JP2012202408A - Electronically-controlled fuel injector for large diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize a control flow rate of an electronically-controlled valve necessary to start a fuel injector and to optimize performance of an electronically-controlled fuel injector for a large diesel engine.SOLUTION: The electronically-controlled fuel injector includes a control chamber 44 in which an oil pressure in a delivery chamber 24 generates a first oil pressure force that pushes a needle 30 in a direction of an open position thereof and which is connected to a fuel supply line 26 via an inflow limiter 48 and is also connected to an exhaust line 50 via a flow limiter 52. The electronically-controlled fuel injector also includes an electronically-controlled type control valve 54 in which the oil pressure in the control chamber 44 generates a second oil pressure force that pushes the needle 30 in a direction of a closed position thereof and which selectively opens and closes oil pressure communication between the control chamber 44 and a low pressure capacity 14. The inflow limiter 48 has a variable choke 60 which can move between a choke position corresponding to a fully closed position of the needle 30 and a non-choke position corresponding to an initial opening position of the needle 30.

Description

  The present invention relates to an electronically controlled fuel injection device for a large diesel engine. In particular, the present invention relates to a fuel injection device for a common rail injection system of a large two-stroke diesel engine such as a diesel engine for marine propulsion.

  A common rail high pressure injection system includes a pump (usually having a constant displacement) designed to pressurize fuel in a high pressure accumulator (common rail) and provides a fuel injection device. The fuel injection device includes a valve seat and a needle that can move between a closed position and an open position in the fuel injection device main body. The position of the needle is determined by the strength of the two oil pressures, which are generated by the action of pressurized fluid on the appropriate affected surface (affected surface).

  The pressurized fuel in the delivery chamber upstream of the valve seat acts in the direction of raising the needle from the valve seat. Therefore, this pressurized fuel acts in the opening direction. The electronically controlled control valve adjusts the hydraulic pressure of the control chamber, which generates a force that acts in the direction of closing the fuel injector. Activating the control valve reduces the pressure in the control chamber to a point where the force acting to open the injector seat exceeds the force acting to close the injector seat, raises the needle from the valve seat, and fuels Let spray.

  The operating principle of the electronically controlled fuel injection device assumes that the control chamber is connected to the high pressure line by an inflow limiter and connected to the exhaust line by an outflow limiter.

  The size of the inflow limiter and the outflow limiter is controlled to a value low enough to ensure that the closing force is less than the opening force when the control valve is opened. It must be chosen so that the pressure in the chamber can drop. When this happens, the needle opens the injector seat, thus allowing fuel transfer to a chamber downstream of the injector seat (so-called sac), and fuel is injected into the combustion chamber through the fuel hole Is done.

  When the fuel injector is opened, the sack is pressurized to a significant portion of the available rail pressure, resulting in an increased force acting in the opening direction. This is because the surface affected by the high pressure fuel covers the entire cross-sectional area of the needle.

  When the fuel injector needs to be closed, the position of the control valve is reset, thereby disabling the connection between the control chamber and the low pressure fuel line. The pressure in the control chamber rises again, but for the reasons explained above, before the needle begins to move again in the direction of the injector seat, it needs to reach a value much higher than that required to start the opening phase. is there.

  The speed of the needle during the closing phase is constrained by technical requirements and the desired value can be obtained by optimizing the size of the flow restrictor relative to the cross-sectional area of the needle in the control chamber.

  The only parameter that can be varied to achieve the required vacuum in the control chamber to begin opening the fuel injector is the size of the spill limiter. The greater the difference between the pressure effect area in the opening direction and the pressure effect area in the closing direction when closing the needle, the larger the outflow limiter should be.

  This means that the size of the flow restrictor increases as it approaches the ratio of the needle seat diameter to the control chamber diameter.

  Larger spill limiters pose more problems with respect to control valve design and injection efficiency. This is because in a typical two-way poppet valve used for these applications, the pressure in the control chamber acts in the direction of opening the valve. Larger effluent limiters require larger poppets (otherwise the main restriction is passing through the valve), which is the cause of the greater control chamber pressure impact. Become. Eventually, this increases the force demand on the spring (to keep the valve closed when there is no command signal) and the force demand on the actuator needed to overcome this spring force. This also means that larger components need to be used. And this is not always acceptable due to geometric constraints on the engine and the requirement for speed of the control valve (eg, larger and stronger solenoids are usually slower).

  Furthermore, since a larger spill amount limiter performs injection control, the flow rate injected by the fuel injection device increases. This is clearly a source of efficiency loss. This is because the energy expended to pressurize the fuel is wasted by spreading it through the control circuit.

  These problems are even more serious in large two-stroke diesel engines. This is because the ratio of seat diameter to control chamber diameter is very large. This is due to the presence of a slide valve on the needle used to reduce unburned hydrocarbons (UHC) and particle emissions, causing the seat diameter to be greater than the slide valve diameter. This causes the selection of a larger spill limiter with a higher injection flow rate.

  These problems make it difficult to apply the indicated common rail technology to fuel injectors for large two-stroke engines.

  The object of the present invention is to provide a solution to the above-mentioned problems.

  According to the invention, this object is achieved by a fuel injection device comprising the features of claim 1.

  The present invention makes it possible to optimize the performance of an electronically controlled fuel injection device for a large diesel engine. In particular, the present invention makes it possible to minimize the control flow that the electronic control valve must inject in order to keep the fuel injector open during the injection cycle.

Control flow reduction provides two main advantages.
(I) A smaller and faster electronic actuator (solenoid or piezoelectric stack) that can be incorporated into the fuel injector body can be used.
(Ii) The efficiency of the fuel injection device increases. That is, this leads to an increase in overall engine efficiency as the auxiliary power demand is reduced.

Further features and advantages of the present invention will become apparent in the course of the following detailed description, given by way of non-limiting example only, with reference to the accompanying drawings.
FIG. 1 is a circuit diagram showing the operating principle of a fuel injection device according to the present invention. FIG. 2 is an axial sectional view of the first embodiment of the fuel injection device according to the present invention. FIG. 3 is an enlarged view of a portion indicated by an arrow III in FIG. FIG. 4 is an axial cross-sectional view of a second embodiment of the fuel injection device according to the present invention. FIG. 5 is an enlarged view of a portion indicated by an arrow V in FIG. FIG. 6 is an enlarged view of a portion indicated by an arrow VI in FIG.

  Referring to FIG. 1, a fuel injection system for a diesel engine is indicated by reference numeral 10. The fuel injection system includes a supply pump 12. The supply pump 12 sucks fuel from the low pressure fuel tank 14 and conveys the pressurized fuel to the high pressure common rail 16. The common rail 16 is connected to a plurality of high-pressure pipes 18 (only one of these high-pressure pipes 18 is shown in FIG. 1), and each of the plurality of high-pressure pipes 18 has its own fuel injection. It is connected to the device 20.

  The fuel injection device 20 includes a main body 22 having a delivery chamber 24 connected to the high-pressure pipe 18 through a fuel supply line 26. The delivery chamber 24 is provided with a conical valve seat 28.

  The fuel injection device 20 includes a needle 30. The needle 30 has a conical sealing surface 32 that extends through the delivery chamber 24 and cooperates with the valve seat 28. The needle 30 is movable along the vertical axis A between a closed position and an open position. In the closed position, the sealing surface 32 contacts the valve seat 28, and in the open position, the sealing surface 32 is spaced apart from the valve seat 28. The spring 34 pushes the needle 30 in the direction of the closed position. The hydraulic pressure of the fuel contained in the delivery chamber 24 generates a first oil pressure that pushes the needle 30 to its open position.

  The body 22 includes a nebulizer 36 having a longitudinal hole or sack 38 fluidly connected to the delivery chamber 24 via a valve seat 28. The sprayer 36 is provided with one or more injection holes 40. The needle 30 is provided with a slide valve 42 entering the sack 38.

  The fuel injection device 20 includes a control chamber 44 sealed from the delivery chamber 24. The control chamber 44 is connected to the fuel supply line 26 via an intake line 46 having an inflow amount limiter 48. The control chamber 44 is also connected to an exhaust line 50 having an outflow limiter 52. The hydraulic pressure in the control chamber 44 generates a second hydraulic pressure that pushes the needle 30 toward its closed position.

  An electronically controlled two-way control valve 54 selectively opens and closes the hydraulic connection between the control chamber 44 and the low pressure capacity (eg, formed by the tank reservoir 14). The control valve 54 is controlled by an electronic actuator 56, and the electronic actuator 56 receives a control signal by an electronic control unit 58.

  When the control valve 54 is closed, the pressure in the control chamber 44 and delivery chamber 24 is equal to the rail pressure. Assuming that the pressure impact surface in the control chamber 44 is greater than the pressure impact surface in the delivery chamber, the force pushing the needle 30 toward the closed position is greater than the force pushing the needle 30 toward the open position. large. When the control valve is opened, the pressure in the control chamber 44 decreases and the force pushing the needle 30 towards the open position becomes greater than the force pushing the needle 30 towards the closed position. Accordingly, the needle 30 moves away from the valve seat 28 and the pressurized fuel contained in the delivery chamber 24 is placed in the sack 38 of the sprayer 36 so that the needle is sufficiently large for the slide valve to remove the covering from the injection hole 40. When it is lifted, fuel is injected through the injection hole 40.

  In order to begin opening the needle 30, the pressure in the control chamber 44 against the valve must be reduced to a certain value. This value is well below the value sufficient to keep the needle 30 in the open position after the needle 30 has lifted enough to pressurize the sack 38.

  According to the prior art, this would require a large spill limiter 52. However, a large spill limiter 52 is actually required only during a fraction of the injection phase. In fact, as soon as the needle 30 is lifted sufficiently to pressurize the sack 38, the force pushing the needle 30 towards the open position becomes very large, maintaining the pressure in the control chamber 44 at a high level. Can do.

  Based on these considerations, the present invention provides that the inflow limiter 48 is between a choke position corresponding to the fully closed position of the injection needle 30 and a non-choke position corresponding to the initial open position of the needle 30. It has a variable choke part that is movable. Therefore, when the needle 30 contacts the valve seat 28, the inflow limiter 48 is largely choked. The choke is then weakened and eventually removed at the first stage of the needle stroke.

  In FIG. 1, the arrow 60 schematically represents the variable choke portion of the inflow limiter 48, and the dotted line 62 represents the fact that the variable choke portion 60 is controlled by the movement of the needle 30.

  In a preferred embodiment of the present invention, the inflow limiter 48 includes at least one orifice that is movable with the needle 30, and the variable choke portion 60 is relative to the first surface movable with the needle 30 and the body 22. A gap formed between the second surface and the fixed second surface.

  In the solution according to the invention, a small spill restrictor 52 is sufficient to bring the pressure in the control chamber 52 to a level sufficient to cause the fuel injector to open. Ideally, if the inflow limiter 48 is fully choked, any size outflow limiter 52 will be sufficient to completely drain the control chamber 44 (only a matter of time). ). As a result, when the needle 30 lifts and the opening force increases due to sack pressurization, the inflow limiter 48 is fully opened and the pressure in the control chamber 44 is close to the level at which the closure phase will begin. Fixed by value.

  In addition to solving the problem of high fuel flow discharged through a large spill restrictor, the solution according to the invention has the further advantage of reducing the switching time of the fuel injector. This is because the pressure level in the control chamber 44 during injection is maintained close to the level required to cause fuel injector closure, which is important in multi-shot and ultra-low load operation. .

  A first embodiment of the invention is shown in FIG.

  In the example shown in FIG. 2, the main body 22 includes a lock nut 64, a lower main body portion 66, a middle main body portion 68, and an upper main body portion 70. The lower main body 66 and the middle main body 68 are fixed to the upper main body 70 by a lock nut 64. The sprayer 36 is fixed to the lower main body 66 by a screw bushing 72.

  In the following detailed description and claims, references to "lower", "upper", "above", "below", etc. are shown in the figures. Reference is made to the position of the fuel injector that is generally associated with the position of use. However, it will be appreciated that the fuel injector can be installed at any location and that references to spatial locations are not intended to limit the scope of the present invention.

  The upper part of the needle 30 is slidably guided in a bushing 74 supported by the lower body part 66. The spring 34 is housed in the delivery chamber 24 and is compressed between the bushing 74 and the radial shoulder of the needle 30.

  The control chamber 44 is formed by the upper front surface of the needle 30, the cylindrical wall portion of the bushing 74, and the front surface of the middle main body portion 68. The outflow limiter is formed by an orifice 52 formed in the middle main body.

  The control valve 54 includes a stem 76 that is movable in the axial direction. The stem 76 is slidable in a guide hole 78 of the middle main body 68. In this exemplary embodiment, the electric actuator 56 has a magnetic core 80 and a coil 82.

  The inflow limiter 48 includes one or more orifices 84 formed in the area of the needle 30 having the conical sealing surface 32. The (each) orifice 84 has a radially inner end that communicates with an elongated hole 86 formed in the needle 30. The upper end of the elongated hole 86 opens into the control chamber 44.

  As best shown in the enlarged detail of FIG. 3, the radially outer end of the (each) orifice 84 is just above the area where the conical sealing surface 32 contacts the valve seat 28 and the needle 30. The conical sealing surface 32 opens.

  The variable choke portion 60 is formed by a gap 88 formed between the conical sealing surface 32 of the needle 30 and the valve seat 28. The size of this gap 88 is minimal when the needle 30 is closed and increases as the needle moves away from the valve seat 28. Thus, the (each) orifice 84 is choked when the needle is closed and becomes non-choke after the initial opening of the needle 30.

  The elongated hole connecting the inflow restrictor 48 to the control chamber 44 reduces the pressure in the control chamber 44 for the time required for the descending wavefront to travel from the control chamber 44 to the outlet and rear of the inflow restrictor 48. In contrast, by delaying the response of the inflow limiter 48, it plays an active role in ensuring the unique functionality of the present invention. This allocates sufficient time to pressurize the sack 38, resulting in the successful opening of the needle 30 with the minimum run size of the spill limiter 52.

  A notable advantage of this solution is that the cost of implementation is negligible due to the use of seats already present in the fuel injector.

  Compared to the conventional structure, the injection device using the present invention can operate at a control flow rate of up to 60% less. This is equivalent to a 0.26% increase in overall engine performance.

  The main advantage gained by such optimization is that the force required to seal and operate the control valve 44 is reduced and a fast and compact actuator that can be integrated into the fuel injector body. Can be used. This is essential in order to obtain a fuel injection device that can operate with the short switching time required in the multi-shot mode.

  A second embodiment of the invention is shown in FIG. Elements corresponding to elements disclosed above are indicated with the same reference numerals.

  The solution shown in FIG. 4 is a larger conventional common rail fuel injector arrangement, in which a separate control piston 90 is used to keep the needle 30 closed. The lower end of the control piston 90 is in contact with the upper end of the needle 30. The control piston 90 moves in the axial direction together with the needle 30. The main body 22 includes a sleeve 92 disposed between the lower main body portion 66 and the middle main body portion 68. The spring 34 is attached to a low pressure chamber formed between the sleeve 92 and the control piston 90.

  The control chamber 44 is formed by the upper front surface of the control piston 90, the cylindrical wall portion of the sleeve 92, and the front surface of the middle main body portion 68. The outflow limiter is formed by an orifice 52 formed in the middle main body 68. The control valve 54 is not changed compared to the first embodiment.

  As better shown in FIG. 5, the flow restrictor 48 is formed in the first annular groove 94 formed in the cylindrical inner surface 96 of the sleeve 92 and in the cylindrical outer surface 100 of the control piston 90. And a second annular groove 98.

  The first annular groove 94 is connected to the fuel supply line 26 by a first orifice 102 formed in the sleeve 92. The second annular groove 98 is connected to the control chamber 44 by a second orifice 104 and a third orifice 106 formed in the control piston 90.

  When the needle 30 is closed, the first annular groove 94 and the second annular groove 98 are offset from each other, as shown in FIG. As the control piston 90 moves upward, the first annular groove 94 and the second annular groove 98 are at least partially overlapped.

  As better shown in FIG. 6, the variable choke 60 is formed by an annular gap 108 formed between the cylindrical inner surface 96 of the sleeve 92 and the cylindrical outer surface 100 of the control piston 90. . When the needle 30 is closed, the control chamber 44 leads to the fuel supply line 26 through two paths. Of these two paths, one path includes an annular gap 108, a first annular groove 94, and a first orifice 102, and the other path includes a second orifice 104, a third orifice 106, and a second annular path. A groove 98, an annular gap 108, a first annular groove 94 and a first orifice 102 are included.

  The annular gap 108 chokes the inflow limiter 48 at the closed position of the needle 30. During the initial opening of the needle 30, the flow restrictor choke is removed because the first annular groove 94 and the second annular groove 98 overlap.

  The size of the annular gap 108 and the length of overlap between the first annular groove 94 and the second annular groove 98 is such that the effective flow rate through the flow restrictor 48 is established before the sack 38 is established. Conveniently selected to allow pressurization.

  The second embodiment is simpler in construction and provides further flexibility in selecting different diameters for the needle 30 and the control chamber 44. Compared to the first embodiment, the second embodiment has a high pressure fuel leak when the fuel injector is closed due to the fuel flow in the gap between the needle, the control piston and the respective sleeve. This has the disadvantage that this leaked high-pressure fuel finally reaches the spring chamber and is discharged into the tank.

Claims (11)

An electronically controlled fuel injection device for a large diesel engine,
A body (22) having a delivery chamber (24) connected to a fuel supply line (26) and provided with a conical valve seat (28);
The needle (30) has a conical sealing surface (32) extending through the delivery chamber (24) and cooperating with the valve seat (28), the needle (30) having the conical sealing surface. A vertical axis between a closed position where (32) contacts the conical valve seat (28) and an open position where the conical sealing surface (32) is spaced apart from the conical valve seat (28). Movable along (A), the hydraulic pressure in the delivery chamber (24) generates a first hydraulic pressure that pushes the needle (30) towards its open position;
A control chamber (44) connected to the fuel supply line (26) via an inflow limiter (48) and connected to the exhaust line (50) via an outflow limiter (52); The hydraulic pressure in this control chamber (44) generates a second hydraulic pressure that pushes the needle (30) towards its closed position;
Fuel injection comprising an electronically controlled control valve (54) for selectively opening and closing hydraulic communication via the exhaust line (50) between the control chamber (44) and the low pressure capacity (14) In the device
The inflow limiter (48) is a variable choke that is movable between a choke position corresponding to the fully closed position of the needle (30) and a non-choke position corresponding to the initial opening of the needle (30). A fuel injection device comprising a portion (60). The fuel injection device according to claim 1,
The inflow limiter (48) has at least one orifice (84, 104, 106) movable along with the needle (30), and the variable choke portion (60) includes the needle (30). And a gap (88, 108) formed between the movable surface (32, 100) and the surface (28, 96) fixed to the main body (22). A fuel injection device. The fuel injection device according to claim 2, wherein
The inflow limiter (48) has at least one orifice (84) formed in the area of the needle (30) provided with the conical sealing surface (32). apparatus. The fuel injection device according to claim 3, wherein
The orifice (84) has a radially inner end that communicates with an elongated hole (86) formed in the needle (30), the elongated hole (86) being connected to the control chamber ( 44) A fuel injection device having an upper end opened in the inside. The fuel injection device according to claim 3, wherein
The orifice (84) is radially outwardly open to the conical sealing surface (32) of the needle (30) directly above the area where the conical sealing surface (32) contacts the valve seat (28). The fuel-injection apparatus characterized by having the edge part. The fuel injection device according to any one of claims 2 to 5,
The variable choke portion (60) is formed by a gap (88) formed between the conical sealing surface (32) of the needle (30) and the conical valve seat (28). A fuel injection device. The fuel injection device according to claim 2, wherein
The control piston (90) is slidably guided in the sleeve (92) and is movable with the needle (30). The control piston (90) is connected to the control chamber (44) and the above-mentioned control piston (90). A fuel injection device arranged between the needle (30) and the fuel injection device. The fuel injection device according to claim 7, wherein
The inflow limiter (48) includes a first annular groove (94) formed in a cylindrical inner surface (96) of the sleeve (92) and a cylindrical outer surface (100) of the control piston (90). And a second annular groove (98) formed in the fuel injection device. The fuel injection device according to claim 8, wherein
The first annular groove (94) is connected to the fuel supply line (26) by a first orifice (102) formed in the sleeve (92), and the second annular groove (98) is controlled. A fuel injection device connected to the control chamber (44) by a second orifice (104) and a third orifice (106) formed in the piston (90). The fuel injection device according to claim 9, wherein
At the closed position of the needle (30), the first annular groove (94) and the second annular groove (98) are offset from each other, and at the position of the initial opening of the needle (30), the first annular groove (98). The fuel injection device, wherein the annular groove (94) and the second annular groove (98) overlap at least partially. The fuel injection device according to any one of claims 8 to 10,
The variable choke portion (60) has an annular gap (108) formed between the cylindrical inner surface (96) of the sleeve (92) and the cylindrical outer surface (100) of the control piston (90). ) Is formed. The fuel injection device characterized by the above-mentioned.

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