Patent Publication Number: US-2011048379-A1

Title: Fluid injector with rate shaping capability

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a single fluid fuel injection system, and more particularly to fuel injection systems with rate shaping capabilities. 
     BACKGROUND 
     Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, exhaust a complex mixture of combustion related constituents. The constituents may be gaseous and solid material, which include nitrous oxides (NOx) and particulate matter. Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of NOx and particulate matter emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. 
     Engineers have come to recognize that undesirable engine emissions, such as NOx, particulate matter, and unburnt hydrocarbons, can be reduced across an engine&#39;s operating range with fuel injection systems with maximum flexibility in controlling injection timing, flow rate, injection quantity, injection rate shapes, end of injection characteristics and other factors known in the art. The desire for maximum flexibility is often tempered by the need to manage costs associated with fuel injection system components and manufacturability, the need for a robust system, the desire to reduce performance variations among fuel injectors in a system, and other factors known in the art. These issues were initially addressed by introducing an electrical actuator into fuel injectors in order to gain some threshold controllability over injection timing and quantity independent of engine crank angle. In the case of common rail fuel injection systems, this threshold control is often accomplished either by including an electronically controllable admission valve or an electronically controllable direct control needle valve. In the former case, the fuel injector&#39;s nozzle chamber is opened and closed to a fluid connection with the high pressure fuel rail by opening and closing an admission valve via an electrical actuator. In some instances, the admission valve is directly coupled to an electrical actuator, such as a solenoid, and in other instances the admission valve is pilot operated. In other common rail fuel injection systems, the nozzle chamber remains fluidly connected to the high pressure rail at all times, but the nozzles are opened and closed by relieving pressure on a closing hydraulic surface of a direct control needle valve. Although these common rail fuel injection systems have many desirable aspects, the ability to maximize flexibility in injection characteristics has remained elusive. 
     In one example common rail fuel injector disclosed in U.S. Pat. No. 5,984,200 to Augustin, a pilot operated admission valve supposedly includes features that allow the fuel injector to provide a relatively slow rate of injection toward the beginning of an injection event to produce what is commonly referred to in the art as a ramp shaped injection event. While it is true that ramp shaped injection events have proven effective in reducing undesirable emissions at some engine operating conditions, other engine operating conditions often demand different injection characteristics to effectively reduce undesirable emissions. Among these other desired injection characteristics are split injections, the ability to produce square front end injection rate shapes, and the ability to abruptly end injection events. Thus, it has proven problematic to produce common rail fuel injectors with an expanded range of capabilities. 
     The disclosed fuel injector with rate shaping capability is directed to overcoming one or more of the problems set forth above. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect, a fluid injector includes an injector body defining a high-pressure inlet, a nozzle supply passage, a low pressure drain and at least one nozzle outlet. A check speed control device having an upper surface, lower surface, and an orifice, positioned within a cavity of the fluid injector having an upper surface and a lower surface. The space between the upper surface of the check speed control device and upper surface of the cavity defines a first check control chamber. The space defined by the lower surface of the check speed control device and the lower surface of the cavity defines a second check control chamber. The first and second check control chambers are in fluid communication with one another via the orifice. The check speed control device is movable within the cavity between a first speed control position wherein at least a portion of the upper surface of the check speed control device is in contact with the upper surface of the cavity, and a second speed control position wherein at least a portion of the upper surface of the check speed control device is spaced away from the upper surface of the cavity. A control valve assembly having a valve member configured to selectively connect the high pressure inlet, the low pressure drain and first check control chamber. A check movable within the fluid injector between a first check position at which the check blocks the at least one nozzle outlet and a second check position at which the check at least partially opens the at least one nozzle outlet. The check further including at least one opening hydraulic surface exposed to a fluid pressure of the nozzle supply passage, and at least one closing hydraulic surface exposed to a fluid pressure of the second check control chamber. 
     In another aspect, a method of controlling a speed of a check in a fluid injector includes a step of providing a fluid injector having a cavity wherein said cavity includes an upper surface and a lower surface. A check speed control device having an upper surface, lower surface, and orifice, positioned within the cavity is also provided. The space between the upper surface of the check speed control device and the upper surface of the cavity defines a first check control chamber, and the space between the lower surface of the check speed control device and the lower surface of the cavity defines a second check control chamber. The first check control chamber and second check control chamber are fluidly connected to one another via the orifice. The check speed control device is movable within the cavity between a first speed control position wherein at least a portion of the upper surface of the check speed control device is in contact with the upper surface of the cavity and a second speed control position wherein at least a portion of the upper surface of the check speed control device is spaced away from the upper surface of the cavity. A check having a first check end and a second check end is also provided. The check is movable a check travel distance defined as a distance between a first check position wherein the first check end blocks a nozzle outlet of the fluid injector, and a second check position at which the first check end at least partially opens the nozzle outlet. The second check end includes at least one closing hydraulic surface, and is exposed to a fluid pressure of the second check control chamber. The speed of the check is limited over the check travel distance with the check speed control device, which controls the rate of fluid expelled from the cavity to a low pressure drain of the fluid injector. 
     In another aspect, an internal combustion engine includes an engine housing defining a plurality of engine cylinders, and a plurality of pistons each being movable within a corresponding one of the engine cylinders. A fuel system including a plurality of fuel injectors associated one with each of the plurality of engine cylinders, each of the fuel injectors including a cavity having an upper surface and a lower surface, and having a check speed control device having an upper and lower surface and an orifice positioned therein. The space between the upper surface of the check speed control device and the upper surface of the cavity defines a first check control chamber, and the space between the lower surface of the check speed control device and the lower surface of the cavity defines a second check control chamber. The first and second check control chambers are fluidly connected to one another via the orifice. Each of the plurality of fuel injectors further includes a check movable a check travel distance to control an injection of fuel into the associated engine cylinder and at least one closing hydraulic surface exposed to a fluid pressure of the second check control chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic schematic of a fuel system using a common rail fuel injector; 
         FIG. 2  is a cross section of a common rail fuel injector utilizing a check speed control device; 
         FIG. 3  is an inset of the injector of  FIG. 2  showing the detail of one embodiment of the check speed control device; 
         FIG. 4  is a plan view of an exemplary check speed control device; 
         FIG. 5  is a graph depicting various injection rate delivery curves; 
         FIG. 6  is a cross section of a nozzle assembly with an alternate embodiment of the check speed control device; 
         FIG. 7  is an inset of the nozzle assembly of  FIG. 6  showing the detail of the alternate embodiment of the check speed control device; 
         FIG. 8  is a schematic of a cross section of an alternate embodiment of a common rail fuel injector utilizing a check speed control device. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a fuel system utilizing a common rail fuel injector  22  is shown. A reservoir  10  contains fuel at an ambient pressure. A transfer pump  12  draws low-pressure fuel through fuel supply line  13  and provides it to high-pressure pump  14 . High-pressure pump  14  then pressurizes the fuel to desired fuel injection pressure levels and delivers the fuel to the fuel rail  16 . The pressure in fuel rail  16  is controlled in part by safety valve  18 , which spills fuel to the fuel return line  20  if the pressure in the rail  16  is above a desired pressure. The fuel return line  20  returns fuel to low-pressure reservoir  10 . 
     Fuel injector  22  draws fuel from rail  16  and injects it into a combustion cylinder of the engine (not shown). Fuel not injected by injector  22  is spilled to fuel return line  20 . Electronic Control Module (ECM)  24  provides general control for the system. ECM  24  receives various input signals, such as from pressure sensor  26  and a temperature sensor  28  connected to fuel rail  16 , to determine operational conditions. ECM  24  then sends out various control signals to various components including the transfer pump  12 , high-pressure pump  14 , and fuel injector  22 . 
     Referring to  FIG. 2 , the internal structure and fluid circuitry of each fuel injector  22  is illustrated. In particular, an injector body  29  defines a high-pressure fuel supply inlet  30  and a fuel supply passage  32 , which are interconnected. Fuel supply passage  32  is in fluid communication with nozzle passage  34 . Fuel supply passage  32  is also in fluid communication with check control line  36  via control valve supply line  38  and a control valve assembly  40 . The operation of the fuel injector  22  is controlled by at least one control valve assembly  40 , that includes a control valve member  42  that moves between a low pressure seat (not shown) and high pressure seat (not shown). In the embodiment shown control valve assembly  40  further includes a piston  45  coupled to an armature  46 . Piston  45  is operably coupled to electrical actuator  44 , through armature  46 . Piston  45  and armature  46  are normally biased downward by a biasing spring  48 . In the embodiment shown, control valve member  42  is in turn, biased downward to close low-pressure seat. When control valve member  42  is in a downward position closing low pressure seat, check control line  36  is in fluid communication with fuel supply passage  32  via control valve supply line  38 . When electrical actuator  44  is energized, the electromagnetic field generated by the electrical actuator  44  causes armature  46  and piston  45  to lift by overcoming the downward force applied by biasing spring  48 . When the downward force applied by biasing spring  48  and piston  45  is removed from control valve member  42 , another smaller biasing spring  49  positioned beneath the control valve member  42  lifts it upwards to close high pressure seat. When the high pressure seat is closed, check control line  36  is fluidly connected to drain outlet  50  via drain passage  52 . It will be appreciated by those skilled in the art that control valve assembly  40  could have many alternate embodiments without deviating from the scope and spirit of this disclosure. These alternate embodiments may include piezo actuation and other armature, spring, and control valve member configurations. 
     Referring now to  FIGS. 2 and 3 , check control line  36  and high-pressure branch passage  37 , are fluidly connected to a check speed control assembly  54  via an a-orifice  55  and a z-orifice  57 , respectively. Check speed control assembly  54  includes a check speed control device  56  disposed within a cavity  58  defined by injector body  29 . Check speed control device  56  may be generally disc-shaped and may include an upper raised surface or lip  62  around its periphery. Lip  62  has a predetermined width and is raised a predetermined height from an upper surface  68 . Upper surface  68  has an orifice  72  that is capable of providing fluid communication through the check speed control device  56 . It is contemplated that the orifice  72  may be centrally located on upper surface  68  any may be restricted or tapered such that it is wider at its top than at its bottom. In the embodiment shown in  FIG. 3 , orifice  72  has a relatively wide tube-shaped upper portion  73  and a relatively thin tube shaped bottom portion  75 . As shown in  FIG. 4 , check speed control device  56  may also have one or more radial guides  59 . The outer edges of the radial guides  59  may be contact with the side walls of cavity  58 . The radial guides  59  may be spaced apart from one another around the periphery of check speed control device  56 . 
     As shown in  FIG. 3 , the check speed control assembly  54  may also include a biasing spring  74  disposed between a check valve  76  and the check speed control device  56 . The biasing spring  74  biases the check speed control device  56  in an upward direction such that the lip  62  of the check speed control device  56  is in contact with the upper surface  82  of cavity  58 . A first check control chamber  84  is defined by the upper surface  82  of the cavity  58  and the upper surface  68  of the check speed control device  56 . A second check control chamber  86  is defined by the bottom surface  80  of the check speed control device  56  and the space of cavity  58  above check  76 . The check speed control device  56  is movable within cavity  58  between a first position wherein lip  62  is in contact with the upper surface  82  of cavity  58 , and a second position wherein lip  62  is out of contact with upper surface  82 . 
     The operation of injector  22  will now be explained. The opening and closing of check  76  is controlled in part by the presence of high-pressure fuel in nozzle passage  34 , check control line  36 , and high-pressure branch passage  37 . Check spring  88  and check speed control device  56  also play a role in the opening and closing of check  76 . When an injection event is not desired, control valve assembly  40  is not energized. High-pressure fuel enters injector  22  through high-pressure fuel inlet  30 . Pressurized fuel is provided to control valve assembly  40 , via control valve supply line  38 . In its deenergized state, control valve assembly  40  provides fluid communication between control valve supply line  38  and check control line  36 . Thus, high-pressure fuel is provided to the first check control chamber  84  via check control line  36  and the a-orifice  55 . Pressurized fuel is also provided to the first check control chamber  84  via nozzle passage  34 , high-pressure branch passage  37 , and z-orifice  57 . At least a portion of the high-pressure fuel that enters the first check control chamber  84  flows through orifice  72  and into the second check control chamber  86 . Pressurized fuel also reaches the second check control chamber  86  because as pressure builds in the first check control chamber  84 , the check speed control device  56  overcomes the force of biasing spring  74  and lip  62  unseats at least partially from the upper surface  82  of cavity  58 . As lip  62  unseats, fluid communication between the first and second check control chambers  84 ,  86  is provided via the one or more spaces in between the radial guides  59 . Once high-pressure fuel fills the first and second check control chambers  84 ,  86 , the pressure within the chambers equalizes and biasing spring  74  returns the check speed control device  56  to its first position. High-pressure fuel is also provided to a nozzle cavity  90  via nozzle passage  34 . 
     The high-pressure fuel that is provided to nozzle cavity  90  seeks to unseat check  76  by applying hydraulic pressure to various surfaces to the check  76 . These forces seek to lift check  76  off of its seat  92 . However, when control valve assembly  40  is deenergized, check  76  remains seated because the hydraulic forces applied to the check are countered by the high pressure fuel provided to the first control chamber via branch passage  37  and check control line  36 . Additionally, check spring  88  is positioned such that it biases check  76  downward toward its closed or first position. 
     When injection is desired, control valve assembly  40  is energized. Specifically, the electrical actuator  44  is energized, causing armature  46  and piston  45  to overcome the force of biasing spring  48  and lift. Control valve member  42  is then moved to its upper position or high-pressure seat by the upward force applied by biasing spring  49 . In this position, pressurized fuel from control valve supply line  38  is no longer in fluid communication with check control line  36 . Instead, check control line  36  is now in fluid communication with drain passage  52 . High-pressure fuel within the first check control chamber  84  vents to drain outlet  50  through the a-orifice  55 . At the same time, high-pressure fuel is also being provided to the first check control chamber  84  via the z-orifice  57 . The a-orifice  55  may be slightly larger than the z-orifice  57 . Thus, fuel leaves the first check control chamber  84  faster than it is being provided thereto. This causes a pressure drop within the first check control chamber  84 . At the same time, pressurized fuel is still being provided to nozzle cavity  90  via nozzle passage  34 . Because of the drop of pressure in the first check control chamber  84 , the pressure in the nozzle cavity  90  than that of the first control chamber. The higher pressure in the nozzle chamber now applies hydraulic forces to the various surfaces of the check  76  causing it to lift off of seat  92 . As the check  76  is unseated, pressurized fuel is injected into a combustion chamber (not shown) through the tip  94 . More specifically, the pressurized fuel is injected through at least one orifice  96  in the tip  94 . 
     The speed at which check  76  raises determines how much and how quickly fuel is delivered to a combustion chamber. In normal common rail injectors without a check speed control device of some type, the check  76  opens fully almost immediately, thereby providing a square shaped main injection curve as shown by curve  98  in  FIG. 5 . However, the injector embodied in  FIGS. 2-4 , has a ramped shaped delivery as shown by ramp shaped main injection curve  100 . This desirable ramped shaped main injection curve  100  is provided because high pressure fuel in the second check control chamber  86  prevents the check  76  from opening fully too quickly. Specifically, as the check  76  is raised, the high-pressure fuel in the second check control chamber  86  has nowhere to go except to press check speed control device  56  against the top of the cavity  58 . Biasing spring  74  also works to press check speed control device  56  against the top of cavity  58 . With check speed control device pressed against the top of cavity  58 , the pressurized fuel in the second check control chamber  86 , still seeking a place to escape, then squeezes out orifice  72  and ultimately out the a-orifice  55  to drain outlet  50 . The bottleneck caused by orifice  72  prevents check  76  from opening fully too quickly. Thus, a ramped shaped main injection curve  100  is produced. 
     When it is desirable to stop injection, electrical actuator  44  is deenergized. As the electromagnetic field generated by electrical actuator  44  dissipates, the force of biasing spring  48  acts on piston  45  and armature  46 . As piston  45  applies a downward force on control valve member  42 , the force of the smaller biasing spring  49  is overcome and control valve member  42  is returned to close the low pressure seat. When the control valve member  42  is on the low pressure seat, the check control line  36  is once again in fluid communication with the high pressure fuel supply passage  32 . Ultimately, the first and second check control chambers,  84 ,  86  are refilled with pressurized fuel, and the injector  22  is once again ready for an injection event. 
     Referring now to  FIGS. 6 and 7 , which depict an alternative embodiment of the check speed control assembly  154 , check control line  136  and high-pressure branch passage  137 , are fluidly connected to a check speed control assembly  154  via an a-orifice  155  and a z-orifice  157 , respectively. Check speed control assembly  154  includes a check speed control device  156  disposed within a cavity  158  defined by injector body  129 . Check speed control device  156  may be generally disc-shaped and may include an upper raised surface or lip  162  around its periphery. Lip  162  has a predetermined width and is raised a predetermined height from an upper surface  168 . Upper surface  168  has an orifice  172  that is capable of providing fluid communication through the check speed control device  156 . It is contemplated that the orifice  172  may be restricted or tapered such that it is wider at its top than at its bottom. In the embodiment shown in  FIGS. 6 and 7 , orifice  172  is wide enough so that a head  177  of check  176  may be movably disposed therein with little to no clearance. The head  177  may be generally disc shaped and have an upper surface  179  and a lower surface  181 . Head  177  may be of a predetermined thickness that is approximately equal to the length of orifice  172 . Head  177  may sit atop a tapered neck  183  that has a diameter smaller than that of the head  177 . Because of the tapered nature of neck  183 , the outer portion of the lower surface  181  forms a flange that acts as a hydraulic surface. Although not shown, it is contemplated that check speed control device  156  may also have one or more radial guides with a similar shape and function as those depicted in  FIG. 4 . As will be apparent to those skilled in the art, the shape of head  177  does not have to be disc like in nature. Head  177  may be any of a myriad of shapes so long as orifice  172  is shaped to match. 
     The check speed control assembly  154  may also include a biasing spring  174  disposed between a check  176  and the check speed control device  156 . The biasing spring  174  biases the check speed control device  156  in an upward direction such that the lip  162  of the check speed control device  156  is in contact with the upper surface  182  of cavity  158 . A first check control chamber  184  is defined by the upper surface  182  of the cavity  158  and the upper surface  168  of the check speed control device  156 . A second check control chamber  186  is defined by the bottom surface  180  of the check speed control device  156  and the space of cavity  158  above check  176 . 
     During an injection event, the embodiment of the check speed control device  156  depicted in  FIGS. 6 and 7  operates in a manner similar to the previously disclosed embodiments. In general, check speed control device  156  operates to prevent check  176  from opening fully too quickly. During injection, fuel is allowed to flow out of the a-orifice  155  to drain outlet (not shown). This relieves the pressure within the first check control chamber  184 . As this is happening, pressure within the nozzle cavity  190  builds and applies force on the hydraulic opening surfaces of check  176 . The force applied to check  176  is sufficient to overcome the downward force of check spring  188 , thereby causing check  176  to unseat. As check  176  unseats fuel is injected into the combustion chamber (not shown). 
     As check  176  is raised, the high-pressure fuel in the second check control chamber  186  has nowhere to go except to press check speed control device  156  against the top of the cavity  158 . Biasing spring  174  also works to press check speed control device  156  against the top of cavity  158 . With check speed control device pressed against the top of cavity  158 , the pressurized fuel in the second check control chamber  186 , still seeking a place to escape, then applies force on the lower surface  181  of head  177 . As the head  177  is pressed upward through orifice  172  the overall speed of check  176  is slowed down and the check  176  is prevented from opening fully too quickly. Thus, the desired ramped shaped main injection curve  100  may be produced. 
     In yet another embodiment, as shown in  FIG. 8 , an injector  222  with increased rate shaping flexibility is disclosed. Injector  222  may have an internal structure and fluid circuitry similar to the injector disclosed in  FIG. 2 , with the exception that this embodiment has a second valve control assembly  340 . In particular, an injector body  229  defines a high-pressure fuel supply inlet  230  and a fuel supply passage  232 , which are interconnected. Fuel supply passage  232  is in fluid communication with nozzle passage  234 . Fuel supply passage  232  is also in fluid communication with check control line  236  via control valve supply line  238  and a first control valve assembly  240 . 
     In the embodiment disclosed, first control valve assembly  240  is a three way valve that includes a control valve member  242  that moves between a low pressure seat (not shown) and high pressure seat (not shown). In the embodiment shown, control valve member  242  is coupled to an armature  246 . Armature  246  is operably coupled to electrical actuator  244 , through armature  246 . Control valve member  242  and armature  246  are normally biased downward by a biasing spring  248 . When control valve member  242  is in a downward position closing low pressure seat, check control line  236  is in fluid communication with fuel supply passage  232  via control valve supply line  238 . When electrical actuator  244  is energized, the electromagnetic field generated by the electrical actuator  244  causes armature  246  and control valve member  242  to lift by overcoming the downward force applied by biasing spring  248 . During the energized state, control valve member  242  lifts upwards to close high pressure seat, such that check control line  236  is fluidly connected to drain outlet  250  via drain passage  252 . It will be appreciated by those skilled in the art that first control valve assembly  240  could have many alternate embodiments without deviating from the spirit of this disclosure. These alternate embodiments may include piezo actuation and other armature, spring, and control valve member configurations. 
     Check control line  236  and high-pressure branch passage  237 , are fluidly connected to a check speed control assembly  254  via an a-orifice  255  and a z-orifice  257 , respectively. Check speed control assembly  254  includes a check speed control device  256  disposed within a cavity  258  defined by injector body  229 . Check speed control device  256  may be generally disc-shaped and may include an upper raised surface or lip  262  around its periphery. Lip  262  has a predetermined width and is raised a predetermined height from an upper surface  268 . Upper surface  268  has an orifice  272  that is capable of providing fluid communication through the check speed control device  256 . 
     The check speed control assembly  254  may also include a biasing spring  274  disposed between a check valve  276  and the check speed control device  256 . The biasing spring  274  biases the check speed control device  256  in an upward direction such that the lip  262  of the check speed control device  256  is in contact with the upper surface  282  of cavity  258 . A first check control chamber  284  is defined by the upper surface  282  of the cavity  258  and the upper surface  268  of the check speed control device  256 . A second check control chamber  286  is defined by the bottom surface  280  of the check speed control device  256  and the space of cavity  258  above check  276 . 
     In this embodiment, the second check control chamber  286  is fluidly coupled to a drain outlet  243  via an s-orifice  261 , a vent passage  247  and the second control valve assembly  340 . The second control valve assembly  340  may be a two way valve including a control valve member  342  coupled to an armature  346 . Armature  346  is operably coupled to an electrical actuator  344 . Control valve member  342  and electrical actuator  344  are normally biased downward by a biasing spring  348 . Because second control valve assembly  340  is a simple two way valve, when control valve member  342  is in a downward position there is no fluid communication between vent passage  247  and drain outlet  243 . Conversely, when electrical actuator  344  is energized, and armature  346  and control valve member  342  are lifted, fluid communication between vent passage  247  and drain outlet  243  is established. It will be appreciated by those skilled in the art that control valve assembly may have alternate embodiments without deviating from the scope and spirit of this disclosure. Likewise, it will be appreciated that drain outlet  243  may be routed within injector to be either separate or coincide with drain outlet  250 . 
     Common rail injectors naturally produce square shaped delivery curves. The addition of a check speed control device such as that disclosed herein changes the natural injection profile of a common rail injector from square to ramped. However, there are times when it may be desirable for a common rail injector to provide a square shaped fuel delivery profile. For example, it is believed that injections that produce square shaped post injection curves  101  may help to reduce smoke. (See  FIG. 5 ). Thus, it may be desirable to inject fuel in a manner that produces a ramped shaped main injection curve  100  and a square shaped post injection curves  101 . The addition of the second control valve assembly  340  allows for increased flexibility with respect to the rate shape of fuel delivered to a combustion chamber. The disclosed injector  222  can perform both square and ramped shaped injections. 
     Those skilled in the art will appreciate that when the first control valve assembly  240  is energized and the second control valve assembly  340  is not energized that injector  222  will function virtually identically to the previously disclosed and described injector  22 . Thus, a ramped shaped delivery curve will be obtained. 
     The production of a square shaped main injection curve  98  or a square shaped post injection curve  101  using injector  222  will now be explained. When injection is desired, first control valve assembly  240  is energized. Specifically, the electrical actuator  244  is energized, causing armature  246  and control valve member  242  to overcome the force of biasing spring  248  and lift. Control valve member  242  is now in its upper position or high-pressure seat. In this position, pressurized fuel from control valve supply line  238  is no longer in fluid communication with check control line  236 . Instead, check control line  236  is now in fluid communication with drain passage  252 . High-pressure fuel within the first check control chamber  284  vents to drain outlet  250  through the a-orifice  255 . At the same time, high-pressure fuel is also being provided to the first check control chamber  284  via the z-orifice  257 . The a-orifice  255  may be slightly larger than the z-orifice  257 . Thus, fuel leaves the first check control chamber  284  faster than it is being provided thereto. This causes a pressure drop within the first check control chamber  284 . At the same time, pressurized fuel is still being provided to nozzle chamber  290  via nozzle line  234 . Because of the drop of pressure in the first check control chamber  284 , the pressure in the nozzle chamber  290  than that of the first control chamber. The higher pressure in the nozzle chamber now applies hydraulic forces to the various surfaces of the check  276  causing it to lift off of seat  292 . As the check  276  is unseated, pressurized fuel is injected into a combustion chamber (not shown) through the tip  294 . More specifically, the pressurized fuel is injected through at least one orifice  296  in the tip  294 . 
     As previously disclosed, a ramped shaped curve is achieved because the pressurized fuel in the second check control chamber  286  is bottlenecked when seeking to escape through a relatively small orifice  272 . However, when the second control valve assembly  340  is energized, fluid communication between vent passage  247  and drain outlet  243  is established. Thus, the pressurized fuel in the second check control chamber  286  that would otherwise be bottlenecked at orifice  272  is now free to flow out of the s-orifice  261 ; into the vent passage; and ultimately out drain  243 . In the absence of pressurized fuel in the second check control chamber  286 , there is nothing preventing check  276  from quickly opening fully. Thus, a square shaped post injection curve  101  is produced. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure finds a preferred application in common rail fuel injection systems. In addition the present disclosure finds preferred application in single fluid, namely fuel injection, systems. Although the disclosure is illustrated in the context of a compression ignition engine, the disclosure could find application in other engine applications, including but not limited to spark ignited engines. The disclosed fuel injectors have the capability of producing ramp injection shapes, square injection shapes, split injections, and relatively abrupt injection endings. Furthermore, these different injection profiles can be selected independent of engine operating condition. Finally, like many electronically controlled fuel injection systems, the fuel injectors  22 ,  222  have relatively precise control over injection timing and quantity, which can be selected independent of engine speed and crank angle. 
     A ramp shaped main injection curve  100  and a square shaped post injection curve  101  may be achieved using a common rail injector  222 . When a ramped shaped main injection curve  100  is desired first control valve assembly  240  is energized while second control valve assembly  340  remains unenergized. Specifically, the electrical actuator  244  is energized, causing armature  46  and control valve member  242  to overcome the force of biasing spring  248  and lift. Control valve member  242  is now in its upper position or high-pressure seat. In this position, pressurized fuel from control valve supply line  238  is in fluid communication with drain passage  252 . High-pressure fuel within the first check control chamber  284  vents to drain outlet  250  through the a-orifice  255 . At the same time, high-pressure fuel is also being provided to the first check control chamber  284  via the z-orifice  257 . The a-orifice  255  may be slightly larger than the z-orifice  257 . Thus, fuel leaves the first check control chamber  284  faster than it is being provided thereto. This causes a pressure drop within the first check control chamber  284 . At the same time, pressurized fuel is still being provided to nozzle chamber  290  via nozzle line  234 . Because of the drop of pressure in the first check control chamber  284 , the pressure in the nozzle chamber  290  than that of the first control chamber. The higher pressure in the nozzle chamber now applies hydraulic forces to the various surfaces of the check  276  causing it to lift off of seat  292 . As the check  276  is unseated, pressurized fuel is injected into a combustion chamber (not shown) through the tip  294 . More specifically, the pressurized fuel is injected through at least one orifice  296  in the tip  294 . 
     A ramped shaped main injection curve  100  is provided because high-pressure fuel in the second check control chamber  286  prevents the check  276  from opening fully too quickly. Specifically, as the check  276  is raised, the high-pressure fuel in the second check control chamber  286  has nowhere to go except to press check speed control device  256  against the top of the cavity  258 . Those skilled in the art will recognize that pressurized fuel within the second check control chamber  286  cannot escape through the s-orifice  261  because second control valve assembly  340  is not energized. Thus, there is no fluid communication between the second check control chamber  286  and drain outlet  243 . With check speed control device  256  pressed against the top of cavity  258 , the pressurized fuel in the second check control chamber  286 , still seeking a place to escape, then squeezes out orifice  272  and ultimately out the a-orifice  255  to drain outlet  250 . The bottleneck caused by orifice  272  prevents check  276  from opening fully too quickly. Thus, a ramped shaped main injection curve  100  is produced. 
     Deenergizing electrical actuator  244  ends the main injection. As the electromagnetic field generated by electrical actuator  244  dissipates, control valve member  242  is returned to close the low-pressure seat (not shown). When the control valve member  242  is on the low-pressure seat, the check control line  236  is once again in fluid communication with the high-pressure fuel supply passage  232 . Ultimately, the first and second check control chambers,  284 ,  286  are refilled with pressurized fuel, and the injector  222  is once again ready for an injection event. 
     A square shaped post injection curve  101  may be achieved by simultaneously actuating control valve assemblies  240  and  340 . The actuation of control valve assembly  240  raises check valve member to its high-pressure seat and thus establishes fluid communication between the first check control chamber  284  and drain outlet  250 . Pressurized fuel within the first check control chamber  284  is allowed to escape through the a-orifice  255 . At the same time, the actuation of second control valve assembly  340  raises control valve member  342  to its open position. Thus fluid communication is established between the second check control chamber  286  and drain outlet  243 . Pressurized fuel is now allowed to escape through the s-orifice  261 . 
     As pressurized fuel is allowed to escape from the first and second check control chambers  284 ,  286 , high-pressure fuel is continually delivered to nozzle chamber  290 . As the pressure builds in nozzle chamber  290  force is applied to the hydraulic opening surfaces of check  276  thereby causing check  276  to lift. As the check  276  is unseated, pressurized fuel is injected into a combustion chamber (not shown) through the tip  294 . More specifically, the pressurized fuel is injected through at least one orifice  296  in the tip  294 . Check  276  quickly opens fully because there is little to no counterbalancing pressure in the first and second check control chambers  284 ,  286 . Because check  276  quickly opens fully, a square shaped post injection curve  101  is delivered. 
     The above description is intended for illustrative purposes only and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate the various modifications that can be made to the illustrated embodiments without departing from the spirit and scope of the disclosure, which is defined in the terms of the claims set forth below.