Abstract:
A fuel system may include an auxiliary fuel pump in communication with a fuel source, a fuel pressure amplifier in communication with the fuel pump, a first chamber defining a first fluid volume in communication with the auxiliary fuel pump, a second chamber defining a second fluid volume, and a fuel injector in communication with the second fluid volume. The fuel pressure amplifier may include a piston mechanism having a first side defining a first surface area and a second side defining a second surface area that is less than the first surface area. The first fluid volume may apply a force to the first side of the piston mechanism that is greater than a second force to the second side resulting in displacement of the piston mechanism. The fuel injector may provide a pressurized fuel supply to an engine based on the displacement of the piston mechanism.

Description:
FIELD 
     The present disclosure relates to engine fuel systems, and more specifically to engine fuel pressure enhancement. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Engine fuel systems may include engine driven fuel pumps that are driven by a rotating engine component. The fuel pump may be indirectly driven by the engine crankshaft through engagement with a camshaft. During engine start conditions, the first several revolutions of the engine crankshaft may be at a speed that is less than a speed required to produce a desired fuel pressure from the fuel pump. This is particularly true in fuel systems such as direct injection fuel systems where fuel at high pressure is injected directly into an engine cylinder. 
     SUMMARY 
     A fuel system may include an auxiliary fuel pump, a fuel pressure amplifier, a first chamber defining a first fluid volume, a second chamber defining a second fluid volume, and a fuel injector. The auxiliary fuel pump may be in communication with a fuel source. The fuel pressure amplifier may be in communication with the fuel pump and may include a piston mechanism. The piston mechanism may include a first side having a first surface area and a second side that is generally opposite the first side and having a second surface area that is less than the first surface area. The first fluid volume may be in communication with the auxiliary fuel pump and may apply a first fluid pressure to the first surface area based on a pressurized fuel source provided by the auxiliary fuel pump to create a first force on the piston mechanism. The second fluid volume may apply a second fluid pressure to the second surface area to create a second force on the piston mechanism that is less than the first force resulting in displacement of the piston mechanism. The fuel injector may be in communication with the second fluid volume and may provide a pressurized fuel supply to an engine based on the displacement of the piston mechanism. 
     An engine assembly may include an engine block defining a cylinder, a fuel injector in communication with the cylinder to selectively provide a fuel flow to the cylinder, an auxiliary fuel pump in communication with a fuel source, a fuel pressure amplifier, and first and second chambers defining first and second fluid volumes. The fuel pressure amplifier may be in communication with the auxiliary fuel pump and may include a piston mechanism. The piston mechanism may include a first side having a first surface area and a second side that is generally opposite the first side and having a second surface area that is less than the first surface area. The first fluid volume may be in communication with the auxiliary fuel pump and may apply a first fluid pressure to the first surface area based on a pressurized fuel source provided by the auxiliary fuel pump to create a first force on the piston mechanism. The second fluid volume may be in communication with the fuel injector and may apply a second fluid pressure to the second surface area to create a second force on the piston mechanism that is less than the first force resulting in displacement of the piston mechanism. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic illustration of an engine assembly in a first operating mode according to the present disclosure; 
         FIG. 2  is a schematic illustration of the engine assembly of  FIG. 1  in a second operating mode; 
         FIG. 3  is a schematic illustration of the engine assembly of  FIG. 1  in a third operating mode; and 
         FIG. 4  is a schematic illustration of an alternate fuel pressure amplifier according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring to  FIGS. 1-3 , an exemplary engine assembly  10  is schematically illustrated. The engine assembly  10  may include an engine  12  in communication with a fuel system  14  and a control module  16 . In the example shown, the engine  12  may include an engine block that defines a plurality of cylinders  18  in communication with the fuel system  14 . 
     The fuel system  14  may include a fuel tank  20 , first and second fuel pumps  22 ,  24 , a pressure amplifier system  26 , a control valve system  28 , a fuel rail  30 , fuel injectors  31 , and first and second conduits  34 ,  36 . The first fuel pump  22  may include an auxiliary fuel pump, for example, a lift pump, that is driven by an electric motor  32  and may be in fluid communication with fuel within the fuel tank  20 . The first fuel pump  22  may be in fluid communication with the second fuel pump  24 . 
     The second fuel pump  24  may include a variety of types of pumps that can be driven by the engine  12 , including but not limited to gerotor pumps, gear pumps, and reciprocating pumps. More specifically, the second fuel pump  24  may be rotationally driven by the engine  12 . The rotational drive may include engagement with a rotationally driven component of the engine  12 , such as a camshaft (not shown) or any other member having rotation powered by the engine  12 . The second fuel pump  24  may be in fluid communication with the pressure amplifier system  26  and the control valve system  28  via the first conduit  34 . 
     The pressure amplifier system  26  may include a housing  38 , a piston  40 , and a biasing member  42 . The housing  38  may include first and second chambers  44 ,  46  that are isolated from one another. The first chamber  44  may be in fluid communication with the first conduit  34  and the second chamber  46  may be in fluid communication with the second conduit  36 . 
     The piston  40  may include first and second ends  48 ,  50 . The first end  48  may have a first diameter (D 1 ) that is greater than a second diameter (D 2 ) of the second end  50 . Therefore, the first end  48  may have a first surface area (A 1 ) that is greater than a second surface area (A 2 ) of the second end  50 . The first and second ends  48 ,  50  of the piston  40  may be sized for a desired pressurization of fuel within the fuel system  14  during an engine start condition. The biasing member  42  may include a compression spring and may initially bias the piston  40  toward the first chamber  44  to the position shown in  FIG. 1  at an engine start condition. 
     Alternatively, as seen in  FIG. 4 , a pressure amplifier system  126  may be incorporated into the engine assembly  10  in place of the pressure amplifier system  26 . The pressure amplifier system  126  may be generally similar to the pressure amplifier system  26  with the exception of the piston  140 . The piston  140  may include a passage  139  having a valve  141  disposed therein to selectively provide communication between the first and second chambers  144 ,  146 . For example, the valve  141  may include a check valve that is calibrated to open when a fluid pressure within the first chamber  144  exceeds a fluid pressure within the second chamber  146 . The first chamber  144  may be in fluid communication with a first conduit  134  that is similar to the first conduit  34  and the second chamber  146  may be in fluid communication with a second conduit  136  that is similar to the second conduit  36 . 
     Referring back to  FIGS. 1-3 , the control valve system  28  may include a solenoid valve that is in communication with the control module  16 . The control valve system  28  may include a valve member  52  that is displaceable between a first position (seen in  FIGS. 1 and 2 ) and a second position (seen in  FIG. 3 ). When the valve member  52  is in the first position the first and second conduits  34 ,  36  may be generally isolated form one another. When the valve member  52  is in the second position, the first and second conduits  34 ,  36  may be in communication with one another. 
     The fuel rail  30  may be in communication with the second conduit  36 . The fuel injectors  31  may be in fluid communication with the fuel rail  30  and may also be in communication with the control module  16  for commanded injection of fuel into the cylinders  18 . The control module  16  may selectively operate the first fuel pump  22 , actuate the control valve system  28 , and control operation of the fuel injectors  31  to adjust fuel delivery at an engine start condition. The control module  16  may additionally be in communication with an engine speed sensor  53  to determine an operating speed of the engine  12  and first and second pressure sensors  55 ,  57  to determine a fuel pressure provided by the second pump  24  and a fuel pressure supplied to the fuel rail  30 , and therefore the fuel injectors  31 . The control module  16  may place the valve member  52  in the second position when the fuel pressure measured by the first pressure sensor  55  indicates a pump out pressure of the second pump  24  that is greater than a predetermined pressure and/or when the engine speed measured by the engine speed sensor  53  is greater than a predetermined engine speed. 
     In the present example, an engine start condition may correspond to a condition where the first and second conduits  34 ,  36  and the first and second chambers  44 ,  46  are filled with fuel and the valve member  52  is in the first (or closed) position. The first chamber  44  may define a first volume (V 1 ) and the second chamber  46  may define a second volume (V 2 ). The first fuel pump  22  may be powered by the electric motor  32  and may begin pressurizing fuel within the first conduit  34  and the first chamber  44  since the first conduit  34  and the first chamber  44  are isolated from the second fluid conduit  36  and the second chamber  46 . The second fuel pump  24  may be driven by the engine  12  and may additionally pressurize fuel within the first conduit  34  and the first chamber  44 . As the pressure increases within the first chamber  44 , the piston  40  may be displaced toward the second chamber  46  (as seen in  FIG. 2 ), pressurizing the fuel within the second conduit  36  and the second chamber  46 . The fuel injectors  31  may be selectively opened to inject fuel into the cylinder  18  based on the pressurized fuel provided by the piston  40  during the engine start condition. 
     The first and second surface areas (A 1 , A 2 ), the first and second volumes (V 1 , V 2 ) and the stroke of the piston  40  may be sized to provide a desired fuel pressure to the fuel injectors  31  over a desired time. The duration and/or frequency of opening the fuel injectors  31  may be adjusted by the control module  16  based on the pressure measurement from the pressure sensor  57  and/or based on an engine speed measurement from the engine speed sensor  53 . For example, the fuel system  14  may include a direct injection fuel system. In direct injection fuel systems, relatively high fuel pressures are typically provided to the fuel injectors  31 . For example, fuel pressures in the range of 10,000 to 15,000 kilopascal (kPa) may be appropriate for a desired operation of the fuel injectors  31 . 
     The first fuel pump  22  may provide significantly less than the pressure needed for direct injection applications. For example, the first fuel pump  22  may provide fuel pressures of 100 to 400 kPa. During the engine start condition the first several rotations of the crankshaft may be at a rotational speed that is less than a speed needed to power the second pump  24  to achieve a desired operating pressure (for example, 10,000-15,000 kPa). The pressure amplifier system  26  may be used to increase the pressure provided to the fuel injectors  31 . If the pressure amplifier system  26  is unable to provide a desired fuel pressure, the duration and/or frequency of opening the fuel injectors  31  may be increased to provide a desired amount of fuel to the cylinders  18 . 
     Based on the displacement of the piston  40 , the fuel within the second conduit  36  and the second chamber  46 , and therefore the fuel provided to the fuel injectors  31 , may be at least ten times the fuel pressure within the first conduit  34  and the first chamber  44 , and more specifically greater than fifty times the fuel pressure within the first conduit  34  and the first chamber  44 . The piston  40  may be displaced to create this pressure differential due to the difference between the first and second surface areas (A 1 , A 2 ). The force (F 1 ) applied to the first end  48  of the piston  40  may generally be equal to the pressure (P 1 ) within the first chamber  44  multiplied by the first surface area (A 1 ) of the first end  48  (F 1 =P 1 *A 1 ). The force (F 2 ) applied to the second end  50  of the piston  40  may generally be equal to the pressure (P 2 ) within the second chamber  46  multiplied by the second surface area (A 2 ) of the second end  50  (F 2 =P 2 *A 2 ). 
     Therefore, the first surface area (A 1 ) may be at least ten times the second surface area (A 2 ), and more specifically greater than fifty times the second surface area (A 2 ) to provide the desired fuel pressure amplification. It is understood that a variety of alternate surface area and pressure relationships may be used to provide a desired fuel pressure amplification. Once the second fuel pump  24  has reached a desired operating speed and/or once the first and second forces (F 1 , F 2 ) are approximately equal to one another, the valve member  52  may move to the second position (seen in  FIG. 3 ) to provide communication between the first and second conduits  34 ,  36 .