Abstract:
In an engine equipped with a common rail fuel injection system, the engine can sometimes experience an overspeed condition, and the pump may respond to this overspeed condition with self-actuation even in the absence of any control signal. In order to prevent an over pressurization condition, a liquid supply into a pumping chamber of the pump is limited during a retraction stroke of a pump plunger by energizing an electrical actuator coupled to a spill valve, to move the spill valve toward a closed position. The electrical actuator is de-energized during a pumping stroke of the pump plunger to allow the spill valve to more toward an open position. Liquid from the pumping chamber is discharged through the spill valve during the pumping stroke, but over pressurization is avoided by limiting the amount of liquid that can enter the pumping chamber during the retraction stroke.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to liquid pumps that are electronically controlled but have an overspeed self actuation mode, and more particularly to limiting pump flow during an overspeed self-actuation condition. 
       BACKGROUND 
       [0002]    Many internal combustion engines are equipped with common rail fuel injection systems. In these systems, a high pressure liquid pump will typically receive pressurized fuel from a transfer pump which draws fuel from a low pressure reservoir. The high pressure pump pressurizes it to injection levels and supplies the same to a common rail. A plurality of individual fuel injectors are fluidly connected to the common rail and provide the means by which fuel is injected into individual cylinders of the engine. These pumps will typically be electronically controlled in order to control output from the pump independent of engine speed and hence control rail pressure through appropriate electronic signals generated by a conventional electronic controller. These pumps are typically driven directly via a gear train connection to the engine&#39;s crank shaft. However, the pump&#39;s output is generally controlled via an electronically controlled valve that determines how much of each pumping stroke produces output to the common rail. Some pumps in this class also include a passive pressure relief valve that opens when pressures rise above some certain threshold to prevent over pressurization damage to the pump or elsewhere in the common rail fuel injection system. Although some pumps in this class are equipped with pressure relief valves, the pressure relief valve will have an inherent flow rate capacity. Therefore, it is important that the pump be operated in a way that prevents the pressure relief valve from being overwhelmed by exceeding its flow capacity under all anticipated operating conditions for the pump. 
         [0003]    In some rare circumstances, an engine will experience a so called “overspeed” condition. One example overspeed condition might be when an over the road truck is utilizing the engine to apply a retarding force to the truck when traveling down hill. In such a condition, the engine speed can rise above an RPM level associated with an overspeed condition, such as in the range of 3000-4000 RPM. In this range, engineers have observed that some common rail high pressure pumps will experience a self-actuation mode where liquid flow and/or other forces within the pump itself cause the output control valve to self actuate, resulting in the pump producing substantial output even when no control signal commanding output is present. For instance, some liquid pumps of common rail fuel systems utilize a latching spill valve that relies upon hydraulic latching to hold the spill valve closed during normal pump operations during a pumping stroke. This is typically accomplished by including a spill valve that moves toward a closed position in a direction away from a pumping chamber and includes a closing hydraulic surface exposed to fluid pressure in the pumping chamber of the pump. During a self-actuation mode, fluid flow around the spill valve can pull it closed when no control signal is present to pull the spill valve closed via a conventional electrical actuator. Thus, under these overspeed conditions, the common rail may be asking for no fluid, yet the pump is operating at a high speed producing a substantial amount of output. In some instances, there may be a danger of an over pressurization condition if the pressure relief valve capacity is exceeded. 
         [0004]    U.S. Pat. No. 5,277,156 to Osuka et al. teaches a high-pressure pump that does not include a pressure relief valve but does have a strategy for dealing with a potential self-actuation overspeed condition. Like the pump discussed earlier, the Osuka et al. pump includes a latching spill/fill valve that allows for the spill valve to be actuated with a brief electric current rather than supplying current to the same for the entire duration of a pumping stroke. In those rare instances when the Osuka et al. system detects a self-actuation overspeed condition, a special logic in the electronic controller is initiated that supplies electrical current continuously to hold the spill/fill valve closed during the entire retraction and pumping stroke until the overspeed condition subsides. Thus, during normal operating conditions, the Osuka et al. pump needs to be provided only brief bursts of electrical current in order to provide normal output control from the pump. However, during an overspeed self-actuation condition, the Osuka et al. system must provide continuous electric current to the electrical actuator for each of a plurality of electronically controlled spill/fill valves simultaneously during their entire retraction and pumping strokes. Thus, the Osuka et al. system suffers from a potential drawback by requiring the ability to provide a substantial amount of electrical power simultaneously to a plurality of electrical actuators associated with its high-pressure pump. 
         [0005]    The present disclosure is directed to one or more of the problems set forth above. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    In one aspect, a method of operating a liquid pump includes a step of rotating a pump drive shaft in excess of a spill valve self-actuation speed. A liquid supply through the spill valve is restricted into the pumping chamber of the pump during a retraction stroke of a pump plunger by energizing an electrical actuator coupled to the spill valve to move the spill valve toward a closed position. The electrical actuator is de-energized during the pumping stroke of the pump plunger to allow the spill valve to move toward an open position. Liquid from the pumping chamber is discharged through the spill valve during the pumping stroke. 
         [0007]    In another aspect, a common rail fuel injection system includes a plurality of fuel injectors fluidly connected to a common rail. A high-pressure pump is fluidly positioned between a low-pressure reservoir and a high-pressure common rail. An electronic controller is configured to limit, but no eliminate, flow into and out of the plunger cavity through a spill valve of the pump when a drive shaft speed of the pump exceeds a spill valve self actuation speed. 
         [0008]    In still another aspect, an engine includes a high-pressure pump with a drive shaft geared to rotate with an engine crankshaft. The high-pressure pump also includes a pressure relief valve and is fluidly connected to a high-pressure common rail. A plurality of fuel injectors are also connected to the high-pressure common rail. The engine also includes a low-pressure reservoir. Finally, there includes means for limiting flow through the pressure relief valve below its capacity when the engine is in an overspeed condition. The means for limiting includes an electronic controller coupled to an electronically controlled valve, which is different from the pressure relief valve, and is fluidly positioned between the low pressure reservoir and the plunger cavity of the high pressure pump. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic view of an engine that includes a partially sectioned perspective view of a high pressure common rail pump; 
           [0010]      FIG. 2  is a flow diagram of a pump output limiting overspeed algorithm according to one aspect of the present disclosure; 
           [0011]      FIG. 3  is a graph of a control signal to an electronically controlled valve for one pumping chamber of the pump shown in  FIG. 1 ; 
           [0012]      FIG. 4  is a graph of pump plunger position verses time for one pumping chamber of the pump of  FIG. 1 ; 
           [0013]      FIG. 5  is a graph of control signal verses time for a second electronically controlled valve associated with a second pumping chamber of the pump of  FIG. 1 ; and 
           [0014]      FIG. 6  is a graph of a second pump plunger position verses time for the pump of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring to  FIG. 1 , an engine  10  includes a common rail fuel injection system  12  with a high-pressure liquid pump  14  and a plurality of fuel injectors  17 . Pump  14  is driven directly by engine  10  via a gear train linkage  13  between crankshaft  11  and pump drive shaft  40 . The pump low-pressure fuel from transfer pump  28  via a transfer line  21 . The transfer pump  28  draws fuel from a low-pressure reservoir  15  via a low-pressure supply line  27 . High pressure pump  14  supplies high-pressure fuel to a common rail  16  via a high-pressure outlet passage  22 . Fuel injectors  17  are fluidly connected to high pressure common rail  16  in a conventional manner, and each fuel injector is fluidly connected to low pressure reservoir  15  via a low pressure return line  26 . 
         [0016]    In the illustrated embodiment, pump  14  includes a pair of pumping plungers  31  and  32  that reciprocate out of phase with one another in response to rotation of cams  41  in a conventional manner. Output from high-pressure pump  14  is controlled via an electronic controller  19  in communication with respective first and second electronically control valves  34  and  35  via communication lines  24  and  25 , respectively. In order to prevent overpressurization of system  12 , rail  16  includes a pressure relief valve  38  that opens above some predetermined pressure, such as the maximum desired rail pressure. Thus, when pressure in the rail  16  is above the predetermined pressure, pressure relief valve  38  will open and allow the excess liquid to be returned toward low pressure reservoir  15  via low pressure line  29  in a conventional manner. 
         [0017]    Since the control and pumping features associated with both the first and second pumping plungers  31  and  32  are identical, the specific features of only one will be described. In particular, pumping plunger  31  reciprocates in a barrel  30  to displace fluid into and out of plunger cavity  33 . Electronically controlled spill valve  34  includes a spill valve member  36  of the latching type that is normally biased out of contact with seat  37  via spring  43 , but may be pulled closed by briefly energizing electrical actuator  42  (e.g., solenoid) during a pumping stroke. In the illustrated embodiment, plunger cavity  33  both fills and spills via electronically controlled valve  34 . In particular, during a retraction stroke, low pressure fuel moves via internal passage ways connected to transfer line  21  past spill valve member  36  and into plunger cavity  33 . During a pumping stroke, when spill valve member  36  is biased towards its normally open position, the fluid is then displaced back toward transfer line  21  past spill valve member  36  and seat  37 . Plunger  31  is made to retract via a return spring  39  that insures that the plunger follows the surface of cam  41  in a conventional manner. Although the illustrated embodiments show filling and spilling into plunger cavity  31  occurring through the same electronically controlled valve, those skilled in the art will appreciate that the present disclosure also applies to the pump having a separate fluid passage way for filling and a separate electronically controlled spill valve, such as that shown in co-owned U.S Patent Application Publication 20040109768. 
       INDUSTRIAL APPLICABILITY 
       [0018]    The present disclosure relates to any liquid pump that is electronically controlled, but may have a mode at high speeds where self-actuation of the pump occurs. Although the present disclosure illustrates a liquid pump who&#39;s output is controlled via a latching spill valve, other pumping and output control mechanisms would fall within the scope of the present disclosure if they exhibit a self-actuation mode where fluid flow forces or other phenomenon (e.g. centripetal force) cause an output control mechanism to self-actuate in the absence of a control signal. 
         [0019]    During normal operations of engine 10 , crankshaft  11  rotates and results in reciprocation of pump plungers  31  and  32  via pump drive shaft  40  and cams  41 . The fuel injection system  12  will typically include a plurality of sensors, including possibly rail pressure sensor, engine speed sensor and others known in the art to determine a timing and quantity of fuel to inject from each of the plurality of fuel injectors  17  in a conventional manner. In addition, the electronic controller will determine a desired injection pressure at which to control the pressure in common rail  16  using known electronic controlling strategies. Although the pumping plungers  31  and  32  will reciprocate through a fixed distance with each rotation of the lobes of cam  41 , only a portion of that fluid displacement may be needed in order to maintain rail pressure at a desired level. Thus, the electronic controller  19  also determines a timing at which electronically controlled spill valves  34  and  35  should be actuated to close the respective spill valve during a pumping stroke so that pressure builds within the plunger cavity  33  and fluid is displaced into high pressure outlet passage  22  past an outlet check valve (not shown) that is positioned between the plunger cavity  33  and common rail  16 . When electrical actuator  42  is energized during a pumping stroke, spill valve  36  is pulled upward to close in contact with seat  37 . Thereafter, pressure quickly builds within plunger cavity  33  and the fluid pressure itself holds the spill valve member  36  closed allowing the liquid to be displaced toward common rail  16 . Thus, only a brief energization of electrical actuator  42  during a pumping stroke is needed, and after the valve is closed via the electrical actuator  42  may be de-energized for the remaining duration of the pumping stroke. After the plunger  31  reaches top dead center and begins its retraction stroke, pressure drops in plunger cavity  33  allowing spill valve member  36  to move toward an open position via the action of biasing spring  43 . During the retraction stroke, fresh fluid is drawn into plunger cavity  33  past spill valve member  36 . When pumping plunger  31  reaches its bottom dead center position and reverses direction for another pumping stroke, the liquid is initially displaced back toward transfer line  21  past spill valve member  36 . When electronic controller  19  determines at some point during the pumping stroke that a portion of the fluid displaced by plunger  31  needs to be supplied to high pressure rail  16  to maintain its pressure, the electrical actuator  42  will be energized and the spill valve member pulled to close in contact with seat  37 . Thus, those skilled in the art will appreciate that during normal operations of engine  10 , fuel is consumed from high pressure rail  16  by fuel injectors  17  and replenished by high pressure pump  14  to control rail pressure to some desired level, which may vary across the engine&#39;s operating range. 
         [0020]    In some instances during the operation of engine  10 , pressure in the common rail  16  may rise to a predetermined maximum level and any further fluid in the plunger cavity  33  that is above that pressure may be displaced to rail  16  and out of pressure relief valve  38  to prevent overpressurization of system  12 . However, depending upon the flow area and other factors relating to pressure relief valve  38 , there may be a limit to how much flow can be pushed through the pressure relief valve. In other words, if there is so much fluid being displaced at such high-pressure levels from the plunger cavities, pressures could conceivably continue to rise to undesirable overpressurization levels even when the pressure relief valve  38  is open. For instance, one such condition might occur when engine  10  is experiencing an overspeed condition. In such a case, the electronic controller may be commanding the fuel injectors  17  to stop injecting fuel, pressure in the common rail  16  is at a relatively high and stable level, and thus, little to no liquid fuel is demanded from pump  14  in order to maintain pressure in the common rail. However, because pump  14  and engine  10  are in an overspeed condition, self-actuation of electronically controlled spill valves  34  and  35  can occur due to flow forces around valve member  36  past seat  37 . When this occurs, shortly after the plunger begins its pumping stroke, the high rate of liquid flow past valve member  36  causes it to move upward and close seat  37  causing pressure to quickly rise within plunger cavity  33 . However, pressure relief valve  38  may not have sufficient capacity to handle the high flow rate of high pressure from the plunger cavities during and overspeed condition. The present disclosure addresses this potential problem via selective use of electronic controller  19  to actuate the electronically controlled spill valves  34  and  35  in a way that reduces potential flow through pressure relief valve  38  to manageable levels within its capacity, even in an overspeed condition. 
         [0021]    Referring now in addition to  FIGS. 2-6 , the electronic controller  19  of  FIG. 1  may include a conventional processor configured to execute programming code stored in memory in a conventional manner, or maybe a dedicated electrical circuitry that is configured to perform in a similar manner. In the illustrated embodiment of  FIG. 2 , electronic controller would be configured to include the pump output limiting overspeed algorithm  50  that controls pump  14  in a manner so as to limit flow through pressure relief valve  38  below its capacity when engine  10  is in an overspeed condition. Those skilled in the art will appreciate that each individual pump application may have a unique speed at which the self-actuation phenomenon begins to occur, and at what higher speed its pressure relief valve could be overwhelmed. The overspeed algorithm begins at a start  51  and proceeds to a speed condition query  52 . At this step, the controller  19  determines whether pump speed, which is linked to, but may be different from, engine speed is above a certain level where the pump self-actuation can occur. If not, the algorithm proceeds to end  60 . Thus, during normal operation of engine  10 , the overspeed algorithm will be circumvented by a negative response to speed query  52 . However, if the engine happens to be operating in an overspeed condition reflective of a possible self-actuation speed for pump  14 , the algorithm will proceed to set flags at step  53 . In particular, the algorithm will set the desired rail pressure to zero and set the pump output duration to zero. Thus, the result of step  53  is to leave electronically controlled spill valves  34  and  35  unenergized so that the pump is commanded to produce no output. When the spill valves are left deactivated at moderate speeds, no output is produced since the fuel is displaced back and forth between plunger cavity  33  and low pressure supply line  21 . The algorithm then proceeds to a speed and pressure query step  54  where it is determined whether the pump is operating at a speed that is not only above a self-actuation level, but is also above a level that exceeds the capacity of the pressure relief valve  38 . In addition, query  54  determines whether rail pressure is above some predetermined high-pressure level. If not, this would be an indication that in the self-actuation mode that there is capacity in both the common rail and the pressure relief valve to handle the fluid being displaced from the plunger cavities in this overspeed condition, and the algorithm will proceed to flag check query  55 . At query  55 , the algorithm checks to see if the pump overspeed flag has been toggled to a true condition. If not, the algorithm again proceeds to end  60 . 
         [0022]    If the pump overspeed flag is determined to be true, the algorithm proceeds to set or reset parameters at step  57 . At step  57 , the pump is reenabled, although the pump output is set to zero. At step  58 , the pump overspeed flag is set to false and the algorithm proceeds to end  60 . Returning to query  54 , if the controller determines that the pump is operating at such a high speed as to be in a self-actuation mode that will overwhelm the pressure relief valve  38 , and rail pressure is at or above some elevated level, the algorithm will proceed to step  56  where the pump overspeed flag is set to true. When this occurs, the algorithm will then proceed to step  59  where the control signals to the electronically controlled spill valves are set in a manner reflected by the graphs of  FIGS. 3-6 . In particular, when in this high overspeed condition, electronic controller will be set to command the electronically controlled spill valves to close during a portion, but not all of, the retraction stroke preventing liquid from entering the plunger cavity past the spill valve member  36 . While this action permits some displacement of liquid into and out of plunger cavity past spill valve member  36 , overpressurization is avoided since the plunger cavity  33  is starved of liquid due to the closure of spill valve  36  during the retraction stroke. This action may result in cavitation within the pump during these pressure overspeed self-actuation conditions. 
         [0023]      FIGS. 3-6  reflect the control signals ( FIGS. 3 and 5 ) and the plunger motion ( FIGS. 4 and 6 ) of the pumping plungers  31  and  32  associated with pump  14  of  FIG. 1  as controlled via overspeed algorithm  50  shown in  FIG. 2 . In particular, a control signal  80  will cause the electrical actuator  42  to be energized  80  during a majority but less than all of the retraction stroke  70 . For example, the electronic controller may command the electronically controlled valve to close at about 150 degrees before top dead center and then maintain valve  34  closed for about 60 degrees or about two thirds of the retraction stroke. In addition, the initial timing of closing the valve and or the duration of the closure may be made a function of the engine speed. For instance, at higher speeds, the duration of valve closure during the retraction stroke may be increased. This will prevent too much liquid from entering plunger cavity  33  and thus avoid overwhelming pressure relief valve  38  in the overspeed self-actuation condition. Thus, when the pump plunger  31  undergoes its pumping stroke  71 , a substantial portion of that stroke will be merely reflected by collapse of cavitation bubbles generated during the retraction stroke, and very little liquid displacement into and out of plunger cavity  33  past spill valve member  36  will occur, and any liquid displaced through pressure relief valve  38  will be well within its capacity. Typically, the electrical actuator will be de-energized before an end of the retraction stroke  70 . When this occurs, liquid may flow into plunger cavity  33 , but that flow will quickly reverse in an opposite direction when the plunger begins its pump stroke  71  and the self-actuation conditions arise. The action of the other pumping plunger  32  and its associated electrically controlled spill valve  35  are illustrated in  FIGS. 5 and 6  which are identical to that of the first pumping plunger, except out of phase with the same. In other words, the electrical actuator associated with electronically controlled spill valve  35  will receive a stepped control signal  81  that includes a pull in current and then a hold in current to hold its spill valve closed during a majority of the retraction stroke  73 . Thereafter, the electrical actuator is de-energized for the duration of the pumping stroke  74 . 
         [0024]    The strategy to prevent overpressurization reflected in the present disclosure includes a number of subtle but important advantages. First, it allows the pressure relief valve  38  to be sized to respond to almost all normal operating conditions, rather than having its design and capacity completely driven by the rare occurrences when an overspeed self-actuation condition could occur at high rail pressures. Thus, the present disclosure could represent a relatively inexpensive software fix to a problem that might otherwise need to be addressed with relatively expensive high capacity pressure relief valve, that could itself drive a complete redesign of an otherwise useful pump. In addition, the strategy of the present disclosure avoids any need to enlarge the electrical capacity of the drivers supplying current to the electrical actuators associated with pump  14 . This is best illustrated in  FIGS. 3 and 5  where each of the electrical actuators are energized individually, and never at the same time, but merely out of phase with the way they would normally be electrically actuated during normal engine operation modes. Thus, the strategy of the present disclosure does not overtask or require resizing of the electronic system that supplies current energy to the electrical actuators that control the electronically control spill valves  34  and  35 . 
         [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.