Abstract:
A two stage intensifier capable of multiple intensification rates comprises a stepped top portion and a shoulder portion, each being actuated by separate fluid passages. A stepped top portion is received into an upper bore of a piston bore and a shoulder is received into a lower bore. The stepped top forms a seal with the upper bore to prevent direct fluid communication between a first actuation cavity above the stepped top and a second actuation cavity above the shoulder.

Description:
TECHNICAL FIELD 
     The present invention relates generally to an intensifier piston capable of multiple intensification rates. 
     BACKGROUND 
     Intensifier pistons can be used in a variety of applications in which it is necessary to intensify the pressure of a fluid from a first pressure to a second pressure. For example, intensifier pistons are very common in valve actuators and fuel injectors. Specifically, in a fuel injector, the intensifier is used to increase the fuel pressure from low or medium pressure to high pressure for fuel injection. 
     Intensifier pistons in a fuel injector can be cam operated or hydraulically operated. With a hydraulically operated intensifier, the top of the intensifier piston is exposed to a pressurized fluid causing the piston to move downward, thereby moving a plunger and pressurizing low pressure fuel in a pressurization chamber. The rate of intensification depends upon the pressure of the actuation fluid on top of the intensifier piston as well as the area of the intensifier piston exposed to the actuation fluid. 
     When intensifiers were first used in fuel injection systems, they were only able to provide one rate of intensification per injection event. This initial problem was solved with a development of a stepped top piston as illustrated in U.S. Pat. No. 5,826,562 issued Chen et al. The stepped top piston allows two different intensification rates during a single injection event. Actuation fluid is exposed to a first area, on the stepped top, causing a first intensification rate. As the piston moves downward, the stepped top comes out of its bore exposing a second actuation area, the shoulder of the intensifier, to actuation fluid and increasing the intensification ratio. Although this is a beneficial design, improvements can be made. First, there is no ability to choose intensification rates; every injection event gets both intensification profiles. Second, the design is inefficient with its actuation fluid usage because the second area must be filled with fluid as the piston moves down before the second area becomes effective. This results in the need for extra actuation fluid in the cavity, a slight delay in increased pressurization and difficulty in fully returning the plunger between injections, especially in cold conditions. 
     The present invention is designed at overcoming one or more of the above problems. 
     SUMMARY OF THE INVENTION 
     In the first embodiment of the present invention, a fuel injector comprises a barrel defining a first fluid passage, a second fluid passage, and a piston bore with an upper bore and a lower bore. An intensifier piston includes a shoulder and a stepped top. A first actuation cavity is defined by the upper bore, the stepped top and the first fluid passage and a second actuation cavity is defined by the lower bore, the shoulder and the second fluid passage. The piston is slidably received in the piston bore, wherein the shoulder is received in the lower bore and the stepped top is received in the upper bore. The stepped top has a first surface open to fluid pressure in the first actuation cavity and the shoulder has a second surface open to the fluid pressure in the second actuation cavity. The piston is movable between the first position and the second piston and the stepped top is sealable with the upper bore when the piston moves between the first position and the second position. Additionally, the fuel injector comprises a source of actuation fluid, a drain passage, and a control valve to open and close fluid communication between the first and second fluid passages and the source of actuation fluid and the drain. 
     In a second embodiment of the present invention, a method for operating an intensifier piston, having a first effective area and a second effective area, comprises delivering a first fluid flow from a common fluid source to the first area, moving the intensifier piston a first pre-selected distance, delivering a second fluid flow from the common fluid source to the second area, moving the intensifier piston a second pre-selected distance, and maintaining the first area in direct fluid isolation from the second area. 
     In the third embodiment of the present invention, a method for operating an intensifier piston system includes delivering a first signal, moving a valve to a first position response to the first signal, allowing fluid flow to a first effective area of an intensifier piston, delivering a second signal, moving the valve to a second position response to the second signal and allowing the fluid flow to a second effective area of the intensifier piston. 
     In a fourth embodiment of the present invention, an intensifier assembly comprises a barrel defining a first fluid passage, a second fluid passage and a piston bore having an upper bore and a lower bore. An intensifier piston includes a shoulder and a stepped top. A first actuation cavity is defined by the upper bore, the stepped top and the first fluid passage. A second actuation cavity is defined by the lower bore, shoulder and the second fluid passage. The piston is slidably received in the piston bore, wherein the shoulder is received in the lower bore and the stepped top is received in the upper bore. The stepped top has a first surface open to fluid pressure in the first actuation cavity and a shoulder has a second surface open to fluid pressure in the second actuation cavity. Finally, the piston is movably between a first position and a second position wherein the stepped top is sealable with the upper bore when the piston moves between the first position and the second position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic cross-section of a fuel injector according to the present invention. 
     FIG. 2 is a diagrammatic illustration of a rate shape according to one embodiment of the present invention. 
     FIG. 3 is a diagrammatic illustration of a rate shape according to one embodiment of the present invention. 
     FIG. 4 is a diagrammatic illustration of a rate shape according to one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a diagrammatic cross-section of a fuel injector  20  according to the present invention. Fuel injector  20  includes a control valve  22  an upper body  24  and a nozzle assembly  26 . Supply line  28  provides actuation fluid through upper body  24  to control valve  22 . 
     Control valve  22  includes a valve body  30 , a three position spool  32  and first valve spring  34  and second valve spring  36 . Spool  32  is actuated by solenoid  38  against the biasing force of first and second valve springs  34  and  36 . Spool valve  32  controls fluid communication of actuation fluid between supply line  28  or drain  40  and first pressure passage  42  and second pressure passage  44 . 
     First pressure passage  42  and second pressure passage  44  carry actuation fluid from control valve  22  through barrel  46 , in the upper body  24 , to piston  48 . Piston  48  is the intensifier piston which intensifies fuel within injector  20 . Piston  48  includes a stepped top  50 , with a first actuation area  52 , and a shoulder  53 , with a second actuation area  54 . Piston  48  is slidably received within piston bore  55 , which has an upper bore  56  and a lower bore  57 . The stepped top  50  is received in upper bore  56  and shoulder  53  is received in lower bore  57 . A first actuation cavity  58  is formed by stepped top  50 , upper bore  56 , and first pressure passage  42 . A second actuation cavity  59  is formed by shoulder  53 , lower bore  56  and second pressure passage  44 . Finally, stepped top  50  forms a seal with upper bore  56  to prevent direct fluid communication between first actuation cavity  58  and second actuation cavity  59 . 
     When first or second actuation areas are exposed to actuation fluid from first or second pressure passages  42  and  44 , piston  48  is moved downward, actuating plunger  60 . When actuated, plunger  60  pressurizes fuel in pressurization chamber  62 . Piston  48  is generally biased in its upward position by piston return spring  63  and piston return spring  63  returns piston  48  to it upward position when first and second pressure passages  42  and  44  are vented to drain  40 . 
     Fuel for injection enters the injector through fuel fill line  64  and passes through ball check  65  into pressurization chamber  62 . Pressurized fuel from pressurization chamber  62  moves through fuel passage  66  and into fuel chamber  68 . Check valve  70 , biased in the close position by check spring  72 , controls fluid communication of fuel between fuel chamber  68  and orifice  74 . Check valve  70  is moved into the open position when fuel in fuel chamber  68  exceeds the spring force of check spring  72 ; called the valve opening pressure (VOP). When check valve  70  is open, fuel injection into the combusting chamber (not shown) can occur. When pressurization stops and the fuel pressure in chamber  68  decreases, check valve  70  is closed by check spring  72  and injection is stopped. 
     Industrial Applicability 
     Intensifier piston  48  provides great flexibility during injection events by allowing for a first pressurization rate, a second pressurization rate or multiple pressurization rates during a single injection event. Different pressurization rates are achieved by controlling how much area of piston  48  is exposed to pressurized fluid. Control valve  22  plays an important role in controlling the flow of actuation fluid between the stepped top  50  and the shoulder  53 . As illustrated in FIG. 1, a single solenoid and a three position spool  32  are is used to control first pressure passage  42  and second pressure passage  44 ; however, alternative control valve embodiments could be used. For example, a multiple control valve scheme could be used in which two solenoids are used to control two, two position spool or poppet valves. 
     In order to achieve only a first pressurization rate during a single injection event, high pressure actuation fluid is supplied through supply line  28  to control valve  22 . It should be noted that the high pressure actuation fluid is preferably lubrication oil but other fluids, such as diesel fuel or another engine fluid, could be used as well. In between injection events, spool  32  is at rest in its first position in which supply line  28  is blocked and both first pressure passage  42  and second pressure passage  44  are open to drain  40 . In order to begin injection at the first pressurization rate, solenoid  38  is energized at a first current level causing spool  32  to move to a second position in which first pressure passage  42  is open to actuation fluid within supply line  28  and second pressure passage  44  is still blocked from supply line  28  and open to drain  40 . In this configuration, actuation fluid travels through first pressure passage  42  into first actuation cavity  58  where it can act upon the first area  52  of stepped top  50 . This causes piston  48 , and therefore plunger  60 , to move downwards, against the force of piston return spring  63 , and pressurize fuel located in pressurization chamber  62 . The pressurized fuel travels through fuel passage  66  into fuel chamber  68 . The pressurized fuel then acts upon check valve  70 , and pushes check valve  70  up against the force of check spring  72 . When the check  70  moves upward, orifice  74  is open allowing fluid communication between fuel chamber  68  and the combustion chamber (not shown). When it is desirable to stop injection, solenoid  38  is de-energized, moving spool  32  back to its first position in which supply line  28  is blocked and both first pressure passage and second pressure passage first pressure passage  42  and second pressure passage  44  are open to drain  40 . When first pressure passage  42  is open to drain, the first actuation fluid cavity  58  is also open to drain and the force of piston return spring  63  pushes piston back to its original or upward position. Additionally, the fuel pressure in fuel chamber  68  is decreased and check spring  72  forces check valve  70  down, closing orifice  74 . 
     In order to maintain only the first pressurization rate through the injection event, the stepped top  50  must remain within upper bore  56  for the entire duration of the injection event. If stepped top  50  were to leave upper bore  56 , actuation fluid from first actuation cavity  58  would be in direct communication with second actuation cavity  59 , allowing actuation fluid to act upon second area  54  of shoulder  53 . This would expose a larger area of piston  48  to actuation fluid and cause piston  48  to increase its pressurization rate. Additionally, it is important that stepped top  50  form an adequate seal with upper bore  56  to prevent direct fluid communication between first actuation cavity  58  and second actuation cavity  59  even when stepped top  50  is in upper bore  56 . 
     In order to obtain only a second pressurization rate during a single injection event, solenoid  38  is energized only with a second current level causing spool  32  to move from its first position, in which both first pressure passage  42  and second pressure passage  44  are open to drain and supply line  28  is blocked, to a third position in which drain  40  is blocked and both first pressure passage  42  and second pressure passage  44  are open to actuation fluid in supply line  28 . In this configuration, actuation fluid travels through both first pressure passage  42  and second pressure passage  44 , exposing first actuation cavity  58  and second actuation cavity  59  to actuation fluid. Therefore, first area  52  of stepped top  50  and second area  54  of shoulder  53  are exposed to high pressure fluid within first actuation cavity  58  and second actuation cavity  59 . This causes piston  48 , and subsequently plunger  60 , to move downward, against the force of piston return spring  63  at a second pressurization rate. This pressurization rate is greater than the first pressurization rate because a greater area of piston  48  is exposed to high pressure actuation fluid. Injection of the fuel and the termination of the injection event are similar to that described above. 
     Multiple pressurization rates can also be achieved during a single injection event. Initially, when solenoid  38  is not energized, spool  32  is in its first position in which actuation fluid from supply line  28  is blocked in both first pressure passage  42  and second pressure passage  44  are open to drain  40 . Solenoid  38  is then energized to a first current level causing spool  32  to move to a second position in which first pressure passage  42  is open to actuation fluid in supply line  28  and second pressure passage  44  is still blocked from supply line  28  and open to drain  40 . As described above, this creates a first pressurization rate for the fuel within the pressurization chamber  62 . As the injection event progresses, solenoid  38  can be energized to a second current level causing spool  32  to move from its second position to its third position in which both first pressure passage  42  and second pressure passage  44  are open to actuation fluid in supply line  28  and drain  40  is blocked. This increases the area of piston  48  that is exposed to actuation fluid causing piston  48  to move downward at a greater rate and increase its pressurization rate of the fuel within pressurization chamber  62 . Injection is stopped when solenoid  38  is de-energized, causing spool  32  to move from its third position back to its first position in which supply line  28  is blocked and both first pressure passage  42  and second pressure passage  44  are opened to drain  40 . By venting first actuation cavity  58  and second actuation cavity  59 , allowing piston return spring  63  moves piston  48  back to its original upward position. 
     Multiple pressurization rates during a single injection event gives the injector flexibility in the injection rate shape. FIGS. 2-4 illustrate different possible rate shapes. In FIGS. 2-4, ( a ) is the current level to the solenoid  28 , ( b ) is the spool  32  motion (spool position) and ( c ) is the injection rate. In all cases the variables are plotted on the vertical axis against time on the horizontal axis. FIG. 2 illustrates a boot injection. FIG. 3 illustrates a pilot and a square and FIG. 4 illustrates a pilot, boot and a post. It should be noted that FIGS. 2-4 illustrate current levels for a spool valve that has initial pull current levels and then a decreased holding level. For example, in FIG. 2 a  a first current level is applied to move spool  32  from its first position to its second position. The current level is then reduced to a holding current which increases efficiency but still holds spool  32  in the second position. A third current level is then applied to move spool  32  from the second position to the third position. Again, after moving the spool, the current level is reduced to a fourth current level to hold the spool in the third position. Finally, current is stopped to move the spool  32  back to the first position. As stated previously, the exact workings of the valve are not critical to the piston&#39;s  48  operation. In the previous descriptions, differentiating between pulling and holding currents was ignored to simplify the description but these current levels as illustrated in FIGS. 2-4 could be used to control spool  32  and ultimately piston  48 . 
     By having two separate areas of piston  48  exposed to actuation fluid through separate means, first actuation cavity  58  and second actuation cavity  59 , plunger  60  return is improved. In previous designs all the actuation fluid acting on the piston needed to be pushed out of the main fluid passage (on top of the stepped piston) or through a rate shaping orifice, which restricted flow to and from the shoulder of the piston. With the present design, both stepped top  50  and shoulder  53  are associated with actuation cavities  58  and  59  that have full sized fluid passages in communication with drain  40 . This allows piston return spring  63  to quickly and smoothly return piston  48  to its original, upward position because the actuation cavities  58  and  59  vent quickly. This in turn, helps the injector during cold starts by insuring piston  48  is quickly returned even though the actuation fluid may be more viscous than normal. 
     The present description has illustrated a conventional check valve nozzle that opens or closes depending upon when fuel pressure is greater than the valve opening pressure (the force of the check spring  72 ). However, the present invention could be used with a direct operated check nozzle as well. A direct operated check would open or close independently when fuel is pressurized. Typically a direct operated check would have its own control valve associated with it, allowing independent pressurization and injection signals to be delivered to the injector. 
     The present invention has also been illustrated as a way to obtain multiple pressurization rates within a hydraulically actuated electronically controlled fuel injector; however, the present intensifier configuration can be used anywhere multiple pressurization rates are necessary including intensified common rail systems and general hydraulic valve actuators. For example, this intensifier design could be implemented in an actuation valve in which different opening positions are achieved based upon pressurization of an actuation fluid. 
     It should be understood that the above description be intended for illustrative purposes only and is not intended to limit the scope of the present invention in anyway. Thus, those skilled in the art will appreciate that other aspects, objects and advantages of the invention can be obtained from a study of the drawings, the disclosure and the claims.