Abstract:
A fuel injector pump in a direct-injection fuel delivery system for an internal combustion engine including a solenoid valve for controlling transfer of fluid from a high pressure chamber to a fuel injector nozzle. A supply passage and a return passage provide a fuel flow circuit for the fuel delivery system, the high pressure chamber being defined in part by a camshaft-driven plunger. An independent fuel leak flow path is provided to accommodate fuel leakage past a plunger of the pump, the fuel leak flow path extending to a zero pressure fuel tank.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 09/756,369, filed Jan. 8, 2001, now U.S. Pat. No. 6,598,579. That application is assigned to the assignee of this application. The disclosure of application Ser. No. 09/756,369 is incorporated by reference in this application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a liquid fuel injection system for a direct-injection engine. 
     2. Background Art 
     A fuel injector for an internal combustion engine, such as a diesel cycle engine, has a fuel injection pump plunger that reciprocates in a plunger cylinder or bore to effect fuel delivery to nozzles for each of the working cylinders of the engine. The plunger is stroked with a frequency directly proportional to engine speed since it is driven by an engine valve camshaft. The fuel injector includes an electromagnetic solenoid actuator for a fuel control valve, which controls delivery of fuel from a high pressure pumping chamber of the injector to the fuel injection nozzles. The solenoid actuator for the valve may be under the control of a digital electronic engine controller, which distributes controlled current pulses to the actuator to effect metering of fuel from the injector to the nozzles as the injector creates pressure pulses for the injection events. 
     The camshaft is located in a cylinder housing for the engine where it is exposed to engine lubricating oil. Any fuel that leaks through a clearance between the plunger and the plunger cylinder or bore tends to commingle with the lubricating oil, thereby creating a lubrication oil dilution problem after an extended operating period. 
     It is possible to reduce leakage past the plunger by reducing the dimensional clearance between the plunger and the plunger cylinder or bore. A reduction in the dimensional clearance, however, increases the risk of plunger seizure. This creates a design problem because mechanical friction losses and increased wear, especially in those instances when the fuel temperature varies throughout a relatively wide temperature range. Furthermore, precise machining required for close tolerance fits between the plunger and the plunger cylinder or bore increases manufacturing costs, which would make such designs impractical for high volume manufacturing operations. 
     A reduction in lubrication oil dilution can be achieved also by increasing the length of the plunger, thereby increasing the leak flow path length. It has been found, however, that this results only in a moderate decrease in leakage. Further, this would require an undesirable increase in the overall dimensions of the injector. Such increased dimensions of the injector would make it impractical in some commercial engine applications because of packaging constraints as well as cost penalties. 
     DISCLOSURE OF INVENTION 
     The present invention is adapted particularly for use with a “dual rail” injector design. That is, fuel is delivered to the injector through a fuel supply rail or passage from a low pressure fuel supply pump. Fuel that is not distributed to the nozzles, which is referred to as spill fuel, is returned to the inlet side of the fuel pump through a separate rail or return flow passage. It is an objective of the invention to reduce engine oil dilution in such a dual rail injector. This is done by decreasing leakage of fuel past the injector plunger into the lubrication oil circuit. This isolates the leak flow path from the region of the engine occupied by the camshaft that drives the injector plunger. 
     The injector of the invention comprises a fuel pump body with a cylinder that receives the injector pump plunger. A plunger spring normally urges the plunger to a retracted position. The plunger is driven during its working stroke by the engine camshaft. 
     The plunger and the cylinder or bore define a high pressure pumping chamber that communicates with an injector nozzle through a high pressure fuel delivery passage. Typically, the pressure may be about 20K psi. The high pressure passage is intersected by a pump control valve. Fuel is supplied to the control valve and to the pumping chamber of the injector by a fuel supply pump. The control valve opens and closes the fuel flow path through the high pressure fuel delivery passage in accordance with commands transmitted to a control valve solenoid actuator by an engine controller. The valve is opened and closed at the desired frequency for the injection pulses. 
     Separate fuel supply and return passages communicate with the control valve and with the pumping chamber. A separate leak-off passage communicates with the injector body and extends to the plunger cylinder at a location intermediate the full stroke position of the plunger and the full retracted position of the plunger. The leak-off passage communicates with a fuel tank, which is under zero gauge pressure. The leak flow path is defined by a predetermined clearance between the plunger and the plunger cylinder. It communicates with the leak-off passage so that leakage fuel will return to the tank rather than flow to the region of the camshaft in the engine cylinder housing. The fuel supply and return circuit is independent of the lubrication oil for the engine so that oil dilution is eliminated or substantially reduced. This increases the durability of the fuel injector and reduces maintenance costs for the engine. 
     In accordance with one embodiment of the invention, the fuel supply passage communicates with the injector pump body and with an internal passage that communicates with the chamber occupied by the flow control valve. A separate flow return passage in the injector pump body, which sometimes is referred to as a spill passage, communicates with an internal groove that in turn communicates with the return passage. Typically, the spill passage within the injector pump body may have a pressure of about 2K psi. 
     In a first alternate embodiment of the invention, the return passage is connected to the injector pump body at the upper end of the body adjacent the control valve. 
     In a second alternate embodiment of the invention, the return passage communicates with the flow control valve through an internal passage in the injector pump body and the supply passage communicates with the region of an actuator for the control valve. 
     In a third alternate embodiment of the invention, the leak-off passage extends generally in the direction of the axis of plunger cylinder in the pump body. The pump body is mounted in a sleeve in the engine cylinder housing. A leak-off passage fitting on the pump body, as well as a fuel supply passage fitting, are conveniently located externally of the engine cylinder housing. 
     In each of the embodiments, the leak-off passage is entirely independent of the supply passage and the return passage and is subjected to zero gauge pressure. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a cross-sectional view of an injector embodying the features of the invention; 
     FIG. 2 is an enlargement of a control valve seat for the injector shown in FIG. 1; 
     FIG. 3 is an enlargement of the control valve and an electromagnetic solenoid actuator for the control valve for the injector of FIG. 1; 
     FIG. 4 is a schematic illustration of a portion of a known diesel engine, partly in cross section, which illustrates the overall arrangement of an injector, a camshaft for driving the plunger of the injector, a nozzle and a working cylinder of the engine; 
     FIG. 5 is a cross-sectional view of a first modified embodiment of the injector of the invention, wherein the flow return passage is located at the top of the injector body; 
     FIG. 6 is a cross-sectional view of a second modified embodiment of the injector of the invention, wherein the fuel supply passage for the injector is located at the top of the injector body adjacent an actuator for the control valve; 
     FIG. 7 is an isometric view of a third modified embodiment of the invention with internal passages shown in phantom; 
     FIG. 8 is a cross-sectional view of the modified unit pump shown in FIG. 7; and, 
     FIG. 9 is a cross-sectional view of the modified unit pump shown in FIG. 7, the plane of the cross-section being angularly offset from the plane of the cross-section of FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although the disclosed injector is a unit pump, the invention may be used also in a unit injector assembly. 
     For the purpose of describing an operating environment for an injector incorporating the features of the invention, reference first will be made to FIG. 4, which illustrates a typical installation of a unit pump, mounted on a diesel engine cylinder housing  22 . The injector in FIG. 4 is illustrated generally at  10 . A plunger  14  is driven by a cam follower  16 , which is biased toward an engine camshaft  18  by plunger spring and spring shoulder  20 . The camshaft is located in the engine housing  22  adjacent the engine cylinders, one of which is shown at  24 . The location of the engine crankshaft is shown at  26 . 
     The engine cylinder housing  22  includes a sleeve  28  in which an injector body  12  is located. A high pressure passage  30  communicates with the injector body  12  and extends to a nozzle assembly  32  in a cylinder head  34 . The nozzle assembly includes a nozzle orifice  36  in the combustion chamber of the engine. Engine lubricating oil is in the region occupied by the camshaft  18  and the crankshaft location  26 . The lubricating oil is isolated from the injector plunger  14 , but any fuel that leaks past the plunger would commingle with the lubricating oil, which would create a dilution problem as previously explained. 
     FIG. 1 shows a first embodiment of the injector pump assembly of the invention. It comprises an injector body  38 , which is located in a cylinder housing sleeve  40  corresponding to the sleeve  28  shown in FIG.  4 . The injection pump assembly of FIG. 1 includes a pumping chamber  42  defined by reciprocating plunger  44  and plunger cylinder or bore  46 . The lower end of the plunger  44  is connected to a spring shoulder  48  received in a spring cage  50 . A spring  52  is seated on follower spring seat  54  formed on injector body  38 . The plunger normally is urged in a downward direction, as viewed in FIG. 1, by the spring  52 . The spring cage  50  carries cam follower  56 , which corresponds to the cam follower  16  of FIG.  4 . Spring cage  50  is received in sleeve  58  extending from the lower portion of the injector body  38 . 
     A valve chamber  60  is transversely disposed in the injector body  38 , its axis being perpendicular to the axis of the plunger. A control valve  62  is situated in the valve chamber  60 . An annular groove  64  on the control valve  62  communicates with high pressure passage  66  extending from pumping chamber  42 . The passage  66  communicates with outlet fitting  68 , which in turn communicates with a high pressure passage corresponding to passage  30  of FIG.  4  and with an injector nozzle. 
     A solenoid actuator, generally indicated at  70 , includes an armature  72 , which is connected to the right end of the valve  62 . The armature is actuated by a solenoid assembly, not visible in FIG.  1 . The valve  62  is urged normally in a left-hand direction, as viewed in FIG. 1, by valve spring  74 . Spring  74  is seated on shoulder element  76  carried by valve  62 . Valve  62  is spring-loaded normally in a left-hand direction against valve stop  78  received in valve stop chamber  80  in the injector body  38 . 
     The chamber  80  communicates with a fuel return passage  82 , which is defined in part by annular groove  84  on the exterior surface of the injector body  38 . That communication is established by internal passage  86  formed in the injector body  38 . 
     Spring chamber  88  for spring  74  communicates with inlet passage  90  through internal passage  92 . Inlet passage  90  is defined in part by annular groove  93  in the injector body  38 . The stop chamber  80  is in fluid communication with the spring chamber  88  through an internal passage, not shown in FIG.  1 . Spring chamber  88  also communicates with an internal passage  94  formed in valve  62 . When the valve  62  is shifted to its closed position by the actuator  70 , internal passage  94  communicates with stop opening  80  and with return passage  82 . 
     A leak-off port  96  formed in injector body  38  extends to the plunger cylinder or bore  46 . It intersects the plunger bore  46  at a location intermediate the upper end  98  of plunger  44  and an annular recess shown at  100 . The leak-off port  96  communicates with a zero pressure leak-off passage  102  through a fluid fitting  104 , which may be held by means of a press-fit in radial opening  106  formed in the injector body  38 . The annular recess  100  communicates with port  96  when the plunger is stroked, thereby facilitating flow of leak-off fuel to the zero pressure leak-off passage  102 . The leak-off passage  102  extends to a fuel tank, which is under zero gauge pressure. 
     The supply passage  90  is isolated from other regions of the fluid fuel flow circuit by O-ring seals  107  and  109 . Zero pressure leak-off port  96  is sealed from other regions of the system by O-ring seals  109  and  111 . 
     FIG. 2 is an enlargement of the left end of the control valve  62 . The control valve, as seen in FIG. 2, includes a circular valve land  108 , which engages valve seat  110  formed on injector body  38  when the actuator  70  is energized. At that time, a small gap  112  is formed between valve land  108  and surface  114  formed on the stop  78 . When the valve  62  is in the position shown in FIG. 2, fuel circulates from the inlet passage  90  through the valve chamber and the spring chamber  88  into the return passage  86  and the return passage  82 . When the actuator  70  is deenergized, the valve spring  74  urges the valve  62  in a left-hand direction, thus closing the gap  112  and opening the passage  66  to the flow return circuit. 
     When the valve  62  is closed, the stroking of the plunger  98  creates a high injection pressure in passage  66 , which is delivered to the nozzle as previously explained. 
     FIG. 3 is an enlargement of the right-hand end of the valve  62 . As seen in FIG. 3, the armature  72  is secured to the right-hand end of the valve  62  by threaded connector  116 . The right-hand end of the spring  74  is seated on annular spring seat  118 , which forms a stationary part of the actuator  70 . 
     FIG. 5 shows an alternate embodiment of the invention. It is mounted in engine housing sleeve  28 ′, which corresponds to engine housing sleeve  28  in FIG.  4 . In the case of the design of FIG. 5, a fuel supply passage communicates with fuel supply groove  120  formed in injector body  38 ′. The fuel supply passage communicates through an internal passage  122  with the spring chamber  88 ′, which corresponds to the spring chamber  88  of FIG.  1 . The elements of the construction of FIG. 1 that have counterpart elements in the construction of FIG. 5 have been designated by a similar reference numerals, although prime notations are used in FIG.  5 . 
     Unlike the design of FIG. 1 where the flow return passage  82  communicates with a groove formed in the injector body  38 , the flow return passage of the design of FIG. 5 is located at the top of the injector body  38 ′, as shown at  124 . Communication between the spring chamber  88 ′ in FIG.  5  and the flow return passage  124  in FIG. 5 is established by an internal passage, not shown in FIG.  5 . The arrangement of FIG. 5 has packaging advantages, compared to the design in FIG. 1, for certain engine installations. 
     In FIG. 5, a zero pressure leak-off passage is shown at  126 . It communicates with zero pressure drain groove  128  and zero pressure leak-off ports  130 . The ports  130  communicate with the plunger chamber  46 ′ at an intermediate location with respect to the upper end of the plunger  44 ′ and annular groove  100 ′. The ports  130  always are covered by the plunger. They are strategically located at the intermediate position between the high pressure chamber  42 ′ and the region of the engine camshaft that drives the plunger  44 ′ so that leak-off fuel that accumulates in annular groove  100 ′ will drain to the zero pressure passage  126 . 
     In another alternate embodiment, shown in FIG. 6, the zero pressure leak-off ports shown at  130 ″ are located relative to the plunger  44 ″ in a manner similar to the zero pressure port location of FIG.  5 . In FIG. 6, elements of the injector that are common to the elements of FIGS. 1 and 5 have been designated by similar reference numerals, although double prime notations are used. 
     In the design of FIG. 6, the return passage communicates with a return annular groove  134  in the injector body  38 ″. A fuel supply passage, unlike the fuel supply passage of the design of FIG. 5, is located at the top of the injector body  38 ″, as shown at  136 . The modes of operation of the embodiments of FIGS. 1,  5  and  6  are essentially the same. 
     The location of the supply passage in the embodiment of FIG. 5 is similar to the location of the supply passage  90  in the embodiment of FIG.  1 . The location of the return passage of the design in FIG. 6 is similar to the location of the supply passage for the design of FIG.  5  and the design of FIG.  1 . The zero pressure leak-off ports for the three designs are located in a similar fashion with respect to the plunger bore. 
     FIGS. 7,  8  and  9  illustrate a further embodiment of the invention. It is adaptable for assembly in an engine cylinder housing of the kind shown, for example, in FIG. 4, without the necessity for modifying the engine cylinder housing. The unit pump illustrated in FIG. 4 readily may be replaced with the unit pump shown in FIGS. 7,  8  and  9 . Thus the zero leak pressure leak-off passage or leak flow passage feature of the embodiment shown in FIGS. 1,  5  and  6  can be incorporated in the same engine casting shown in FIG. 4 by using the unit pump of FIGS. 7,  8  and  9 . The zero pressure leak flow passage of the design in FIGS. 7,  8  and  9  does not require special machining of the engine casting to create a fluid flow path from the unit pump to a zero pressure fuel tank. 
     As seen in FIG. 8 the unit pump of the further embodiment of the invention comprises an injector body  140 , which is formed with fuel flow inlet fitting  144 . A high pressure flow outlet fitting  146  is formed on the upper end of body  140 . The lower end of body  140  is received in the upper end of a sleeve  148 , which encloses a plunger spring  150 . A spring cage  152  is slidably received in the sleeve  148 . The lower end of the spring cage  152  is connected to a cam follower, generally indicated in FIG. 8 by numeral  154 . This cam follower would correspond to the cam follower  56  of the FIG. 1 embodiment. 
     The cam follower  154  is connected to a plunger  156 , which is received in a plunger cylinder or bore formed in the body  140 . The bore is not shown in FIG. 8 since it is located out of the plane of the cross section of FIG.  8 . 
     A portion of a fluid inlet passage extending from the fitting  144  to a valve chamber in the body  140  is shown at  158 . A zero pressure leak flow passage  160  extends in a vertical direction through the body  140 . At its upper end, the leak flow passage  160  communicates with a leak flow fitting opening  162 . The lower end of the leak flow passage  160  communicates with a zero pressure leak flow port  164 , which extends in a generally radial direction toward the centerline of the plunger cylinder or bore that receives plunger  156 . The lower end of the passage  160  is closed by a plug in plug opening  165 . The radially outward end of the port  164  is blocked by the sleeve  148 , best seen in FIG.  9 . 
     The port  164  corresponds to the port  96  of the FIG. 1 embodiment, ports  130  of the FIG. 5 embodiment and ports  130 ″ of the FIG. 6 embodiment. The port  164  is best seen by referring to FIG. 9, which illustrates the intersection of the port  164  with the zero pressure leak flow passage  160 . 
     A return flow groove is shown in FIGS. 7,  8  and  9  at  166 . A portion of the return flow passage in the body  140 , which communicates with the groove  166 , is shown in FIGS. 7 and 9 at  168 . 
     FIG. 9 shows the high pressure pumping chamber or cavity  170  at the upper end of plunger cylinder or bore  172 . Chamber  170  communicates with the high pressure outlet fitting  146  through internal high pressure passage  174 . 
     The valve chamber for the design of FIGS. 7,  8  and  9  is best seen in FIG. 7 at  176 . A fuel supply passage  178  extends to the interior of the valve chamber  176  and is connected to the fuel inlet flow fitting  144 , seen in FIGS. 8 and 9. The valve chamber receives a valve assembly corresponding to the valve assembly of FIGS. 1,  5  and  6 . A large diameter portion of the valve chamber defines a valve spring chamber that corresponds to the spring chamber  88  of FIG.  1  and the spring chamber  88 ′ of FIG.  5 . The end of the valve chamber opposite to the valve spring chamber defines a stop chamber, partially shown in phantom in FIG. 7 at  180 . As in the case of the embodiments of FIGS. 1,  5  and  6 , the stop chamber  180  receives a valve stop that corresponds to the valve stop  78  of FIG. 1, stop  78 ′ of the FIG. 5 embodiment and stop  78 ″ of the FIG. 6 embodiment. Stop chamber  180  surrounds the stop and communicates with the fuel return groove  166  through the internal passage best seen in FIG. 7 at  168 . 
     The zero pressure leak flow passage  160  communicates with a zero pressure connector, partially shown in FIG. 7 at  184 , which is received in zero pressure leak flow fitting opening  162 , seen in FIG.  8 . 
     Seen in FIG. 7 is a crossover passage  186 , which connects the chamber  180  surrounding the valve stop with the valve spring chamber at the opposite end of the valve chamber  176 . 
     Seen also in FIG. 7 are mounting bolt openings  188 ,  188 ′,  188 ″ and  188 ′″, which secure a solenoid actuator assembly, not shown in FIGS. 7 and 8 but which is generally indicated by reference number  190  in FIG.  9 . 
     An advantage of the design of FIGS. 7,  8  and  9  is its adaptability for use with an existing cast engine housing without requiring modifications to the engine housing. The zero pressure leak flow feature can be used advantageously with an engine for a vehicle that requires long idle periods. The same engine can be used in other heavy duty vehicles intended for high power, continuous operation at highway speed with a relatively low percentage idle time where the need for a flow feature is of lesser importance. 
     The zero pressure leak flow feature is more advantageous when the engine is used with a high percentage of idle time or when the vehicle has frequent stops and starts as in the case of urban transit vehicles; e.g., busses and garbage trucks. If the same engine is used with highway transit vehicles in which the largest percentage of operating time is at advanced throttle and at continuous highway speeds, the opportunity for lubricating oil dilution is reduced since the high pressures developed in the injector pumping chamber typically would result in a slight injector body distortion or strain in a radial direction in the region of the high pressure pumping chamber. This condition would result in a reduction in clearance for the plunger at locations in the plunger bore near the cam follower assembly, thereby tending to reduce leakage. 
     Although selected embodiments of the invention have been disclosed, it will be apparent to persons skilled in the art that modifications may be made without departing from the scope of the invention. Such modifications and equivalents thereof are intended to be covered by the following claims.