EP2975256A1

EP2975256A1 - Electromagnetic fuel injector with hydraulic braking device

Info

Publication number: EP2975256A1
Application number: EP15176731.6A
Authority: EP
Inventors: Stefano Petrecchia; Massimo Mattioli; Romito Tricarico
Original assignee: Magneti Marelli SpA
Current assignee: Marelli Europe SpA
Priority date: 2014-07-14
Filing date: 2015-07-14
Publication date: 2016-01-20
Anticipated expiration: 2035-07-14
Also published as: EP2975256B1; JP2016048066A; JP6639820B2

Abstract

A fuel injector (1) comprising: an injection nozzle (3); an injection valve (7) provided with a mobile plunger (17); an electromagnetic actuator (8) to move the plunger (17) between a closing position and an opening position of the injection valve (7); a hydraulic braking device (31), which is coupled to a supply hole (30) of a mobile armature (9) of the electromagnet (8), is provided with a valve element (32) which is coupled to the supply hole (30) of the mobile armature (9) and has an elastic blade (33) which is partially fixed to a surface (34) of the mobile armature (9), and is provided with a stop element (36), which is coupled to the elastic blade (33) and is arranged at a given distance from the elastic blade (33) to stop an opening movement of the elastic blade (33) itself in a fixed, predetermined position.

Description

TECHNICAL FIELD

The present invention relates to an electromagnetic fuel injector.

PRIOR ART

Generally, an electromagnetic fuel injector (e.g. of the type described in patent application EP1619384A2 ) comprises a cylindrical tubular body having a central supply channel, which has a fuel conveying function, and ends with an injection nozzle adjusted by an injection valve controlled by an electromagnetic actuator. The injection valve is provided with a plunger, which is displaced by the action of the electromagnetic actuator itself between a closing position and an opening position of the injection nozzle against the bias of a closing spring, which tends to maintain the plunger in the closing position. The electromagnetic actuator is normally provided with a closing spring which pushes the plunger towards the closing position and an electromagnet which pushes the plunger towards the opening position against the elastic force generated by the spring.
The electromagnet comprises a coil, which is externally arranged in a fixed position about the tubular body, a mobile armature, which is rigidly connected to the plunger and is moveably mounted inside the tubular body, and a fixed magnetic pole, which is made of ferromagnetic material, arranged within the tubular body at the coil and adapted to attract the mobile armature magnetically. The magnetic pole has a central through hole with the function of allowing fuel to flow towards the injection nozzle. The closing spring is arranged inside the central hole and is compressed between a perforated catch body driven into the central hole and the mobile armature to push the mobile armature, and thus the plunger integral with the mobile armature, towards the closing position of the injection nozzle.
The manufacturers of Otto cycle (i.e. spark ignited engines) thermal engines require to increase the fuel supply pressure (even in excess of 60-70 Mpa) to improve the mixing of fuel with the supporter of combustion (i.e. the air aspired in the cylinders) and thus reduce the generation of black smoke (which indicates poor combustion) and to increase the dynamic performance of the electromagnetic injectors (i.e. to increase the response speed of the electromagnetic injectors to commands) to be able to inject small amounts of fuel with the goal of fractionating the fuel injection into multiple separate injections (the generation of polluting substances during combustion can be reduced in this manner).
When the injection valve is closed, an autoclave force of hydraulic origin pushes on the shutter and keeps the shutter in the closing position (obviously, the higher the fuel supply pressure, the higher the autoclave force). So, in order to be able to open the injection valve, the electromagnetic actuator must generate a force which overcomes the autoclave force added to the elastic force exerted by the closing spring on the plunger; however, the autoclave force suddenly disappears as soon as the injection valve opens, thus the injection valve opens very rapidly and violently with an extremely fast movement of the plunger. Such a fast and violent opening of the injection valve determines a very steep and often irregular ramp in the initial part (named ballistic zone) of the injection law of the injector (i.e. the law which binds the actuation time, i.e. the control time, to the amount of injected fuel).
The fact that the initial part (i.e. the ballistic zone) of the injection law has a very steep, and often irregular (i.e. not very repeatable) ramp makes correctly controlling the fuel injection very complex, because at such a very steep ramp tiny differences in the injection time, i.e. in the control time, determine substantial differences in the amount of injected fuel.
In order to obtain a more regular (i.e. more repeatable) operation of the fuel injector in the initial part (i.e. in the ballistic zone) of the injection law, European patent 14164844.4 suggests to use a hydraulic braking device which is coupled to the mobile armature of the electromagnet and has the function of hydraulically dissipating kinetic energy to decelerate the opening travel of the plunger when the plunger is moved towards the opening position of the injection valve. The hydraulic braking device comprises a series of valve elements, each of which is coupled to a corresponding supply hole of the mobile armature (through which the fuel flows towards the injection nozzle) and has a different permeability to the passage of the fuel as a function of the direction of displacement of the plunger (i.e. if the plunger is closing or opening the injection valve). In particular, each valve element comprises an elastic blade, which is partially fixed to an upper face of the mobile armature and has a small size calibrated hole arranged at the supply hole.
When the injection valve opens and the autoclave force suddenly disappears, the action of the braking device described above determines a deceleration of the opening movement (i.e. the upward movement) of the plunger, because it determines a hydraulic dissipation of the kinetic energy possessed by the plunger. Such a deceleration action determined by the hydraulic braking device described above is particularly valuable, because it prevents the injection valve from opening very rapidly and violently with an extremely fast upward movement of the plunger; substantially, by virtue of the presence of the hydraulic braking device described above, the opening of the injection valve is decelerated to the advantage of improved controllability (i.e. higher accuracy and repeatability) of fuel injection in the ballistic zone of the injection law.
However, it has been observed that the deceleration action of the hydraulic braking device described above may have an irregular operation in the initial part (i.e. in the ballistic zone) of the injection law substantially due to the fact that the elastic blades which form the valve elements move during the movement of the mobile armature with oscillatory movements which are exhausted only after the initial part (i.e. the ballistic zone) of the injection law has ended. In order to attempt to solve this problem, it has been suggested to stiffen the elastic foils of the valve elements; however, such a solution although allowing to limit the oscillations of the elastic foils of the valve elements has the disadvantage of significantly decelerating the opening speed of the elastic blades of the valve elements and thus reducing the overall efficiency of the hydraulic braking device.
Patent application EP1039122A1 is the closest prior art and describes an electromagnetic fuel injector as established in the pre-characterizing part of independent claim 1.

DESCRIPTION OF THE INVENTION

It is the object of the present invention to make an electromagnetic fuel injector which is free from the drawbacks described above, i.e. which allows to improve the initial part (i.e. the ballistic zone) of the injection law, and which at the same time is easy and cost-effective to make.
According to the present invention, an electromagnetic fuel injector is made as disclosed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings, which show a non-limitative embodiment thereof, in which:

figure 1 is a longitudinal section of a fuel injector made in accordance with invention;
figure 2 shows an injection valve of the injector in figure 1 on an enlarged scale;
figure 3 shows part of an electromagnetic actuator of the injector in figure 1 on an enlarged scale;

figure 4 shows part a mobile armature of an upper electromagnet of the electromagnetic actuator in figure 3 on an enlarged scale;
figure 5 shows a cross section of the injector of figure 1 at a hydraulic braking device coupled to a lower face of the mobile armature in figure 4;
figures 6, 7 and 8 are plan views of corresponding elements which form the hydraulic braking device in figure 5; and
figures 9 and 10 are two views on enlarged scale of a detail of the hydraulic braking device in figure 5 during the opening of the injection valve and during the closing of the injection valve, respectively.

PREFERRED EMBODIMENTS OF THE INVENTION

In figure 1, reference numeral 1 indicates as a whole a fuel injector, which has an essentially cylindrical symmetry about a longitudinal axis 2 and is adapted to be controlled to inject fuel from an injection nozzle 3 which leads directly into a combustion chamber (not shown) of a cylinder. The injector 1 comprises a supporting body 4, which has a variable section cylindrical tubular shape along the longitudinal axis 2, and a supply channel 5 which extends along the entire length of supporting body 4 itself to supply pressurized fuel towards injection nozzle 3.
The supporting body 4 houses an electromagnetic actuator 6 at an upper portion thereof and an injection valve 7 (shown in greater detail in figure 2) at a lower portion thereof; in use, the injection valve 7 is actuated by the electromagnetic actuator 6 to adjust the fuel flow through the injection nozzle 3, which is obtained at the injection valve 7 itself.
As shown in figure 3, the electromagnetic actuator 6 comprises a pair of twin electromagnets 8 (upper and lower, respectively), which are activated together to work simultaneously. When energized, each electromagnet 8 is adapted to displace a respective mobile armature 9 made of ferromagnetic material along the axis 2 from a closing position to an opening position of the injection valve 7 against the bias of a single common closing spring 10 which tends to keep the mobile armature 9 in the closing position of the injection valve 7. Each electromagnet 8 comprises a coil 11, which is electrically supplied by a control unit (not shown) and is housed externally with respect to supporting body 4, and a magnetic armature 12 (or magnetic pole 12), which is housed in the supporting body 4 and has a central hole 13 to allow the fuel to flow towards the injection nozzle 3. A catch body 14 (shown in figure 1), which has a tubular cylindrical shape (possibly open along a generating line) to allow the fuel flow towards injection nozzle 3 and is adapted to keep common spring 10 compressed against mobile armature 9 of the upper electromagnet 8, is driven into the central hole 13 of the magnetic armature 12 of the electromagnet 8.
Each coil 11 is wound directly inside an annular cavity 15 thereof, which is obtained by stock removal in the outer surface of the supporting body 4. Each coil 11 consists of a enameled conductor wire provided with a self-bonding paint and has an axial dimension (i.e. a dimension measured along the longitudinal axis 2) contained to minimize the dispersed magnetic fluxes. At the coils 11, a protection body 16 is coupled about the supporting body 4, which protection body has a tubular shape and is used to guarantee suitable mechanical protection to the coils 11, to allow to close the magnetic flux lines generated by the coils 11 and to increase the mechanical strength of the supporting body 4 at structural weak points which are inevitably introduced by the presence of the cavities 15.
The mobile armatures 9 are part of a mobile equipment, which further comprises a shutter or plunger 17, having an upper portion integral with each mobile armature 9 and a lower portion cooperating with a valve seat 18 (shown in figure 2) of the injection valve 7 to adjust the fuel flow through injection nozzle 3 in known manner.
In use, when the electromagnets 8 are de-energized, each mobile armature 9 is not attracted by its magnetic armature 12 and the elastic force of the spring 10 pushes the mobile armatures 9 together with the plunger 17 downwards; the injection valve 7 is closed in this situation. When the electromagnets 8 are energized, each mobile armature 9 is magnetically attracted by its magnetic armature 12 against the elastic force of the spring 10 and the mobile armatures 9 together with the plunger 17 move upwards to determine the opening of the injection valve 7.
In order to determine the upward travel of the plunger 17 in accurate manner, the effective travel of the mobile armature 9 of the upper electromagnet 8 is shorter than the effective travel of the mobile armature 9 of the lower electromagnet 8. In this manner, when the electromagnets 8 are energized, only the mobile armature 9 of the upper electromagnet 8 will ever come into contact and abut with its magnetic armature 12 regardless of inevitable construction tolerances. In order to limit the effective travel of the mobile armature 9 of the upper electromagnet 8, either the lower surface of the armature 12 or the upper surface of the mobile armature 9 is coated with a layer of hard, non-ferromagnetic metallic material, preferably chromium; in this manner, the thickness of the chromium layer determines the reduction of the effective travel of the mobile armature 9 of the upper electromagnet 8. Further functions of the chromium layer are increasing the shock resistance of the zone and above all avoiding magnetic sticking phenomena caused by a direct contact between the ferromagnetic material of the mobile armature 9 and the ferromagnetic material of the armature 12. In other words, the chromium layer defines a gap, which prevents the magnetic attraction forces caused by the residual magnetism between the mobile armature 9 and the armature 12 from reaching excessively high values, i.e. higher than the elastic force of the spring 10.
Furthermore, only the plunger 9 of the upper electromagnet 8 is subjected to precision mechanical machining to have a calibrated outer diameter which is substantially equal (obviously rounded down) to the inner diameter of the supply channel 5; on the contrary, the mobile armature 9 of the lower electromagnet 8 has a non-calibrated outer diameter which is always smaller than the inner diameter of the supply channel 5. In this manner, only the mobile armature 9 of the upper electromagnet 8 performs the upper guiding function of the plunger 17 to control the axial sliding of the plunger 17 along the longitudinal axis 2. Such a constructive choice allows to reduce manufacturing costs, because only the mobile armature 9 of the upper electromagnet 8 must be subjected to precision, and thus costly, mechanical machining.
As shown in figure 2, the valve seat 18 is defined in a sealing element 19, which is monolithic, seals the bottom of the supply channel 5 of the supporting body 4, and is crossed by the injection nozzle 3. In particular, the sealing element 19 comprises a disc-shaped plugging element 20, which seals the bottom of the supply channel 5 of the supporting body 4 and is crossed by the injection nozzle 3. A guiding element 21 rises from the capping element 20, which guiding element has a tubular shape, houses within a plunger 17 to define a lower guide of the plunger 17 itself and has an outer diameter which is smaller than the inner diameter of the supply channel 5 of the supporting body 4, so as to define an outer annular channel 22 through which the pressurized fuel may flow.
Four through supply holes 23 (only two of which are shown in figure 2), which lead towards the valve seat 18 to allow the flow of pressurized fuel towards the valve seat 18 itself, are made in the lower part of the guiding element 21. The supply holes 23 may be either offset with respect to a longitudinal axis 2 so as not to converge towards longitudinal axis 2 itself and to impress a vortical flow to the corresponding fuel flows in use, or the supply holes 23 may converge towards the longitudinal axis 2. As shown in figure 4, the supply holes 23 are arranged inclined at an 80° angle (more in general comprised between 70° and 90°) with the longitudinal axis 2; according to a different embodiment (not shown), the supply holes 23 form a 90° angle with the longitudinal axis 2.
The plunger 17 ends with a substantially spherical shutter head 24, which is adapted to rest in fluid-tight manner against the valve seat 18; alternatively, the shutter head 24 may be substantially cylinder shaped and only the abutment zone may be spherical. Furthermore, the shutter head 24 slidingly rests on an inner surface of the guiding element 21 so as to be guided in its movement along longitudinal axis 2. The injection nozzle 3 is defined by a plurality of through injection holes 25 which are obtained starting from an injection chamber 26 arranged downstream of the valve seat 18.
As shown in figure 3, each mobile armature 9 is cylinder shaped and has a central through hole 29 adapted to receive a portion of the plunger 17 and a plurality of peripheral through supply holes 30 (only two of which are shown in figure 3) adapted to allow the flow of fuel towards the injection nozzle 3. The plunger 17 is made integral to each mobile armature 9 by means of an annular welding which surrounds the central hole 29.
As mentioned above, the outer diameter of the mobile armature 9 of the upper electromagnet 8 is substantially identical to the inner diameter of the corresponding portion of the supply channel 5 of the supporting body 4; in this manner, such a mobile armature 9 may slide with respect to the supporting body 4 along the longitudinal axis 2, but cannot perform any movement transverse to the longitudinal axis 2 with respect to the supporting body 4. Being the plunger 17 rigidly connected to the mobile armature 9 of the upper electromagnet 8, it is apparent that such a mobile armature 9 also performs the function of upper guide of the plunger 17; consequently, the plunger 17 is guided by the mobile armature 9 of the upper electromagnet 8 on the top and by the guiding element 21 on the bottom.
A hydraulic braking device 31 is connected to the upper face of the upper mobile armature 9 (i.e. to the mobile armature 9 of the upper electromagnet 8) to brake (decelerate) the movement of the plunger 9 both when the plunger 17 moves from the opening position to the closing position of the injection valve 7 and when the plunger 17 moves from the closing position to the opening position of the injection valve 7. When the plunger 17 moves from the opening position to the closing position of the injection valve 7, the hydraulic braking device 31 brakes (decelerates) the movement of the plunger 17 to limit the elastic rebound of the plunger 17 against the valve seat 18 (i.e. during this step, the hydraulic braking device 31 performs an anti-rebound function). When the plunger 17 moves from the closing position to the opening of the injection valve 7, the hydraulic braking device 31 brakes (decelerates) the movement of the plunger 17 to limit the opening speed of the injection valve 7.
The hydraulic braking device 31 comprises a plurality of valve elements 32, each of which is coupled to a respective supply hole 30 of the upper mobile armature 9 and has a different permeability to the passage of the fuel as a function of the movement of the plunger 17 (i.e. if the plunger 17 is closing or opening the injection valve 7). In particular, each valve element 32 comprises an elastic blade 33, which is partially fixed to a lower surface 34 of the mobile armature 9 only on one side of the respective supply hole 30 and has a small-sized calibrated hole 35 size aligned with the supply hole 30 itself. Furthermore, each valve element 32 has a stop element 36, which is rigid (i.e. has a substantially negligible elasticity), is coupled to the corresponding elastic blade 33, and is arranged at a given distance from the elastic blade 33 to stop the opening movement of the elastic blade 33 itself in a fixed, predetermined position; in other words, each stop element 36 forms a limit stop which limits (interrupts) the movement of the elastic blade 33 from the corresponding supply hole 30 (i.e. from the lower surface 34 of the mobile armature 9) establishing a maximum opening position of the elastic blade 33 itself.
Consequently, the stop element 36 determines the maximum opening travel of the elastic blade 33 of each valve element 32, and thus determines the fuel passage section through each valve element 32.
A spacer 37 is arranged between each elastic blade 33 and the corresponding stop element 36 which spacer has a calibrated thickness and establishes in certain manner the axial distance (i.e. measured along the longitudinal axis 2) existing between the elastic blade 33 and the corresponding stop element 36.
As shown in greater detail in figure 6, an annular crown 38 is provided which is fixed to the lower surface 34 of the upper mobile armature 9 by welding (preferably by means of laser spot welding) and supports the elastic blades 33 of the valve elements 32. In particular, the elastic blades 33 extend from the annular crown 38 inwards (i.e. towards the corresponding supply holes 30), each elastic blade having an annular shutter arranged at the respective supply hole 30 and a thin stem (i.e. having a significantly greater length than its width) which connects the circular shutter to the annular crown 38 and which is adapted to be deformed under the bias of the fuel. In other words, for each elastic blade 33, the deformation which occurs in use under the bias of the fuel is substantially caused by the elastic deformation of the corresponding stem (while the corresponding circular shutter has a more modest elastic deformation).
As shown in figure 7, the spacer 37 is shaped as an annular crown which is superimposed on the annular crown 38 supporting the elastic blades 33 of the valve elements 32.
As shown in greater detail in figure 8, an annular crown 39 is provided which is fixed to the annular crown 38 supporting the elastic blades 33 of the valve elements 32 with the interposition of the spacer 37 and supports the stop elements 36 which overhangingly protrude towards the inside from the annular crown 39 itself.
As shown in figures 4 and 5, the annular crown 38 supporting the elastic blades 33 of the valve elements 32, the spacer 37 and the annular crown 39 supporting the stop elements 36 are sandwiched to one another (i.e. superimposed and packed) and preferably joined by welding (normally by means of laser spot welding) to form a single body.
According to a preferred embodiment shown in figures 5-8, the annular crown 38 supporting the elastic blades 33 of the valve elements 32, the spacer 37 and the annular crown 39 supporting the stop elements 36 each have a pair of mutually opposite centering recesses 40 which ensure a correct positioning of the fuel injector 1 in the supporting body 4.
The operation of the hydraulic braking device 31 is described below with particular reference to figures 9 and 10.
As shown in figure 9, the hydraulic braking device 31 decelerates the opening movement of the plunger 17, i.e. the movement with which the plunger 17 moves from the closing position to the opening position of the injection valve 7. In other words, when the plunger 17 moves from the closing position to the opening position of the injection valve 7 the hydraulic braking device 31 determines a hydraulic dissipation of the kinetic energy possessed by the plunger 17 (i.e. generates a braking force of hydraulic origin which works on the plunger 17). In particular, when the fuel flows downwards, i.e. towards the injection nozzle 3, the elastic blade 33 of each valve element 32 is deformed under the bias of the fuel becoming detached from the lower surface 34 of the upper mobile armature 9 and resting on the stop element 36 (as shown in figure 9) creating an annular fuel passage gap of calibrated size which locally causes a "bottleneck" to the flow of fuel and determines the onset of significant losses of hydraulic load (such losses of hydraulic load dissipate part of the kinetic energy possessed by the plunger 17 and thus hydraulically decelerate the movement of the plunger 17 itself).
When the injection valve 7 is closed, an autoclave force of hydraulic nature pushes on the shutter head 24 and keeps the shutter head 24 in the closing position. So, in order to be able to open the injection valve 7, the electromagnetic actuator 6 needs to generate a force to overcome the autoclave force added to the elastic force exerted by the closing spring 10 on the plunger 17; however, the autoclave force suddenly disappears as soon as the injection valve 7 opens, thus the injection valve 7 would tend to open very rapidly and violently with an extremely fast upward movement of the plunger 17. When the injection valve 7 opens and the autoclave force suddenly disappears, the action of the hydraulic braking device 31 described above decelerates the opening movement (i.e. the upward movement) of the plunger 17, because it determines a hydraulic dissipation of part of the kinetic energy possessed by the plunger 17. Such a deceleration action determined by the hydraulic braking device 31 is particularly valuable, because it prevents the injection valve 7 from opening very rapidly and violently with an extremely fast upward movement of the plunger 17; substantially, by virtue of the presence of the hydraulic braking device 31 the opening of the injection valve 7 is decelerated to the benefit of greater controllability (i.e. better accuracy and repeatability) of the fuel injection in the ballistic zone of the injection law (i.e. the law which binds the actuation time, i.e. the control time, to the amount of injected fuel). In other words, the action of the hydraulic braking device 31 allows to stabilize the initial part (i.e. the ballistic zone) of the injection law.
As shown in figure 10, the hydraulic braking device 31 decelerates the closing movement of the plunger 17, i.e. the movement with which the plunger 17 moves from the opening position to the closing position of the injection valve 7. In other words, when the plunger 17 moves from the opening position to the closing position of the injection valve 7 the hydraulic braking device 31 determines a hydraulic dissipation of the kinetic energy possessed by the plunger 17 (i.e. generates a braking force of hydraulic origin which works on the plunger 17). In particular, when the fuel flow upwards, i.e. in the direction opposite to the injection nozzle 3, the elastic blade 33 of each valve element 32 is pressed under the bias of the fuel against the lower surface 34 of the upper mobile armature 9 leaving its calibrated hole 35 as the only opening for the fuel. The forced passage of fuel through each calibrated hole 35 locally causes a "bottleneck" to the flow of fuel which determines the onset of significant losses of hydraulic load (such losses of hydraulic load dissipate part of the kinetic energy possessed by the plunger 17 and thus hydraulically decelerate the movement of the plunger 17 itself).
In brief, the same hydraulic braking device 31 decelerates the opening movement of the plunger 17, i.e. the movement with which the plunger 17 moves from the closing position to the opening position of the injection valve 7, and the closing position of the plunger 17, i.e. the movement with which the plunger 17 moves from the opening position to the closing position of the injection valve 7. During the opening movement of the plunger 17, i.e. when the plunger 17 moves from the closing position to the opening position of the injection valve 7, the elastic blade 33 of each valve element 32 separates from the lower surface 34 of the upper mobile armature 9 and rests on the corresponding stop element 36 (as shown in figure 9); in this condition, the fuel flows towards the injection nozzle 3 passing through the annular gaps each delimited on one side by the lower surface 34 of the upper mobile armature 9 and on the opposite side by the elastic blade 33 of a corresponding valve element 32. During the closing movement of the plunger 17, i.e. when the plunger 17 moves from the opening position to the closing position of the injection valve 7, the elastic blade 33 of each valve element 32 rests on the lower surface 34 of the upper mobile armature 9; in this condition, the fuel flows in the direction opposite to the injection nozzle 3 passing through the calibrated hole 35 of the elastic blade 33 of each valve element 32.
In other words, the hydraulic braking device 31 is an asymmetric damping system of the kinetic energy possessed by the mobile armature 9 of the upper electromagnet 8 which brakes the closing movement of the plunger 17 more than the opening movement of the plunger 17; indeed, the passage area of the annular gap delimited on one side by the lower surface 34 of the upper mobile armature 9 and on the opposite side by the elastic blade 33 of each valve element 32 is significantly greater than the passage area of the corresponding calibrated hole 35.
As mentioned above, the hydraulic braking device 31 hydraulically dissipates kinetic energy (i.e. generates a braking force) to decelerate the travel of plunger 17 both when the plunger 17 moves towards an opening position of the injection valve 7 and when the plunger 17 moves towards a closing position of the injection valve 7. In particular, the hydraulic braking device 31 has an asymmetrical behavior and, when the plunger 17 moves towards the closing position of the injection valve 7, it hydraulically dissipates a greater amount of kinetic energy than when the plunger 17 moves towards the opening position of the injection valve 7; i.e. the hydraulic braking device 31 has an asymmetrical behavior and, when the plunger 17 moves towards the closing position of the injection valve 7, it hydraulically generates a braking force greater than when the plunger 17 moves towards the opening position of the injection valve 7. According to a preferred (but not binding) embodiment, the hydraulic braking device 31 hydraulically dissipates an amount of kinetic energy when the plunger 17 moves towards the closing position of the injection valve 7 which is comprised between 1.25 and 5 times (preferably 1.25 and 2.5 times) the amount of kinetic energy hydraulically dissipated when the plunger 17 moves towards the opening position of the injection valve 7; i.e. the hydraulic braking device 31 hydraulically generates a braking force when the plunger 17 moves towards the closed position of the injection valve 7 which is comprised between 1.5 and 10 times (preferably 1.5 and 5 times) the braking force which is hydraulically generated when the plunger 17 moves towards the opening position of the injection valve 7.
In the embodiment illustrated in the accompanying figures, the same hydraulic braking device 31 has both the function of decelerating the opening movement of the plunger 17, i.e. the movement with which the plunger 17 moves from the closing position to the opening position of the injection valve 7, and of decelerating the closing movement of the plunger 17, i.e. the movement with which the plunger 17 moves from the opening position to the closing position of the injection valve 7 (anti-rebound function). According to a different embodiment not shown and implemented as described in European patent 14164844.4 , the hydraulic braking device 31 has only the function of decelerating the opening movement of the plunger 17, i.e. the movement with which the plunger 17 moves from the closing position to the opening position of the injection valve 7, and a further hydraulic braking device is provided, which is arranged at an upper surface of the mobile armature 9 of the upper electromagnet 8 (i.e. on the side opposite to the hydraulic braking device 31) and has the function of decelerating the closing movement of the plunger 17, i.e. the movement with which the plunger 17 moves from the opening position to the closing position of the injection valve 7 (anti-rebound function). In this embodiment, the mechanical inertia of the two braking devices of hydraulic type are differentiated so as to make the hydraulic braking device 31 intervene more rapidly when operating during the opening movement of the plunger 17 and to make the other hydraulic braking device intervene more slowly during the closing movement of the plunger 17 (i.e. which operates as anti-rebound).
In the embodiment shown in the accompanying figures, the plunger 9 of the upper electromagnet 8 is the only upper guide of the plunger 17 and supports the hydraulic braking device 31. The hydraulic braking device 31 is preferably coupled to the mobile armature 9 of the upper electromagnet 8, because such a mobile armature 9 provides for a better lateral hydraulic sealing with respect to the inner surface of the supply channel 5 (i.e. less lateral leakage of the fuel) and thus allows to obtain a better operation of the hydraulic braking device 31 itself. According to an alternative, perfectly equivalent embodiment (not shown), the mobile armature 9 of the lower electromagnet 8 forms the only upper guide of the plunger 17 and thus, in this case, the hydraulic braking device 31 would be preferably coupled to the mobile armature 9 of the lower electromagnet 8. According to a further, perfectly equivalent embodiment (not shown), both mobile armatures 9 could form the two upper guides of the plunger 17 and thus, in this case, the hydraulic braking device 31 could be indifferently coupled either to the plunger 9 of the lower electromagnet 8 or to the mobile armature 9 of the upper electromagnet 8.
The plunger 17 has a cylindrical symmetry stem, to which the substantially spherical shutter head 24 is connected by means of an annular welding. In turn, the stem is connected to each mobile armature 9 by means of an annular welding.
The fuel injector 1 described above has many advantages.
Firstly, the fuel injector 1 described above has a linear, uniform (i.e. without irregularities) injection law (i.e. the law which links the driving time to the amount of fuel injected), also for short driving times (i.e. in the ballistic zone) and thus for small amounts of injected fuel. In this manner, the injector 1 described above allows to inject small amounts of fuel in accurate, repeatable manner.
Such a result is obtained also by virtue of the fact that, by effect of the presence of the stop elements 36, the opening movement (i.e. the detachment from the lower surface 34 of the upper mobile armature 9) of the elastic blades 33 of the hydraulic braking device 31 occurs practically without oscillations, i.e. each elastic blade 33 separates from the lower surface 34 of the upper mobile armature 9 and nearly instantaneously abuts against the corresponding stop element 36 without appreciable oscillations. The absence of oscillations in the opening movement of the elastic blades 33 of the hydraulic braking device 31 avoids the introduction of randomness in the dynamic behavior of the hydraulic braking device 31 and thus makes the dynamic performance of the hydraulic braking device 31 (and thus the dynamic behavior of the fuel injector 1) much more stable, predictable and repeatable with accuracy to the advantage of linearity and uniformity of the injection law particularly for short control times (i.e. in the ballistic zone).
By varying the thickness of the spacer 37 (i.e. replacing one spacer 37 with another spacer 37 of different thickness) it is possible to adjust the travel of the elastic blades 33 of the hydraulic braking device 31 accurately to adjust the intensity of the braking action of the hydraulic braking device 31 during the opening movement of the plunger 17 as a consequence. Instead, by adjusting the diameter of the calibrated holes 35 of the elastic blades 33 of the hydraulic braking device 31 it is possible to adjust the intensity of the braking action of the hydraulic braking device 31 as a consequence during the closing movement of the plunger 17 (anti-rebound function).
The fuel injector 1 described above is particularly stable also by virtue of the fact that the hydraulic braking device 31 is not very sensitive to fuel pressure oscillations because the elastic blades 33 of the hydraulic braking device 31 are not substantially subject to mechanical oscillations (i.e. to vibration) by effect of the presence of the corresponding stop elements 36.
By virtue of the presence of the stop elements 36 which block the oscillations of the corresponding blades 33 of the hydraulic braking device 31, the elastic blades 33 may also be extremely light (i.e. with low mechanical inertia) and thus allow a very rapid intervention of the hydraulic braking device 31.
In the fuel injector 1 described above, the hydraulic braking device 31 works by decelerating the movement of the plunger 17 both during the opening movement and during the closing movement allowing to eliminate the rebounds of the plunger 17 during the opening movement (i.e. eliminating the rebounds deriving from the impact of the upper mobile armature 9 against the corresponding magnetic armature 12), and in the closing movement (i.e. eliminating the rebounds deriving from the impact of the shutter head 24 against the valve seat 18). By virtue of the complete absence of appreciable rebounds of the plunger 17 during both the opening movement and the closing movement, the linearity and the uniformity (i.e. the repeatability) of the injection law is substantially improved also in case of short control times (i.e. in the ballistic zone). Furthermore, the noise generated by the fuel injector 1 described above during its operation is significantly decreased by virtue of the complete lack of appreciable rebounds of the plunger 17 in the opening movement and in the closing movement.
In addition to guaranteeing very well controllable small injections, the fuel injector 1 described above also allows to reduce the collision forces of the plunger 17 both during the step of opening (i.e. the collision forces deriving from the impact of the upper mobile armature 9 against the corresponding magnetic armature 12), and during the step of closing (i.e. the collision forces deriving from the impact of the shutter head 24 against the valve seat 18) in significant manner; the collision force reduction of the plunger 17 allows to reduce mechanical wear and thus increase the working lifespan on the fuel injector 1 described above.
When the injection valve 7 is open, the fuel flows towards the injection nozzle 3 through the supply holes 30 of the upper mobile armature 9 (i.e. the mobile armature 9 of the upper electromagnet 8) and thus passing through the corresponding valve elements 32 in which the elastic blades 33 are detached from the lower surface 34 of the upper mobile armature 9 and rest on the stop elements 36 (as shown in figure 9) defining corresponding annular gaps through which the fuel must pass.
As mentioned above, the passage of fuel through the open valve elements 32 (i.e. with the elastic blades 33 detached from the lower surface 34 of the upper mobile armature 9 and resting on the stop elements 36) causes a hydraulic dissipation of part of the kinetic energy possessed by the plunger 17 generating as a consequence a braking force which positively decelerates the opening movement of the plunger 17 itself.
Furthermore, the fuel passage through the open valve elements 32 (i.e. with the elastic blades 33 detached from the lower surface 34 of the upper mobile armature 9 and resting on the stop elements 36) causes a small but not negligible loss of load straddling the valve elements 32 (i.e. the fuel pressure over the upper mobile armature 9 is higher than the fuel pressure under the upper mobile armature 9); such a pressure difference (which is small but not negligible) straddling the upper mobile armature 9 acts on the entire surface of the upper mobile armature 9 and generates an autoclave force of hydraulic origin (having intensity equal to the pressure difference straddling the upper mobile armature 9 multiplied by the area of the upper mobile armature 9) which pushes the upper mobile armature 9 towards the injection nozzle 3, i.e. pushes the plunger 17 towards the closing position of the injection valve 7. This autoclave force of hydraulic origin which exists when the injection valve 7 is open and pushes the plunger 17 towards the closing position of the injection valve 7 has a positive effect, because it is added to the elastic force generated by the closing spring 10 and contributes to accelerating the closing of the injection valve 7 when the electromagnetic actuator 6 is switched off (i.e. this autoclave force of hydraulic origin substantially reduces the closing time of the injection valve 7 when the electromagnetic actuator 6 is switched off). By virtue of this autoclave force of hydraulic origin which exists when the injection valve 7 is open, the closing spring 10 can be undersized (i.e. a closing spring 10 with a low elastic load can be used) and consequently the electromagnetic force generated by the electromagnetic actuator 6 can be reduced (i.e. a smaller electromagnetic actuator 6, and thus lighter, more economical and with less mechanical or magnetic inertia can be used).
It is worth noting that the autoclave force of hydraulic origin which exists when the injection valve 7 is open is generated because the upper mobile armature 9 has a very low lateral clearance with respect to the supporting body 4 (as described in greater detail above) and thus allows to establish a non-negligible pressure difference straddling the upper mobile armature 9 itself.
The fuel injector 1 described above is simple and cost-effective to make because a single component (the hydraulic braking device 31) performs the hydraulic braking device both during the opening movement of the plunger 17 and during the closing movement of the plunger 17. In other words, in the injector 1 described above the hydraulic braking device 31 performs functions which in similar known fuel injectors are performed by two different, separate devices to the advantage of overall cost-effectiveness and simplicity of assembly.
It is worth noting that in the injector 1 described above the structure of the mobile armatures 9 is simpler and more cost-effective than similar fuel injectors by virtue of the particular conformation of the hydraulic braking device 31.
Finally, the performance of the fuel injector 1 described above is extremely dynamic (i.e. the injection valve 7 can be opened and closed very rapidly) even when the fuel supply pressure is high (even higher than 60-70 Mpa). Such a result is obtained substantially by virtue of the fact that two twin electromagnets 8 of relatively small size are used, thus having low mechanical and magnetic inertia.
It is worth noting that the fuel injector 1 described above may be used to inject any type of fuel in internal combustion engines operating according to the Otto cycle (i.e with spark controlled ignition of the mixture) or in fuel injectors operating according to the Diesel cycle (i.e. with compressed injection of the mixture).

Claims

A fuel injector (1) comprising:
an injection nozzle (3);

an injection valve (7), which is provided with a mobile plunger (17) to adjust the flow of fuel through the injection nozzle (3);

an electromagnetic actuator (6) to move the plunger (17) between a closing position and an opening position of the injection valve (7) and provided with at least one electromagnet (8) comprising a coil (11), a fixed magnetic armature (12), and a mobile armature (9), which is mechanically connected to the plunger (17) and has at least one supply through hole (30) for the passage of fuel towards the injection nozzle (3);

a hydraulic braking device (31), which is coupled to the supply hole (30) and has the function of hydraulically generating a braking force to decelerate the travel of plunger (17) both when the plunger (17) moves towards the opening position of the injection valve (7) and when the plunger (17) moves towards a closing position of the injection valve (7);

a closing spring (10), which tends to hold the plunger (17) in the closing position; and

a supporting body (4) with a tubular shape and provided with a central channel (5), which houses the fixed magnetic armature (12) and the mobile armature (9);

wherein the hydraulic braking device (31) comprises: a valve element (32), which is coupled to the supply hole (30) of the mobile armature (9) and comprises an elastic blade (33), which is partially fixed to a surface (34) of the mobile armature (9); and a stop element (36), which is coupled to the elastic blade (33) and is arranged at a given distance from the elastic blade (33) to stop an opening movement of the elastic blade (33) itself in a fixed and predetermined position,

the injector (1) is characterized in that the hydraulic braking device (31) comprises a spacer (37), which is interposed between the elastic blade (33) and the stop element (36) and establishes the axial distance existing between the elastic blade (33) and the stop element (36).
An injector (1) according to claim 1, wherein the hydraulic braking device (31) has an asymmetrical behavior and, when the plunger (17) moves towards the closing position of the injection valve (7), hydraulically generates a braking force greater than when the plunger (17) moves towards the opening position of the injection valve (7).
An injector (1) according to claim 2, wherein the hydraulic braking device (31) hydraulically generates a braking force when the plunger (17) moves towards the closing position of the injection valve (7) which is comprised between 1.5 and 10 times the braking force which is hydraulically generated when the plunger (17) moves towards the opening position of the injection valve (7).
An injector (1) according to claim 2, wherein the hydraulic braking device (31) hydraulically generates a braking force when the plunger (17) moves towards the closing position of the injection valve (7) which is comprised between 1.5 and 5 times the braking force which is hydraulically generated when the plunger (17) moves towards the opening position of the injection valve (7).
An injector (1) according to any of the claims from 1 to 4, wherein the stop element (36) is stiffer than the elastic blade (33).
An injector (1) according to any of the claims from 1 to 5, wherein the stop element (36) is a limit stop, which limits the movement of the elastic blade (33) away from the supply hole (30), thus establishing a maximum opening position of the elastic blade (33).
An injector (1) according to one of claims from 1 to 6, wherein the spacer (37) has an annular shape.
An injector (1) according to any of the claims from 1 to 7, wherein the hydraulic braking device (31) comprises a first annular crown (38), which is fixed to a surface (34) of the mobile armature (9) and supports the elastic blade (33) of the valve element (32).
An injector (1) according to claim 8, wherein the elastic blade (33) has a circular shutter, which is arranged at the supply hole (30), and a stem, which connects the circular shutter to the first annular crown (38) and is adapted to be elastically deformed under the bias of the fuel.
An injector (1) according to any of the claims from 1 to 9, wherein the hydraulic braking device (31) comprises a second annular crown (39), which supports the stop element (36), which projects inwards from the second annular crown (39).
An injector (1) according to any of the claims from 1 to 10, wherein the elastic blade (33) of the valve element (32) has a calibrated through hole (35), which is arranged at the supply hole (30).
An injector (1) according to any of the claims from 1 to 11, wherein the elastic blade (33) of the valve element (32) is partially fixed to a lower surface (34) of the mobile armature (9) facing towards the injection nozzle (3).
An injector (1) according to any of the claims from 1 to 12, wherein the hydraulic braking device (31) has an asymmetrical behavior having different permeability to the passage of fuel as a function of the movement direction of the plunger (17).
An injector (1) according to any of the claims from 1 to 13, wherein the spacer (37) has a calibrated thickness.