Fuel injector with rate shaping control through piezoelectric nozzle lift

Abstract: A fuel injector (10) includes an injector body (11) that defines a nozzle outlet (14). A needle valve member (40) is mounted in the injector body (11) and moveable a lift distance between an open position in which the nozzle outlet (14) is open, and a closed position in which the nozzle outlet (14) is blocked. A piezoelectric actuator (30) is mounted in the injector body (11) and is moveable a piezo distance between an off position and an on position. A coupling linkage (18) interconnects the needle valve member (40) to the piezoelectric actuator (30) such that a movement of the piezoelectric actuator (30) is multiplied into a larger movement of the needle valve member (40).

Description: The present invent relates generally to fuel injectors, and more particularly to fuel injectors that include a piezoelectric actuator. Although there exists a wide variety of mechanisms for pressurizing fuel in fuel injection systems, almost all fuel injectors include a spring biased needle check valve to open and close the nozzle outlet. In almost all fuel injectors, the needle valve member is only stoppable at two different positions: fully open or fully closed. Because the needle valve members in these fuel injectors are not stoppable at a partially open position, fuel injection mass flow can only be controlled through changes in fuel pressure. E.g. EP 0 826 876 A1 discloses a fuel injection device which utilizes the fuel pressure in a balance chamber for closing an open-close valve to prevent fuel leakage from the open-close portion. When the open-close valve is opened, a valve stem of the open-close valve piercing through the exhaust passage in the control member moves toward the balance chamber. A valve head opens the port of the exhaust passage on the balance chamber side to lower the fuel pressure in the balance chamber, with the result that a needle valve lifts, injection the fuel. When the open-close valve is closed by a return spring, the fuel pressure in the balance chamber acts on the valve head to urge the open-close valve into the valve closing direction, preventing the leakage of fuel through the open-close valve. Over time, engineers have come to recognize that undesirable exhaust emissions can be reduced by having the ability to produce at least three different rate shapes across the operating range of a given engine. These rate shapes include a ramp, a boot shape and square fuel injection profiles. In addition to these rate shapes, there is often a need for the injector to have the ability to produce split injections in order to further improve combustion efficiency at some operating conditions, such as at idle. While some fuel injectors have the ability to produce split injections and produce some rate shaping, a fuel injector that can reliably produce all of these rate shaping effects remains somewhat elusive. While it has been proposed in the art that piezoelectric actuators could be employed in fuel injection systems, the use of piezoelectric actuators to directly control needle lift has proven somewhat problematic. First, this is due in part to the fact that only so much space is available within a fuel injector to place a piezoelectric crystal stack. Given the space limitations, the maximum piezoelectric deformation possible in the space available is generally on the order of less than about one hundred microns. Since typical needle valve lifts are on the order of several hundreds of microns, direct piezoelectric control of needle valve lift is not realistic without making substantial - and likely unrealistic - changes in the nozzle area of a fuel injector. The present invention is directed to overcoming these and other problems associated with the use of piezoelectric actuators in controlling needle valve lift within fuel injectors. These problems are solved in accordance with a fuel injector as defined in claim 1. An example of a fuel injector according to the present invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a sectioned side diagrammatic view of a fuel injector according to the present invention. Figure 2 is a graph of piezoelectric crystal voltage versus time for an example injection event according to one aspect of the present invention. Figure 3 is a graph of injection mass flow rate versus time for the example fuel injection event of Figure 2. Referring now to Figure 1, a fuel injector 10 includes an injector body 11 made up of various components attached together in a manner well known in the art. Injector body 11 defines a high pressure inlet 12 connected to a source of high pressure fuel 21 via a high pressure supply passage 20. Injector body 11 also defines a low pressure return drain 13 connected to a drain return reservoir 23 via a drain passage 22. Fuel injector 10 is preferably mounted in an internal combustion engine in a conventional manner, such as being positioned so that nozzle outlet 14 is in the combustion space, in the case of a diesel type engine. In order to control the opening and closing of nozzle outlet 14, a needle valve member 40 is movably positioned in injector body 11. Needle valve member 40 is normally biased downward by a compression spring 47 to a position in contact with needle seat 45 to close nozzle outlet 14. Needle valve member 40 includes an outer lifting hydraulic surface 41 exposed to fluid pressure in nozzle chamber 16, and in inner lifting hydraulic surface 43 exposed to fluid pressure in the space between needle seat 45 and nozzle outlet 14. Nozzle chamber 16 is connected to the high pressure inlet 12 via a nozzle supply passage 15. In addition to lifting hydraulic surfaces 41 and 43, needle valve member 40 includes a closing hydraulic surface 44 located on the upper side of a piston portion 42 of the needle valve member. Closing hydraulic surface 44 is exposed to the fluid pressure in a needle control chamber 18, which is defined by injector body 11. Needle control chamber 18 is connected to nozzle supply passage 15 via a branch passage 17. Needle control chamber 18 is also connected to a low pressure area 28 via a drain return passage 27 and an outlet control passage 25. Drain return passage 27 and outlet control passage 25 are separated by a valve seat 26. Low pressure area 28 is connected to low pressure return drain 13 as shown. In order to control the flow of fuel from needle control chamber 18 into outlet control passage 25, a piezoelectric actuator 30 is mounted in injector body 11 and operably attached to a control valve member 31. Piezoelectric actuator 30 moves control valve member 31 with respect to valve seat 26 to open and close outlet control passage 25. When no voltage is applied to piezoelectric actuator 30, control valve member 31 is pushed into contact with seat 26 to close control outlet passage 25. When a voltage is applied to the piezoelectric crystal stack, the crystal(s) deform and move control valve member 31 out of contact with valve seat 26. Those skilled in the art will recognize that the distance that the control valve member 31 moves will be a function of voltage applied to piezoelectric actuator 30. This distance will in turn determine the flow area past seat 26 into drain return passage 27. By having the ability to control the flow area past seat 26, the fluid pressure within needle control chamber 18 can be controlled relative to the relatively high pressure existing in nozzle supply passage 15. This is accomplished at least in part by properly sizing the flow area through branch passage 17 such that the fluid pressure in needle control chamber 18 is always less than the fluid pressure in nozzle supply passage 15 when piezoelectric actuator 30 is energized and the control valve member 31 is at least partial opened. When piezoelectric actuator 30 is de-energized so that seat 26 is closed, the fluid pressure in needle control chamber 18 is the same as that in nozzle supply passage 15. Piezoelectric actuator 30 has the ability to control the lift of needle valve member 40 indirectly through the coupling linkage provided by the fluid pressure existing in needle control chamber 18. When actuator 30 is de-energized, outlet control passage 25 is closed and the needle valve member 40 is held in its downward closed position since the fluid pressure in needle control chamber 18 and nozzle supply passage is the same but the area of closing hydraulic surface 44 is much greater than the area of outer lifting hydraulic surface 41. In order to lift needle valve member 40 upward to open seat 45 and allow fuel to spray out of nozzle outlet 14, there must be a net upward force on needle valve 40. In this embodiment, there are four different forces acting on needle valve member 40: a downward spring force from compression spring 47, a downward hydraulic force acting on closing hydraulic surface 44, an upward force acting on opening hydraulic surface 41 and an upward force acting on inner opening hydraulic surface 43. In order to stop needle valve member 40 at a partially opened position, these four forces must achieve an equilibrium. The present invention has the ability to stop the needle valve member at a plurality of partially opened positions, between its closed position and a fully opened position, by adjusting the voltage on the piezoelectric actuator 30, which controls the fluid pressure in needle control chamber 18. An equilibrium at any partially opened position can be accomplished by knowing that the fluid pressure acting on inner opening hydraulic surface 43 is related to the flow area past seat 45 and hence the lift distance of needle valve member 40. The higher that the needle valve member 40 is lifted off of seat 45, the higher the pressure acting on inner lifting hydraulic surface 43. However, the higher the needle valve member 40 is lifted, the higher the spring force acting in a closing direction. Thus, by appropriately sizing compression spring 47 the area of closing hydraulic surface 44, the opening hydraulic surfaces 41 and 43 as well as the variable flow area past seat 45, the flow area to nozzle outlet 14 can be made as a direct function of the voltage applied to piezoelectric actuator 30. Thus, the piezoelectric actuator 30 is able to indirectly control the lift distance of needle valve member 40 via the coupling linkage provided by needle control chamber 18. It should be pointed out, though, that the maximum lift distance of needle valve member 40 is many times the maximum movement distance of piezoelectric actuator 30 and control valve member 31. Thus, each movement of piezoelectric actuator 30 is multiplied into a larger movement of needle valve member 40. The high pressure fuel entering fuel injector 10 at inlet 12 can be pressurized in a wide variety of known ways, including but not limited to hydraulic pressurization, cam driven pressurization, or even a high pressure reservoir fed by a high pressure pump. Between injection events, piezoelectric actuator 30 is de-energized, outlet control passage 25 is closed and needle valve member 40 is in its downward closed position. Each injection event is initiated by applying a desired voltage to piezoelectric actuator 30 that corresponds to a desired flow rate out of nozzle outlet 14. Referring now in addition to Figures 2 and 3, a split injection that includes a small pilot injection and a ramp shaped main injection is illustrated. As can be seen, the pilot injection event is accomplished by applying a relatively low voltage to piezoelectric actuator 30 for a brief amount of time. At this relatively low voltage, control valve member 31 lifts a known distance off of seat 26 to allow an amount of flow from needle control chamber 18 to low pressure area 28. This causes the pressure in needle control chamber 18 to drop relative to that in nozzle supply passage 15. This results in a net upward force on needle valve member 40 causing it to begin to lift. The needle valve member stops at a partially opened position when the various hydraulic and spring forces come to a new equilibrium, which is a function of the applied voltage on piezoelectric actuator 30. The pilot portion of the injection event is ended by de-energizing the piezoelectric actuator 30 for an amount of time. The main injection event having a ramp shape is accomplished by again energizing piezoelectric actuator 30 with a steadily growing voltage. The needle valve member 40 responds by lifting in proportion to the applied voltage so that the flow area past needle seat 45 steadily grows to increase the mass flow rate out of nozzle outlet 14. The maximum flow rate is achieved when the flow area past seat 45 is about equal to the flow area out of nozzle outlet 14. At this point, the applied voltage remains constant for the remainder of the injection event. The injection is ended by abruptly dropping the voltage in piezoelectric actuator 30 to zero. This causes outlet control chamber 25 to abruptly close and the pressure in needle control chamber 18 to abruptly rise to equalize with that nozzle supply passage 15. This results in the hydraulic force acting on closing hydraulic surface 44 rising rapidly to quickly move needle valve member 40 downward to a closed position to end the injection event. The above description is intended for illustrated purposes only and is not intended to limit the scope of the present invention in any way. For instance, while the illustrated embodiment uses pressurized fuel on both the opening and closing hydraulic surfaces of the needle valve, those skilled in the art will appreciate that a different fluid, such as pressurized lubricating oil, could be used on the closing hydraulic surface without otherwise altering the performance of the present invention. Thus, those skilled in the art will appreciate that various modifications could be made to the illustrated embodiment without departing from the scope of the present invention, which is defined in terms of the claims set forth below.

Claims: A fuel injector (10) comprising: an injector body (11) defining a nozzle outlet (14); a nozzle chamber (16) connected to a high pressure inlet (12); a needle valve member (40) mounted in said injector body (11) and being movable a lift distance between an open position in which said nozzJe outlet (14) is open, and a closed position in contact with a needle seat (45) in which said nozzle outlet (14) is blocked, said needle valve member (40) having a closing hydraulic surface (44), said needle valve member (40) including an outer lifting hydraulic surface (41) and an inner lifting hydraulic surface (43) biasing said needle valve member (40) toward said open position, said outer lifting hydraulic surface being exposed to fluid pressure in said nozzle chamber (16), and said inner lifting hydraulic surface (43) being exposed to fluid pressure in a space between said needle seat (45) and said nozzle outlet (14); a compression spring (47) biasing said needle valve member (40) toward said closed position; a needle control chamber (18) connected to said high pressure inlet (12) via a branch passage (17); said needle control chamber (18) providing a fluid pressure coupling linkage interconnecting said closing hydraulic surface (44) of said needle valve member (40) to a low pressure area (28) by way of an outlet control passage (25) and a drain return passage (27), a piezoelectric actuator (30) mounted in said injector body (11and operably attached to a control valve member (31) positioned to controllably engage a valve seat (26) located between said outlet control passage (25) and said drain return passage (27) to open and close said outlet control passage (25), wherein when no voltage is applied to said piezoelectric actuator (30), said control valve member (31) is pushed into contact with said valve seat (26) to close said outlet control passage (25), and when a voltage is applied to said piezoelectric actuator (30), said control valve member (31) is moved out of contact with said valve seat (26) wherein the distance that the control valve member (31) moves is a function of the voltage applied to said piezoelectric actuator (30); wherein said coupling linkage multiplies the movement of said piezoelectric actuator (30) into a larger movement of said needle valve member (40); and wherein said needle valve member (40) is stoppable in a partially open position between said open position and said closed position when a voltage is applied to said piezoelectric actuator (30) to responsively move said controt valve member (31) to a partially opened position such that the forces acting on the needle valve member (40) due to the compression spring (47) and the downward hydraulic force acting on the closing hydraulic surface (44), and the upward hydraulic forces acting on the outer and inner lifting hydraulic surfaces (41, 43) achieve an equilibrium. The fuel injector (10) of claim 1, wherein the flow area past said valve seat (26) is a function of a positioning of said piezoelectric actuator (30). The fuel injector (10) of claim 1 or 2, wherein said needle valve member (40) is held in said closed position at least in part by said coupling linkage when said piezoelectric actuators (30) is in said The fuel injector (10) of any of claims 1 to 3, wherein said outer lifting hydraulic surface (41) and an inner lifting hydraulic surface (43) of said needle valve member (40) are exposed to different fluid pressures depending upon a positioning of said needle valve member (40). The fuel injector (10) of any of claims 1 to 4, wherein when a voltage is applied to said piezoelectric actuator (30), said needle valve member (40) responds by lifting in proportion to the applied voltage.

Inventors: RAJAGOPALAN SENTHILKUMAR, SHINOGLE RONALD D, RAJAGOPALAN, SENTHILKUMAR, SHINOGLE, RONALD D.
Applicants: CATERPILLAR INC, CATERPILLAR INC.
Application year: 1999
Main classification: F02M45
IPC codes: F02M45, F02M47, F02M59