Method for determining closing time of electromagnetic fuel injector

Abstract

To provide a method for determining a closing point of an electromagnetic fuel injector.SOLUTION: In this method, at the time of starting an injection operation, a positive voltage is applied to a coil of an electromagnetic actuator, so that a current for determining an opening operation of an injection valve flows through the coil. At the time of completing the injection operation, a negative voltage is applied to the coil of the electromagnetic actuator, so as to cancel the current flowing through the coil. After cancelling the current flowing through the coil, first time-variant voltage progress is detected at least at one end of the coil of the electromagnetic actuator. The time-variant voltage progress for starting is compared to the time-variant progress for comparison, and a closing timing of an electromagnetic fuel injector is determined based on comparison between the time-variant voltage progress for starting and the time-variant voltage progress for comparison.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] This application claims priority to Italian Patent Application No. 102018000005760, filed May 28, 2018, the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002] The present invention relates to a method for determining the closing time of an electromagnetic fuel injector.

[0003] An electromagnetic fuel injector (such as described in EP 1 619 384 A1) comprises a cylindrical tubular body with a central feed channel performing the function of a fuel conduit and terminating in an injection nozzle controlled by an injection valve operated by an electromagnetic actuator. The injection valve comprises a plunger rigidly connected to the movable armature of the electromagnetic actuator so as to be moved between the closed and open positions of the injection nozzle by the action of the electromagnetic actuator against the action of a closing spring which presses the plunger towards the closed position. The valve seat is defined in a sealing element having the shape of a disk, which seals the central channel of a support body at its underside and is crossed by the injection nozzle. The electromagnetic actuator comprises a coil arranged on its outer surface around the tubular body and a fixed pole made of ferromagnetic material and arranged inside the tubular body to magnetically attract the movable armature.

[0004] The injection valve is normally closed by the closing spring urging the plunger to a closed position in which the plunger presses against the valve seat of the injection valve and the moving armature is spaced from the fixed pole. To open the injection valve, i.e. to move the plunger from the closed position to the open position, the coil of the electromagnetic actuator is energized to generate a magnetic field that attracts the moving armature towards the fixed pole against the elastic force exerted by the closing spring, and during the opening phase, the travel of the moving armature is stopped when it strikes the fixed pole.

[0005] According to FIG. 3, the injection law of the electromagnetic injector (i.e., injection time T INJ or a law relating the control time to the injected fuel quantity Q, INJ - the law represented by the injected fuel quantity Q curve) can be divided into three regions: INJ an initial region A without opening, where the force of the closing spring is too short so that the energy provided to the electromagnet coil is not sufficient to overcome the force of the closing spring and the plunger still remains in the closed position of the injection nozzle; an instantaneous region B, where the plunger moves from the closed position of the injection nozzle towards the fully open position (where the moving armature integral with the plunger abuts and collides with the fixed pole) but is unable to reach the fully open position and therefore returns to the closed position before reaching the fully open position; and a linear region C, where the plunger moves from the closed position of the injection nozzle to the fully open position and remains there for a predetermined length of time.

[0006] The burst region B is highly non-linear and, in particular, as a result of the large variation in injection characteristics from injector to injector, the use of electromagnetic injectors in the burst region B is very problematic, since the control time T required to inject the desired amount of fuel Q cannot be predicted with sufficient accuracy.

[0007] Manufacturers of spark-ignited internal combustion engines (i.e. engines operating according to the Otto cycle) desire electromagnetic injectors capable of injecting very small fuel quantities, on the order of one milligram, with sufficient precision, due to the fact that fragmenting the fuel injection into different individual injections can lead to reduced pollutant emissions during combustion. As a result, manufacturers are required to use electromagnetic fuel injectors even in the burst region B, since the fuel quantities of about one milligram can only be injected when operating in the burst region B.

[0008] Considering the fact that the large injector to injector variation in the injection characteristics of the instantaneous region B is primarily associated with the variation in the thickness of the magnetic gap existing between the moving armature and the fixed pole of the electromagnet, but small changes in the thickness of the magnetic gap have a significant impact on the injection characteristics of the instantaneous region B, it turns out that reducing the variation in the thickness of the magnetic gap and therefore the variation in the injection characteristics of the instantaneous region B is very complicated and therefore very costly.

[0009] To further complicate the situation, aging phenomena which normally affect fuel injectors will cause the injection characteristics to drift over time.

[0010] EP 2 375 036 A1 discloses a method for determining the closing time of an electromagnetic fuel injector, since knowing the actual closing time (i.e. the actual closing time) of the electromagnetic injector allows an accurate estimation of the actual amount of fuel injected by the injector for each injection operation (particularly when the injector is used to inject small amounts of fuel); in this way, even in the burst region B, electromagnetic fuel injectors can be used to inject very small amounts of fuel (of the order of 1 milligram) while ensuring adequate accuracy of injection.

[0011] The method for determining the closing point (and therefore the closing time) of an electromagnetic fuel injector disclosed in Patent Document 2 comprises the steps of applying a positive voltage to a coil of an electromagnetic actuator at the start of an injection operation to pass a current determining the opening operation of the injection valve through said coil, applying a negative voltage to said coil at the end of an injection operation to cancel the current flowing through said coil of the electromagnetic actuator, detecting the time evolution of the voltage at each end of said coil after cancellation of the current through the electromagnetic actuator coil and until the voltage is cancelled, identifying a voltage perturbation at each end of said coil after cancellation of the current flowing through said coil, and recognizing the closing point of the injector which coincides with the moment of the voltage perturbation at each end of said coil after cancellation of the current flowing through said coil.

[0012] Patent document 3 (US Patent Application Publication No. 2013 / 073188) discloses a method for determining the closing time of an electromagnetic fuel injector, in which at the start of an injection operation, a positive voltage is applied to a coil of an electromagnetic actuator in order to pass a current determining the opening operation of an injection valve through the coil, and at the end of the injection operation, a negative voltage is applied to the coil of the electromagnetic actuator in order to cancel the current flowing through the coil, and after cancellation of the current flowing through the electromagnetic actuator coil, a measured voltage evolution with time is detected at at least one end of the coil, the measured voltage evolution with time is compared with a comparative voltage evolution with time, and the closing time of the electromagnetic injector is determined based on the comparison between the measured voltage evolution with time and the comparative voltage evolution with time. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] European Patent Application Publication No. 1619384 [Patent Document 2] European Patent Application Publication No. 2375036 [Patent Document 3] US Patent Application Publication No. 2013 / 073188 Summary of the Invention [Problem to be solved by the invention]

[0014] SUMMARY OF THE DISCLOSURE It is an object of the invention to provide a method for determining the closing time of an electromagnetic fuel injector, which makes it possible to determine the closing time with high accuracy and which is in particular easy and inexpensive to implement. [Means for solving the problem]

[0015] According to the present invention there is provided a method for determining the closing time of an electromagnetic fuel injector as claimed in the accompanying claims.

[0016] The appended claims describe preferred embodiments of the invention and form an integral part of the description.

[0017] The invention will now be described with reference to the accompanying drawings which show non-limiting examples thereof. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of a common path injection system for implementing the method according to the present invention; [Diagram 2] 2 is a schematic cross-sectional side view of an electromagnetic fuel injector of the injection system of FIG. 1; [Diagram 3] 2 is a graph showing the injection characteristics of an electromagnetic fuel injector of the injection system of FIG. 1. [Figure 4] 2 is a graph showing the evolution over time of some physical quantities of an electromagnetic fuel injector of the injection system of FIG. 1 controlled to inject fuel in the burst operating region; [Diagram 5] 2 is a graph showing the evolution over time of some physical quantities of an electromagnetic fuel injector of the injection system of FIG. 1 , which is controlled for such a short period that injection of fuel is avoided; [Figure 6]2 is a graph showing the evolution over time of the voltage at each end of the coil of an electromagnetic fuel injector of the injection system of FIG. 1, the corresponding reference voltage, and their difference; [Figure 7] 4 is a graph showing the evolution over time of the first time derivative of the difference between the voltage at each end of the coil and a reference voltage; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In Fig. 1, the number 1 generally denotes a common-path injection system for direct injection of fuel in an internal combustion engine 2 with four cylinders 3. The injection system 1 comprises four electromagnetic fuel injectors 4, each of which injects fuel directly into a respective cylinder 3 of the engine 2 and receives fuel under pressure from a common path 5. The injection system 1 comprises a high-pressure pump 6 which delivers fuel to the common path 5 and is operated directly by the drive shaft of the engine 2 by means of a mechanical transmission, with an actuation frequency directly proportional to the rotational speed of the drive shaft. The high-pressure pump 6 is in turn fed by a low-pressure pump 7 arranged inside a fuel tank 8. Each electromagnetic injector 4 injects a variable amount of fuel into the corresponding cylinder 3 under the control of an electronic control unit 9.

[0020] According to Fig. 2, each electromagnetic fuel injector 4 has substantially cylindrical symmetry about a longitudinal axis 10 and is controlled to inject fuel from an injection nozzle 11. The electromagnetic injector 4 comprises a support body 12 having a cylindrical tubular shape with a variable cross-sectional area along the longitudinal axis 10 and comprising a feed channel 13 extending along its entire length to feed fuel under pressure to the injection nozzle 11. In its upper region, the support body 12 supports an electromagnetic actuator 14 and in its lower region an injection valve 15 which bounds the feed channel 13 at the bottom and which is actuated by the electromagnetic actuator 14 in use to regulate the flow of fuel through the injection nozzle 11 obtained in the region of the injection valve 15.

[0021] The electromagnetic actuator 14 comprises a coil 16 arranged on the outer surface around the tubular body 12 and enclosed in a toric casing 17 made of plastic material, and a fixed magnetic pole 18 made of ferromagnetic material and arranged inside the tubular body 12 in the region of the coil 16. Furthermore, the electromagnetic actuator 15 comprises a movable armature 19 having a cylindrical shape, made of ferromagnetic material, and designed to be magnetically attracted by the magnetic pole 18 when the coil 16 is excited (i.e. when a current flows through it). Finally, the electromagnetic actuator 15 comprises a tubular magnetic armature 20 made of a ferromagnetic material and arranged on the outer surface of the tubular body 12, the tubular magnetic armature 20 comprising an annular seat 21 which houses the coil 16 inside, and an annular shaped magnetic washer 22 made of a ferromagnetic material which is arranged above the coil 16 and guides the completion of the magnetic flux around the coil 16.

[0022] The movable armature 19 is part of a movable machine, which further comprises a shutter or plunger 23 having an upper part integral with the movable armature 19 and a lower part cooperating with a valve seat 24 of the injection valve 15 in order to regulate in a known manner the flow of fuel towards the injection nozzle 11. In particular, the plunger 23 terminates in a closing head with a substantially spherical shape designed to seat in a sealing manner against the valve seat.

[0023] The pole 18 is centrally drilled and has a central through hole 25 which partially accommodates a closing spring 26 which biases the movable armature 19 towards the closed position of the injection valve 15. In particular, inside the central hole 25 of the pole 18 is fitted an abutment element 27 which keeps the closing spring 26 compressed against the movable armature 19 in a fixed position.

[0024] In use, when the electromagnetic actuator 14 is de-energized, the moving armature 19 is not attracted by the magnetic poles 18, and the elastic force of the closing spring 26 urges the moving armature 19 together with the plunger 23 (i.e. the moving machine) downwards to a lower limit position where the closing head of the plunger 23 is pressed against the valve seat 24 of the injection valve 15, thereby blocking the injection nozzle 11 from fuel under pressure. When the electromagnetic actuator 14 is energized, the moving armature 19 is magnetically attracted by the magnetic pole 18 against the elastic force of the closing spring 26, and the moving armature 19 (i.e. the moving machine) integral with the plunger 23 moves to an upper limit position where, due to the magnetic attraction exerted by the magnetic pole 18, the moving armature 19 abuts and strikes against the magnetic pole 18, and the closing head of the plunger 23 is lifted against the valve seat 24 of the injection valve 15, thereby allowing fuel under pressure to flow through the injection nozzle 11.

[0025] 2, the coil 16 of the electromagnetic actuator 14 of each electromagnetic fuel injector 4 is powered by an electronic control unit 9 which applies to terminals 100 and 101 (i.e. each end) of the coil 16 a time-variable voltage V which determines the time-variable current i flowing through the coil 16. Terminal 100 of the coil 16 is a high-voltage terminal and may be connected to a power supply voltage through at least one first control transistor of the electronic control unit 9, while terminal 101 of the coil 16 is a low-voltage terminal and may be connected to electrical ground through at least one second control transistor of the electronic control unit 9.

[0026] According to FIG. 3, the injection law of each electromagnetic fuel injector 4 (i.e., injection time T INJ or a law relating the control time to the injected fuel quantity Q, INJ - the law represented by the injected fuel quantity Q curve) can be divided into three regions: INJan initial region A of no opening, where the time required for the energy provided to the coil 16 of the electromagnetic actuator 14 to open creates a force that is not sufficient to overcome the force of the closing spring 26 and the plunger 23 still remains in the closed position of the injection valve 15; an instantaneous region B, where the plunger 23 moves from the closed position of the injection valve 15 towards the fully open position (where the movable armature 19 integral with the plunger 23 abuts and collides with the fixed pole 18) but is unable to reach the fully open position and therefore returns to the closed position before reaching the fully open position; and a linear region C, where the plunger 23 moves from the closed position of the injection valve 15 to the fully open position and remains there for a predetermined length of time.

[0027] The graph of Figure 4 shows the evolution over time of some physical quantities of an electromagnetic fuel injector 4 controlled to inject fuel in the instantaneous operation region B. In other words, the injection time T INJ is shortened (by about 0.15-0.30 ms, depending on the fuel pressure and the type of injector), so that due to the electromagnetic attractive force generated by the electromagnetic actuator 14, the plunger 23 (together with the moving armature 19) moves from the closed position of the injection valve 15 towards the fully open position (where the moving armature 19, which is integral with the plunger 23, abuts and strikes the fixed pole 18), which is not reached, because the electromagnetic actuator 14 is closed before the plunger 23 (together with the moving armature 19) can reach the fully open position of the injection valve 15. 14 is de-energized, and as a result, when the plunger 23 is still "flying" (i.e. in an intermediate position between the closed and fully open positions of the injection valve 15) and is moving towards the fully open position, the electromagnetic actuator 14 is de-energized and the thrust generated by the closing spring 26 interrupts the movement of the plunger 23 towards the fully open position of the injection valve 15, so that the plunger 23 is moved in the reverse direction until it reaches the initial closed position of the injection valve 15.

[0028] According to Fig. 4, the logic control command C of the electromagnetic injector 4 involves the activation (excitation) of the electromagnetic actuator 14 (shift of the logic control command C from the OFF state to the ON state) at time t1 and the deactivation (de-excitation) of the electromagnetic actuator 14 (shift of the logic control command C from the ON state to the OFF state) at time t3. INJ is equal to and short of the time interval that elapses between times t1 and t3, the electromagnetic fuel injector 4 operates in the instantaneous operation region B.

[0029] At time t1, the coil 16 of the electromagnetic actuator 14 is excited, so that it starts to generate a driving force against the force of the closing spring 26, and when the driving force generated by the coil 16 of the electromagnetic actuator 14 exceeds the force of the closing spring 26, i.e. at time t2, the position p of the plunger 23 (integral with the moving armature 19) starts to change from the closed position of the injection valve 15 (denoted as "closed" in FIG. 4) to the fully open position of the injection valve 15 (denoted as "open" in FIG. 4), in other words, the injection valve 15 starts to open at time t2 and the time that elapses between times t1 and t2 is called the opening time T O (i.e. the time that elapses between the time t1 when the excitation of the electromagnetic actuator 14 begins and the time t2 when the injection valve 15 actually begins to open). In the injection law (shown in FIG. 3), the rise time T O establishes the boundary between the initial region A without opening and the region B of instantaneous operation, and in fact, the injection time T INJ is the rise time T O If it is shorter, the injection valve 15 will not open, so the state is in the initial region A without opening, but the injection time T INJ is the rise time T O If the injection time T is longer, the injection valve 15 opens, so the state is in the instantaneous operation region B (or the injection time T INJ If is long enough, the state lies in the linear region C).

[0030] At the instant t3, the position p of the plunger 23 has still not reached the fully open position of the injection valve 15 and, due to the termination of the logic control command C of the electromagnetic injector 4, it returns to the closed position of the injection valve 15, which is reached at the instant t5 (i.e. the moment when the closing head of the plunger 23 abuts and seats in a sealing manner against the valve seat of the injection valve 15). Before the instant t5 (i.e. the moment when the injection valve 15 is closed), the instant t4 is identified, at which the current i flowing through the coil 16 is cancelled (i.e. reaches a zero value) and the voltage v applied to each end of the coil 16 starts to decrease (in absolute value) and moves towards a zero value. The closing time T C is the time interval that elapses between the instants t3 and t5, i.e. between the end of the logic control command C of the electromagnetic injector 4 and the closing operation of the electromagnetic injector 4. C is also the zeroing time T included between the times t3 and t4. Z and there is still a current i flowing through the coil 16 (and therefore the electromagnetic actuator 14 still generates a magnetic attractive force on the moving armature 19). Z and the flight time T included between time t4 and t5 F and the flight time T during which only the elastic force generated by the closing spring 26 acts on the moving armature 19, since the current i flowing through the coil 16 is equal to zero. F It is also equal to the sum of.

[0031] At time t1, the voltage v applied to each end of the coil 16 of the electromagnetic actuator 14 of the electromagnetic injector 4 is increased until it reaches a positive power-up peak serving to rapidly increase the current i flowing through the coil 16, and at the end of the power-up peak the voltage v applied to each end of the coil 16 is controlled according to a "chopper" technique involving cyclically varying the voltage v between positive and zero values ​​in order to maintain the current i at a desired maintained value (for simplicity, the cyclical variation of the voltage v is not shown in Figure 4). At time t3, the voltage v applied to each end of the coil 16 is rapidly reduced until it reaches a negative power-down peak serving to rapidly cancel the current i flowing through the coil 16. Once the current i reaches its zero value at time t4, the residual voltage v decreases in an exponential manner until it is cancelled and during the cancellation phase of the voltage v, the electromagnetic injector 4 closes (at time t4 when the plunger 23 reaches the closed position of the injection valve 15) and in fact the plunger 23 starts its closing stroke towards the closed position of the injection valve 15 only when the force of the closing spring 26 exceeds the electromagnetic attractive force generated by the electromagnetic actuator 14 which is proportional to the current i (i.e. equal to zero when the current i reaches its zero value).

[0032] The graph of FIG. 5 shows an injection time T 1 that is so short that it cannot reach the opening of the injection valve 15 (but is equal to the time interval that elapses between the start time t1 of the injection operation and the end time t3 of the injection operation). INJ (That is, it belongs to the initial region A without opening and has a rise time T O Injection time T shorter than INJ ) is controlled by the injection time T INJ is the rise time T O Since the injection time is shorter than the injection time, the injection time is short (approximately 0.05 to 0.15 ms) so that the electromagnetic attractive force generated by the electromagnetic actuator 14 on the plunger 23 (integral with the movable armature 19) remains always smaller than the elastic force generated by the closing spring 26.

[0033] According to Fig. 5, the logic control command C of the electromagnetic injector 4 involves the activation (excitation) of the electromagnetic actuator 14 (shift of the logic control command C from the OFF state to the ON state) at time t1 and the deactivation (de-excitation) of the electromagnetic actuator 14 (shift of the logic control command C from the ON state to the OFF state) at time t3. INJ is equal to and short of the time interval that elapses between times t1 and t3, the electromagnetic fuel injector 4 operates in the initial region A without opening.

[0034] At time t1, the coil 16 of the electromagnetic actuator 14, being excited, begins to generate a driving force that counteracts the force of the closing spring 26, but the driving force generated by the electromagnetic actuator 14 never acts to overcome (exceed) the elastic force generated by the closing spring 26, so that the plunger 23 (integral with the moving armature 19) never moves from the closed position of the injection valve 15 (labeled "closed" in FIG. 5). At time t4, the current i flowing through the coil 16 is cancelled (i.e., reaches a zero value) and the voltage v applied to each end of the coil 16 begins to decrease (in absolute value) and approaches a zero value. Once the current i reaches a zero value at time t4, the residual voltage v decreases in an exponential manner until it is cancelled.

[0035] In the following, in order to determine the closing time t5 of the electromagnetic fuel injector 4, a closing time T C The procedure used by the electronic control unit 9 to determine

[0036] As already mentioned above when considering FIG. 4, at the start of the injection operation t1, the electronic control unit 9 applies a positive voltage v to the coil 16 of the electromagnetic actuator 14 in order to pass therethrough an activation current i which determines the opening operation of the injection valve 15, and at the end of the injection operation t3, the electronic control unit 9 applies a negative voltage v to the coil 16 of the electromagnetic actuator 14 in order to cancel (at time t4) the activation current i flowing through the coil 16.

[0037] At the end of the injection operation (i.e. after the end time t3 of the injection operation), after the cancellation of the activation current i flowing through the coil 16 (i.e. after time t4) and until the cancellation of the voltage v, the electronic control unit 9 detects (measures) the activation time voltage evolution v1 (shown in FIG. 6 ) at at least one end (i.e. one terminal 100 or 101) of the coil 16 of the electromagnetic actuator 14. Subsequently, the electronic control unit 9 compares the activation time voltage evolution v1 with a comparison time voltage evolution v2, which is predetermined in a manner described below. Finally, the electronic control unit 9 determines the closing time t5 of the electromagnetic fuel injector 4 based on the comparison between the activation time voltage evolution v1 and the comparison time voltage evolution v2.

[0038] In order to determine the comparative temporal voltage evolution v2, the electronic control unit 9 performs a test on the electromagnetic injector 4 in advance, i.e. before determining the closing time t5 of the electromagnetic injector 4, and determines an injection time T t 2 that is short enough not to reach the opening operation of the injection valve 15 (but is equal to the time interval that elapses between the start time t1 of the injection operation and the end time t3 of the injection operation), as shown in FIG. INJ (That is, it belongs to the initial region A without opening and has a rise time T O Injection time T shorter than INJ) is performed. In other words, at a start time t1 of the test, the electronic control unit 9 applies a positive voltage v to the coil 16 of the electromagnetic actuator 14 in order to pass a test current i through the coil 16, which does not determine the opening operation of the injection valve 15, and at an end time t3 of the test, the electronic control unit 9 applies a negative voltage v to the coil 16 of the electromagnetic actuator 14 in order to cancel the test current i flowing through the coil 16 without determining the opening operation of the injection valve 15. Finally, the electronic control unit 9 detects (measures) a comparative temporal voltage development v2 (shown in FIG. 6 ) at at least one end (i.e., one terminal 100 or 101) of the coil 16 of the electromagnetic actuator 14 after cancellation of the test current i flowing through the coil 16 without determining the opening operation of the injection valve 15; in other words, the electronic control unit 9 identifies a comparative temporal voltage development v2 after cancellation of the test current i flowing through the coil 16 without determining the opening operation of the injection valve 15.

[0039] According to a possible but non-limiting embodiment, the electronic control unit 9 comprises a hardware anti-aliasing filter (i.e. an anti-aliasing filter acting on an analog signal before digitization) acting on the measurement of the voltage v at at least one end (i.e. one terminal 100 or 101) of the coil 16 of the electromagnetic actuator 14. The anti-aliasing filter is an analog signal used before sampling of the voltage v signal in order to narrow the signal band so as to approximately satisfy the Nyquist-Shannon sampling theorem.

[0040] When the closing head of the plunger 23 strikes the valve seat of the injection valve 15 (i.e. when the electromagnetic injector 4 closes), the moving armature 19, which is integral with the plunger 23, changes its law of motion very quickly (i.e. it goes almost instantaneously from a relatively high speed to zero speed and, if necessary, it can even perform a small recoil that reverses the speed direction) and this essentially instantaneous change in the law of motion of the moving armature 19 causes a perturbation in the magnetic field associated with the coil 16, and therefore also determines a perturbation of the voltage v at each end of the coil 16.

[0041] As a result, there is a (detectable) difference between the start-up voltage evolution v1 with a closing movement of the injection valve 15 at the end of the movement of the plunger 23 and the comparison voltage evolution v2 without a closing movement of the injection valve 15 since the plunger 23 does not move, this difference being due to the fact that in the start-up voltage evolution v1 with a closing movement of the injection valve 15 at the end of the movement of the plunger 23 there is a perturbation due to the plunger 23 abutting against the valve seat of the injection valve 15, but in the comparison voltage evolution v2 without a closing movement of the injection valve 15 since the plunger 23 does not move there is no perturbation due to the plunger 23 abutting against the valve seat of the injection valve 15. By examining this perturbation (due to the impact of the plunger 23 on the valve seat of the injection valve 15) in a comparison between the voltage evolution v1 over time for a start-up with a closing movement of the injection valve 15 at the end of the movement of the plunger 23 and the voltage evolution v2 over time for a comparison without a closing movement of the injection valve 15 since the plunger 23 does not move, it is possible to determine the closing time t5 of the electromagnetic injector 4.

[0042] According to a preferred embodiment, the electronic control unit 9 synchronizes the starting voltage development v1 with the comparison voltage development v2 by aligning in a time manner a first point in time t4 at which the starting current i flowing through the coil 16 is cancelled to a second point in time t4 at which the test current i flowing through the coil 16 is cancelled.

[0043] According to a preferred embodiment, the electronic control unit 9 calculates (by simple subtraction) the voltage difference Δv (shown in FIG. 6) between the activation voltage evolution v1 and the comparison voltage evolution v2 and determines the closing time t5 of the electromagnetic injector 4 based on said voltage difference Δv. The electronic control unit 9 preferably, but not necessarily, applies a low pass filter, in particular a moving window filter, to the voltage difference Δv in order to remove high frequency noise.

[0044] According to a preferred embodiment, the electronic control unit 9 calculates the first time derivative dΔv / dt of the voltage difference Δv (as shown in FIG. 7) and therefore determines the closing time t5 of the electromagnetic injector 4 based on the first time derivative dΔv / dt of the voltage difference Δv. In particular, the electronic control unit 9 determines an absolute minimum of the first time derivative dΔv / dt of the voltage difference Δv and identifies a closing time t5 of the electromagnetic injector 4 in the region of the absolute minimum of the first time derivative dΔv / dt of the voltage difference Δv (as shown in FIG. 7).

[0045] According to a possible, but non-limiting, embodiment, at the closing time t5 determined as described above, a predetermined time advance is applied which compensates for the phase delay introduced by all the filters to which the voltage v is subjected; in other words, the closing time t5 determined as described above is advanced by a predetermined time interval in order to take into account the phase delay introduced by all the filters to which the voltage v at each end of the coil 16 is subjected.

[0046] The electronic control unit 9 detects that the voltage difference Δv exceeds the first threshold value in absolute value. tree, Or, the electronic control unit 9 recognizes the presence of the closing operation of the electromagnetic injector 4 only when the first time derivative value dΔv / dt of the voltage difference Δv exceeds the second threshold value in absolute value. In other words, the electronic control unit 9 recognizes the presence of the closing operation of the electromagnetic injector 4 only when the voltage difference Δv is smaller than the first threshold value in absolute value, and 1, If the first-order time differential value dΔv / dt of the voltage difference Δv is smaller than the second threshold value in absolute value, tree, The absence of a closing operation of the electromagnetic injector 4 is recognized. Therefore, the voltage difference Δv ,alsoIf the first time derivative dΔv / dt of the voltage difference Δv is too small (in absolute value), the electronic control unit 9 establishes that there was no closing action of the electromagnetic injector 4 (i.e. a closing action of the electromagnetic injector 4 was absent) since the activation voltage evolution v1 in time is completely similar to the comparison voltage evolution v2 in time.

[0047] According to a possible embodiment, a test for detecting a comparative voltage development in time v2 is performed immediately before each fuel injection operation, so that the comparative voltage development in time v2 is used to determine the closing time t5 of the electromagnetic injector 4 for the single corresponding injection operation which follows immediately thereafter. In other words, for each fuel injection operation, a specific comparative voltage development in time v2 is (instantly) determined, and then immediately afterwards, a fuel injection is performed and said specific comparative voltage development in time v2 is used to determine the closing time t5.

[0048] According to an alternative embodiment, a test for detecting a comparative voltage evolution v2 in time is carried out in each case, so that one comparative voltage evolution v2 in time is used to determine the closing time t5 of the electromagnetic fuel injector 4 for different injection operations. In other words, one comparative voltage evolution v2 can be applied (used) for different injection operations occurring at different instants. In this case, different comparative voltage evolutions v2 in time can be stored when the fuel pressure in the common path 5 fluctuates. Furthermore, the different comparative voltage evolutions v2 are detected and then statistically processed and regularly updated.

[0049] According to a possible embodiment, the voltage v is measured by the electronic control unit 9 between the two terminals 100 and 101 of the coil 16 when the first and second voltage developments in time v1 and v2 are detected, but this solution involves a differential measurement, which is more complicated since it requires the use of two separate voltage sensors connected to the two terminals 100 and 101 of the coil 16. Alternatively, the voltage v is measured by the electronic control unit 9 between the low voltage terminal 101 of the coil 16 and electrical earth, when the voltage developments in time v1 and v2 are detected, which solution is more simple since it involves one single voltage sensor connected to the low voltage terminal 101 of the coil 16.

[0050] During normal operation of the internal combustion engine 1, the electronic control unit 9 determines the corresponding closing time T C The injection time T must be known. INJ Generally, in the short term, the corresponding closing time T C The injection time T must be known. INJ Therefore, it is unlikely that the engine control requires that the electromagnetic injector 4 be strictly controlled, and as a result, the electronic control unit 9 will in any case only determine the corresponding closing time T C The injection time T must be known. INJ In particular, the electronic control unit 9 establishes a rotational speed target and a torque target to be generated for the internal combustion engine 2, and then determines a total amount of fuel Q to be injected based on the rotational speed target and the torque target to be generated, and subsequently the electronic control unit 9 determines a corresponding closing time T C The first injection time T to be determined INJ1 is used to control the electromagnetic fuel injector 4, and the first injection time T INJ1At this point, the electronic control unit 9 determines a second partial fuel quantity Q2 equal to the difference between the total fuel quantity Q and the first partial fuel quantity Q1, and determines a second injection time T based on the second partial fuel quantity Q2 to exactly inject the second partial fuel quantity Q2. INJ2 Finally, the electronic control unit 9 determines the second injection time T INJ2 is used to control the electromagnetic fuel injector 4.

[0051] The electronic control unit 9 determines the first injection time T 1 such that the difference between the total fuel quantity Q and the first partial fuel quantity Q1 exceeds a predetermined threshold (i.e. is large enough to allow the second partial fuel quantity Q2 to be injected with an acceptable accuracy). INJ1 Select .

[0052] It must be pointed out that the above-described method for determining the closing time t5 of the electromagnetic injector 4 applies in any operating condition of the electromagnetic injector 4, i.e. both when the electromagnetic injector 4 operates in the instantaneous region B, where at the end of the injection operation t3 the plunger 23 has not yet reached the fully open position of the injection valve 15, and when the electromagnetic injector 4 operates in the linear region C, where at the end of the injection operation t3 the plunger 23 has reached the fully open position of the injection valve 15. However, knowing the closing time t5 of the electromagnetic injector 4 is particularly useful when the electromagnetic injector 4 operates in the instantaneous region B, where the injection characteristic of the electromagnetic injector 4 is very non-linear and varies, but generally it is less useful when the electromagnetic injector 4 operates in the linear region C, where the injection characteristic of the electromagnetic injector 4 is linear and does not vary too much.

[0053] In the following description, the rise time T O The procedure used by the electronic control unit 9 to determine is now described.

[0054] The electronic control unit 9 determines a series of progressively increasing excitation times T INJ and for each control of the electromagnetic injector 4, the electronic control unit 9 determines, according to the procedure described above, the presence or absence of a closing operation of the injection valve 15 (i.e., whether the injection valve 15 was actually opened or not), and finally, the electronic control unit 9 determines the last excitation time T of the electromagnetic actuator 14, during which the absence of a closing operation of the injection valve 15 was determined. INJ and the first excitation time T of the electromagnetic actuator 14 at which the presence of a closing movement of the injection valve 15 is determined. INJ Rise time T equal to the midpoint between O Identify.

[0055] According to a preferred embodiment, the control unit 9 determines the rise time T O , and a series of gradually increasing excitation times T INJ , and the rise time T O , centered on said expected value.

[0056] According to a preferred embodiment, the electronic control unit 9 establishes a time resolution in determining the presence or absence of a closing action of the injection valve 15, and then determines the presence or absence of a closing action of the injection valve 15 by a series of progressively increasing excitation times T INJ Each excitation time T of the electromagnetic actuator 14 INJ with an increment equal to said time resolution. In carrying out the measurements, the ability to detect small variations in said physical quantity (i.e. the ability to detect whether an opening operation of the injection valve 15 has occurred or not) is examined.

[0057] According to a preferred embodiment, the presence or absence of a closing action of the injection valve 15 during the control of the electromagnetic injector 4 (i.e. whether the injection valve 15 is actually open or not) is determined as described above (i.e. by analysing the voltage difference Δv and / or the first time derivative dΔv / dt of the voltage difference Δv), according to a different embodiment, the presence or absence of a closing action of the injection valve 15 during the control of the electromagnetic injector 4 (i.e. whether the injection valve 15 is actually open or not) can be determined by a procedure different from that described above.

[0058] Hence, the embodiments described in this specification can be combined with each other without exceeding the scope of protection of the invention.

[0059] The above described method for determining the closing time of an electromagnetic fuel injector 4 has many advantages.

[0060] Firstly, the above-described method for determining the closing instant of an electromagnetic fuel injector 4 allows the actual closing instant of the electromagnetic injector 4 to be identified with a high degree of precision. This result is due to the fact that the "behavior" of the electromagnetic injector 4 at the moment of the closing of the injection valve 15 (i.e. the activation voltage evolution in time v1) is compared "with itself", i.e. with the "behavior" of the very same electromagnetic injector 4 in the very same conditions in the absence of an opening (and therefore closing) of the injection valve 15 (i.e. the comparison voltage evolution in time v2), in this way "cancelling" all the influences of all the unpredictable variables (assembly tolerances, aging of the individual components, fuel pressure, operating temperature, ...) that determine the (even considerable) variations in the operating modes. It is clear that when the comparison voltage development v2 is acquired only a few milliseconds before the acquisition of the activation voltage development v1, said acquisition is carried out not only with respect to the same component (i.e. the same electromagnetic injector 4) but also under exactly the same ambient conditions (fuel pressure, operating temperature, ...), so that the comparison between the activation voltage development v1 and the comparison voltage development v2 is in no way influenced by unpredictable variables, allowing the closing time t5 of the injection valve 15 to be determined with high precision.

[0061] As already mentioned above, when the injector is used to inject small amounts of fuel, it is very important to know the actual closing time of the electromagnetic injector 4, since in this way the actual amount of fuel injected by the injector for each injection operation can be estimated with high accuracy. In this way, the electromagnetic fuel injector 4 can also be used in the burst region to inject very small amounts of fuel (of the order of one milligram) while ensuring a proper accuracy of the injection operation. It must be pointed out that the accuracy in the injection of very small amounts of fuel is not achieved by reducing the dispersion of the individual characteristics of the injector (this is a very complicated and expensive operation), but by the possibility of using the fact of knowing the actual amount of fuel injected by the injector for each injection operation to instantly correct deviations from the ideal conditions (the actual amount of fuel injected is estimated by using the fact of knowing the actual closing time).

[0062] Furthermore, the above-described method for determining the closing time of the electromagnetic fuel injector 4 is easy and cheap even in an existing electronic control unit 9, since it does not require the addition of additional hardware to the hardware already typically present in a fuel injection system, does not require large computing power, and does not require large memory space.

[0063] The rise time T of the electromagnetic fuel injector 4 O The above-described method for determining has many advantages.

[0064] First, the rise time T O The above-described method for determining the actual rise time T O This allows the actual rise time T of the electromagnetic injector 4 to be identified with good accuracy. O It is important to know the rise time T O establishes the boundary between the initial region A without opening and the region B of instantaneous operation, and in fact, the injection time T INJ is the rise time T OIf it is shorter, the injection valve 15 will not open, so the state is in the initial region A without opening, but the injection time T INJ is the rise time T O If the injection time T is longer, the injection valve 15 opens, so the state is in the instantaneous operation region B (or the injection time T INJ (If is long enough, the state is in the linear region C). Therefore, the actual rise time T O Knowing the law of injection leads to a better knowledge of the corresponding injection law, so that the electromagnetic injector 4 can be controlled with high precision.

[0065] Furthermore, the rise time T O The above described method for determining is easy and cheap to implement even in existing electronic control units 9, since it does not require the addition of additional hardware to the hardware already typically present in a fuel injection system, it does not require large computing power, and it does not require large memory space. The present disclosure also includes the following inventions. The first aspect is The present invention relates to a method for determining a closing time (t t ) of an electromagnetic fuel injector (4) comprising: a movable plunger (23) that moves between a closed position and an open position to open and close an injection valve (15); and an electromagnetic actuator (14) that includes a coil (16) and is designed to move the movable plunger (23) between the closed position and the open position. 5 ), comprising the steps of: The method comprises: At the start of the test (t 1 applying a positive voltage (v) to the coil (16) of the electromagnetic actuator (14) to pass a test current (i) through the coil (16) that does not determine the opening operation of the injection valve (15); At the end of the test (t 3 applying a negative voltage (v) to the coil (16) of the electromagnetic actuator (14) to cancel the test current (i); After the cancellation of the test current (i), a comparative voltage evolution (v 2 ) detecting The start time of the injection operation (t 1 ) applying a positive voltage (v) to the coil (16) of the electromagnetic actuator (14) to pass an activation current (i) through the coil (16) that determines the opening operation of the injection valve (15); The end of the injection operation (t 3 applying a negative voltage (v) to the coil (16) of the electromagnetic actuator (14) to cancel the starting current (i); After the cancellation of the starting current (i), a starting voltage evolution (v 1 ) detecting The voltage evolution in time for the start-up (v 1 ) and the comparative voltage evolution over time (v 2 ) calculating a voltage difference (Δv) between calculating a first-order time derivative (dΔv / dt) of the voltage difference (Δv); calculating an absolute minimum value of the first-order time derivative (dΔv / dt) of the voltage difference (Δv); The electromagnetic fuel injector (4) is closed based on the first-order time differential (dΔv / dt) of the voltage difference (Δv). 5 and identifying the The method comprises: calculating a maximum value of the first-order time derivative (dΔv / dt) of the voltage difference (Δv); identifying the presence of a closing operation of the electromagnetic fuel injector (4) only when the maximum value of the first time derivative (dΔv / dt) of the voltage difference (Δv) exceeds a first threshold value in absolute value; and identifying the absence of closing operation of the electromagnetic fuel injector (4) only when the maximum value of the first time derivative (dΔv / dt) of the voltage difference (Δv) is, in absolute value, less than or equal to the first threshold value. The second aspect is The comparative voltage evolution over time (v 2 The test for detecting the voltage evolution over time (v 2 ) is the closing time (t 5 ) is used to determine The third aspect is The comparative voltage evolution over time (v 2 Since the above test for detecting the voltage evolution over time (v 2 ) is the closing time (t 5 ) is used to determine The fourth aspect is The method includes, in a timed manner, determining a first time point (t 4 ) at a second time point (t 4 ) to the time-dependent voltage evolution (v 1 ) is the time evolution of the voltage for comparison (v 2 The method of any one of the first, second or third aspects, comprising the further step of synchronizing the The fifth aspect is The method comprises: calculating a maximum value of the voltage difference (Δv); identifying the presence of a closing operation of the electromagnetic fuel injector (4) only when the maximum value of the voltage difference (Δv) exceeds a second threshold value in absolute value; and identifying an absence of closing operation of the electromagnetic fuel injector (4) if the maximum value of the voltage difference (Δv) is equal to or less than the second threshold value, in absolute value. The sixth aspect is The method according to any one of the first to fifth aspects, comprising a further step of applying a low-pass filter, in particular a moving window filter, to the voltage difference (Δv). The seventh aspect is The method further comprises: determining a time instant (t 5 ) a predetermined time advance that compensates for the phase delay introduced by all of the applied filters. The eighth aspect is The method further comprises: 1 、v 2 The method of any one of the first to seventh aspects, comprising the further step of applying an anti-aliasing filter to the positive voltage (v) or the negative voltage (v) when a positive voltage (v) or a negative voltage (v) is detected. The ninth aspect is The coil (16) of the electromagnetic actuator (14) has a high voltage terminal (100) and a low voltage terminal (101), and The positive voltage (v) or the negative voltage (v) has a first temporal voltage evolution (v 1 ) and the second voltage evolution over time (v 2 The method according to any one of the first to eighth aspects, wherein when a voltage Vcc is detected, a current Vcc is measured between the two terminals (100, 101) of the coil (16). A tenth aspect is The coil (16) of the electromagnetic actuator (14) has a high voltage terminal (100) and a low voltage terminal (101), and The positive voltage (v) or the negative voltage (v) is 1 ) and the second temporal voltage evolution (v 2 The method according to any one of the first to eighth aspects, wherein when a voltage difference between the two low voltage terminals (101) of the coil (16) is detected, the voltage difference between the two low voltage terminals (101) of the coil (16) and electrical ground is measured. An eleventh aspect is The method comprises: establishing a rotational speed target and a torque target to be generated for an internal combustion engine (2) in which the electromagnetic fuel injector (4) is installed; determining a total quantity of fuel (Q) to be injected based on the rotational speed target and the torque target to be generated; The corresponding closing time (T C The first injection time (T INJ1 controlling the electromagnetic fuel injector (4) using a Said first injection time (T INJ1 ) to calculate the first partial fuel quantity actually injected (Q 1 ) determining The total fuel quantity (Q) and the first partial fuel quantity (Q 1 ) and a second partial fuel quantity (Q 2 ) determining The second partial fuel quantity (Q 2 ) based on the second injection time (T INJ2 ) and determining the second partial fuel quantity (Q 2 ) and precisely injecting the Said second injection time (T INJ2 and controlling the electromagnetic fuel injector (4) using a control signal. A twelfth aspect is The method further comprises: determining the total fuel quantity (Q) to be injected and the first partial fuel quantity (Q 1 The first injection time (T) is adjusted so that the difference between the first injection time (T) and the second injection time (T) exceeds a predetermined threshold. INJ1 In an eleventh embodiment, the method comprises the further step of selecting [Explanation of symbols]

[0066] 1 Injection system 2 Engine 3 Cylinder 4 injector 5 Common Route 6. High Pressure Pump 7. Low Pressure Pump 8. Tank 9. Electronic Control Unit 10 Longitudinal axis of injector 4 11 Injection nozzle 12 Support body 13. Supply Channel 14 Electromagnetic Actuator 15 Injection valve 16 Coils 17 Annular casing 18 fixed magnetic pole 19 Moving armature 20 magnetic armature 21 Circular Pedestal 22 Magnetic washer 23 Plunger 24 Valve Seat 25 Central hole 26 Closing spring 27 Impact Body 100 Terminals 101 Terminal At time t1 At time t2 At time t3 At time t4 At t5 A initial area B. Instantaneous Region C linear region Q Fuel amount T INJ Injection time T HYD Hydraulic Time T C Closing time T Z Zeroing Time T F flight time T O Rise Time v1 first voltage evolution v2 The second voltage evolution over time Δv Voltage difference

Claims

1. The present invention relates to a method for determining a closing time (t t ) of an electromagnetic fuel injector (4) comprising: a movable plunger (23) that moves between a closed position and an open position to open and close an injection valve (15); and an electromagnetic actuator (14) that includes a coil (16) and is designed to move the movable plunger (23) between the closed position and the open position. ５ ) , comprising the steps of: The method comprises: The start time of the test (t １ ) applying a positive voltage (v) to the coil (16) of the electromagnetic actuator (14) in order to pass a test current (i) through the coil (16) which does not determine the opening operation of the injection valve (15); At the end of the test (t ３ applying a negative voltage (v) to the coil (16) of the electromagnetic actuator (14) to cancel the test current (i); After the cancellation of the test current (i), a comparative voltage evolution (v ２ ) detecting The start time of the injection operation (t １ ) applying a positive voltage (v) to the coil (16) of the electromagnetic actuator (14) to pass an activation current (i) through the coil (16) that determines the opening operation of the injection valve (15); The end time of the injection operation (t ３ ) applying a negative voltage (v) to the coil (16) of the electromagnetic actuator (14) to cancel the activation current (i); After the cancellation of the starting current (i), a starting voltage evolution (v １ ) detecting The voltage evolution in time for the start-up (v １ ) and the comparative voltage evolution over time (v ２ ) calculating a voltage difference (Δv) between Calculating a first-order time derivative (dΔv / dt) of the voltage difference (Δv); The closing time (t ５ and recognizing said The method comprises: calculating the first time derivative (dΔv / dt) of the voltage difference (Δv); calculating the voltage difference (Δv); recognizing the presence of a closing operation of the electromagnetic fuel injector (4) only when the voltage difference (Δv) exceeds a first threshold value in absolute value or when the first time derivative (dΔv / dt) of the voltage difference (Δv) exceeds a second threshold value in absolute value; recognizing an absence of a closing operation of the electromagnetic fuel injector (4) when the voltage difference (Δv) is smaller in absolute value than the first threshold value and when the first time derivative (dΔv / dt) of the voltage difference (Δv) is smaller in absolute value than the second threshold value; determining a closing time (t5) of the electromagnetic fuel injector (4) based on a transition from a step of recognizing the absence of a closing operation of the electromagnetic fuel injector (4) to a step of recognizing the presence of a closing operation of the electromagnetic fuel injector (4).

2. The comparative voltage evolution over time (v ２ The test for detecting the voltage evolution over time (v ２ ) is the closing time (t ５ 2. The method of claim 1 , wherein the method is used to determine

3. The comparative voltage evolution over time (v ２ ) is carried out, one comparative voltage evolution over time (v ２ ) is the closing time (t ５ 2. The method of claim 1 , wherein the method is used to determine

4. The method includes determining a first point in time (t ４ ) at a second time point (t ４ ) to the time evolution of the voltage for the actuation (v １ ) to the comparative time voltage evolution (v ２ 4. The method of claim 1, 2 or 3, comprising the further step of synchronizing with said first and second inputs.

5. The method according to any one of claims 1 to 4, wherein the method comprises the further step of applying a low pass filter to the voltage difference (Δv).

6. The method further comprises: determining a time (t ５ 6. The method of claim 5, comprising the further step of applying a predetermined time advance to said first filter, said second filter, said first filter being equal to or greater than said second filter, said second filter being equal to or greater than said first filter.

7. The method further comprises the step of: １ , v ２ The method according to any one of claims 1 to 6, comprising the further step of applying an anti-aliasing filter to the positive voltage (v) or the negative voltage (v) when a positive voltage (v) or a negative voltage (v) is detected.

8. The coil (16) of the electromagnetic actuator (14) has a high voltage terminal (100) and a low voltage terminal (101), and The positive voltage (v) or the negative voltage (v) is the time-dependent voltage progression (v １ ) and the comparative voltage evolution over time (v ２ The method according to any one of claims 1 to 7, wherein the measured voltage is measured between the two terminals (100, 101) of the coil (16) when a voltage Vcc is detected.

9. The coil (16) of the electromagnetic actuator (14) has a high voltage terminal (100) and a low voltage terminal (101), and The positive voltage (v) or the negative voltage (v) is the time-dependent voltage progression (v １ ) and the comparative voltage evolution over time (v ２ 8. The method according to claim 1, wherein a voltage between the low voltage terminal (101) of the coil (16) and electrical earth is measured when a voltage difference between the low voltage terminal (101) of the coil (16) and electrical earth is detected.

10. The method comprises: establishing a rotational speed target and a torque target to be generated for an internal combustion engine (2) in which the electromagnetic fuel injector (4) is installed; determining a total quantity of fuel (Q) to be injected based on the rotational speed target and the torque target to be generated; The corresponding closing time (T Ｃ The first injection time (T ＩＮＪ１ controlling the electromagnetic fuel injector (4) using a The first injection time (T ＩＮＪ１ ) to determine the first partial fuel quantity actually injected (Q １ ) determining The total fuel quantity (Q) and the first partial fuel quantity (Q １ ) and a second partial fuel quantity (Q ２ ) determining The second partial fuel quantity (Q ２ ) based on the second injection time (T ＩＮＪ２ ) and determining the second partial fuel quantity (Q ２ ) and precisely injecting the The second injection time (T ＩＮＪ２ A method according to any one of claims 1 to 9, comprising the step of controlling the electromagnetic fuel injector (4) using a control signal.

11. The method further comprises: determining a fuel quantity to be injected (Q) based on the total fuel quantity to be injected (Q) and the first partial fuel quantity (Q １ ) exceeds a predetermined threshold value. ＩＮＪ１ 11. The method of claim 10, comprising the further step of selecting a first sigma-based filter.

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