Patent Application
20080022973
Referring to
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.
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.
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'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.
During normal operations of engine10, 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's operating range.
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.
Referring now in addition to
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
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
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.
