Abstract:
A hydraulically-actuated system includes a fix displacement variable delivery pump with a plurality of parallel disposed pistons that reciprocate in a pump housing the defines a high pressure portion and a low pressure area. A control device is attached to the pump housing and moveable between a first position in which the pistons displace fluid into the high pressure portion and a second position in which pistons spill fluid back to the low pressure area. The control device includes an electrically driven linear motion device, a linkage and a plurality of sleeves, one being disposed on each piston. Linear movement of the control device in turn causes linear movement of the sleeves. The position of the sleeves in turn determines the amount of output of the pump.

Description:
TECHNICAL FIELD 
     The present invention relates generally to hydraulically-actuated system, and more particularly to a electro-hydraulic closed loop actuator of a variable delivery fixed displacement pump. 
     BACKGROUND ART 
     U.S. Pat. No. 6,035,828 to Anderson et al. describes a variable delivery actuating fluid pump for a hydraulically-actuated fuel injection system. In this system, a high pressure rail supplies pressurized lubricating oil to a plurality of hydraulically-actuated fuel injectors mounted in a diesel engine. The high pressure rail is pressurized by a variable delivery fixed displacement type pump that is driven directly by the engine. Pump pressure control is provided by hydraulically varying the high pressure output of the pump. This is accomplished by providing a piston arrangement in the pump that incorporates a moveable sleeve on the outside of the pistons. Depending upon the position of the sleeve, a spill port on the piston is opened or closed. When the spill port is opened, the fluid is spilled back into the low pressure side of the pump, instead of being pushed into the high pressure rail. The position of the sleeve is maintained by a hydraulic actuator. Fluid in the hydraulic actuator moves an actuator shaft, which in turn moves the sleeve. 
     While the Anderson et al. hydraulically-actuated system using a variable delivery pump performs better than previous systems there remains room for improvement. The complicated mechanical structure of the pump and hydraulic actuator provides potential leak paths for hydraulic fluid. Also, because the viscosity of lubricating oil varies due to temperature, control of the pump may be sluggish when the oil is of an extremely cold temperature. 
     The present invention is directed to overcoming problems associated with, and improving upon, hydraulically-actuated systems of the prior art. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention a variable delivery fixed displacement pump is provided. The pump includes an actuator having an actuator bore, a first directional port and a second directional port. An actuator shaft is disposed within the bore and moveable in a first direction and a second direction in response to receiving fluid from the first or second directional port. The actuator shaft is adapted to vary the amount of fluid output from the pump. A valve having a spool, a first solenoid coil and a second solenoid coil directs fluid to one of the first or second directional ports in response to a signal from a controller. 
     In another aspect of the invention a fluid delivery system is provided. The fluid delivery system includes a controller, a pump having a high pressure outlet and an actuator having a position sensor. A pressure sensor is provided to sense the pressure in a high pressure rail is included. A valve between the high pressure outlet and one of the first or second directional ports, directs fluid to he actuator. 
     In yet another aspect of the present invention a method for controlling a variable delivery fixed displacement is provided. The method includes delivering a flow to one of a first or second directional port. An actuator shaft is moved in one of a first direction and a second direction in response to delivering flow to one of the first and second directional flows. Fluid flow from the pump is varied depending upon position of the actuator shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a hydraulically-actuated system according to the present invention. 
     FIG. 2 is a sectioned side diagrammatic view of a variable delivery fixed displacement pump of the present invention. 
     FIG. 3 is a sectioned side diagrammatic view of an electro-hydraulic actuator according to one of the present invention. 
     FIG. 4 is a is a section side diagrammatic view of an electro-hydraulic actuator according to another aspect of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, a hydraulically actuated system  10  is attached to an internal combustion engine  12 . The hydraulically actuated system  10  includes a high pressure rail  14  that supplies actuation fluid to a plurality of hydraulically-actuated devices, such as hydraulically-actuated fuel injectors  16 . Those skilled in the art will appreciate that other hydraulically-actuated devices, such as actuators for gas exchange valves for exhaust brakes, could be substituted for the fuel injectors  16  illustrated in the example embodiment. The high pressure rail  14  is pressurized by a variable delivery fixed displacement pump  18 , via a high pressure supply conduit  22 . The pump  18  draws actuation fluid along a low pressure supply conduit  24  from a source of low pressure fluid, which is preferably the engine&#39;s lubricating oil sump  26 . Although other available liquids could be used, the present invention preferably utilizes engine lubricating oil as its hydraulic medium. After the high pressure fluid does work in the individual fuel injectors  16 , the actuating fluid is returned to sump  26  via a drain passage  28 . p As is well known in the art, a desired pressure in high pressure rail  14  is generally a function of the engines  12  operating condition. For instance, at high speeds and loads, the rail pressure is generally desired to be significantly higher than the desired rail pressure when the engine  12  is operating at an idle condition. An operating condition sensor  32  is attached to engine  12 , the sensor  32  provides an electronic control module  34  with sensor data, which includes engine speed and load conditions, via a first communication line  36 . In addition, a pressure sensor  38  periodically provides the electronic control module  34  with the measured fluid pressure in the high pressure rail  14  via a second communication line  40 . The electronic control module  34  compares the desired rail pressure with the actual rail pressure, as provided by the pressure sensor  38 . The electronic control module  34  sends a control signal to a control device  42 , which in turn adjusts the amount of fluid output from the pump  18 . 
     Referring now to FIG. 2, various components of the pump  16  are contained within a pump housing  43 . Pump  18  includes a rotating pump shaft  44  that is coupled directly to the engine  12 , such that the rotation rate of the pump shaft  44  is directly proportional to rotation of the crank shaft (not shown) of the engine  12 . A fixed angle swash plate  46  is attached to the pump shaft  44 . The rotation of swash plate  46  causes the plurality of parallel disposed pistons  48  to reciprocate from left to right. In this example, the pump  18  includes five pistons  48  that are continuously urged toward the swash plate  46  by individual return springs  52 . Each of the return springs  52 . maintains a shoe  53 , which is attached to one end of each piston  48 , in contact with the swash plate  46  in a conventional manner. Because the swash plate  46  has a fixed angle, the pistons  48  reciprocate through a fixed reciprocation distance with each rotation of the pump shaft  44 . Thus, the pump  18  can be thought of as a fixed displacement pump  18 . However the control device, which includes an electro-hydraulic actuator  54 , determines if the fluid displaced by each piston  48  is pushed into a high pressure outlet  68  past a check valve  56  or spilled back into a low pressure portion  58  of the pump  18 . 
     Each piston  48  includes an internal passage  62  that extends axially within the piston  48 . A spill port  63  extends radially outward from the internal passage  62  to an outer surface  64 . The outer surface  64  is disposed within the low pressure portion  58  of the pump  18 . Pressure within a pumping chamber  66 , under each piston  48 , can only build when the spill port  63  is covered by a sleeve  67 . The sleeve  67  is adapted to slide axially on the outer surface  64  of the piston  48 . When the sleeve  67  covers the spill port  63 , fluid displaced by the piston  48  is pushed past the check valve  56 , into the high pressure portion  55 , and eventually out of a high pressure outlet  68  to the high pressure rail  14 . When the pistons  48  are undergoing the retracting portion of their stroke due to the action of the return spring  52 , low pressure fluid is drawn into pumping chamber  66  from the low pressure portion  58 . The sleeves  67  are axially fixed to a linkage  70  that is further fixed to the electro-hydraulic actuator  54 . The electro-hydraulic actuator  54  may be disposed within the pump housing  43  or located externally. 
     Referring now to FIGS. 3 and 4, the electro-hydraulic actuator  54  of the present invention is illustrated. The electro-hydraulic actuator  54  includes a body  72 , an actuator portion  74  and a spool valve portion  76 . In this embodiment the actuator portion  74  and spool valve portion  76  are disposed in one body  72 . It should be realized that the actuator portion  74  could be disposed in a separately than that of the spool valve portion  76  without deviating from the intended scope of the invention. 
     The spool valve portion  76  of the body includes a bore  78  extending from a first side  79  to a second side  80 . A high pressure inlet port  82  extends from the bore  78  to an outer body surface  84 . A high pressure fluid source, preferably the high pressure rail, is connected to the inlet port  82 . The inlet port  82  is located approximately at a midpoint  83  between the first end  128  and the second end  132 . A first directional port  86  and a second directional port  88  extend from the bore  78  to the actuator portion  74  of the body  72 . The directional ports  86 , 88  are spaced at an predetermined distance  90  to the left or right of the midpoint  83 . A left solenoid coil  92  and a right solenoid coil  94  are adapted to be received by the body  72  at each end of the bore  78 . The left coil  92  and the right coil  94  are connected to the electronic control module  34  via a signal line  96 . A valve spool  102  having a first end  104 , a second end  106  and a predetermined diameter is slideably positioned within the bore  78 . The valve spool  102  includes a first directional land  112  and a second directional land  114  that extend radially outward from the spool  102 . The first and second directional lands  112 ,  114  have a diameter that is slightly smaller than that of the bore  78 , permitting sliding movement within the bore  78 . The first directional land  112  and second directional land  114  are disposed a distance left or right of a midpoint of the spool  102  equal to the predetermined distance  90 , so that when the spool  102  is centered in the bore  78  the first and second directional ports  86 ,  88  are closed. A first drain land  116  and a second drain land  118  are disposed to the left and right, respectively, of the first and second directional lands  112 ,  114 . The first and second drain lands  116 ,  118  are also of a diameter that is slight smaller than that of the bore  78 . A left armature  122  and a right armature  124  are disposed toward the left end and the right end of the spool  102 . The left and right armatures  122 ,  124  are slidingly positioned within the left and right solenoid coils  92 ,  94 . When the left coil  92  is energized the spool  102  moves left of the midpoint  83 , permitting flow of high pressure fluid from the inlet port  82 , through the bore  78  to the left directional port  86 . Conversely, when the right coil  94  is energized the spool  102  moves toward the right permitting high pressure fluid to flow from the inlet port  82  through to the right directional port  88 . Energizing both the left and right coils  92 ,  94  causes the spool  78  to center and blocking fluid flow to either of the left or right directional ports  86 ,  88 . 
     The actuator portion  74  includes an actuator body  126  having a first side  79  and a second side  80 . A shaft bore  134  having a piston cavity  136  extends from the first side  79 , through the actuator body  126  to the second side  80 . The piston cavity  136  includes a first end  138  and a second end  142 . The first directional port  86 , connects the piston cavity near first end  138  and the second directional port  88 , connects the piston cavity  136  near the second end  142 . An actuator shaft  144  having a first end  146  and second end  148  is slidingly positioned in the shaft bore  134 . An actuator piston  152  having a left face  154  and a right face  156  extends radially outward from the actuator shaft  144 , at a position within the cavity  136 . The actuator piston  152  is positioned in the cavity  136  between the first and second directional ports  86 ,  88 . Fluid flow from the first directional port  86  moves the actuator shaft  144  and piston  152  toward the right. Movement of the piston  152  toward the right, causes fluid on the right side of the piston to be forced into the right directional port  88  and flow back through the spool valve portion  76  into the low pressure drain  89 . The linkage  70  mechanically couples the actuator shaft  144  to the control device  42  of the pump  18 . 
     A position sensor  158  is operatively positioned within the actuator portion  74  to sense the position of the actuator shaft  144  relative to the actuator body  126 . The position sensor  158  is of conventional construction and will not be discussed in detail. The position sensor  158  may alternatively be positioned within the pump housing  42  to sense position of the control valve. The position sensor  158  provides an electronic signal to the electronic control module  34  related to the axial position of the control device  42  or actuator shaft  144 . The position sensor  158  sends the position signal via a third communication line  162 . The electronic control module  34  stores data related to the position of the control device  42  and processes the data to determine a need to modify control signals to the control device  42 . 
     Referring now to FIG. 4, another embodiment of the present invention is illustrated. Similar to FIG. 3, the electro-hydraulic actuator  52  of the present invention includes a actuator portion  74 ′ and a spool valve portion  76 ′. The spool valve portion  76 ′ includes only a right solenoid coil  94 ′, and the spool  102 ′ includes only one right armature  124 ′. The first end  104  of the spool  102 ′ is biased toward the right by a spring  85 . The electronic control module  34  energizes the right coil  94 ′ to move the spool  102 ′ toward the spring  85 . 
     INDUSTRIAL APPLICABILITY 
     In operation an internal combustion engine  12  drives a fixed displacement variable delivery pump  18 . The pump  18  draws fluid from a lubricating oil sump  26  into a low pressure portion  58  of the pump  18 . Rotation of a plurality of pistons  48  around a shaft  44 , causes the pistons  48  to move in an axial direction. Movement of the pistons  48  is caused by a fixed angle swash plate  46 . The pistons  48  move between a first position, and a second position nearest a high pressure portion  55 . In the first position fluid flows from the low pressure portion  58  of the pump  18  into the piston  48 . As the piston  48  moves toward the second position, fluid is pushed into the high pressure portion  55  of the pump  18 . A control device  42  controls the amount of fluid output from the piston  48  to the high pressure portion  55  of the pump  18 . An electronic control module  34  sends a signal to the electro-hydraulic actuator  54  via a signal line  96 . 
     The electronic control module  34  receives a signal from a pressure sensor  38  located in the high pressure common rail  14  via a communication line  40 . Additionally, the electronic control module  34  receives a signal from an operating condition sensor  32  on the internal combustion engine  12  via communication line  36 . The operating condition sensor  32  signals the electronic control module  32  the status of a plurality of operating parameters of the internal combustion engine  12 . The position sensor  158  also sends data related to the position of the actuator shaft  144  and/or the control device  42  to the electronic control module  34 . Based on the need to alter fluid pressure in the high pressure rail  14  the electronic control module  32  commands movement of the electro-hydraulic actuator  54 . 
     The present invention decreases the complexity of prior art hydraulically-actuated systems by providing a signal electro-hydraulic actuator  54  for controlling pressure in the high pressure rail  14 . Responses time of the electro-hydraulic actuator  54  is not as greatly effected by the temperature of oil as with prior systems. Faster pump  18  control during lower temperature operation improves emissions output of the internal combustion engine  12 . Additionally, the elimination of a number of pump  18  components and fluid seals within the pump  18  reduces the possibility of oil leakage from the pump  18 . 
     The above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. For instance, other types of actuators could be substituted for the example illustrated actuator without departing from the intended scope of the present invention. Thus, those skilled in the art will appreciate that various modifications can be made to the illustrated embodiment without departing from the spirit and scope of the present invention, which is defined in terms of the claims set forth below.