Abstract:
A hydraulic actuator for pump control is disclosed. The hydraulic actuator includes two hydraulically isolated chambers for actuation in one direction and two hydraulically isolated chambers for actuation in an opposite direction. Each of the four chambers is connected to a source of high pressure fluid by an electronically controlled pressure reducing valve.

Description:
RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from U.S. Provisional Application No. 61/254,786 by Michael G. Cronin et al., filed Oct. 26, 2009, the contents of which are expressly incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to a hydraulic actuator, and more particularly, to a high response hydraulic actuator for controlling a variable displacement pump. 
       BACKGROUND 
       [0003]    Variable displacement hydraulic pumps are widely used in hydraulic systems to provide pressurized hydraulic fluid for various applications. Many types of machines such as dozers, loaders, and the like, rely heavily on hydraulic systems to operate, and utilize variable displacement pumps to provide a greater degree of control over fixed displacement pumps. 
         [0004]    Various control schemes have been utilized to control the swashplate angle of such variable displacement hydraulic pumps. One such control scheme is disclosed in U.S. Pat. No. 6,553,891, filed Jul. 9, 2001, to Carsten Fiebing, which is hereby incorporated by reference. However, it may be beneficial to provide a control scheme offering greater responsiveness and stability. 
       SUMMARY OF THE INVENTION 
       [0005]    In one aspect of the disclosure, a hydraulic system includes a source of pressurized fluid; a hydraulic actuator; and first and second hydraulically isolated chambers configured to expand and contract, wherein expansion of the first and second chamber actuates the actuator in a first direction. The hydraulic system further includes third and fourth hydraulically isolated chambers configured to expand and contract, wherein expansion of the third and fourth chamber actuates the actuator in a second direction opposite the first direction. Each of the chambers has an associated pressure reducing valve that selectively communicates the respective chamber with either a source of pressurized fluid or a tank. 
         [0006]    In another aspect, a variable displacement hydraulic device is disclosed having a swashplate; a hydraulic actuator operable to selectively increase and decrease an inclination of the swashplate; a first chamber configured to expand and contract, wherein expansion of the first chamber actuates the actuator in a first direction; a first valve fluidly connected to the first chamber, wherein the first valve selectively communicates pressurized fluid with the first chamber; and a second chamber configured to expand and contract, wherein expansion of the second chamber actuates the actuator in the first direct. According to this aspect, the first chamber and the second chamber are substantially hydraulically isolated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a side-view diagrammatic illustration of an exemplary disclosed machine; 
           [0008]      FIG. 2  is a schematic illustration of an exemplary disclosed transmission; and 
           [0009]      FIG. 3  is a schematic illustration of an exemplary disclosed hydraulic pump and associated control hardware. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  illustrates an exemplary machine  10 . Machine  10  may be a fixed or mobile machine that performs operations associated with an industry such as mining, construction, farming, or any other industry known in the art. For example, machine  10  may be an earth moving machine such as a dozer, a loader, a backhoe, an excavator, a motor grader, a dump truck, or any other earth moving machine. Machine  10  may also embody a generator set, a pump, a marine vessel, or any other suitable machine. Referring to  FIGS. 1 and 2 , machine  10  may include a frame  12 , an implement  14 , a hydraulic actuator, an engine  16 , fraction devices  18  such as wheels or tracks, and a transmission  20  to transfer power from the engine  16  to the traction devices  18 . 
         [0011]    As illustrated in  FIG. 2 , the transmission  20  may be a hydrostatic transmission and may include a primary pump  22 , a motor  24  and a bypass relief valve  26 . In practice, transmission may be a continuously variable transmission (CVT), parallel path variable transmission (PPV), or other transmission known in the art. According to the present disclosure, the main pump  22  may be a variable displacement pump such as a variable displacement axial piston pump, and the motor  24  may be a fixed displacement hydraulic motor. However, the motor  24  may alternatively be a variable displacement motor. The transmission  20  may further include a charge pump  28  providing pressurized fluid to swashplate control hardware  30 , which is illustrated in greater detail in  FIG. 3 . 
         [0012]      FIG. 3  illustrates the primary pump  22 , which includes pistons  50  disposed in a cylinder block  52 . The pistons  50  are slidably supported by swashplate  54 , and swashplate  54  has a variable angle of inclination that affects the displacement of the pistons  50  for each revolution of the pump  22 . In the illustrated embodiment, swashplate  54  is connected to an actuation arm  56  that is, in turn, connected to an actuation member  58 . Movement of actuation arm  56  may effect a change in the inclination of swashplate  54 . For example, moving actuation arm  56  to the left, with respect to  FIG. 3 , may increase the inclination of swashplate  56 , whereas moving actuation arm  56  to the right, with respect to  FIG. 3 , may decrease the inclination of swashplate  54 . Actuation member  58  is slidable about a shaft  60 , which is fixed with respect to the pump housing  62 . 
         [0013]    As seen in  FIG. 3 , many components of the swashplate control hardware  30  may be similar on both the left and right sides of the pump  22 ; such similar components may be denoted with common reference numbers. Disposed within actuation member are proximal spring retainers  64   a  and distal spring retainers  64   b , which together enclose springs  65 . Proximal spring retainer members  64   a  may be slidable about shaft  60 , but may be constrained from sliding toward the center of the shaft  60  by a lip  68  on the shaft  60 . Distal spring retainers  64   b  may be slidable about shaft  60 , but constrained from movement away from the center of actuation member  58  by a restraining ring  70 , and constrained from movement away from the center of shaft  60  by another restraining ring  72 . Both proximal spring retainers  64   a  and distal spring retainers  64   b  may include fluid passageways  74  to allow fluid to pass through the spring retainers  64   a ,  64   b.    
         [0014]    A cap member  77  may further be partially disposed in actuation member  58 . In the illustrated embodiment, cap member  77  is constrained from movement with respect to actuation member  58  by restraining ring  70  and restraining ring  78 . Cap member  77  also passes through a restrictive portion  80  of pump housing  62 , and is surrounded by a seal  82  at the restrictive portion  80 . 
         [0015]    In the illustrated embodiment, with respect to the left side of the pump  22  in  FIG. 3 , seal  82  defines a boundary between interior chamber  100   a  and anterior chamber  102   a . With respect to the right side of the pump  22  in  FIG. 3  seal  82  defines a boundary between interior chamber  100   b  and anterior chamber  102   b . In the illustrated embodiment, each chamber  100   a ,  100   b ,  102   a ,  102   b  is selectively connected to charge pump  28  by a pressure reducing valves  110   a ,  110   b ,  112   a ,  112   b , respectively. The use of pressure reducing valves to control the displacement of a variable displacement pump is discussed in U.S. patent application Ser. No. 11/269,392 to Michael Cronin (Pub. No. 2007/0101709), which is hereby incorporated by reference. As illustrated, pressure reducing valves  110   a ,  110   b ,  112   a ,  112   b  may be infinitely variable, three way valves that selectively communicate their respective chamber  100   a ,  100   b ,  102   a ,  102   b  with either the charge pump  28  or tank  115 . Furthermore, pressure reducing valves  110   a ,  110   b ,  112   a ,  112   b  may be electronic pressure reducing valves and may be selectively actuated by solenoids. 
       INDUSTRIAL APPLICABILITY 
       [0016]    In operation, swashplate  54  inclination can be changed by moving actuation member  58 , and hence actuation arm  56 . Actuation member  58  can be moved by selectively directing pressurized fluid in and out of chambers  100   a ,  100   b ,  102   a ,  102   b . For example, with reference to  FIG. 3 , to move actuation member  58  to the left, the solenoids corresponding to pressure reducing valve  110   b  and pressure reducing valve  112   b  may be energized such that pressurized fluid from charge pump  28  is passed to both interior chamber  100   b  and anterior chamber  102   b , thereby causing both chambers to expand. The expansion of chambers  100   b ,  102   b  actuates actuation member  58  to the left. While some leakage may pass between the anterior chamber  102   b  and interior chamber  100   b , seal  82  causes interior chamber  100   b  to be substantially hydraulically isolated from anterior chamber  102   b . As flow is passed through two valves  110   b ,  112   b , actuation member  58  can be actuated more quickly because pressurized fluid can be provided through the two valves  110   b ,  112   b  at a higher combined rate than a similar system having only a single valve of similar size that must effectively provide fluid to both chambers. Furthermore, as the two chambers  100   b ,  102   b  are substantially hydraulically isolated, interference and cross-talking between the two valves  110   b ,  112   b  may be reduced or avoided. 
         [0017]    To further the example discussed above, to move actuation member  58  to the left, the solenoids corresponding to pressure reducing valve  110   a  and pressure reducing valve  112   a  may be de-energized such that fluid in interior chamber  100   a  and anterior chamber  102   a  can flow to tank  115 , causing these chambers  100   a ,  102   a  to contract, which permits actuation member  58  to move left. In a similar manner, actuation member  58  may be moved to the right by energizing solenoids associated with pressure reducing valve  110   a  and pressure reducing valve  112   a , and de-energizing solenoids associated with pressure reducing valve  110   b  and pressure reducing valve  112   b.    
         [0018]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed hydraulic system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed hydraulic system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.