Patent Publication Number: US-11661913-B2

Title: Fuel pump with inlet valve assembly

Description:
TECHNICAL FIELD OF INVENTION 
     The present invention relates to a fuel pump which supplies fuel to an internal combustion engine, more particularly to such a fuel pump which includes an inlet valve assembly, and even more particularly to such a fuel pump with an inlet valve assembly which is robust to exterior environmental fluid exposure. 
     BACKGROUND OF INVENTION 
     Fuel systems in modern internal combustion engines fueled by gasoline, particularly for use in the automotive market, employ gasoline direct injection (GDi) where fuel injectors are provided which inject fuel directly into combustion chambers of the internal combustion engine. In such systems employing GDi, fuel from a fuel tank is supplied under relatively low pressure by a low-pressure fuel pump which is typically an electric fuel pump located within the fuel tank. The low-pressure fuel pump supplies the fuel to a high-pressure fuel pump which typically includes a fuel pump housing and a pumping plunger which is reciprocated, by a camshaft of the internal combustion engine, within the fuel pump housing. Reciprocation of the pumping plunger further pressurizes the fuel in order to be supplied to fuel injectors which inject the fuel directly into the combustion chambers of the internal combustion engine. During operation, the internal combustion engine is subject to varying demands for output torque. In order to accommodate the varying output torque demands, the mass of fuel delivered by each stroke of the pumping plunger must also be varied. One strategy to vary the delivery of fuel by the high-pressure fuel pump is to use an inlet valve assembly which includes a solenoid. The inlet valve assembly may allow a full charge of fuel to enter the pumping chamber during each intake stroke, however, the solenoid may be operated to cause the inlet valve assembly to remain open during a portion of a compression stroke of the pumping plunger to allow some fuel to spill back toward the source. When the solenoid is then operated to allow the inlet valve assembly to close, the remainder of the compression stroke pressurizes the fuel and discharges the fuel to the fuel injectors. It is known for the inlet valve assembly to be received within a bore of the fuel pump housing and extends outside of the fuel pump housing. In order to prevent leakage of fuel a sealing arrangement is provided to seal between the fuel pump housing and the inlet valve assembly. In some arrangements such as provided in U.S. Pat. No. 10,947,942 to Stritzel et al., a portion of the inlet valve assembly is welded to fuel pump housing in order to provide a sealed interface. In other arrangements such as provided in U.S. Pat. No. 7,401,594 to Usui et al., the inlet valve assembly may be sealed to the fuel pump housing by providing an O-ring radially between the inlet valve assembly and the fuel pump housing. In each case, the sealing arrangement is provided for preventing fuel from exiting the fuel pump housing between the inlet valve assembly and the fuel pump housing. However, portions of the inlet valve assembly which extend outside of the fuel pump housing may be exposed to environmental conditions which may cause liquids, such as rainwater or saltwater from deiced roadways, from being deposited on the outlet control valve. These liquids may seep into interfaces of components that form the inlet control valve or solenoid and over time may compromise one or more of the components of the inlet control valve or solenoid which may lead to undesired operation of the inlet control valve. 
     What is needed is a fuel pump which minimizes or eliminates one or more of the shortcomings as set forth above. 
     SUMMARY OF THE INVENTION 
     Briefly described, a fuel pump includes a fuel pump housing with a pumping chamber defined therein and an inlet valve bore extending along an inlet valve bore axis to an exterior of the fuel pump housing; a pumping plunger which reciprocates within a plunger bore such that an intake stroke of the pumping plunger increases volume of the pumping chamber and a compression stroke of the pumping plunger decreases volume of the pumping chamber; and an inlet valve assembly which 1) selectively provides fluid communication between an inlet of the fuel pump and the pumping chamber and 2) selectively prevents fluid communication between the inlet of the fuel pump and the pumping chamber. The inlet valve assembly includes an inner housing which is received within the inlet valve bore such that the inner housing extends to the exterior of the fuel pump housing and such that an outer periphery of the inner housing is sealed to an inner periphery of the inlet valve bore such that fuel is prevented from passing radially between the inner housing and the inlet valve bore to the exterior of the fuel pump housing; an outer housing which is located outside of the fuel pump housing and circumferentially surrounds the inner housing, wherein an annular chamber is defined radially between the inner housing and the outer housing and axially between the outer housing and the fuel pump housing; and a sealing ring which is made of an elastomer material and which is annular in shape and located within the annular chamber such that the sealing ring is compressed axially against the fuel pump housing and the outer housing. The fuel pump as described herein with the sealing ring minimizes the likelihood of liquids from the exterior environment from reaching elements of inlet valve assembly which could otherwise lead to undesired operation. 
     Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       This invention will be further described with reference to the accompanying drawings in which: 
         FIG.  1    is a schematic view of a fuel system including a fuel pump in accordance with the present invention; 
         FIG.  2    is a cross-sectional view of the fuel pump of  FIG.  1   ; 
         FIG.  3    is an exploded isometric view of an inlet valve assembly of the fuel pump of  FIGS.  1  and  2   ; 
         FIG.  4    is an enlargement of a portion of  FIG.  2    showing the inlet valve assembly of the fuel pump in a first position; 
         FIG.  5    is the view of  FIG.  4   , now showing the inlet valve assembly in a second position; 
         FIG.  6    is the view of  FIGS.  4  and  5   , now showing the inlet valve assembly in a third position; 
         FIG.  7    is the view of  FIGS.  4 - 6   , now showing the inlet valve assembly in a fourth position; and 
         FIG.  8    shows a sealing cap in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In accordance with a preferred embodiment of this invention and referring initially to  FIG.  1   , a fuel system  10  for an internal combustion engine  12  is shown is schematic form. Fuel system  10  generally includes a fuel tank  14  which holds a volume of fuel to be supplied to internal combustion engine  12  for operation thereof; a plurality of fuel injectors  16  which inject fuel directly into respective combustion chambers (not shown) of internal combustion engine  12 ; a low-pressure fuel pump  18 ; and a high-pressure fuel pump  20  where the low-pressure fuel pump  18  draws fuel from fuel tank  14  and elevates the pressure of the fuel for delivery to high-pressure fuel pump  20  where the high-pressure fuel pump  20  further elevates the pressure of the fuel for delivery to fuel injectors  16 . By way of non-limiting example only, low-pressure fuel pump  18  may elevate the pressure of the fuel to about 500 kPa or less and high-pressure fuel pump  20  may elevate the pressure of the fuel to above about 14 MPa and even above 35 MPa in some applications. While four fuel injectors  16  have been illustrated, it should be understood that a lesser or greater number of fuel injectors  16  may be provided. 
     As shown, low-pressure fuel pump  18  may be provided within fuel tank  14 , however low-pressure fuel pump  18  may alternatively be provided outside of fuel tank  14 . Low-pressure fuel pump  18  may be an electric fuel pump as are well known to a practitioner of ordinary skill in the art. A low-pressure fuel supply passage  22  provides fluid communication from low-pressure fuel pump  18  to high-pressure fuel pump  20 . A fuel pressure regulator  24  may be provided such that fuel pressure regulator  24  maintains a substantially uniform pressure within low-pressure fuel supply passage  22  by returning a portion of the fuel supplied by low-pressure fuel pump  18  to fuel tank  14  through a fuel return passage  26 . While fuel pressure regulator  24  has been illustrated in low-pressure fuel supply passage  22  outside of fuel tank  14 , it should be understood that fuel pressure regulator  24  may be located within fuel tank  14  and may be integrated with low-pressure fuel pump  18 . 
     Now with additional reference to  FIG.  2   , high-pressure fuel pump  20  includes a fuel pump housing  28  which includes a plunger bore  30  which extends along, and is centered about, a plunger bore axis  32 . As shown, plunger bore  30  may be defined by a combination of an insert and directly by fuel pump housing  28 . High-pressure fuel pump  20  also includes a pumping plunger  34  which is located within plunger bore  30  and reciprocates within plunger bore  30  along plunger bore axis  32  based on input from a rotating camshaft  36  of internal combustion engine  12  (shown only in  FIG.  1   ). A pumping chamber  38  is defined within fuel pump housing  28 , and more specifically, pumping chamber  38  is defined by plunger bore  30  and pumping plunger  34 . An inlet valve assembly  40  of high-pressure fuel pump  20  is received within an inlet valve bore  28   a  of fuel pump housing  28  such that inlet valve bore  28   a  extends to the exterior of fuel pump housing  28 , along an inlet valve bore axis  28   b  the high-pressure fuel pump  20  selectively provides and prevents fluid communication between an inlet  20   a  of high-pressure fuel pump  20  and pumping chamber  38  via a pump housing inlet passage  41  of fuel pump housing  28  while an outlet valve assembly  42  is located within an outlet passage  43  of fuel pump housing  28  and selectively allows fuel to be communicated from pumping chamber  38  to fuel injectors  16  via a fuel rail  44  to which each fuel injector  16  is in fluid communication. In operation, reciprocation of pumping plunger  34  causes volume of pumping chamber  38  to increase during an intake stroke of pumping plunger  34  (downward as oriented in  FIG.  2   ) in which a plunger return spring  46  causes pumping plunger  34  to more downward, and conversely, the volume of pumping chamber  38  decrease during a compression stroke (upward as oriented in  FIG.  2   ) in which camshaft  36  causes pumping plunger  34  to move upward against the force of plunger return spring  46 . In this way, fuel is selectively drawn into pumping chamber  38  during the intake stroke, depending on operation of inlet valve assembly  40  as will be described in greater detail later, and conversely, fuel is pressurized within pumping chamber  38  by pumping plunger  34  during the compression stroke and discharged through outlet valve assembly  42  under pressure to fuel rail  44  and fuel injectors  16 . For clarity, pumping plunger  34  is shown in solid lines in  FIG.  2    to represent the intake stroke and pumping plunger  34  is shown in phantom lines in  FIG.  2    to represent the compression stroke. High-pressure fuel pump  20  also includes a pressure relief valve assembly  48  which is arranged downstream of outlet valve assembly  42  in order to provide a fluid path back to pumping chamber  38  if the pressure downstream of outlet valve assembly  42  reaches a predetermined limit which may pose an unsafe operating condition if left unmitigated. 
     Outlet valve assembly  42  generally includes an outlet valve member  42   a , an outlet valve seat  42   b , and an outlet valve spring  42   c . Outlet valve member  42   a , illustrated by way of non-limiting example only as a ball, is biased toward outlet valve seat  42   b  by outlet valve spring  42   c  where outlet valve spring  42   c  is selected to allow outlet valve member  42   a  to open when a predetermined presser differential between pumping chamber  38  and fuel rail  44  is achieved. Outlet valve assembly  42  is oriented such that fuel is allowed to flow out of pumping chamber  38  through outlet valve assembly  42 , however, fuel is not allowed to flow into pumping chamber  38  through outlet valve assembly  42 . 
     Pressure relief valve assembly  48  generally includes a pressure relief valve member  48   a , a pressure relief valve seat  48   b , and a pressure relief valve spring  48   c . Pressure relief valve member  48   a , illustrated by way of non-limiting example only as a ball, is biased toward pressure relief valve seat  48   b  by pressure relief valve spring  48   c  where pressure relief valve spring  48   c  is selected to allow pressure relief valve member  48   a  when a predetermined presser differential between pumping chamber  38  and fuel rail  44  is achieved. Pressure relief valve assembly  48  is oriented such that fuel is allowed to flow into of pumping chamber  38  through pressure relief valve assembly  48 , however, fuel is not allowed to flow out of pumping chamber  38  through pressure relief valve assembly  48 . 
     Inlet valve assembly  40  will now be described with particular reference to  FIGS.  3 - 7   . Inlet valve assembly  40  includes a valve body  50 , a valve spool  52  located within valve body  50 , a check valve  54 , and a solenoid assembly  55 . The various elements of inlet valve assembly  40  will be described in greater detail in the paragraphs that follow. 
     Valve body  50  is centered about, and extends along, inlet valve bore axis  28   b  such that valve body  50  extends from a valve body first end  50   a  to a valve body second end  50   b . A valve body bore  58  extends into valve body  50  from valve body first end  50   a  and terminates at a valve body end wall  60  which extends to valve body second end  50   b  such that valve body bore  58  is preferably cylindrical. A valve body first inlet passage  62  extends through valve body  50  such that valve body first inlet passage  62  extends from a valve body outer periphery  50   c  of valve body  50  and opens into valve body bore  58 . A valve body second inlet passage  64  (not visible in  FIG.  3   , but visible in  FIGS.  4 - 7   ) extends through valve body  50  such that valve body second inlet passage  64  extends from valve body outer periphery  50   c  and opens into valve body bore  58 . As shown in the figures, valve body first inlet passage  62  and valve body second inlet passage  64  are spaced axially apart from each other along inlet valve bore axis  28   b  such that valve body second inlet passage  64  is located axially between valve body first end  50   a  and valve body first inlet passage  62 . Also as shown in the figures, a plurality of valve body first inlet passages  62  may be provided such that each valve body first inlet passage  62  is located in the same axial location along inlet valve bore axis  28   b , however, each valve body first inlet passage  62  is spaced apart from the other valve body first inlet passages  62  around valve body outer periphery  50   c . While only one valve body second inlet passage  64  is illustrated, it should be understood that a plurality of valve body second inlet passages  64  may be provided at the same axial location along inlet valve bore axis  28   b  but spaced apart from each other around valve body outer periphery  50   c.    
     A valve body central passage  66  extends through valve body end wall  60  such that valve body central passage  66  connects valve body second end  50   b  with valve body bore  58  and such that valve body central passage  66  is centered about, and extends along, inlet valve bore axis  28   b . A plurality of valve body outlet passages  68  is provided in valve body end wall  60  such that each valve body outlet passage  68  extends through valve body end wall  60  and such that each valve body outlet passage  68  connects valve body second end  50   b  with valve body bore  58 . Each valve body outlet passage  68  is laterally offset from valve body central passage  66  and extends through valve body end wall  60  in a direction parallel to inlet valve bore axis  28   b.    
     As shown in the figures, valve body outer periphery  50   c  may include three sections of distinct diameters. A valve body outer periphery first portion  50   d  of valve body outer periphery  50   c  begins at valve body first end  50   a  and extends to a valve body outer periphery second portion  50   e  of valve body outer periphery  50   c  such that valve body outer periphery first portion  50   d  is smaller in diameter than valve body outer periphery second portion  50   e . As shown in the figures, valve body outer periphery first portion  50   d  may be located entirely outside of pump housing inlet passage  41  and valve body outer periphery second portion  50   e  includes valve body first inlet passage  62  and valve body second inlet passage  64  such that valve body first inlet passage  62  and valve body second inlet passage  64  are each in constant fluid communication with the portion of pump housing inlet passage  41  that is upstream of inlet valve assembly  40 , i.e. valve body first inlet passage  62  and valve body second inlet passage  64  are each in constant fluid communication with the portion of pump housing inlet passage  41  that is between inlet valve assembly  40  and low-pressure fuel pump  18 . A valve body outer periphery third portion  50   f  of valve body outer periphery  50   c  extends from valve body outer periphery second portion  50   e  to valve body second end  50   b  such that valve body outer periphery third portion  50   f  is larger in diameter than valve body outer periphery second portion  50   e . Valve body outer periphery third portion  50   f  is sealingly engaged with pump housing inlet passage  41  such that fluid communication through pump housing inlet passage  41  past inlet valve assembly  40  at the interface of pump housing inlet passage  41  and valve body outer periphery third portion  50   f  is prevented and fluid communication through pump housing inlet passage  41  past inlet valve assembly  40  is only possible through valve body bore  58 . 
     Valve spool  52  is made of a magnetic material and is centered about, and extends along, inlet valve bore axis  28   b  from a valve spool first end  52   a  to a valve spool second end  52   b . Valve spool  52  includes a valve spool first portion  52   c  which is proximal to valve spool first end  52   a  and a valve spool second portion  52   d  which is proximal to valve spool second end  52   b . Valve spool first portion  52   c  has a valve spool outer periphery  52   e  which is complementary with valve body bore  58  such that valve spool outer periphery  52   e  and valve body bore  58  are sized in order to substantially prevent fuel from passing between the interface of valve spool outer periphery  52   e  and valve body bore  58 . As used herein, substantially preventing fuel from passing between the interface of valve spool outer periphery  52   e  and valve body bore  58  encompasses permitting small amounts of fuel passing between the interface which still allows operation of high-pressure fuel pump  20  as will readily be recognized by a practitioner of ordinary skill in the art. Valve spool second portion  52   d  includes a base portion  52   f  which extends from valve spool first portion  52   c  such that base portion  52   f  is smaller in diameter than valve spool first portion  52   c , thereby providing an annular space radially between base portion  52   f  and valve body bore  58 . Valve spool second portion  52   d  also include a tip portion  52   g  which extends from base portion  52   f  and terminates at valve spool second end  52   b . Tip portion  52   g  is smaller in diameter than base portion  52   f , thereby defining a valve spool shoulder  52   h  where tip portion  52   g  meets base portion  52   f . Tip portion  52   g  is sized to be located within valve body central passage  66  of valve body  50  such that tip portion  52   g  is able to slide freely within valve body central passage  66  in the direction of inlet valve bore axis  28   b . In use, tip portion  52   g  is used to interface with check valve  54  as will be described in greater detail later. 
     Valve spool first portion  52   c  is provided with a valve spool groove  70  which extends radially inward from valve spool outer periphery  52   e  such that valve spool groove  70  is annular in shape. Valve spool groove  70  is selectively aligned or not aligned with valve body first inlet passage  62  and valve body second inlet passage  64  in order to control fluid communication through pump housing inlet passage  41  as will be described in greater detail later. One or more valve spool passages  72  is provided which extend from valve spool groove  70  through valve spool first portion  52   c  toward valve spool second end  52   b , thereby providing fluid communication between valve spool groove  70  and valve body outlet passages  68 . 
     A valve spool end bore  74  extends into valve spool  52  from valve spool first end  52   a . As shown, valve spool end bore  74  may include a valve spool end bore first portion  74   a  which is an internal frustoconical shape and a valve spool end bore second portion  74   b  which is cylindrical and terminates with a valve spool end bore bottom  74   c . A valve spool connecting passage  76  provides fluid communication between valve spool groove  70  and valve spool end bore  74  such that, as shown in the figures, valve spool connecting passage  76  may be formed, by way of non-limiting example only, by a pair of perpendicular drillings. 
     Check valve  54  includes a check valve member  78  and a travel limiter  80 . Check valve  54  is arranged at valve spool second end  52   b  such that check valve member  78  is moved between a seated position which blocks valve body outlet passages  68  (shown in  FIGS.  5 - 7   ) and an open position which unblocks valve body outlet passages  68  (shown in  FIG.  4   ) as will be described in greater detail later. Check valve member  78  includes a check valve central portion  78   a  which is a flat plate with check valve passages  78   b  extending therethrough where it is noted that only select check valve passages  78   b  have been labeled in  FIG.  3    for clarity. Check valve passages  78   b  are arranged through check valve central portion  78   a  such that check valve passages  78   b  are not axially aligned with valve body outlet passages  68 . A plurality of check valve legs  78   c  extend from check valve central portion  78   a  such that check valve legs  78   c  are resilient and compliant. Free ends of check valve legs  78   c  are fixed to valve body second end  50   b , for example, by welding. Consequently, when the pressure differential between valve body bore  58  and pumping chamber  38  is sufficiently high, check valve central portion  78   a  is allowed to unseat from valve spool  52  due to elastic deformation of check valve legs  78   c , thereby opening valve body outlet passages  68 . Travel limiter  80  includes a travel limiter ring  80   a  which is axially spaced apart from valve body second end  50   b  to provide the allowable amount of displacement of check valve member  78 . Travel limiter  80  also includes a plurality of travel limiter legs  80   b  which provides the axial spacing between travel limiter ring  80   a  and valve body second end  50   b . Travel limiter legs  80   b  are integrally formed with travel limiter ring  80   a  and are fixed to valve body second end  50   b , for example by welding. 
     Solenoid assembly  55  includes an inner housing  82 , a pole piece  84  located within inner housing  82 , a return spring  86 , a spool  88 , a coil  90  a flux washer  91 , an overmold  92 , and an outer housing  94 . The various elements of solenoid assembly  55  will be described in greater detail in the paragraphs that follow. 
     Inner housing  82  is hollow and is stepped both internally and externally such that an inner housing first portion  82   a  is open and larger in diameter than an inner housing second portion  82   b  which is closed by an inner housing end wall  82   c . Inner housing  82  is centered about, and extends along inlet valve bore axis  28   b . Inner housing first portion  82   a  is received within inlet valve bore  28   a  such that inner housing first portion  82   a  is sealed to fuel pump housing  28  in order to prevent leakage of fuel from pump housing inlet passage  41  to the exterior of fuel pump housing  28 . This sealing may be accomplished, by way of non-limiting example only, by one or more of interference fit between inner housing first portion  82   a  and inlet valve bore  28   a , welding around the inner corner where inner housing first portion  82   a  meets fuel pump housing  28 , and adhesives. An annular gap is provided between the inner periphery of inner housing first portion  82   a  and valve body outer periphery second portion  50   e  in order to provide fluid communication between pump housing inlet passage  41  and valve body second inlet passage  64 . The inner periphery of inner housing second portion  82   b  mates with valve body outer periphery first portion  50   d  to prevent communication of fuel between the interface of the inner periphery of inner housing second portion  82   b  and valve body outer periphery first portion  50   d.    
     Pole piece  84  is made of a magnetically permeable material and is received within inner housing second portion  82   b  such that pole piece  84  is centered about, and extends along, inlet valve bore axis  28   b . A pole piece first end  84   a  is frustoconical such that the angle of pole piece first end  84   a  is complementary to the angle of valve spool end bore first portion  74   a . In this way, pole piece first end  84   a  is received within valve spool end bore first portion  74   a . A pole piece second end  84   b , which is opposed to pole piece first end  84   a , is located at the closed end of inner housing  82 . A pole piece bore  84   c  extends axially through pole piece  84  from pole piece first end  84   a  to pole piece second end  84   b  such that the larger diameter portion of pole piece bore  84   c  extends into pole piece  84  from pole piece first end  84   a , thereby defining a pole piece shoulder  84   d  which faces toward valve spool end bore bottom  74   c . Return spring  86  is received partially with pole piece bore  84   c  such that return spring  86  abuts pole piece shoulder  84   d . Return spring  86  is also partially received within valve spool end bore second portion  74   b  and abuts valve spool end bore bottom  74   c . Return spring  86  is held in compression between pole piece shoulder  84   d  and valve spool end bore bottom  74   c , and in this way, return spring  86  biases valve spool  52  away from pole piece  84 . 
     Spool  88  is made of an electrically insulative material, for example plastic, and is centered about, and extends along, inlet valve bore axis  28   b  such that spool  88  circumferentially surrounds inner housing second portion  82   b  in a close-fitting relationship. Coil  90  is a winding of electrically conductive wire which is wound about the outer periphery of spool  88  such that coil  90  circumferentially surrounds pole piece  84 . Consequently, when coil  90  is energized with an electric current, valve spool  52  is magnetically attracted to, and moved toward, pole piece  84  and when coil  90  is not energized with an electric current, valve spool  52  is moved away from pole piece  84  by return spring  86 . A more detailed description of operation will be provided later. 
     Outer housing  94  circumferentially surrounds inner housing  82 , spool  88 , and coil  90  such that spool  88  and coil  90  are located radially between inner housing  82  and outer housing  94 . An annular chamber  96  is formed radially between inner housing first portion  82   a  and outer housing  94  such that annular chamber  96  is located axially between the exterior of fuel pump housing  28  and a flange  94   a  of outer housing  94  which is annular in shape and which extends inward toward inner housing second portion  82   b . Flange  94   a  provides a path for magnetic flux to pass when electric current is applied to coil  90 , and as a result, a very small radial clearance is provided radially between inner housing  82  and flange  94   a . A first sealing ring  98  is located within annular chamber  96  and is compressed axially between, and by, fuel pump housing  28  and flange  94   a . First sealing ring  98  is made of an elastomer material, the specific composition of which is selected based on environmental factors such as temperature and liquids which may come into contact with first sealing ring  98  as would be readily recognized by a practitioner of ordinary skill in the art. First sealing ring  98  prevents liquids from the outside environment from migrating to inner housing  82  where the liquids could otherwise collect and be difficult to dry out which could cause degradation to inner housing  82 , particularly in the small radial gap between inner housing  82  and flange  94   a  of outer housing  94  where crevasse corrosion erosion can occur if liquid is allowed to accumulate. It is important to note that first sealing ring  98  plays no role in sealing fuel within high-pressure fuel pump  20 , i.e. first sealing ring  98  is not exposed to fuel within high-pressure fuel pump  20 , and is provided to prevent intrusion of liquids that are present in the environment outside of high-pressure fuel pump  20 . In addition to the main purpose of preventing intrusion of liquids that are present in the environment outside of high-pressure fuel pump  20 , first sealing ring  98  may also provide suppression of vibrations and audible noise created from operation of high-pressure fuel pump  20  during operation that could otherwise be transmitted to the environment. 
     Flux washer  91  is located within outer housing  94  such that the outer periphery of flux washer  91  engages the inner periphery of outer housing  94  and such that spool  88  and coil  90  are located axially between flange  94   a  and flux washer  91 . Flux washer  91  provides a path for magnetic flux to pass when electric current is applied to coil  90 , and as a result, a very small radial clearance is provided radially between inner housing  82  and flux washer  91 . 
     Overmold  92  is an electrically insulative material, for example plastic, which fills the void between spool  88 /coil  90  and outer housing  94  such that overmold  92  extends axially from outer housing  94  to define an electrical connector  100  which includes terminals (not shown) that are connected to opposite ends of coil  90 . Electrical connector  100  is configured to mate with a complementary electrical connector (not show) for supplying electric current to coil  90  in use. Overmold  92  includes a central aperture  92   a  which extends to flux washer  91  along inlet valve bore axis  28   b . Inner housing  82  extends into central aperture  92   a  such that an annular gap  102  is formed radially between overmold  92  and inner housing  82 . A second sealing ring  104  is located within annular gap  102  and is compressed radially between, and by, overmold  92  and inner housing  82 . Second sealing ring  104  is made of an elastomer material, the specific composition of which is selected based on environmental factors such as temperature and liquids which may come into contact with second sealing ring  104  as would be readily recognized by a practitioner of ordinary skill in the art. Unlike first sealing ring  98  which is circular in cross-sectional shape prior to installation, second sealing ring  104  may be elongated in a direction parallel to inlet valve bore axis  28   b  prior to installation in order to provide structural integrity to second sealing ring  104  since second sealing ring  104  is not captured in a direction parallel to inlet valve bore axis  28   b . This cross-sectional shape also prevents rolling of second sealing ring  104  during installation into annular gap  102 . Second sealing ring  104  prevents liquids from the outside environment from migrating to the small radial clearance between inner housing  82  and flux washer  91  where the liquids could otherwise collect and be difficult to dry out and crevasse corrosion erosion can occur if liquid is allowed to accumulate. It is important to note that second sealing ring  104  plays no role in sealing fuel within high-pressure fuel pump  20 , i.e. second sealing ring  104  is not exposed to fuel within high-pressure fuel pump  20 , and is provided to prevent intrusion of liquids that are present in the environment outside of high-pressure fuel pump  20 . In addition to the main purpose of preventing intrusion of liquids that are present in the environment outside of high-pressure fuel pump  20 , second sealing ring  104  may also provide suppression of vibrations and audible noise created from operation of high-pressure fuel pump  20  during operation that could otherwise be transmitted to the environment. 
     Operation of high-pressure fuel pump  20 , and in particular, inlet valve assembly  40 , will now be described with particular reference to  FIG.  4    which shows valve spool  52  in a first position which results from no electric current being supplied to coil  90  of solenoid assembly  55 . When no electric current is supplied to coil  90 , return spring  86  urges valve spool  52  away from pole piece  84  until valve spool shoulder  52   h  abuts valve body end wall  60  which allows tip portion  52   g  of valve spool  52  to protrude beyond valve body second end  50   b  such that tip portion  52   g  holds check valve member  78  in an unseated position which permits flow through valve body outlet passages  68  and such that valve body outlet passages  68  are in fluid communication with pumping chamber  38 . Also in the first position, valve spool groove  70  is aligned with valve body first inlet passage  62 , however, it is noted that valve spool groove  70  is not aligned with valve body second inlet passage  64 . In this way, valve spool  52  maintains check valve member  78  in the unseated position and valve body first inlet passage  62  is in fluid communication with valve body outlet passages  68 . It should be noted that in the first position, alignment between valve spool groove  70  and valve body first inlet passage  62  provides a path to pump housing inlet passage  41 . In this way, the first position is a default position that provides limp-home operation of high-pressure fuel pump  20 , that is, if electrical power to solenoid assembly  55  is unintentionally interrupted, fuel in sufficient quantity and pressure is supplied to fuel injectors  16  by low-pressure fuel pump  18  for continued operation of internal combustion engine  12 , although without the fuel being pressurized by high-pressure fuel pump  20  since check valve member  78  being held in the unseated position by valve spool  52  prevents pressurization of fuel by pumping plunger  34 . It should be noted that the path to pump housing inlet passage  41  which enables the limp-home operation of high-pressure fuel pump  20  also enables the use of only one pressure-relief valve, i.e. pressure relief valve assembly  48 . 
     Now with particular reference to  FIG.  5   , valve spool  52  is shown in a second position which results from electric current being supplied to coil  90  of solenoid assembly  55  at a first duty cycle. When electric current is supplied to coil  90  at the first duty cycle, valve spool  52  is attracted to pole piece  84 , thereby moving valve spool  52  toward pole piece  84  and compressing return spring  86  to a greater extent than in the first position. Valve spool connecting passage  76  allows fuel located between valve spool  52  and pole piece  84  to be displaced toward valve body outlet passages  68  during movement of valve spool  52  toward pole piece  84  and also allows pressure to equalize on each axial end of valve spool  52 . In the second position, tip portion  52   g  is positioned to no longer protrude beyond valve body second end  50   b , and consequently, check valve member  78  is moved to a seated position which prevents flow into valve body bore  58  through valve body outlet passages  68 . Also in the second position, valve spool groove  70  is not aligned with valve body first inlet passage  62  and is also not aligned with valve body second inlet passage  64 , and in this way, fuel is prevented from entering or exiting valve body bore  58  through valve body first inlet passage  62  and valve body second inlet passage  64 . Consequently, valve body first inlet passage  62  and valve body second inlet passage  64  is not in fluid communication with valve body outlet passages  68 . The second position of valve spool  52  is used when internal combustion engine  12  is in operation but is not requesting fuel to be supplied from fuel injectors  16  as may occur during a fuel deceleration cutoff event when an automobile is coasting and no fuel is being commanded. In this way, the second position prevents fuel from being supplied to fuel injectors  16 . 
     Now with particular reference to  FIG.  6   , valve spool  52  is shown in a third position which results from electric current being supplied to coil  90  of solenoid assembly  55  at a second duty cycle which is greater than the first duty cycle used to achieve the second position of valve spool  52 . When electric current is supplied to coil  90  at the second duty cycle, valve spool  52  is attracted to pole piece  84 , thereby moving valve spool  52  toward pole piece  84  and compressing return spring  86  to a greater extent than in the second position. Just as in the second position, the third position results in tip portion  52   g  being positioned to no longer protrude beyond valve body second end  50   b , and consequently, check valve member  78  is moved to a seated position which prevents flow into valve body bore  58  through valve body outlet passages  68 . However, it should be noted that check valve member  78  is able to move to the unseated position when the pressure differential between valve body bore  58  and pumping chamber  38  is sufficiently high, i.e. during the intake stroke. Also in the third position, valve spool groove  70  is not aligned with valve body first inlet passage  62 , however, valve spool groove  70  is now aligned with valve body second inlet passage  64 , and in this way, fuel is allowed to valve body bore  58  through valve body second inlet passage  64 . Consequently, during the intake stroke of pumping plunger  34 , a pressure differential is created which allows fuel to flow through inlet valve assembly  40  through valve body second inlet passage  64 , thereby moving check valve member  78  to the unseated position which allows fuel to flow into pumping chamber  38 . During the compression stroke of pumping plunger  34 , pressure increases within pumping chamber  38 , thereby causing check valve member  78  to move to the seated position which prevents fuel from flowing from pumping chamber  38  into valve body bore  58  and which allows the pressurized fuel within pumping chamber  38  to be discharged through outlet valve assembly  42 . The third position of valve spool  52  is used when internal combustion engine  12  is required to produce a light output torque since it is noted that alignment of valve spool groove  70  with valve body second inlet passage  64  provides a restricted passage which thereby meters a small amount of fuel to pumping chamber  38  during the intake stroke of pumping plunger  34  to support fueling of internal combustion engine  12  at light loads. 
     Now with particular reference to  FIG.  7   , valve spool  52  is shown in a fourth position which results from electric current being supplied to coil  90  of solenoid assembly  55  at a third duty cycle which is greater than the second duty cycle used to achieve the third position of valve spool  52 . When electric current is supplied to coil  90  at the third duty cycle, valve spool  52  is attracted to pole piece  84 , thereby moving valve spool  52  toward pole piece  84  and compressing return spring  86  to a greater extent than in the third position. Just as in the second and third positions, the fourth position results in tip portion  52   g  being positioned to no longer protrude beyond valve body second end  50   b , and consequently, check valve member  78  is moved to a seated position which prevents flow into valve body bore  58  through valve body outlet passages  68 . However, it should be noted that check valve member  78  is able to move to the unseated position when the pressure differential between valve body bore  58  and pumping chamber  38  is sufficiently high, i.e. during the intake stroke. Also in the fourth position, just as in the third position, valve spool groove  70  is not aligned with valve body first inlet passage  62 , however, valve spool groove  70  is now aligned with valve body second inlet passage  64 , and in this way, fuel is allowed to valve body bore  58  through valve body second inlet passage  64 . Consequently, during the intake stroke of pumping plunger  34 , a pressure differential is created which allows fuel to flow through inlet valve assembly  40  through valve body second inlet passage  64 , thereby moving check valve member  78  to the unseated position which allows fuel to flow into pumping chamber  38 . During the compression stroke of pumping plunger  34 , pressure increases within pumping chamber  38 , thereby causing check valve member  78  to move to the seated position which prevents fuel from flowing from pumping chamber  38  into valve body bore  58  and which allows the pressurized fuel within pumping chamber  38  to be discharged through outlet valve assembly  42 . As should now be apparent, the third and fourth positions of valve spool  52  are nearly identical, however, the fourth position differs from the third position in that the alignment of valve spool groove  70  with valve body second inlet passage  64  is less restrictive than in the third position. Consequently, the fourth position of valve spool  52  is used when internal combustion engine  12  is required to produce a higher output torque since the alignment of valve spool groove  70  with valve body second inlet passage  64  provides a less restrictive passage which thereby meters a larger amount of fuel, compared to the third position, to pumping chamber  38  during the intake stroke of pumping plunger  34  to support fueling of internal combustion engine  12  at high loads. 
     As should now be clear, different duty cycles can be provided to vary the amount of fuel metered to pumping chamber  38  where the different duty cycles result in varying magnitudes of alignment of valve spool groove  70  with valve body second inlet passage  64 , thereby varying the magnitude of restriction. In other words, the third and fourth positions as described above are only examples of positions of valve spool  52 , and other duty cycles can be provided in order to provide different metered amounts of fuel to pumping chamber  38  in order to achieve different output torques of internal combustion engine  12 . An electronic control unit  106  may be used to supply electric current to coil  90  at the various duty cycles described herein. Electronic control unit  106  may receive input from a pressure sensor  108  which senses the pressure within fuel rail  44  in order to provide a proper duty cycle to coil  90  in order to maintain a desired pressure in fuel rail  44  which may vary based on the commanded torque desired to be produced by internal combustion engine  12 . 
     While inner housing  82  has been illustrated and described herein as directly engaging and being welded directly to fuel pump housing  28 , it should be understood that an intermediate element, such as a sleeve (not shown), may be provided radially between inner housing  82  and fuel pump housing  28  and this intermediate element will be considered within the scope of this disclosure to be fuel pump housing  28 . 
     In addition to or in the alternative to second sealing ring  104 , a sealing cap  110  may be provided as shown in  FIG.  8    which closes off the open end of central aperture  92   a  which is opposite from flux washer  91 . Sealing cap  110  may include a sidewall  110   a  which is annular in shape and which fits within central aperture  92   a  in an interference fit, for example by way of one or more annular ribs  100   b  of sidewall  110   a  which circumferentially surround sidewall  110   a , in order to retain sealing cap  110  to overmold  92  and to prevent intrusion of liquids. Sealing cap  110  may also include an end wall  110   c  which closes off one open end of sidewall  110   a  such that end wall  110   c  extends radially outward from sidewall  110   a , thereby forming a stop which limits the extent to which sealing cap  110  is inserted into central aperture  92   a . Sealing cap  110  is made of an elastomer material, the specific composition of which is selected based on environmental factors such as temperature and liquids which may come into contact with first sealing ring  98  as would be readily recognized by a practitioner of ordinary skill in the art. Sealing cap  110  prevents liquid from entering central aperture  92   a , thereby preventing liquid from migrating to areas which can cause degradation as described previously with respect to second sealing ring  104 . It is important to note that sealing cap  110  plays no role in sealing fuel within high-pressure fuel pump  20 , i.e. sealing cap  110  is not exposed to fuel within high-pressure fuel pump  20 , and is provided to prevent intrusion of liquids that are present in the environment outside of high-pressure fuel pump  20 . In addition to the main purpose of preventing intrusion of liquids that are present in the environment outside of high-pressure fuel pump  20 , sealing cap  110  may also provide suppression of vibrations and audible noise created from operation of high-pressure fuel pump  20  during operation that could otherwise be transmitted to the environment. 
     High-pressure fuel pump  20  as described herein with one or more of first sealing ring  98 , second sealing ring  104 , and sealing cap  110  minimizes the likelihood of liquids from the exterior environment from reaching elements of inlet valve assembly  40  and solenoid assembly  55  which could otherwise lead to undesired operation of inlet valve assembly  40  or solenoid assembly  55 . Furthermore, vibrations and audible noise created from operation of high-pressure fuel pump  20  may be suppressed. 
     While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.