed by various embodiments of the present invention, a first aspect of which comprises a bore liner formed from a ceramic sleeve having a first end, a second end and a sidewall having a split. 
   Another aspect of the invention comprises a rotor body having a plurality of cylindrical bores each adapted to receive a piston for reciprocating movement therein and each being lined with a ceramic liner having a split. 
   An additional aspect of the invention comprises a method of forming a rotor having a ceramic bore liner that includes the steps of providing a rotor body having at least one bore, providing a ceramic bore liner having a first end, a second end and a split having a width, and compressing the bore liner to decrease the width and securing the bore liner in the at least one bore. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These aspects and features of the invention and others will be better understood after a reading of the following detailed description together with the following drawings of which: 
       FIG. 1  is side elevational view, partly in section, of a rotor having bores with split ceramic liners and pistons slidably mounted in the bores; 
       FIG. 2  is a split ceramic bore liner according to a first embodiment of the present invention; 
       FIG. 3  is a split ceramic bore liner according to a second embodiment of the present invention; 
       FIG. 4  is a detail view of region IV of  FIG. 3 ; 
       FIG. 5  is a split ceramic bore liner according to a third embodiment of the present invention; 
       FIG. 6  is a split ceramic bore liner according to a fourth embodiment of the present invention; 
       FIG. 7  is a split ceramic bore liner according to a fifth embodiment of the present invention; 
       FIG. 8  is a split ceramic bore liner according to a sixth embodiment of the present invention; 
       FIG. 9  is a split ceramic bore liner according to a seventh embodiment of the present invention; 
       FIG. 10  is a split ceramic bore liner according to an eighth embodiment of the present invention; 
       FIG. 11  is a split ceramic bore liner according to a ninth embodiment of the present invention; 
       FIG. 12  is a partial end elevational view of the rotor of  FIG. 1  having two different split ceramic bore liners installed therein; and 
       FIG. 13  illustrates a method of forming a rotor having a ceramic bore liner according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings, wherein the showings are for purposes of illustrating several presently preferred embodiments of the invention only and not for the purpose of limiting same,  FIG. 1  illustrates a fluid transfer device  10  comprising a housing  12  having an interior  14  in which a rotor  16  is mounted for rotation. Rotor  16  is supported by first and second sets of bearings  18  and comprises a rotor shaft  20  and a rotor body  22 . Rotor body  22  includes a plurality of cylinders  24 , two of which are illustrated in  FIG. 1 . Generally, an odd number of cylinders will be provided. Rotor body  22  includes a balance land or front face  26  having first and second openings  28  communicating with cylinders  24 . First and second pistons  30  are mounted for sliding movement in cylinders  24  in an axial direction generally parallel to the axis  32  of rotor shaft  20 . Each of pistons  30  includes a first end  34  facing openings  28  and a second end  36  projecting from rotor body  22  and terminating in a shoe assembly  38 . A cam plate  40  (also known as a swash plate) is mounted in interior  14  of housing  12 , and shoe assembly  38  are held against the cam plate  40 . 
   Each of the cylinders  24  includes a ceramic bore liner  42 , having, as illustrated in  FIG. 2 , at least one split  44  and a longitudinal axis  46 . Bore liners  42  may be formed from a ceramic material such as, but not limited to alumina, silicon nitride, silicon carbide, or a cermet such as tungsten-carbide cobalt. For certain types of processing, such as electro-discharge machining (EDM), it may be desirable to use a ceramic such as the material disclosed in U.S. Pat. No. 5,177,037 to Schuldies, the disclosure of which is hereby incorporated by reference. Other ceramic materials known to those of ordinary skill in the art may also be used based on the operating requirements of the fluid transfer device without departing from the present invention. 
   With continued reference to  FIG. 2 , bore liner  42  includes a split  44  extending from a first end  48  to a second end  50 . The split  44  is defined by a first wall  52  spaced from a second wall  54 . First and second walls  52 ,  54 , generally lie in parallel planes which may project on opposite sides of axis  46  as illustrated in  FIG. 2  making split  44  generally normal to axis  46 . When bore liner  42  is installed in a rotor, first wall  52  and second wall  54  may remain spaced, as shown in bore  60  in  FIG. 12 , or may contact one another when the bore liner  42  is compressed to fit within a bore as illustrated in bore  62 . Generally all bore liners in a given rotor will have similar gaps;  FIG. 12  includes one bore liner having spaced walls and a second bore liner having a gap between two walls for illustration purposes only. 
   Split  42  may be formed in any of a variety of ways. For example, an uncured ceramic cylinder may be provided with a suitable split prior to densification. Alternately, a densified ceramic cylinder can be cut or otherwise machined to produce a split. Such cutting operations may be carried out by, for example, diamond grinding, abrasive water jet cutting, laser cutting, ultrasonic machining or electro-discharge machining. The use of the term “split” herein is intended to describe the result of such an operation and is not intended to specify or limit the manner in which the split is formed. 
   In operation, pistons  30  reciprocate within bores  24  as rotor  20  rotates and fluid moves into and exits from bores  24 . Pistons  30  have an outer diameter slightly smaller than the inner diameter of bores  24 , therefore a certain amount of leakage occurs between the pistons  30  and walls of cylinders  24  during use. Advantageously, this leakage provides lubrication for pistons  30  and also helps to cool the pistons and the rotors. Leakage occurs whether or not a split is provided in bore liner  42 ; however split  44  can controllably increase leakage which in turn may help to better cool the pistons and rotor. 
   The distance between first wall  50  and second wall  52  is selected to provide for a desired degree of leakage and will be selected based on the anticipated operating temperatures and lubrication requirements of the rotor. The split can be sized so that first wall  50  and second wall  52  will contact one another in use, as illustrated in bore  60  of  FIG. 12 , when it is important to control leakage. Alternately, the split can be sized so that first wall  50  and second wall  52  remain spaced after the bore liner  42  is installed as illustrated in bore  62  in  FIG. 12 . Notably, whether first wall  50  and second wall  52  contact one another in use or remain spaced, the presence of split  44  helps to relieve stresses that occur during installation and use and should reduce the failure rate of the cylindrical bore liner. 
   A second embodiment of the present invention is illustrated in  FIGS. 3 and 4  wherein elements common to the first embodiment are identified using the same reference numerals. Elements related to elements of the first embodiment are identified with a prime. In this embodiment, ceramic bore liner  42  includes a split  44 ′ defined by a first wall  52 ′ and a second wall  54 ′ where the first and second walls  52 ′,  54 ′ lay in parallel planes both of which pass to the same side of longitudinal axis  46  of bore liner  42 . This arrangement may help maintain a more constant rate of leakage even as the distance between first wall  50 ′ and second wall  52 ′ changes with temperature and operating conditions. 
   A third embodiment of the invention is illustrated in  FIG. 5 . In this embodiment, a bore liner  70  includes a split  72  that extends from a first end  74  to a second end  76  of bore liner  70 . In this embodiment, first end  75  of split  72  is circumferentially spaced from second end  77  while split  72  is generally linear. 
   A fourth embodiment of the invention is illustrated in  FIG. 6 . In this embodiment, a bore liner  80  has a split  82  that extends from a first end  84  to a second end  86  of bore liner  80  and includes first and second bends  88 . Like the third embodiment discussed above, the ends of the split  82  of bore liner  80 , as well as first and second bends  88 , are circumferentially spaced. 
   A fifth embodiment of the invention is illustrated in  FIG. 7  wherein a bore liner  90  having a helical split  92  is disclosed which split extends from a first end  94  to a second end  96  of bore  90 . The use of such a helical split  92  should reduce the likelihood of liner failure and at the same time may help direct a leakage flow around the circumference of cylinder  24  and thus provide more even cooling. The configuration of the split could also be varied to provide greater or lesser cooling in different areas depending on the cooling needs of a particular cylinder and rotor. Helical split  92 , by directing the leakage flow around the periphery of the cylinder, may also provide more even lubrication and help avoid the condition known as hydraulic lock. Hydraulic lock occurs when pressure due to leakage flow becomes greater on one side of a piston than on the other causing increased friction between the piston an cylinder on the under-lubricated side and often leading to piston or bore damage. 
     FIG. 8  illustrates a sixth embodiment of the present invention in which a bore liner  100  includes a serpentine split  102  extending from a first end  104  to a second end  106  of the bore liner  100 . This embodiment provides many benefits of the previous embodiments while at the same time may be useful for limiting a leakage flow from one end of the bore liner to the other due to the winding path that the leaking fluid must traverse. 
     FIG. 9  illustrates a seventh embodiment of the present invention in which a bore liner  110  includes a first end  112  and a second end  114 . A first split  116  extends from first end  112  of bore liner  110  but does not extend as far as second end  114 ; a second split  118  extends from second end  114  of bore liner  110  but does not extend as far as first end  112 . More than two splits may be provided, and the circumferential spacing of the splits may be varied. This arrangement may also help to minimize leakage flow while still improving the flexibility of and reducing the fracturing of the ceramic bore liner. 
     FIG. 10  illustrates an eighth embodiment of the invention wherein a bore liner  120  is provided having a split  122  that defines a plurality of generally rectangular teeth  124  on either side of split  122 . 
     FIG. 11  illustrates a ninth embodiment of the present invention wherein a ceramic bore liner  130  is provided having a first split  132  and a second split  134  each extending from a first end  136  to a second end  138  of the bore liner  130 . While generally linear splits  132 ,  134  are illustrated, other split configurations or combinations of split configurations from the previously discussed embodiments could also be used. Since producing two splits  132 ,  134  results in a two-piece bore liner, the bore liner  130  can generally not be shrink fitted or press fitted into bore  24  as may optionally be done with the bore liners of the previous embodiments. Instead, it will generally be necessary to braze bore liner  130  in place. 
   A method of installing a ceramic bore liner according to one of the first through eighth embodiments of the invention will be described in connection with  FIG. 13 . As illustrated in this figure, a method of installing a ceramic bore liner includes the steps of providing a rotor body having at least one bore at a step  140 , providing a ceramic bore liner having a first end, a second end and a split at a step  142  and compressing the bore liner to decrease the width of the split and securing the bore liner in the at least one bore at a step  144 . 
   The present invention has been described herein in terms of several preferred embodiments. Variations and additions to these embodiments will become apparent to those skilled in the relevant arts upon a reading of the foregoing descriptions. It is intended that all such obvious modifications and additions form a part of the present invention to the extent they fall within the scope of the several claims appended hereto.

Technology Category: f