Patent Publication Number: US-2019170099-A1

Title: Partial Charging of Single Piston Fuel Pump

Description:
BACKGROUND 
     The present invention relates to high pressure fuel pumps, and particularly to the inlet valve for feeding low pressure fuel to the high pressure pumping chamber. 
     Single piston and multi-piston high pressure common rail fuel pumps have been implemented to provide the high fuel pressures required by modern direct injected gasoline and diesel engines. These engine mounted pumps are volume controlled to minimize parasitic losses while maintaining rail pressure. Volume control is achieved either by inlet throttling using a magnetic proportional control valve, or indirect digital control of the inlet valve by a magnetic actuator. Either execution requires that the pump be controlled by an electrical signal from the engine ECU. 
     Because the indirect inlet valve actuator control requires a separate actuator for each pump piston, it has become common for multi-piston pumps to use a single inlet throttling proportional valve, in order to avoid a high part count and cost. Many modern single piston pumps use an indirect inlet valve actuator with a separate magnetically controlled armature assembly. These devices typically employ three separate components: inlet valve, magnetic armature, and the intervening engaging or connecting member. Different variants of this concept can be seen in U.S. Pat. Nos. 6,526,947, 7,513,240, 6,116,870, and 7,819,637. Due to the high complexity and precision of these devices, they typically account for at least ⅓ of the cost of a single piston pump. These digital type devices also suffer from high reciprocating mass and noise due to impact of the armature and valve assemblies during energizing and de-energizing events. 
     SUMMARY 
     The object of the present invention is to improve the control, and reduce the cost and noise, of the inlet valve actuator for fuel pumps. 
     In one embodiment, the inlet valve is directly magnetically controlled. The valve assembly and associated pump, direct a magnetic flux path such that a carefully timed magnetic force is directly applied to the inlet valve member when a coil is energized. As a result, direct actuation of the inlet valve is achieved. This accommodates a new partial charge operating strategy that has a significant benefit to inlet pressure pulsations. The benefit of a partial charging strategy is reduced inlet pulsations and noise, especially during vehicle idle conditions when it is most objectionable. 
     In a standard digital control valve (with separate armature and valve) the valve automatically opens on the charging ramp of the cam, because it is decoupled from the armature. This results in a full charge of fuel into the pumping chamber. With the timing control of a direct magnetically actuated inlet valve, the inlet valve can be close it at any point on the cam, because it is directly coupled to the magnetic field. 
     The preferred direct magnetic inlet valve system to be controlled according to the present disclosure is described in U.S. application Ser. No. 15/062,774 filed Mar. 7, 2016 for “Direct Magnetically Controlled Inlet Valve for Fuel Pump”, the disclosure of which is hereby incorporated by reference. However, the benefit of the present invention can also be realized in other embodiments with other types of actuators if the valve is directly coupled to the armature. 
    
    
     DETAILED DESCRIPTION 
     The basic functional aspects of the preferred hardware are evident from  FIGS. 1 and 2 . During the pump charging phase when piston  10  is reciprocally moving away from pumping chamber  7 , low pressure fuel enters the pump through inlet fitting  1 , passes around the pressure damper  2  and then into the pump housing  3  and a series of low pressure passages. It then enters into inlet annulus  4  assembly for the direct magnetically controlled inlet valve assembly  5 , passes around the direct magnetically controlled inlet valve  22  through the passage  6  and into the pumping chamber  7 . Upon completion of the charging phase the pumping camshaft acts upon a tappet  12 , urging the piston  10 , to slide in piston sleeve  11 . When the direct magnetically controlled inlet valve assembly  5  is energized with an electrical current to coil assembly  15 , a magnetic force is generated urging the inlet valve  22  to close and seal at surface  20 , thereby enabling fuel trapped in the pumping chamber  7  to compress and build pressure. When sufficient pressure is built, the outlet valve  9  will open, allowing high pressure discharge flow to pass from the pumping chamber through the high pressure passages  8  past the outlet valve  9  and into the high pressure line, rail, and finally to feed the fuel injectors. The pump is equipped with a relief valve  13  in case there is a system malfunction. 
       FIGS. 3 and 4  provide more detail into the functional aspects of the preferred embodiment. When the direct magnetically controlled inlet valve assembly  5  is de-energized during the charging phase of the pump, valve member  22  opens and fuel is allowed to pass along inlet fluid flow path circuit  19 . During the charging phase fuel flows along path portion  19   a  from inlet fitting  1  to inlet valve inlet annulus  4 , through the inlet valve  5 , then along path portion  19   b  through passage  6  toward the pumping chamber. In the disclosed embodiment, the valve assembly  5  functions as both an inlet check valve and a quantity metering valve. During the charging phase, the downward movement of the pumping piston fills the pumping chamber with low pressure fuel from the inlet circuit  19 . During the high pressure pumping phase of the piston, highly pressurized fuel cannot be permitted to backflow through passage  19 ′ to the inlet fitting. During this phase the valve member  22  is closed against sealing surface  20 , due to both the energization of the coil and the high pressure fuel acting on the top surface of the valve member  22 . In order to control the quantity (volume) pumped at high pressure, the energization of the coil is timed to close the valve member  22  corresponding to a certain position on the upward stroke of the cam/piston. Prior to the valve closure, when the piston is moving upward, low pressure is being pushed backwards from the pumping chamber past the inlet valve  22  all the way to the pressure dampers  2  and inlet fitting  1 . The dampers absorb much of the pressure spike associated with this backflow. This can be considered a “pumping bypass” phase of the overall piston reciprocation cycle. The overall cycle thus comprises a charging phase, a pumping bypass phase, and a high pressure pumping phase. 
     In a known manner, the electromagnetic coil assembly  15  is analogous to a solenoid, with a multi-winding coil situated around an axially extending, ferromagnetic cylinder or rod  21  (hereinafter referred to as magnetic pole). One end of the pole projects fronm the coil. When an electrical current is passed through the coil assy  15 , a magnetic field is generated, which flows about the magnetic circuit along magnetic flux lines across radial air gap  23 , generating an axial force onto the face of the valve  22  via the varying magnetic air gap  16 . When the magnetic force exceeds the force of the inlet valve return spring  24 , the valve  22  will close against valve sealing surface  20 . The magnetic pole  21  integrally defines sealing surface  20  and is also a part of the magnetic flux path  32 . Preferably, an inlet valve stop  14  aids in positioning of the valve  22  for accurate stroke control. 
     First magnetic break  17  and second magnetic break  18  surround the sealing face  20  to direct the correct magnetic flow path and avoid a magnetic short circuit. Both breaks  17  and  18  should be fabricated from a non-magnetic material and for best performance valve stop  14  should also be fabricated from a non-magnetic material. Breaks  17  and  18  surround the projecting portion of the magnetic pole to prevent magnetic flux from travelling radially to the housing from the pole and thereby short-circuiting the valve member  22 . The breaks therby assure that the flux circuit passes through the coils, the magnet pole, through the sealing surface  20  and air gap  16 , through the inlet valve member  22 , across radial air gap  23 , through conductive ring  31  and pump housing  3 , back to the coil  15 . In an alternative embodiment, the sealing surface  20 ′ is not unitary with the pole  21 ; it could be integrated with the second magnetic break  18 . 
       FIG. 5  shows additional features which contribute to efficient performance of the disclosed inlet valve assembly. The periphery of the valve member  22  includes a plurality of magnetic flow rim sections or lobes  26  which control the radial air gap  23 , and a plurality of hydraulic flow notches  25  which facilitate adequate fuel flow along fluid flow path  19  when the valve opens. The lobes have a rim diameter (max OD) and the notches have a base diameter (min OD). The base diameter is larger than the ID of the valve sealing surface  20 , so when the valve  22  is closed during the pumping stroke no flow can pass from pumping chamber across the valve  22  back to the inlet annulus  4 ′. The min OD should also be at approximately the same diameter as the diameter of the sealing surface  20  to allow sufficient magnetic force across magnetic air gap  16 . When valve  22  opens during the charging stroke, fuel flows from the inlet annulus  4 ′ through the notches and through the radial air gap  23 . The notches are provided because the air gap  23  must be minimized to maintain sufficient magnetic force, but as a result the annular flow area would otherwise be too small to permit the necessary inlet flow rate to the pumping chamber. 
     As a stand-alone unit, the disclosed fuel inlet valve assembly  5  shown in  FIGS. 3 and 4  can be considered as providing a controlled intermediate flow path within the overall pump inlet flow path  19 . A magnetic valve member  22  is situated within the intermediate flow path. The intermediate flow path comprises a valve assembly inflow path  19 ′ fluidly connected to inlet path  19   a  and starting at inlet annulus  4 , and valve assembly outflow path  19 ″ starting downstream of the valve member  22  and ending at flow path  19   b  into passage  6 . The magnetic pole  21  is a rod or cylinder or the like coaxially situated within the magnetic coil  15  and includes one end  27  projecting from the coil  15 . A portion  19 ′ of the inflow path passes through transverse holes  28  in the projection of the pole and into a central bore  29 , which opens through a sealing face  20  integrally formed at the end of the projection. The inlet valve member  22  is a flat plate that constitutes an armature in relation to the coil  15  and has a sealing face  30  that confronts the sealing surface  20  through a magnetic air gap  16 . When lifted off the sealing surface  20 , the valve member  22  opens fluid communication from the inflow path  19 ′ (upstream of the sealing surface  20 ) to the outflow path  19 ″ (downstream of the sealing surface). The valve member  22  includes a periphery with a rim  26  that provides magnetic flux paths transversely through the valve member and notches  25  that form another portion of the valve assembly outflow flow path when the valve member is open. 
     The present improvement is preferably implemented in the previously described hardware, entirely via digitally controlled timing of the magnetic field at the valve. The valve is either directly coupled to the magnetic field or physically attached to an armature that is in turn directly coupled to the magnetic field. In  FIG. 2 , the engine control unit (ECU) is shown receiving an input signal from a sensor of the cam angular position and the ECU outputs an actuation signal to the inlet valve actuator for implementing the timing for the partial charge operating strategy. The ECU also monitors engine RPM and rail pressure. 
       FIGS. 6-8  depict the conventional baseline “full charge” strategy and two methods for the inventive partial charge strategy. The resulting benefits are shown in  FIGS. 9 and 10 . In normal operation mode, the pumping bypass cycle occurs when the plunger pushes the fuel backwards out of the pumping chamber (with actuator valve open) but does not pressurize it. The vapor generation cycle and vapor collapse cycle are terms to describe the conditions in the pumping chamber during a partial charge operating scenario. 
     The conventional operating scheme can be characterized as “fully charge, spill, then pump over the cam nose.” The inventive scheme can be characterized as “partial charge, then pump over the cam nose”; this is a form of “inlet metered”. 
       FIGS. 7 and 8  support the general concept of a single piston fuel pump comprising a pumping plunger reciprocally driven in a pumping chamber by a rotating cam, with the pumping chamber subject to intermittent charging of feed fuel by an inlet valve that is either directly coupled to a magnetic field or physically attached to an armature that is directly coupled to a magnetic field; and a control system responsive to the angular position of the cam, for controlling the inlet valve by altering the magnetic field to partially charge the pumping chamber before the plunger pressurizes the partially charged fuel while driven along the nose of the cam. 
     According to the exemplary scheme of  FIG. 7 , the pumping chamber is partially charged while the plunger is driven along the downslope of the nose and remains partially charged until the plunger pressurizes the partially charged fuel along the upslope of the nose of the cam. According to the exemplary scheme of  FIG. 8 , the pumping chamber is partially charged while the plunger is driven on the upslope approaching the nose of the cam and plunger pressurizes the partially charged fuel on the upslope of the nose of the cam. 
     For the depicted three-lobe cam, each lobe has a 120 deg. cycle. For an idle condition, the pump partial charging is completed within less than 15 deg. of cam rotation (i.e., while the valve is open). However, the angular duration of the open valve for charging depends on the quantity demand, and can include full charging. Similarly, the pumping cycle at idle is shown as implemented along an angular span of about 15 deg. This can also increase as demand increases. For idle and low demand conditions, the partial charging and associated pumping both occur along only a small angular span of the nose of the cam. For present purposes, the nose can be considered as about one-third of the total cam profile, centered at top-dead center. In general, the pumping will occur along the upslope of the nose up to the cam top dead center. 
     It should thus be appreciated that the present invention does not require partial charging under all operating conditions. Rather, the partial charging is a feature that is present during at least some of the operating conditions, especially at idle.