Patent Document

TECHNICAL FIELD  
         [0001]    The present invention relates generally to variable discharge pumps, and more particularly to variable discharge pumps having a pair of pumping plungers.  
         BACKGROUND  
         [0002]    In one class of fluid systems, such as common rail fuel systems for internal combustion engines, a variable discharge pump is utilized to maintain a pressurized fluid supply for a plurality of fuel injectors. For instance, European Patent Specification EP 0,516,196 teaches a variable discharge high pressure pump for use in a common rail fuel injection system. The pump maintains the common rail at a desired pressure by controllably displacing fluid from the pump to either the high pressure common rail or toward a low pressure reservoir with each pumping stroke of each pump piston. This is accomplished by associating an electronically controlled spill valve with each pump piston. When the pump piston is undergoing its pumping stroke, the fluid displaced is initially pushed into a low pressure reservoir past a spill control valve. When the spill control valve is energized, it closes the spill passageway causing fluid in the pumping chamber to quickly rise in pressure. The fluid in the pumping chamber is then pushed past a check valve into a high pressure line connected to the common rail. In this type of system, the pump typically includes several pump pistons or the system is maintained with several individual unit pumps. The various pump pistons are preferably out of phase with one another so that at least one piston is pumping at about the same time one of the hydraulic devices is consuming fluid from the common rail. This strategy allows the pressure in the common rail to be more steadily controlled in a highly dynamic environment.  
           [0003]    As stated, in the pump of the above identified patent, fluid is initially displaced from each pump chamber through a spill control valve toward a low pressure reservoir when the individual pump pistons begin their pumping stroke. When the spill control valve is energized, this spill passageway is closed allowing fluid pressure to build and be pushed past a check valve toward the high pressure common rail. Like many pumps of its type, the spill control valve is a pressure latching type valve in which the valve member is held in its closed position via fluid pressure so that the actuator can be deenergized after the spill control valve has been closed, which can conserve electrical energy. In other words, the fluid pressure in the pumping chamber itself holds the spill control valve closed until that pressure drops toward the end of the pumping stroke, where a spring or other bias pushes the spill control valve back to its open position. When the pump piston undergoes its retracting stroke, fresh fluid is drawn into the pumping chamber past the spill control valve. Thus, the identified patent teaches a spill control valve that both fills the pump cavity with inlet fluid and spills the pump cavity during the time preceding the closing of the valve and the commencement of pump discharge toward the high pressure common rail.  
           [0004]    One problem associated with pumps of the type previously described is that the process of filling the pumping chamber and that of spilling the pumping chamber before high pressure pumping begins tend to conflict with one another. Optimizing the spill control valve details for spilling requires designing the valve and valve body geometry to, among other things, avoid shutting the valve due to flow forces before the electrical actuator is energized. This design criteria often conflicts with the need to fill the pumping chamber through the same fluid circuit. Thus, the pump previously described suffers from two potential drawbacks in that a separate spill control valve is needed for each pumping plunger, and each pump cavity both fills and spills through the spill control valve, resulting in design compromises to efficiently achieve both effective spilling and filling.  
           [0005]    The present invention is directed to overcoming one or more of the problems set forth above.  
         SUMMARY OF THE INVENTION  
         [0006]    In one aspect, a pump includes first and second plungers positioned to reciprocate in first and second pumping chambers of first and second barrels, respectively. At least one spill passage is fluidly connected to the first and second pumping chambers. A spill control valve is fluidly connected to at least one spill passage. At least one supply passage is fluidly connected to the first and second pumping chambers but fluidly disconnected from the spill control valve.  
           [0007]    In another aspect, a pump includes a first barrel with a first pumping chamber and a second barrel with a second pumping chamber. A first plunger is positioned to reciprocate in the first barrel, and a second plunger is positioned to reciprocate in the second barrel out of phase with the first plunger. A shuttle member has a first hydraulic surface exposed to fluid pressure in the first pumping chamber, and a second hydraulic surface oriented in opposition to the first hydraulic surface and exposed to fluid pressure in the second pumping chamber.  
           [0008]    In still another aspect, a method of operating a pump includes a step of reciprocating a pair of plungers out of phase with one another in respective first and second pumping chambers. Fluid is supplied to the first and second pumping chambers via at least one supply passage. Fluid is spilled from the first and second pumping chambers via at least one spill passage. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic illustration of a common rail fuel system according to one aspect of the present invention;  
         [0010]    [0010]FIG. 2 is a front sectioned view of a pump from the fuel system shown in FIG. 1;  
         [0011]    [0011]FIG. 3 is a side sectioned view of the pump of FIG. 2;  
         [0012]    [0012]FIG. 4 is an enlarged front sectioned view of the fill and spill portion of the pump of FIGS. 2 and 3; and  
         [0013]    [0013]FIG. 5 is a schematic illustration of a pump according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]    Referring to FIG. 1, a fuel system  10  includes a plurality of fuel injectors  22 , which are each connected to a high pressure fuel rail  20  via an individual branch passage  21 . The high pressure fuel rail  20  is supplied with high pressure fuel from a high pressure pump  16 , which is supplied with relatively low pressure fluid by a fuel transfer pump  14 . Fuel transfer pump  14  draws fuel from a fuel tank  12 , which is also fluidly connected to the fuel injectors  22  via a leak return passage  23 . Fuel system  10  is controlled in its operation in a conventional manner via an electronic control module  18  which is connected to an electrical actuator  28  of pump  16  via a control communication line  29 , and connected to the individual fuel injectors  22  via other communication lines (not shown). When in operation, control signals generated by electronic control module  18  determine when and how much fuel displaced by pump  16  is forced into common rail  20 , as well as when and for what duration (fuel injection quantity) that fuel injectors  22  operate.  
         [0015]    Referring in addition to FIGS. 2 and 3, high pressure pump  16  includes a high pressure outlet  30  fluidly connected to the high pressure rail  20 , a low pressure outlet  32  connected to fuel tank  12 , and an inlet  33  fluidly connected to fuel transfer pump  14 . Pump  16  also includes a first plunger  45  positioned to reciprocate in a first pumping chamber  46  of a first barrel  44 . In addition, pump  16  includes a second plunger  55  positioned to reciprocate in a second pumping chamber  56  of a second barrel  54 . Although not necessary, first and second barrels  44 ,  54  are preferably portions of a common pump housing  40 . A pair of cams  34  and  35  are operable to cause plungers  45  and  55  to reciprocate out of phase with one another. In this embodiment, cams  34  and  35  each include three lobes such that one of the plungers  45  or  55  is undergoing a pumping stroke at about the time that one of the fuel injectors  22  is injecting fuel. Thus, cams  34  and  35  are preferably driven to rotate directly by the engine at a rate that preferably synchronizes pumping activity to fuel injection activity in a conventional manner.  
         [0016]    When plunger  45  is undergoing its retracting stroke, fresh low pressure fuel is drawn into pumping chamber  46  past a first inlet check valve  48  from a low pressure gallery  37  that is fluidly connected to inlet  33 . Likewise, when plunger  55  is undergoing its retracting stroke, fresh low pressure fuel is drawn into the second pumping chamber  56  past a second inlet check valve  58  from the shared low pressure gallery  37 . When first plunger  45  is undergoing its pumping stroke, fluid is displaced from pumping chamber  46  either into low pressure gallery  37  via first spill passage  41  and spill control valve  38 , or into high pressure gallery  39  past first outlet check valve  47 . Likewise, when second plunger  55  is undergoing its pumping stroke, fuel is displaced from second pumping chamber  56  either into low pressure gallery  37  via second spill passage  51  and spill control valve  38 , or into high pressure gallery  39  past second outlet check valve  57 .  
         [0017]    Referring now in addition to FIG. 4, only one of the pumping chambers  46  or  56  is fluidly connected to spill control valve  38  at a time. These fluid connections are controlled by a shuttle valve member  80  that includes a first hydraulic surface  81  exposed to fluid pressure in first pumping chamber  46 , and a second hydraulic surface  82 , which is oriented in opposition to first hydraulic surface  81  and exposed to fluid pressure in second pumping chamber  56 . Because pumping plungers  44  and  54  are out of phase with one another, one pumping chamber will be at low pressure (retracting) when the other pumping chamber is at high pressure (advancing), and vice versa. This action is exploited to move shuttle valve member  80  back and forth to connect either first spill passage  41  to spill control valve  38 , or fluidly connect second spill passage  51  to spill control valve  38 . Thus, first hydraulic surface  81  and second hydraulic surface  82  actually define a portion of first spill passage  41  and second spill passage  51 , respectively. This allows pumping chambers  46  and  56  to share a common spill control valve  38 . In other words, when first plunger  44  is undergoing its pumping stroke while second plunger  54  is undergoing its retracting stroke, shuttle valve member  80  will be in a position shown in FIG. 4 in which first pumping chamber  56  is fluidly connected to spill control valve  38 . This is caused by hydraulic fluid pressure acting on first hydraulic surface  81  from pumping chamber  44  pushing shuttle valve member  80  to the right to close second spill passage  51 . The affect of this is twofold. First, a single spill control valve  38  can be used to control high pressure discharge from two separate pumping chambers. And second, second pumping chamber  56  is refilled past a second inlet check valve  58  rather than past the spill control valve as in the prior art. These features allow the spill control valve  38  to be optimized for flow in one direction, namely in the spill direction without requiring it to also perform the duty of reverse flow to fill a pumping chamber(s). In addition, this strategy also allows for the usage of a simple cartridge check valve  58  for controlling low pressure fill into the second pumping chamber  56 . When second plunger  54  is undergoing its pumping stroke and first plunger  44  is undergoing its retracting stroke, shuttle valve member  80  moves to the left to connect second spill passage  51  to spill control valve  38 , while low pressure fuel refills first pumping chamber  46  past first inlet check valve  48 .  
         [0018]    Spill control valve  38  has a structure that shares many features in common with known valves of its type. For instance, it includes a spill valve member  60  that includes a closing hydraulic surface  62  that produces a latching affect when valve member  60  is in contact with valve seat  63 . Spill valve member  60  is normally biased downward toward its open position, as shown in FIG. 4, via a biasing spring  64 . However, spill valve member  60  can be moved upward to close valve seat  63  by energizing electrical actuator  28 . In the illustrated embodiment, electrical actuator  28  is a solenoid that includes an armature  36  attached to move with spill valve member  60 . Nevertheless, those skilled in the art will appreciate that electrical actuator  28  could take a variety of forms, including but not limited to piezo and/or piezo bender actuators. In the illustrated embodiment, electrical actuator  28  controls the output from a pair of pumping chambers.  
         [0019]    Referring now to FIG. 5, a schematic illustration of a high pressure pump  116  according to another embodiment of the present invention is similar to the previous embodiment in that it includes a shuttle valve member  180  that permits the sharing of a single spill control valve  138  between a pair of pumping plungers  145  and  155 . This embodiment differs from the earlier embodiment in that no inlet check valves are needed, and the two pumping chambers  146  and  156  share a common outlet check valve  148 . When first plunger  145  is undergoing its pumping stroke and second plunger  155  is undergoing its retracting stroke, as shown, the pressure differentials produced in respective pumping chambers  146  and  156  cause shuttle valve member  180  to move to the right to the position shown. This is caused by an increase of fluid pressure acting on first hydraulic surface  181  via a first pressure communication passage  42  while a lower pressure force is acting on second hydraulic surface  182  via a second pressure communication passage  152 . When shuttle valve member  180  is in the position shown, first pumping chamber  146  is fluidly connected to outlet gallery  139  via first outlet passage  143 . In addition, first pumping chamber  146  is also fluidly connected to spill control valve  138  via first spill passage  144  and common spill passage  141 . Finally, first pumping chamber  146  is fluidly disconnected from low pressure gallery  137  and supply passage  136  due to shuttle valve member  180  closing first supply passage  147 . Thus, when spill control valve  138  is energized, common spill passage  141  will close and high pressure fluid will be displaced from first pumping chamber  146  past outlet check valve  148 .  
         [0020]    At the same time that first plunger  145  is undergoing its pumping stroke, second plunger  155  is undergoing its retracting stroke, and fresh low pressure fuel is drawn into second pumping chamber  156  from low pressure gallery  137  via supply passage  136  and second supply passage  157 . At the same time shuttle valve member  180  blocks second spill passage  154  and second outlet passage  153 . Thus, the spool valve nature of shuttle valve member  180  allows for the elimination of inlet check valves and allows for the sharing of a single outlet check valve as well as the sharing of a single spill control valve between two separate plungers reciprocating out of phase with one another.  
       INDUSTRIAL APPLICABILITY  
       [0021]    The present invention finds potential application in any fluid system where there is a desire to control discharge from a pump. The present invention finds particular applicability in variable discharge pumps used in relation to fuel injection systems, especially common rail fuel injection systems. Nevertheless, those skilled in the art will appreciate that the present invention could be utilized in relation to other hydraulic systems that may or may not be associated with an internal combustion engine. For instance, the present invention could also be utilized in relation to hydraulic systems for internal combustion that use a hydraulic medium, such as engine lubricating oil, to actuate various sub-systems, including but not limited to hydraulically actuated fuel injectors and gas exchange valves, such as engine brakes. A pump according to the present invention could also be substituted for a pair of unit pumps in other fuel systems, including those that do not include a common rail.  
         [0022]    Referring to FIG. 1, when fuel system  10  is in operation, cams  34  and  35  rotate causing pump plungers  45  and  55  to reciprocate in respective barrels  44  and  54  out of phase with one another. When first plunger  45  is undergoing its pumping stroke, second plunger  55  will be undergoing its retracting stroke. This action is exploited via shuttle valve member  80  to either connect first pumping chamber  46  or second pumping chamber  56  to spill control valve  38 . As one of the plungers begins its pumping stroke, fluid is initially displaced from the pumping chamber through spill control valve  38  to low pressure gallery  37 . When there is a desire to output high pressure from the pump, electrical actuator  28  is energized to close spill control valve  38 . This causes fluid in the pumping chamber to be pushed past the respective check valve  47  or  57  into high pressure gallery  39  and then into high pressure rail  20 . Those skilled in the art will appreciate that the timing at which electrical actuator  28  is energized determines what fraction of the amount of fluid displaced by the plunger action is pushed into the high pressure gallery and what other fraction is displaced back to low pressure gallery  37 . This operation serves as a means by which pressure can be maintained and controlled in high pressure rail  20 . While one plunger is pumping, the other plunger is retracting drawing low pressure fuel into its pumping chamber past one of the respective inlet check valves  48  or  58 . This action allows for the spill control valve  38  to be optimized for flow in one direction, namely in a spill direction. Likewise, the spill action of the pump can be optimized for features known in the art independent of spill control valve  38 .  
         [0023]    Referring now to FIG. 5, pump  116  operates in much a similar manner as pump  16  described earlier accept that shuttle valve member  180  is a spool valve member that allows for the elimination of inlet check valves and allows for the sharing of a single outlet check valve between the two pumping plungers  145  and  155 . Thus, pump  116  works in a virtually identical manner with a more complex shuttle valve member but a lower part count regarding check valves associated with the pump.  
         [0024]    Thus, the present invention utilizes one electrical actuator valve combination to control the discharge of two plungers. To facilitate that arrangement, a shuttle valve is located between the plunger pumping cavities and the spill control valve. The pumping action of the first plunger combined with the intake action of the second forces the shuttle valve to a position that blocks fluid entry into the filling plunger while providing an open path between the pumping plunger and the spill control valve. The spill control valve can then be activated at any time between the commencement of the pumping plunger&#39;s motion and the end of its motion. Closing the valve initiates a rise in plunger cavity pressure, an opening of the outlet check valve and a start of the delivery of high pressure fuel to the high pressure fuel rail. The increase in pressure holds the shuttle valve shut until the plunger slows and stops at the end of its motion, at which time the solenoid biasing spring opens the spill control valve in preparation for the next plunger&#39;s action. As the second plunger switches modes from filling to pumping (and the first plunger switches from pumping to filling), the shuttle valve moves to the other side of its cavity blocking fluid entry into the filling plunger, and opening the path between the pumping plunger and the spill control valve allowing the spill control valve to control the discharge of the second plunger cavity.  
         [0025]    It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Technology Category: f