Abstract:
A gasoline direct injection system of an engine has a high pressure pump with an output connected to a fuel rail that supplies a plurality of fuel injectors. A control valve is connected in parallel with the pump to maintain the fuel rail pressure at a consistent level as the fuel injectors open and close. A valve element engages and disengages a seat to control the flow of fuel through the control valve. The high pressure from the fuel supply rail acts on surfaces of the valve element which are designed to produce a force imbalance that serves to rapidly open the control valve. An electromagnetic actuator, that closes the control valve, has a low impedance coil and pole pieces made of soft magnetic composite material to minimize eddy currents that impede valve performance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation in part of U.S. patent application Ser. No. 10/212,331 filed on Aug. 5, 2002. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The present invention relates to fuel injection systems for internal combustion engines, and particularly to valves for controlling pressure of fuel delivered to injector valves in the engine.  
           [0005]    2. Description of the Related Art  
           [0006]    For many decades gasoline internal combustion engines used a carburetor to mix fuel with incoming air. The resulting air/fuel mixture was distributed through an intake manifold and mechanical intake valves to each of the engine cylinders. Multi-port fuel injection systems have replaced the carburetion systems for most engines. A multi-port fuel injection system has a separate fuel injector valve which injects gasoline under pressure into the intake port at each cylinder where the gasoline mixes with air flowing into the cylinder. Even with multi-port fuel injection, there are limits to the fuel supply response and combustion control which can be achieved.  
           [0007]    More recently a third approach to supplying fuel into the engine cylinders has been devised. Known as “gasoline direct injection” or “GDI”, this techniques injects the fuel directly into the combustion cylinder through a port that is separate from the air inlet passage. Thus the fuel does not premix with the incoming air, thereby allowing more precise control of the amount of fuel supplied to the cylinder and the point during the piston stroke at which the fuel is injected. Specifically, when the engine operates at higher speeds or higher loads, fuel injection occurs during the intake stroke which optimizes combustion under those conditions. During normal driving conditions, fuel injection happens at a latter stage of the compression stroke and provides an ultra-lean air to fuel ratio for relatively low fuel consumption. Because the fuel may be injected while high compression pressure exists in the cylinder, gasoline direct injection requires that the fuel be supplied to the injector valve at a relatively high pressure, for example 100 times that used in multi-port injection systems.  
           [0008]    There are periods when all of the injector valves are closed and thus the gasoline in the conduit, known as the fuel supply rail, between the outlet passage of the fuel pump and cylinders has no place to go. This has not presented a significant problem in prior fuel systems that operated at lower pressure. However, at the significantly greater pressure of the gasoline direct injection system, the fuel system components down stream of the fuel pump must be capable of withstanding that pressure. In addition, a very high back pressure load occurs at the fuel pump at those times.  
           [0009]    Therefore it is desirable to provide a mechanism for maintaining a consistent pressure level in the section of the fuel system that is downstream of the fuel pump outlet passage even as the injector valves open and close.  
         SUMMARY OF THE INVENTION  
         [0010]    A direct injection fuel delivery system for a motor vehicle includes a pump with an inlet connected to a fuel supply and an outlet which supplies the liquid fuel at a high pressure. A common fuel rail coupled to the outlet of the pump and at least one fuel injector nozzle connected to the common fuel rail. A flow control valve is connected between the inlet and the outlet of the pump to selectively provide a fluid path there between.  
           [0011]    The flow control valve comprises a valve stem, a valve element, and a solenoid actuator. The valve stem has a bore with a valve seat at one end and has an inlet port that opens into the bore. The inlet of the pump communicates with the one end of the bore and the outlet of the pump communicates with the inlet port. The valve element is received within the bore and selectively engages the valve seat to control flow of fluid between the inlet and the outlet of the pump. The valve element has an exterior groove in communication with the inlet port. The exterior groove has a first surface proximate to the valve seat and a second surface remote from the valve seat. The first surface is larger than the second surface so that pressure in the exterior groove tends to move the valve element away from the valve seat. The solenoid actuator is operatively coupled to the valve element so that activation of the solenoid actuator moves the valve element toward the valve seat.  
           [0012]    To ensure high speed operation of the flow control valve, components of the solenoid actuator preferably are fabricated from a soft magnetic composite material. This material provides a non-electrically conductive path for the magnetic flux, thereby reducing the eddy currents that slow build-up of the magnetic flux and thus the speed of the actuator. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic view of a direct gasoline injection fuel system for a motor vehicle;  
         [0014]    [0014]FIG. 2 side view of a first embodiment of a solenoid valve in the fuel system;  
         [0015]    [0015]FIG. 3 is a cross sectional view along line  3 - 3  in FIG. 2;  
         [0016]    [0016]FIG. 4 is a cross sectional view along line  4 - 4  in FIG. 2; and  
         [0017]    [0017]FIG. 5 is an enlargement of the valve area in FIG. 3;  
         [0018]    [0018]FIG. 6 is a cross sectional view of a second embodiment of a solenoid valve for the fuel system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    With initial reference to FIG. 1, a direct gasoline injection (GDI) fuel system  100  for the engine of a motor vehicle has an electric feed pump  112  located in or adjacent to the fuel tank  114 . The feed pump  112  forces gasoline through fuel line  116  at a relatively low pressure (e.g. 2-5 bar) to a conventional fuel filter  118  and then through an inlet line  119  to a supply pump  120  located near the engine. This latter supply pump  120  furnishes the gasoline under relatively high pressure (e.g. 200-250 bar) through a pump outlet line  125  and a non-return check valve  126  to the common fuel rail  128  which feeds a plurality of individual fuel injectors  131 ,  132 ,  133  and  134  for the engine cylinders. A standard mechanical pressure relief valve  136  is provided in parallel with the supply pump  120  to relieve any dangerously high pressure from occurring in the pump outlet line  125 .  
         [0020]    A control valve  130  manages the instantaneous outlet pressure of the supply pump  120  by diverting and modulating the pressure of the discharge gasoline flow in the pump outlet line  125 . Specifically, the control valve  130  relieves the high pressure at the pump outlet by returning the gasoline to the lower pressure inlet line  119  for the pump. The control valve  130  is normally open and closes when a solenoid actuator is energized. The timing and duration of solenoid activation is controlled by the engine management system that includes an electronic control unit (ECU)  138  which controls the flow of gasoline through the control valve  130 . The electronic control unit  138  also electrically operates the fuel injectors  131 - 134 .  
         [0021]    During steady state operation above the idle speed of the engine, the fuel injections into the cylinders are discrete events, beginning at regular time intervals and having identical duration. During an injection event, the control valve  130  is closed so that pressure in the pump outlet line  125  rises to the desired high supply level (e.g. 200 bar). Between fuel injection events, the control valve  130  is opened so that the fuel displaced by the high pressure supply pump  120  is recycled to the inlet line  119 . Without that displacement of fuel, pressure in the common fuel rail  128  would rise above 200 bar. Opening the control valve  130  maintains the pressure in the common fuel rail  128  at approximately the 200 bar level when all the fuel injectors are closed Each activation of the control valve  130  and thus each occurrence of high pressure in pump outlet line  125  has a longer duration than the associated injection event. The injection event, control valve activation, and high pump outlet line pressure all terminate substantially simultaneously. Operation of this type of gasoline direct injection system is described in detail in U.S. Pat. No. 6,494,182.  
         [0022]    With reference to the FIGS. 2 and 3, an electrohydraulic flow control valve  10  mounts within an aperture  11  in the body  12  of the supply pump  120 . The pump outlet line  125  opens into the aperture  11  through a side wall and the bottom of the aperture  11  communicates with the inlet line  119 . The flow control valve  10  has a tubular stem  18  which extends into the fuel pump aperture  11  and interfaces with both the inlet line  119  and outlet line  125  to control the fluid flow there between. Specifically, the valve stem  18  has a longitudinal bore  15  extending there through with a transverse inlet port  19  coupling the outlet line  125  to the aperture. A valve seat  20  is formed at an end opening of the bore  15  which communicates with the inlet line  119 . A valve element  22  is slidably received in the bore  15  of the valve stem  18  and has an interior end with a tapered section that abuts the valve seat  20  in the closed state of the flow control valve.  
         [0023]    The other end of valve element  22  is mechanically joined, such as by brazing or welding for example, into a central aperture in an armature disk  24 . On the opposite side of the armature disk  24  is a solenoid actuator  28 , which has a plastic outer housing  29  that encloses a magnetically conductive pole piece  30  with a central aperture  32  and an annular groove  34  extending around the central aperture (see FIG.  4 ). An electromagnetic coil  36  is wound within the annular groove  34  and has leads which extend to a connector  38  for connection to the controller that governs engine operation. The electromagnetic coil  36  has an inductance that is less than 3.0 mH and a resistance that is less than 1.0 Ohm. Preferably the inductance of the electromagnetic coil  36  is 2.5 mH and the resistance is 0.2 Ohm. A spring  40  within the central aperture  32  of the pole piece biases the armature disk  24  so as to push the valve element  22  away from the valve seat  20  and open the valve.  
         [0024]    Energizing electromagnetic coil  36  produces a magnetic field indicated by flux lines  42  which attracts the armature disk  24  toward the pole piece  30  to pull the valve element  22  against the valve seat  20  closing the valve, as illustrated in FIG. 3. The magnetic flux flows through the armature disk  24  and pole piece  30 , The size of the electromagnet coil required to generate the necessary force is reduced by providing large cross section areas and very small air gaps through which the flux  42  flows.  
         [0025]    The pole piece  30  is made of “soft-magnetic composite material” which is a powder comprising a plurality of ferromagnetic particles with an electrical insulating coating. The coating imparts electrical insulation adjacent the ferromagnetic particles of at least one milliohm-cm. The valve component  30  is fabricated by compacting the ferromagnetic powder. Soft magnetic composite materials and processes for fabricating electromagnet cores from them are described in U.S. Pat. No. 6,251,514. Because the individual particles ferromagnetic powder are electrically insulated from one another, the pole piece  30  provides a non-electrically conductive path for the magnetic flux which reduces the eddy currents that otherwise would slow reversal of the flux. Reduction of eddy currents enables the electromagnet actuator of the valve to have a fast response time as compared to actuators with conventional electromagnet pole pieces.  
         [0026]    A key factor in the valve operation is that the armature disk  24  does not come into contact with the liquid fuel flowing through the flow control valve  10 . A seal  44  prevents the fuel from traveling between the valve element  22  and the outer section  46  of the valve stem  18  and thus from reaching the armature disk  24 . The isolation of the armature disk  24  from the fluid being controlled is a significant feature of the present flow control valve  10 .  
         [0027]    With reference to FIGS. 3 and 5, the forces due to the fluid pressures acting on the valve element  22  are substantially imbalanced to provide a fast open time. Specifically, the valve element has an outer circumferential groove  50  with a first end surfaces  52  proximate the valve seat  20  and a second end surface  54  remote from the valve seat, with both end surfaces being exposed to the high pressure fluid in the outlet line  125  from the fuel supply rail. The diameter of the valve stem bore  15  in the vicinity of the circumferential groove  50  is slightly larger that the diameter of the bore closer to the armature  24 , thereby creating a lip  55  adjacent the first end surface  52  (FIG. 5). As a result, the area of the second end surface  54  is substantially smaller than the area of the first end surface  52  which is exposed to the high pressure fluid when the valve is closed.  
         [0028]    Because of this surface area differential, the force produced by the high pressure fluid acting on those end surfaces  52  and  54  is greater in a direction which tends to move the valve element  22  away from the valve seat  20 , i.e. open the valve. As a consequence, a relatively small force from the spring  40  is able to overcome force exerted on the nose  56  of the valve element  22  by the relatively low pressure in the inlet line  119  and thus open the flow control valve  10 . However, the magnetic force from the electromagnetic coil  36 , required to close the flow control valve  10 , must be great enough to overcome the inlet passage pressure and the spring force.  
         [0029]    The present valve  10  has particular use in regulating the pressure in the fuel rail  120  of the fuel injection system  100  for an internal combustion engine. In that application, the valve is opened and closed very rapidly many times during each cycle of the engine to relieve pressure at the fuel pump outlet. The flow control valve  10  has several features that contributes to the ability to operate at such high speeds. The size differential of the end surfaces of the groove  50  in the valve element, and the relatively low inductance and resistance of the solenoid actuator are two of these features. Other features include the use of soft magnetic composite material for the pole piece of the solenoid which reduces eddy currents. Another factor enhancing performance of the flow control valve  10  is that the armature  24  of the solenoid actuator  28  does not come into contact with the fuel flowing through the valve and thus the armature motion encounters a lower fluidic resistance of air as compared to liquid fuel.  
         [0030]    However, it is not absolutely essential that fuel be prevented from contacting the armature  24 . In this regard, FIG. 6 illustrates a second embodiment of a control valve  60  which has the same exterior appearance as shown in FIG. 2. The components that are the same as those in the first control valve  10  in FIG. 3 have been assigned the same identification numerals. The armature  24  has a central aperture with a tubular connector pin  66  welded therein. The connector pin  66  also is press fitted into a valve element  22  that extends completely through the valve element  70  which, except for that through bore, has the same construction as the valve element  22  in the first valve  10 . Thus fuel in the pump inlet line  119  is able to flow through the valve element  22  and the connector pin  66  into the central aperture  64  and the groove  34  for the electromagnetic coil  36  in the solenoid actuator  28 .  
         [0031]    To prevent this fuel from leaking from the control valve  60 , a metal cup  68  extends over the solenoid actuator  28 . A circular lip  72  of the metal cup  68  is welded to the base plate  74  of the control valve thereby providing a fluid tight seal that is able to withstand the high pressure in the pump outlet line  125 . Thus the metal cup  68  and base plate  74  enclose the solenoid actuator  28 . A plastic outer housing  76  is molded over the metal cap  68 .  
         [0032]    The second control valve differs from the first one in that the interior of the solenoid actuator  28  is not sealed from the fuel lines  119  and  125  and thus the fuel comes into contact with the internal components, such as the armature  24  and the electromagnetic coil  36 .  
         [0033]    The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.