Patent Publication Number: US-7900602-B2

Title: Direct injection assembly of the common-rail type provided with a shut-off valve for controlling the delivery of a high-pressure fuel pump

Description:
PRIORITY CLAIM 
     The present application claims the benefit of European Patent Application Serial No. 08425135.4, filed Mar. 4, 2008, which application is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     An embodiment of the present invention relates to a direct injection assembly of the common-rail type provided with a shut-off valve for controlling the delivery of a high-pressure fuel pump. 
     BACKGROUND ART 
     In a direct injection assembly of the common-rail type, it is known to use a high-pressure pump which receives a fuel flow from a tank by means of a low-pressure pump and feeds the fuel to a common-rail hydraulically connected to a plurality of injectors. As known, in such a direct injection assembly of the common-rail type, the pressure of the fuel inside the common-rail must be constantly controlled according to the driving point either by varying the instantaneous delivery of the high-pressure pump or by constantly feeding an excess of fuel to the common-rail and by discharging the fuel in excess from the common-rail itself by means of an adjustment valve. Generally, the solution of varying the instantaneous delivery of the high-pressure pump is preferred, because this solution displays a much better energy efficiency and does not result in overheating the fuel inside the tank. 
     In order to vary the instantaneous fuel flow of the high-pressure pump, it has been proposed, for example in EP-A-0481964, which is incorporated by reference, to use a varying delivery high-pressure pump able to feed to the common-rail only the amount of fuel needed to keep the pressure of the fuel inside the common-rail equal to a desired value. 
     Specifically, the high-pressure pump proposed in EP-A-0481964 is provided with an electromagnetic actuator able to vary instant-by-instant the delivery of the high-pressure pump itself by varying the closing instant of an intake valve of the high-pressure pump. 
     Alternatively, in order to vary the instantaneous delivery of the high-pressure pump, it has been proposed instead to insert an adjustment device including a continuously varying hydraulic resistor, upstream of the pumping chamber, which hydraulic resistor is controlled according to the required pressure in the common-rail. 
     Both the above-described solutions for varying the instantaneous delivery of the high-pressure pump are mechanically complex and do not allow to adjust the instantaneous delivery of the high-pressure pump with high accuracy required in principle. Furthermore, in the delivery adjustment device, the varying section hydraulic resistor includes a relatively small introduction section in case of low deliveries such as to determine a local pressure drop (local load drop) which may compromise the correct operation of an intake valve which adjusts the fuel inlet into a pumping chamber of the high-pressure pump. 
     For this reason, it has been proposed, e.g., which is incorporated by reference, in EP-A-1612402, a solution which includes the use of a high-pressure pump including a number of pumping elements actuated in a reciprocating motion by means of corresponding intake and delivery strokes, and in which each pumping element is provided with a relative intake valve in communication with an intake pipe fed by the low pressure pump. On the intake pipe a shut-off valve is arranged for adjusting the instantaneous delivery of fuel fed to the high-pressure pump; in other words, the shut-off valve is a known valve of the open/closed (ON/OFF) type which is driven by modifying the ratio between the duration of the opening time and the duration of the closing time so as to vary the instantaneous delivery of fuel fed to the high-pressure pump. By operating in this manner, a shut-off valve may be used in which the introduction section is sufficiently large to avoid an appreciable local pressure drop (local load drop). 
     When the shut-off valve of the open/closed (ON/OFF) type is closed, a hydraulic phenomenon known as “water hammer” occurs in the intake pipe. The “water hammer” occurs in the intake pipe when the fuel flow therein is either interrupted by closing the shut-off valve or, on the other hand, when the shut-off valve is closed and opened in an essentially short interval of time. The “water hammer” consists in an overpressure which originates in proximity of the shut-off valve due to the impact of the moving fuel against a shutter of the shut-off valve and propagates along the intake pipe, resulting in an increase of noise generated by the injection assembly. The generated overpressure, in addition to depending on the dimensions of the intake pipe, i.e., on the length and the diameter of the intake pipe, also depends on the speed and density of the fluid and, above all, depends on the closing and opening time of the shut-off valve of the open/closed (ON/OFF) type, which is essentially reduced, i.e., in the order of 0.5*10 −3  sec. 
     SUMMARY 
     An embodiment of the present invention provides a direct injection assembly of the common-rail type provided with a shut-off valve for controlling the delivery of a high-pressure fuel pump, such an injection assembly being free from the above-described drawbacks and being easy and cost-effective to implement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments of the present invention will now be described with reference to the accompanying drawings, which disclose a non-limitative embodiment thereof, in which: 
         FIG. 1  diagrammatically illustrates, partially in blocks, an embodiment of the direct injection assembly of the present invention; 
         FIG. 2  shows a detail in  FIG. 1  in section and on enlarged scale; and 
         FIG. 3  shows a detail of  FIG. 2  on an enlarged scale. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , numeral  1  indicates as a whole an injection assembly of the common-rail type for the direct injection of fuel into an internal combustion engine  2  provided with four cylinders  3 . 
     The injection assembly  1  includes four injectors  4 , of known type, each of which is connected to a corresponding cylinder  3 , includes a hydraulically actuated needle (not shown) and is adapted to inject the fuel directly into the corresponding cylinder  3  and to receive the pressurized fuel from a manifold  5  (named “common-rail”). 
     Furthermore, the injection assembly  1  includes a high-pressure varying delivery pump  6 , which is adapted to feed the fuel to the manifold  5  by means of a delivery pipe  7 ; and a low-pressure pump  8 , which is arranged inside a fuel tank  10  and is adapted to feed the fuel to an intake pipe  9  of the high-pressure pump  6 , which intake pipe is provided with a fuel filter (not shown). 
     Furthermore, the injection assembly  1  includes a return channel  11 , which leads into the tank  10  and is adapted to receive the fuel in excess both from the injectors  4  and from a mechanical pressure-limiting valve  12 , which is hydraulically connected to the manifold  5 . The valve  12  is calibrated to open automatically when the pressure of the fuel inside the manifold  5  exceeds a safety value to ensure the tightness and the safety of the injection assembly  1 . 
     Each injector  4  is adapted to inject a varying amount of fuel into the corresponding cylinder  3  under the control of an electronic control unit  13  constituting part of the injection assembly  1 . As previously mentioned, each injector  4  is provided with a hydraulically actuated needle (not shown) and must receive, from the manifold  5   a , a quantity of high-pressure fuel sufficient to actuate the corresponding needle (not shown) and to feed the corresponding cylinder  3  at a relatively high pressure. In order to do this, each injector  4  is fed with an amount of fuel in excess with respect to that actually injected and the excess is fed, by means of the return channel  11 , to the tank  10  upstream of the low-pressure pump  8 . 
     The electronic control unit  13  is connected to a sensor  14  for measuring the fuel pressure inside the manifold  5  and feedback controls the delivery of the high-pressure pump  6  so as to keep the pressure of the fuel inside the manifold  5  equal to a desired value which generally varies in time according to the driving point. 
     The high-pressure pump  6  includes a plurality of pumping elements, in this case a pair of pumping elements  15 , each consisting of a cylinder  16  having a pumping chamber  17 , in which a movable piston  18  slides in a reciprocating motion under the thrust of a eccentric  19  actuated by a mechanical transmission  20 , which receives the motion from a drive shaft  21  of the internal combustion engine  2 . Each compression chamber  17  is provided with a corresponding intake valve  22  in communication with the intake pipe  9 , and with a corresponding delivery valve  23  in communication with the delivery pipe  7 . The two pumping elements  15  are reciprocally actuated in phase opposition; consequently, the fuel sent to the high-pressure pump  6  through the intake pipe  9  is taken in by only one pumping element  15  at a time and, specifically, by the pumping element  15  which in that instant is performing the intake stroke (in the same instant, the intake valve  22  of the other pumping element  15  is obviously closed, the other pumping element  15  being at compression phase). 
     Along the intake pipe  9  a shut-off valve  24  is arranged, which displays an electromagnetic actuation, is controlled by the electronic control unit  13  and is of the open/closed (on/off) type; in other words, the shut-off valve  24  may only take either an entirely opening position or an entirely closing position. Specifically, the shut-off valve  24  displays a sufficiently wide introduction section to allow to feed each pumping element  15  without causing any substantial pressure drop. 
     The delivery of high-pressure pump  6  is controlled only by using the shut-off valve  24  which is feedback controlled by the electronic control unit  13  according to the fuel pressure in the manifold  5 . Specifically, the electronic control unit  13  determines a desired fuel pressure value inside the manifold  5  instant-by-instant according to the driving point and adjusts the instantaneous delivery of fuel fed by the high-pressure pump  6  to the manifold  5  to follow the desired fuel pressure value inside the manifold  5  itself; in order to adjust the instantaneous delivery of fuel fed by the high-pressure pump  6  to the manifold  5 , the electronic control unit  13  adjusts the instantaneous delivery of the fuel taken in by the high-pressure pump  6  through the shut-off valve  24  by varying the ratio between the duration of the opening time and the duration of the closing time of the shut-off valve  24  itself. 
     As shown in  FIG. 2 , the shut-off valve  24  is connected to a pressure regulator  25  and the two elements are accommodated next to each other in a supporting body  26 . One segment  27  of the intake pipe  9  is also accommodated within the supporting body  26  and leads into a feeding channel  28  also obtained in the supporting body  26 . The feeding channel  28  connects the shut-off valve  24  to the pressure regulator  25  and is provided with an intermediate opening  29  for connecting to the low-pressure pump  8  by means of a segment  27  of the intake pipe  9 . The shut-off valve  24  and the pressure regulator  25  display two openings, indicated by numerals  30  and  31  respectively, for the introduction of fuel; the two openings  30  and  31 , respectively, are arranged reciprocally perpendicular and are connected together by means of the feeding channel  28 . Furthermore, the shut-off valve  24  displays a second fuel outlet opening  32 , perpendicular to the opening  30 , for connecting the shut-off valve  24  itself to the high-pressure pump  6  by means of a segment  33  of the intake pipe  9 , also accommodated within the supporting body  26 . 
     As shown in  FIG. 3 , the pressure regulator  25  displays a symmetry about a longitudinal axis  34  and axially receives the fuel conveyed into the intake channel  28 , i.e., coaxially to the longitudinal axis  34 . The fuel exiting from the pressure regulator  25  is instead fed radially, i.e., perpendicularly to the longitudinal axis  34 , to an exhaust pipe  35 , which is partially accommodated inside the supporting body  26 , extends transversally to both the feeding channel  28  and to the longitudinal axis  34 , and is adapted to convey the fuel to the fuel tank  10 . 
     The pressure regulator  25  includes a central body  36  provided with an externally threaded portion to allow the coupling thereof with a nut screw embedded within the supporting body  26 ; on the external surface of the central body  36  a seat is obtained for accommodating a sealing ring  37  made of elastic material. 
     The top of the central body  36  is closed, has a varying section along the longitudinal axis  34  and protrudes beyond the supporting body  26  with an upper portion  38  thereof. 
     The central body  36  includes an axial inlet pipe  39 , which is connected to the feeding channel  28  at the opening  31  and includes an inlet portion  40  accommodating a sleeve  41  and displays a plurality of radial outlet pipes  42  arranged immediately downstream of the inlet portion  40 . The sleeve  41  includes a cylindrical inlet portion  43  accommodated inside the inlet portion  40  of the inlet pipe  39  and an outflow portion  44 , which have an external truncated-cone shape and is arranged partially facing the radial outlet pipes  42 . The outflow portion  44  displays an annular end defining a resting seat  45  of a shutter  46  including a small plate  47 , axially movable against the bias of a calibrated spring  48 , from a normal closing position, in contact with the resting seat  45 , to an opening and communication position of the inlet pipe  39  with the radial outlet pipes  42 . 
     The radial outlet pipes  42  put the inlet pipe  39  into communication with an annular chamber  49 , which is obtained in the supporting body  26 , communicates with the exhaust pipe  35  and is adapted to receive the fuel from the pressure regulator  25  and to direct it to the exhaust pipe  35  itself. 
     In use, when the shut-off valve  24  is closed in an essentially rapid manner, the fuel inside the feeding channel  28  impacts against a shutter of the shut-off valve  24  itself, thus generating an overpressure which propagates backwards along the feeding channel  28  to the pressure regulator  25 . As a consequence of this pressure wave, the fuel penetrates through the opening  31  into the inlet pipe  39  and impacts against the small plate  47  of the shutter  46  arranged in the closing position in contact with the resting seat  45 . If the pressure of the entering fuel is higher than the thrust of the spring  48 , the small plate  47  is moved away from the resting seat  45  putting the inlet pipe  39  with the radial outlet pipes  42  and, thus, through the annular chamber  49  into communication with the exhaust pipe  35  and the tank  10 . The calibration of the pressure regulator  25 , during the step of assembling, occurs by adjusting the driving rate of the sleeve  41  within the central body  36 . 
     The pressure regulator  25  includes four radial outlet pipes  42  (only two of which are shown in  FIGS. 2 and 3 ) regularly distributed about the longitudinal axis  34 . According to a variant (not shown), the pressure regulator  25  includes at least one radial outlet pipe  42  and the radial outlet pipes  42  may be regularly distributed about the longitudinal axis  34 . 
     According to a variant (not shown), the supporting body  26  is directly integrated on the supporting body (not shown) of the high-pressure pump  6 . 
     According to a further variant (not shown), the exhaust pipe  35  is adapted to convey the fuel to the return channel  11  which leads into the tank  10 . 
     To ensure the correct operation of the system consisting of the pressure regulator  25  and the shut-off valve  24 , the two components have similar reaction times so as to be able to fully dispose of the overpressure which is generated in the feeding channel  28  when the shut-off valve  24  is closed. For this purpose, the small plate  47  is made so as to display a relatively low inertia and the calibrated spring  48  is made with a relatively low number of turns so as to reduce the resistive force exerted by the shutter  46 . Similarly, the profile of the outflow portion  44  of the sleeve  41  allows the fuel to fully exploit the port of the radial outlet pipes  42 . 
     The overpressure which is generated in the feeding channel  28  when the shut-off valve  24  is closed further depends on the dimensions, i.e., on the length and the diameter, of the connection channels in which the fuel is conveyed. The load loss of the fuel which flows through the channels of the supporting body  26  is reduced to a minimum by arranging the shut-off valve  24  and the pressure regulator  25  side-by-side inside the supporting body  26 . 
     The above-described injection assembly  1  displays several advantages because, by optimizing the weight of the shutter  46  and the layout of the connection channels in which the fuel flows, the reaction speed of the pressure regulator  25  is equivalent to that of the shut-off valve  24 , i.e., of the order of 0.5*10 −3  sec, and the injection assembly is able to fully dispose of the overpressure generated inside the feeding channel  28  by closing the shut-off valve  24  of the intake pipe. 
     The injection assembly  1  may be part of an engine assembly that may be part of a vehicle such as an automobile. 
     Naturally, in order to satisfy local and specific requirements, a person skilled in the art may apply to the solution described above many modifications and alterations. Particularly, although the present invention has been described with a certain degree of particularity with reference to described embodiment(s) thereof, it should be understood that various omissions, substitutions and changes in the form and details as well as other embodiments are possible. Moreover, it is expressly intended that specific elements and/or method steps described in connection with any disclosed embodiment of the invention may be incorporated in any other embodiment as a general matter of design choice.