Patent Publication Number: US-6662783-B2

Title: Digital valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §§119(e) and 120 of U.S. Provisional Patent Application Ser. No. 60/336,708, filed Dec. 7, 2001, and is a continuation-in-part of U.S. patent application Ser. No. 09/983,037, filed Oct. 22, 2001, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an oil activated fuel injector. More particularly, the present invention relates to a digital control valve used with an oil activated, electronically or mechanically controlled fuel injector. 
     2. Background Description 
     There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically, or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two-, three-, or four-way valve systems, each having grooves or orifices that allow fluid communication between working ports, high pressure ports, and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid that is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber. 
     In current designs, a driver will deliver a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as “grooves”) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine. 
     However, in such a conventional system, a response time between the injection cycles may be slow, thus decreasing the efficiency of the fuel injector. This is mainly due to the slow movement of the control valve spool. More specifically, the slow movement of the control valve may result in a slow activation response time to begin the injection cycle. To remedy this inadequacy, additional pressurized working fluid may be needed; however, additional energy from the high pressure oil pump must be expended in order to provide this additional working fluid. This leads to an inefficiency in the operations of the fuel injector itself. Also, the working fluid at an end of an injection cycle may not be vented at an adequate response rate due to the slow movement of the control valve spool. 
     Other prior art systems use a small step at the end of the spool to reduce the area where the spool and the solenoid are in contact. However, these steps introduce wear due to impact between parts and reduced magnetic force between the spool and the solenoids. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, a control valve for a fuel injector generally includes a valve body and a spool positioned within a bore of said valve body. The spool is slideable between a first and second position. The control valve also comprises a first bore in fluid communication with a rail inlet of the fuel injector, a cross bore positioned within the valve body and offset from the first bore, and a groove located about the spool. The cross bore, in embodiments, leads to ambient, and the first bore may be located within the valve body. The groove provides fluid communication between the cross bore and the first bore when the spool is in the first position, and seals fluid communication when the spool is in the second position. At least two solenoids are provided on opposing sides of the spool for moving the spool between the first and second positions, and a non-magnetic barrier is provided for controlling latching forces between the spool and at least one of the at least two solenoids when the spool is in the first position or the second position. The latching forces are created by a current pulse of one of the at least two solenoids. In embodiments, the solenoids are provided in end caps. The non-magnetic barrier may be a non-magnetic shim or a non-magnetic coating, and is preferably selected based upon the required or developed latching forces between the spool and the solenoids. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an oil activated fuel injector used with a control valve according to the present invention; 
     FIG. 2 shows an embodiment of the present invention; 
     FIG. 3 a  shows an exploded view of the control valve of the present invention; 
     FIG. 3 b  shows an exploded view of an embodiment of the control valve body of the present invention; 
     FIG. 4 shows an exploded view of the control valve of the present invention in a closed position; 
     FIG. 5 shows an exploded view of the control valve of the present invention in an open position; 
     FIG. 6 shows an embodiment of the valve body with a spool in a first position used with the control valve of the present invention; and 
     FIG. 7 shows the embodiment of the valve body with a spool in a second position used with the control valve of the present invention. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
     The present invention is directed to an oil activated, electronically, mechanically, or hydraulically controlled fuel injector, and more particularly to a digital control valve used with an oil activated fuel injector. The digital control valve of the present invention is capable of providing a short control valve stroke that, in turn, translates into a fast response time for the outflow of the inlet rail pressure. The oil activated fuel injector of the present invention will thus increase efficiency of the injection cycle. 
     Embodiments of the Oil Activated Fuel Injector of the Present Invention 
     Referring now to FIG. 1, the fuel injector is generally depicted as reference numeral  100  and includes an inlet port  102 , which receives working fluid, for example engine lubricant, from an inlet rail (not shown). The fuel injector  100  also includes a body  104  having a flat body area  106  and a central bore  108 . The central bore  108  includes a first diameter  108   a  and a second diameter  108   b . In embodiments, the first diameter  108   a  is slightly smaller than the second diameter  108   b . A spool  110  is slidably positioned within the central bore  108  and includes a groove  112  positioned within the first diameter  108   a . The groove includes a first leading edge  112   a  and a second leading edge  112   b , and provides fluid communication between the inlet port  102  and the bore or working port  114 , which leads to the intensifier chamber. A venting space  107  is developed between the first leading edge  112   a  and the flat body area  106  in the position of the spool  110  of FIG.  1 . It should be recognized by those of ordinary skill in the art that the venting space  107  is sealed when the spool  110  is moved in the direction of arrow “A.” As discussed in more detail below, the working fluid in the intensifier chamber is allowed to vent via the space  107  at the termination of the injection cycle. 
     The spool  110  further includes a throttle  116 , which provides fluid communication between the inlet port  102  and a pressure chamber  118 . The pressure chamber  118  is defined by a partial bore  118   a  within the spool  110  and a servo piston  119 . The servo piston  119  is partly located within the partial bore  118   a  and further includes a central bore  119   a . The central bore  119   a  is in fluid communication with the pressure chamber  118 , which provides, in part, a mechanism for the working fluid to be vented to ambient during an initial stage of the injection cycle. 
     Still referring to FIG. 1, a control valve  120  includes a spool body  124  (also referred to as a control valve body or valve body) having a bore  122  in axial alignment with the central bore  119   a  of the servo piston  119 . The spool body  124  also includes a cross bore  125  leading to ambient. A spool  126 , slidably positioned within the spool body  124 , includes a groove  126   a , which, in a first, or activated, position of the spool  126 , overlaps with the bore  122  and the cross bore  125  to provide fluid communication therebetween. In turn, this position of the groove  126   a  (that is, when the spool  126  is activated) provides a flow path for the working fluid from the inlet port  102  to ambient via (i) the inlet port  102 ; (ii) the throttle  116 ; (iii) the pressure chamber  118 ; (iv) the central bore  119   a ; (v) the bore  122 ; (vi) the groove  126   a ; (vii) the cross bore  125 ; and (viii) ambient. At this pressure stage, the pressure within the pressure chamber  118  will be substantially equal to that of the inlet rail pressure. 
     In more particularity, in a first, or activated, position of the spool  126 , the groove  126   a  overlaps both the bore  122  and the cross bore  125 . In this position, the pressure within the pressure chamber  118  will be lower than that of the inlet rail pressure, which, in turn, allows the slideable spool  110  to move in the direction of arrow “A.” At this spool  110  position, the first leading edge  112   a  is positioned within the inside edge of the flat body area  106  (that is, within the central bore  108 ), thus sealing the venting space  107 . This allows working fluid to flow from the inlet port  102  through the bore  114  and into the intensifier body in order to begin an injection cycle. 
     In a second, or deactivated, position of the spool  126 , the groove  126   a  no longer overlaps with the bore  122  and the cross bore  125 , and hence will not lead the working fluid to ambient. In this spool  110  position, the working fluid will flow from the inlet port  102  to the pressure chamber  118  via the throttle  116 . This will increase the pressure within the pressure chamber  118  to a pressure which is substantially equal to that of the inlet rail pressure. In turn, this increased or higher pressure will force the slideable spool  110  to move in the direction of arrow “B” to a second position, thus moving the first leading edge  112   a  beyond the outside edge of the flat body area  106 , and hence forming the venting space  107 . The working fluid within the intensifier chamber will be vented to ambient via the venting space  107 , thus ending the injection cycle. 
     FIG. 1 further shows the remaining portions of the fuel injector  100  used with the control valve  120  of the present invention. It should be understood by one skilled in the art that the control valve  120  of the present invention may equally be used with other configurations of fuel injector  100 . By way of example only, and without limitation, these other configurations may include a ball valve mechanism at the fuel inlet or other angled or straight bores leading to the nozzle of the injector  100 . 
     An intensifier body  128  is mounted to the body  104  via any conventional mounting mechanism. A seal  130 , for example, an o-ring, may be positioned between the mounting surfaces of the intensifier body  128  and the body  104 . A piston  131  is slidably positioned within the intensifier body  128  and is in contact with an upper end of a plunger  132 . An intensifier spring  133  surrounds a portion (e.g., shaft) of the plunger  132  and is further positioned between the piston  131  and a flange or shoulder formed on an interior portion of the intensifier body  128 . The intensifier spring  133  urges the piston  131  and the plunger  132  in a first position proximate to the body  104 . 
     As further seen in FIG. 1, a fuel inlet  134  is formed within the intensifier body  128  proximate an end portion  132   a  of the plunger  132 . The fuel inlet  134  provides fluid communication between a high pressure chamber  136  and a fuel area (not shown). This fluid communication allows fuel to flow into the high pressure chamber  136  from the fuel area during an up-stroke of the plunger  132 . A check disk  135  is positioned below the intensifier body  128  remote from the inlet port  102 . The combination of an upper surface  135   a  of the check disk  135 , the end portion  132   a  of the plunger  132 , and an interior wall  128   a  of the intensifier body  128  forms the high pressure chamber  136 . The check disk  135  also includes a fuel bore  138  in fluid communication with the high pressure chamber  136 . 
     FIG. 1 further shows a nozzle  140  and a spring cage  142 . The spring cage  142  is positioned between the nozzle  140  and the check disk  135 , and includes a fuel bore  144  in fluid communication with the fuel bore  138  of the check disk  135 . The spring cage  142  also includes a centrally located bore  148  having a first bore diameter  148   a  and a second, smaller bore diameter  148   b . A spring  150  and a spring seat  151  are positioned within the first bore diameter  148   a  of the spring cage  142 , and a pin  154  is positioned within the second, smaller bore diameter  148   b.    
     The nozzle  140  includes an angled bore  146  in alignment with the bore  144  of the spring cage  142 . A needle  156  is preferably centrally located within the nozzle  140  and is urged downwards by the spring  150  via the pin  154 . A fuel heart chamber  152  surrounds the needle  156  and is in fluid communication with the bore  146 . In embodiments, a nut  160  is threaded about the intensifier body  128 , the check disk  135 , the nozzle  140 , and the spring cage  142 . 
     FIG. 2 shows an embodiment of the present invention. In this embodiment, the high pressure chamber  118  is positioned between the end of the spool  110  and the valve body  124 . That is, a portion of the central bore  108  forms the high pressure chamber  118  between the spool  110  and the valve body  124 . The bore  119   a  is located within the spool  110  and provides fluid communication between the high pressure chamber  118  and the throttle  116 . The embodiment of FIG. 2 further shows the high pressure chamber  118  in fluid communication with the bore  122 , with all of the remaining features and advantages substantially the same ad the embodiment of FIG.  1 . 
     As to the advantages and remaining features, it is noted by way of example only that in a first, or activated, position of the spool  126 , the slidable spool  110  will move in the direction of arrow “A” such that the first leading edge  112   a  is positioned within the inside edge of the flat body area  106 . As previously discussed, this allows working fluid to flow in to the intensifier body in order to begin an injection cycle. In a second, or deactivated, position of the spool  126 , working fluid will flow into the pressure chamber  118 , thus increasing the pressure therein to a higher pressure than that of the inlet rail pressure. This is due to the fact that the groove  126   a  is no longer overlapping with the bore  122  and the cross bore  125 , and hence will not lead to ambient. In turn, this higher pressure will force the slidable spool  110  top move in the direction of arrow “B,” thus allowing the working fluid to vent from the intensifier chamber to ambient via the space  107  provided between the flat body  106  and the first leading edge  112   a.    
     FIG. 3 a  is an exploded view of the control valve  120  of the present invention. In this view, it is readily seen that the control valve  120  of the present invention includes the valve body  124  having the bore  122  and the cross bore  125 . Also, the spool  126  is slidably positioned within the spool body  124 , and includes a groove  126   a  that provides fluid communication between the bore  122  and the cross bore  125  when the spool  126  is in the first position. The control valve body also includes end caps  123  mounted to the control valve body  124  via a nut and bolt mechanism  127  or other mounting mechanism. A pair of coils  141  (e.g., solenoids) are used to activate and deactivate the spool  126  between the first, or open, position and the second, or closed, position, respectively. By a short current pulse of a coil  141 , the spool  126  will change positions, moving towards the activated coil  141  and remaining there by latching forces. A high latching force will delay the switching process, while a very low latching force will not guarantee that the spool  126  will stay in position. 
     In embodiments, the valve control body (spool body)  124  is further provided with non-magnetic shims  300  and  301  between the spool  126  and the coils  141 . Preferably, non-magnetic shims  300 ,  301  are made of stainless steel and are between 10 and 60 microns in thickness. Alternatively, a non-magnetic coating (e.g., ceramic, chrome, etc.) could be used at ends of the spool  126  or on the inner pole of the coils  141  (FIG. 3 a ). In further embodiments, as shown in FIG. 3 b , the non magnetic coatings or shims  300 ,  301  may be on the outer pole between the end cap  124   a  and the spool body  124 . In this case, the non magnetic coating would no longer be required at ends of the spool  126  or on the inner pole of the coils. Thus, the present invention provides a large contact surface between the spool  126  and the coils  141 . This allows for less wear and improved durability of the control valve  120 . Furthermore, greater control over the latching forces is advantageously achieved, as the thickness of nonmagnetic shims  300 ,  301  or non-magnetic coatings is easily controlled in response to variations in the developed or required latching force. 
     FIGS. 4 and 5 are exploded views of circle  45  in FIG.  3 . In FIG. 4, the groove  126   a  is offset from the cross bore  125  by a distance “a” when the spool  126  is in the closed, or deactivated, position. In FIG. 5, the groove  126   a  overlaps with the cross bore  125  by a distance “b” when the spool  126  is in the activated, or open, position. In the activated position, the groove  126   a  is also in fluid communication with the bore  122 . As seen in FIGS. 4 and 5, the groove  126   a  moves a total distance “s” between the open and closed positions of the spool  126 . 
     FIG. 6 shows an embodiment of the valve body used with the control valve of the present invention. In this embodiment, the body  104  includes a larger diameter central bore  108 , which provides more flow area for the working fluid. The body  104  further includes a cross bore  200  (leading to ambient), which has a connection to groove  202 . A front portion  204  of the spool  110  acts as a guide with a small passage to prevent piston effects. Control edges  206  and  208  of the spool  110  and control edges  210  and  212  of the body  104  are also provided. A ledge or stepped portion  214  is also provided in the valve body  108 . 
     As shown in FIG. 6, the control edge  206  is aligned with an edge of the groove  202 , and the control edge  212  is aligned with the working port  114 . In this position (that is, a second position), the return oil from the intensifier piston is in fluid communication with ambient via the bore  114 , the spool control edge  206 , the body control edge  210  to the groove  202 , and cross bore  200 . As shown in FIG. 7, to activate, the injection control valve opens to ambient so that the pressure in the space  118  drops. The spool then moves to the right, providing a connection between the inlet port  102  and the working port  114  by the control edges  212  of the body  104  and the control edge  208  of the spool  110 . The advantage of this embodiment is a larger flow area for given dimensions and less oil consumption to control the spool  110 . Additionally, the stop position (FIG. 6) is better defined with the stepped portion  214 . The closed position can also be more easily adjusted using shims (not shown). 
     Operation of the Oil Activated Fuel Injector of the Present Invention 
     In operation, a driver (not shown) will first energize a coil  141 . The energized coil  141  will then shift the spool  126  to an open position. In the open position, the groove  126   a  will overlap with the bore  122  and the cross bore  125 . This provides a fluid path for the working fluid to flow from the inlet port to ambient. In this position, the working fluid pressure within the pressure chamber  118  should be much lower than the rail inlet pressure. At this pressure stage, the spool  110  moves in the direction of arrow “A,” thus sealing the venting space  107 . This will allow the working fluid to flow between the inlet port  102  and the intensifier chamber via the working port  114 . 
     Once the pressurized working fluid is allowed to flow into the working port  114 , it begins to act on the piston  131  and the plunger  132 . That is, the pressurized working fluid will begin to push the piston  131  and the plunger  132  downwards, thus compressing the intensifier spring  133 . As the piston  131  is pushed downwards, fuel in the high pressure chamber  136  will begin to be compressed via the end portion  132   a  of the plunger  132 . A quantity of compressed fuel will be forced through e bores  138 ,  144 ,  146  into the heart chamber  152  surrounding the needle  156 . As the pressure increases further still, the fuel pressure will rise above a needle check valve opening pressure until the needle spring  150  is urged upwards. At this stage, the injection holes are open in the nozzle  140 , thus allowing a main fuel quantity to be injected into the combustion chamber of the engine. 
     To end the injection cycle, the driver will energize the closed coil  141 . The magnetic forced generated in the coil  141  will shift the spool  126  into the closed position, which, in turn, will offset the groove  126   a  from the cross bore  125  (FIG.  4 ). At this stage, the pressure will begin to increase in the pressure chamber  118 , forcing the spool  110  in the direction of arrow “B.” This will open the venting space  107  between the flat body area  106  and the leading edge  112   a  of the spool  110 . Also, the inlet port  102  will no longer be in fluid communication with the working port  114  and intensifier chamber. The working fluid within the intensifier chamber will then be vented to ambient, and the needle spring  150  will urge the needle  156  downward towards the injection holes of the nozzle  140 , thereby closing the injection holes. Similarly, the intensifier spring  133  will urge the plunger  132  and the piston  131  into the closed, or first, position adjacent to the control valve  120 . As the plunger  132  moves upwards, fuel will again begin to flow into the high pressure chamber  136  of the intensifier body. 
     While the invention has been described in terms of its preferred embodiment, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims. Thus, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting, and the invention should be defined only in accordance with the following claims and their equivalents.