Abstract:
A pressure regulator having a first orifice that permits a flow of liquid and maintains a back pressure in the supply line, and a second orifice that provides a second, greater flow of fluid responsive to a pressure increase in the inlet line.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of U.S. provisional patent application Serial No. 60/299,317, filed on Jun. 18, 2001. The priority of the prior application is expressly claimed and its disclosure is hereby incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to diesel engines, and in particular to fuel pressure regulators for use in conjunction with diesel engines.  
           [0003]    Diesel engines are widely used in trains and trucks. Most modern diesel engines use electronic unit injection to provide fuel to the engine. Fuel supply systems for diesel engines that incorporate electronic unit injection require excess fuel flow and pressure to cool the injectors and to suppress cavitation. Cavitation is the formation and collapse of small amounts of fuel, and typically occurs as the fuel is accelerated along an interior pump surface. Cavitation is harmful to the fuel pump because it causes high rates of erosion of the interior surface of the pump. It is common practice to use either an engine driven positive displacement fuel pump whose output varies with engine rpm, or a constant speed electric motor driven pump to supply constant fuel flow.  
           [0004]    To maintain the required back-pressure in the system either a fixed orifice restriction, or a pressure regulating mechanism is used at the end of the fuel line where the excess fuel not burned by the engine is returned to the fuel tank. The fixed orifice has the advantage of simplicity and reliability, but at best achieves poor back-pressure regulation. The pressure regulating mechanism is more accurate, but is subject to failure modes and effects that may cause problems with the operation of the engine. The pressure regulating mechanism may also be cause pump priming problems on system startup since, in the absence of pressure, it is basically a closed valve. As such it may not allow the system to vent properly while priming. Another problem with the pressure regulating mechanism is cavitation erosion associated with high escape velocities into regions of low static pressure where vapor bubbles can form and subsequently collapse with detrimental effect on nearby surfaces.  
           [0005]    The object of the present invention is to provide an improved pressure regulating mechanism for a diesel engine fuel system that combines the simplicity of the fixed orifice with the accuracy of the pressure regulator while at the same time reducing the detrimental effect of cavitation and potential failure modes.  
           [0006]    Another object of the invention is to provide a fuel pressure regulating mechanism for a diesel engine that will maintain substantially constant fuel pressure over the full range of fuel flow provided by an engine driven fuel pump.  
           [0007]    Still another object of the invention is to provide such a system that is cost-effective, highly reliable and simple to produce.  
           [0008]    Yet another object of the invention is to provide such a system that is based on standard hydraulic fittings such as a coupling or an elbow.  
           [0009]    The invention includes two different sized orifices in series with a pressure regulating mechanism interposed between them. The intermediate pressure regulating mechanism provides a fuel bypass around the first orifice and introduces an additional flow to the second orifice. The entire assembly is either contained within a standard hydraulic fitting or is installed into a suitable housing designed for the purpose.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a cross-sectional side view along line B-B of FIG. 5 showing a first embodiment of the invention, and showing the regulator in a position wherein flow of fuel at low engine operating speeds is directed entirely through a first orifice.  
         [0011]    [0011]FIG. 2 is a second cross-sectional side view of the embodiment shown in FIG. 1, and showing the regulator in a position wherein flow of fuel at higher engine operating speeds is directed through the first orifice and a second orifice.  
         [0012]    [0012]FIG. 3 is a cross-sectional view of another preferred embodiment wherein the orifice and sealing surfaces are formed of an insert of a material different from that of the orifice plate and piston.  
         [0013]    [0013]FIG. 4 is a cross-sectional view of another embodiment of the invention wherein the flow of fuel at low flow rates is regulated by a predetermined gap between the piston and a sealing surface.  
         [0014]    [0014]FIG. 5 is an end elevational view from the inlet side of the regulator.  
         [0015]    [0015]FIG. 6 is an end elevational view from the outlet side of the regulator. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Referring now to FIGS.  1 - 6 , a pressure regulating valve according to the invention is shown generally at  10 . Valve  10  includes a body having an inlet  12  and an outlet  14 . In preferred embodiments, the body is modified from a standard hydraulic fitting such as an elbow or connector. Each end of the outer surface of valve  10  includes threads  16  and  18 , and is thereby plumbed into the fuel system. An orifice plate  20  is threaded into the inlet  12 , and is and is locked in position by locking screw  22 . Orifice plate  20  includes a central orifice  24  extending longitudinally through the orifice plate. Orifice plate  20  also includes a surface that, together with the interior surface of inlet  20 , defines a fluid passage  26  through which fuel can bypass central orifice  24  to accommodate high flow conditions, as described in greater detail below. Orifice plate  24  terminates in a distal annular portion  27  that defines an annular sealing surface  28 .  
         [0017]    An annular piston  30  is slidably mounted in the valve body. A first end of piston  30  includes a second orifice  34  that is in communication with the valve outlet  14 . In the preferred embodiment, the second orifice  34  is larger than central orifice  24  as will be explained in greater detail below. The first end of piston  30  terminates in an annular sealing surface  31 . In one operative position (FIG. 1) sealing surface  31  registers in sealing engagement with annular sealing surface  28 . Spring  36  is mounted in piston  30  and biases piston  30  toward the first operative position. In a second operative position (FIG. 2) sealing surface  31  is spaced apart from annular sealing surface  28 , and permits fuel to flow from fluid passage  26  to outlet  14 , bypassing central orifice  24 . Spring  36  is positioned within piston  30 , and bears against shoulder  38  of piston  30 . Spring  36  is retained in the valve body by retainer  40  and circlip  42  that is engaged with groove  44 . Valve  10  includes inlet sealing ring  46  and outlet sealing ring  48  for sealing engagement with the mating surfaces of the fuel system connections (not shown).  
         [0018]    In an alternate embodiment shown in FIG. 3, an orifice insert  50  is mounted in orifice plate  24 . Insert  50  can be of any desired material, and provides the option of varying the orifice size for specific applications. Insert  50  also permits replacement of the orifice without the need to replace the entire orifice plate. In this embodiment, piston  30  includes an orifice insert  52  that, like insert  50 , can be of a different material than piston  30 , can be varied in size, and can be replaced without replacing the entire piston assembly. In this embodiment, spring  36  bears against a flange  54  on insert  52 . Flange  54  in turn bears against flange  56  of piston  30 .  
         [0019]    In yet another embodiment (FIG. 4) central orifice  24  is dispensed with altogether. Instead of central orifice  24  being provided to regulate low pressure flow, piston  30  is positioned in its first position to provide a predetermined space  57  between sealing surface  31  of piston  30  and a continuous sealing surface  58  of an insert  60 . Insert  60  is mounted on inlet plate  21 . Insert  60  and inner surface  62  of valve  10  define a fluid flow path  64  through which fuel flows at a restricted flow rate through space  57 , second orifice  34 , and through outlet  14  of the valve.  
         [0020]    Having described the structure of several preferred embodiments, their operation will now be described.  
         [0021]    Referring again to FIGS. 1 and 2, central orifice  24  is fixed in place and is sized to create the required back-pressure at the low fuel flow rate that the engine driven pump delivers at idle rpm. This is illustrated in FIG. 1. Fuel enters valve  10  through inlet  12 . A predetermined amount of fuel flows through central orifice  24 . At the same time, the restricted flow through central orifice  24  creates a predetermined back pressure in the inlet  12 . Central orifice  24  also bypasses the pressure regulating mechanism to vent the fuel flow through to the second orifice  34  for priming. The second orifice  34  is located in piston  30 , and is sized to create the required back-pressure at the fuel flow rate that exists at maximum rpm of the engine.  
         [0022]    When the engine speed increases the increased flow from the pump causes the pressure drop through the central orifice  24  to exceed the pressure set by spring  36 .  
         [0023]    This causes piston  30  to move toward outlet  14 , compressing spring  30  and opening an annular passage between the end of piston  30  and the annular sealing surface  28  (FIG.  2 ). Fuel then flows through this passage, bypasses the central orifice  24 , and maintains the required back pressure on the fuel system. At the useful levels of power where the engine spends most of its operating time except for idling, the pressure drop through the second orifice raises the region of low static pressure in the pressure regulator to a value that substantially eliminates the effects of cavitation. When the engine approaches its maximum output the annular passage of the pressure regulator is wide open. At this point both the pressure regulator and the first orifice are substantially out of the picture and the system pressure is maintained solely by the second orifice.  
         [0024]    As an added benefit, the pressure regulating mechanism also operates in a similar manner to regulate the system pressure during variations in flow due to fuel burned by the engine at any particular time.  
         [0025]    During periods of idling all the available flow will be going through the smaller first orifice and passing directly through the larger second orifice. The pressure regulator is normally closed and inactive at this point. This is one situation where cavitation may still be an issue unless the pressure regulator is tightly sealed when closed. To this end it may be necessary to change the sealing materials used in the orifice plate and the piston to materials that promote better sealing. This is illustrated in FIG. 3.  
         [0026]    For fuel systems that incorporate an electric motor driven fuel pump rather than an engine driven fuel pump the fuel flow is constant and equal to the specified flow required to operate the engine. Thus there is little need for the first orifice except for priming and for stabilizing the flow through the regulator assembly. In this case priming relief can be provided by other means, or by simply a loose-fitting pressure regulator piston as shown in FIG. 4.  
         [0027]    The pressure regulator setting is adjustable over its useful range by means of the threaded recess  66  in the valve body  10  in which the corresponding threaded outer surface of the orifice plate  20  is engaged. The position of the orifice plate  20  and therefore the force of the spring can be adjusted by rotating the orifice plate  20 . A locking screw is provided to prevent the orifice plate from moving after its position has been set.  
         [0028]    While the invention has been described with reference to the foregoing preferred embodiments, those of skill in the art will appreciate that numerous changes in detail and arrangement are possible without departing from the scope of the following claims. For example, the invention has been described in the context of a diesel fuel system. However, the invention is not intended to be limited to diesel fuel systems, or even fuel systems, but could also find application in any fluid system requiring back-pressure regulation at varying flow rates.