Abstract:
A rotating group of a bent-axis axial piston pump/motor is assembled as a subassembly with a removable stabilizing component that holds together and compresses the subassembly while it is outside of the pump/motor case. A yoke that carries a permanent or attachable back plate is installed in the case and positioned aside to allow clearance for installation of the rotating group. After the rotating group is installed, the yoke is moved back into proximity with the barrel, the stabilizing component is removed, and the remaining connections are completed.

Description:
CROSS-REFERENCE To RELATED APPLICATION 
     This application claims priority to U.S. provisional patent application 61/707,104, “Low Cost Production Design and Method for Assembling a Bent-Axis Pump/Motor,” filed Sep. 28, 2012. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The disclosed embodiments are directed generally to the production and assembly of a bent-axis hydraulic, pump or motor having a case and a rotating group. 
     2. Description of the Related Art 
     Bent-axis axial piston hydraulic pumps and motors (which will be collectively referred to herein as pump/motors, but with the intent to encompass both bent-axis axial piston pumps and motors even if such may be used primarily or exclusively in applications as solely a pump or motor without reversible operation) are employed in hydraulic hybrid vehicles as Weil as other hydraulic devices. Such pump/motors typically include a rotating group that comprises several rotating components, such as a power shaft, a barrel, a plurality of working pistons reciprocating within bores in the barrel, a tripod between the barrel and power shaft, and a drive plate that connects the working pistons to the power shaft. The rotating group normally resides within a stationary pump motor case which is provided with fluid supply connections and arcane for installation in a vehicle or other device. 
     In modern manufacturing systems it is often advantageous to assemble a device as a group of two or more subassemblies, with each subassembly being assembled in a different location and then transported to a final assembly location. The different locations may be within the same factory, which may require hand carrying or transportation by shop cart, or in different buildings or different countries, which requires more robust packaging and transportation. However, for hydraulic pump/motors, although there may be benefits in assembling a rotating group as a subassembly, many of the individual parts of a rotating group are only loosely held together and will easily come apart when outside of a pump/motor case, making it difficult to handle or transport as a subassembly. For these reasons, the rotating group is commonly assembled piece by piece within the pump/motor case. This limits flexibility on the assembly line by tying up the pump/motor case assembly for a longer time while the intricate parts of the rotating group are painstakingly placed into the ease one part at a time. 
     OBJECT OF THE INVENTION 
     It is therefore an object of the invention to provide a method for more convenient and inexpensive production and assembly of a bent-axis pump/motor. 
     SUMMARY OF THE INVENTION 
     The invention is a production design and method for low-cost fabrication and assembly of a bent-axis pump/motor, in which the rotating group is assembled separately from the case and held together by a removable stabilizing component. The preferred embodiment applies to an over-center yoke-based design, but the invention can also be applied to non-over-center designs as well as those with a removable back plate. 
     In particular, as the rotating group is assembled, a removable stabilizing component, such as a rod, wire, or other longitudinal member, is employed to hold together and compress the rotating group components and allow for their transport and installation as a subassembly. In an over-center yoke-based pump/motor, or in a single-sided yoke-based pump/motor, yoke components are installed into the case, and then the yoke is swung aside to an extreme position. With the yoke out of the way, the preassembled and stabilized rotating group is then installed into the case. The yoke is then moved back to a zero displacement position, the stabilizing component is removed, and the connections between the rotating group and the yoke are completed. Alternatively, if the portion of the yoke containing the hack plate is configured to be detachable from the yoke leg(s), that portion is not installed until after the rotating group has been installed, and the yoke need not be swung out of the way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a rotating group showing selected components held together by a removable stabilizing, assembly rod. 
         FIG. 2  is a sectional view of a pump/motor case with a yoke installed in the case. 
         FIG. 3  is a sectional view of the pump/motor case of  FIG. 2  taken at section A-A. 
         FIG. 4  is a sectional view of the pump/motor case with the yoke swung aside to art extreme position. 
         FIG. 5  is a sectional view showing the rotating group of  FIG. 1  installed into the pump/motor case. 
         FIG. 6  shows the yoke swung back to a zero displacement position prior to completion of the assembly. 
         FIG. 7  shows the assembly rod removed, allowing the rotating group to uncompress and the barrel to be connected to the yoke. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a rotating group  100  of a bent-axis axial piston pump/motor is shown. Ordinarily, rotating group  100  would be installed in a pump/motor case (not shown) that provides the necessary bearing surfaces for shaft  107  as well as fluid supply means. As is familiar in the bent-axis pump/motor art. barrel  101  contains a plurality of bores  103  in which pistons  102  reciprocate. Baud  101  is configured to move (“articulate”) with respect to shaft  107  to change displacements in the known way that is characteristic of bent-axis pump/motors. Tripod  106  resides between barrel  101  and shaft  107 , causing the three parts to rotate together even as the barrel and shaft articulate. Spring  108  provides a degree of compressive force to help the parts remain in contact when installed in a pump/motor case. As is commonly understood, a tripod design such as  106  provides only a rotational linkage, and is not positively retained by either the barrel  101  or the shaft  107 , and therefore will not prevent the barrel and shaft from coming, apart when the assembly is outside of the case. Further, pistons  102  are not positively retained in bores  103  when the assembly is outside of the case. Therefore, to assemble rotating group  100  independently of its case requires that the parts be held together by sonic means so that they can be conveniently handled. transported and assembled without coming apart. 
     According to a feature of the invention, assembly rod  110  passes through the center of the rotating group assembly, holding the components together and providing some structural rigidity to prevent articulation while the assembly is outside of the case. In one embodiment of the invention, as shown in  FIG. 1 , collars  111   a  and  111   b,  preferably in the form of threaded nuts, are engaged to rod  110  (alternatively, collars  111   a  and/or  111   b  could be engaged with the rod by clamping or other means). When either or both nuts are advanced (e.g., turned) toward the other, surface  161   a  of nut  111   a  bears against surface  162   a  of barrel  101 , while surface  161   b  of nut  111   b  bears against surface  162   b  of shaft  107 , placing rod  110  in tension and therefore exerting a retentive force that prevents barrel  101  from separating from the shaft  107  or from articulating with respect to the shaft. Stiffness of rod  110  also provides additional resistance against articulation, although the rod  110  does not need to be particularly strong to serve the purpose. Further tightening of either of nuts  111   a,b  acts to compress spring  108 . reducing the overall length of the rotating group as needed to facilitate installation (as discussed later). Alternatively, it is not necessary for both nuts  111   a  and  111   b  to be positionable (e.g. by being threaded) along the rod, as one could be fixedly attached to the rod as long as the other is positionable. 
     In an alternative embodiment, instead of nut  111   a  bearing against the inner surface of barrel  101 , a threaded connection could be made between assembly rod  110  and barrel rod bore  112  through which it passes. A similar threaded connection with the shaft could alternatively replace nut  111   b.  Also alternatively, because rod  110  acts primarily in tension, it could be replaced with a flexible wire or similar structure that could be placed in tension by any known means, such as a turnbuckle, wire tensioner, or similar device attached to or gripping the wire and bearing against either surface  162   b  (preferably) or  162   a.    
     Referring now to  FIGS. 2 and 3 , pump/motor case  130  (approximately one half of which is shown, not including the portion which covers the yoke swing path) houses yoke leg  120  which pivots about yoke pivot hearing  123 . Yoke leg  120  includes fluid passages (not shown) which conduct working fluid between hack plate  121  and yoke pivot  123 . Low pressure fluid is conducted through other openings (not shown) in fluid communication with the fluid filled interior of case  130 . Preferably, a second non-fluid-conducting (i.e., only structural) yoke leg (not shown) connects at flange  127  to second pivot bearing  128 . Alternatively, both yoke legs could be fluid conducting as is known in the art. Also, although it is seen that the example provided in the figures is an over-center pump/motor in which the yoke may pivot to positive and negative quadrants with respect to the zero angle position A 0 , the invention is also applicable to a single-sided pump/motor in which the yoke pivots into only one quadrant. 
     In  FIG. 3 , yoke  120  is shown at a zero displacement position at is zero degree angle (A 0 ) with the shaft bore in an over-center pump/motor unit In  FIG. 4 , yoke  120  has been pivoted to a maximum angle A max  (to yoke position P max ), allowing unobstructed access to the case interior from the yoke side of the case (as depicted, the left side). In  FIG. 5 , according to the invention, rotating group  100 . stabilized by assembly rod  110 , has been installed onto bearing surfaces  131 - 133  from the yoke side of the ease while yoke  120  is at position P max . 
     Completion of assembly includes connection of back plate  121  to barrel  101  by means of center post  140  ( FIGS. 6 and 7 ). This requires yoke  120  (in particular, hack plate  121 ) and barrel  101  to be brought into proximity and properly aligned. However, in order for back plate  121  to clear the outer end of barrel  101  (with which it is normally in contact when assembled), the overall length of the rotating group must be temporarily shortened so that the barrel is moved slightly inward toward the yoke pivot. Accordingly, assembly rod  110  is installed with sufficient tension to compress spring  108  and thereby reduce the overall length of rotating group  100 , creating clearance  134  ( FIG. 6 ). The amount of tension necessary depends on the strength of spring  108  and the specific geometries of the yoke, back plate, and barrel, but can be set at whatever amount is necessary to provide adequate clearance. 
     In  FIG. 7 , back plate  121  and barrel  101  have been brought into contact, eliminating clearance  134  of  FIG. 6 . This is achieved by release of nut  111   a  and/or  111   b  (or, in the alternative embodiment, unscrewing the threaded portion of rod  110  from barrel rod bore  112 ), whereupon the tension is released and spring  108  expands. Once barrel  101  is in or near contact with back plate  121 , center post  140  may be installed to full depth, preferably by thermal or press fit, so as to rotatably mount barrel  101  on yoke  120 , against back plate  121 . 
     As can be seen in  FIGS. 4 and 5 , the pump/motor case  130  must be fabricated with sufficient clearances so that when yoke  120  is moved to its maximum angular position, rotating group  100  can be installed into pump/motor case  130  without interference with the yoke  120  and back plate  121 . Alternatively, yoke  120  can be fabricated with the portion holding the back plate being detachable from the leg, so that rotating group  100  could be installed in pump/motor case  130  without the need to pivot yoke  120 . 
     Accordingly, a preferred assembly process for a bent-axis pump/motor according to the invention includes the steps of (1) assembling a rotating group that includes a removable. stabilizing component for stabilization of the assembly when outside of case: (2) installing at least one yoke leg (which includes a back plate surface) into the case; (3) positioning the yoke leg at an angle at which it does not obstruct access to the shaft axis of the case (preferably at or near a maximum yoke angle A max ); (4) installing the rotating group, with the stabilizing component installed, into the case; (5) moving the yoke into alignment with the rotating group (preferably at or near a zero degree yoke angle A 0 ); (6) inserting the center post to initially axially align the rotating group and the yoke; (7) removing the stabilizing, component, thus causing the barrel of the rotating group to contact or nearly contact the back plate; and (8) completing installation of the center post to firmly connect the back plate with the barrel (preferably by thermal or press fit, but alternatively by other means such as, for example, threading, bolting, or surface bonding). 
     The application is intended to be limited solely by the claims hereto.