A METHOD FOR MONITORING A COMMON-RAIL INJECTOR FOR LARGE DIESEL AND DUAL-FUEL ENGINES AND INJECTOR CONFIGURED TO IMPLEMENT THIS METHOD

Abstract

A method for monitoring an injector for common-rail injection systems includes detecting an electrical signal indicative of a deformation of a diaphragm of a head plate having a reaction surface facing a control chamber of the injector and processing the deformation signal to determine characteristic data of the operation of the injector.

Claims

1. A method for monitoring an injector for common-rail injection systems, comprising: detecting an electrical signal indicative of a deformation of an integral diaphragm of a head plate, wherein said diaphragm has a reaction surface facing a control chamber of the injector and against which a head surface of an injector needle strikes in an open position of the injector, and processing said electrical signal to determine characteristic data of operation of the injector.

2. The method according to claim 1, wherein the electrical signal indicative of the deformation of said diaphragm is provided by a piezoelectric sensor housed in a blind hole formed in the head plate and isolated from the control chamber of the injector by said diaphragm.

3. The method according to claim 1, wherein said electrical signal is indicative of the deformation of said diaphragm along a longitudinal axis of the injector needle.

4. The method according to claim 1, wherein said electrical signal indicative of the deformation of said diaphragm is analyzed to determine one or more of the following operating parameters of the injector: opening time of a control valve; opening time of the injector needle; start time of delivery of a maximum flow rate; time of reaching a stroke-end position of opening of the injector needle; start time of closing of the injector needle; end time of delivery of the maximum flow rate; time of closure of the injector needle, and maximum injected flow rate.

5. An injector for common-rail injection systems, comprising: a delivery chamber connected to a pressurized fuel supply line and provided with a valve seat, an injector needle extending through said delivery chamber and having a sealing surface that cooperates with said valve seat, wherein the injector needle is movable along a longitudinal axis between a closed position in which said sealing surface abuts against said valve seat, and an open position in which said sealing surface is spaced apart from said valve seat, a control chamber connected to said fuel supply line through a calibrated inlet orifice and connected to a discharge line by means of a calibrated outlet orifice, wherein the control chamber is delimited partly by a head surface of the injector needle and partly by a reaction surface of a head plate, and wherein the head surface of the injector needle in the open position of the injector needle abuts against said reaction surface, and an electrically-operated control valve arranged to selectively open and close hydraulic communication between the control chamber and the discharge line, wherein said head plate has an integral diaphragm on which said reaction surface is formed, and wherein the injector comprises a sensor which supplies an electrical signal indicative of deformations of said diaphragm.

6. The injector according to claim 5, wherein said sensor is a piezoelectric transducer.

7. The injector according to claim 5, wherein said sensor is housed in a blind hole formed in the head plate and isolated from the control chamber of the injector by said diaphragm.

8. The injector according to claim 7, wherein said blind hole has a side surface coaxial to said longitudinal axis and a bottom surface parallel and opposite to the reaction surface of the diaphragm.

9. The injector according to claim 5, wherein said sensor comprises two piezoelectric elements oriented perpendicularly to said longitudinal axis and an electrode arranged between said piezoelectric elements.

10. The injector according to claim 5, comprising an electronic board located on the injector and configured for connection to a processing system for processing the electrical signal provided by said sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will now be described in detail with reference to the attached drawings, given purely by way of non-limiting example, wherein:

[0033] FIG. 1 is a schematic view illustrating the operation of an injector for common-rail injection systems,

[0034] FIG. 2 is an axial cross-section of an injector for common-rail injection systems,

[0035] FIG. 3 is a cross-section on an enlarged scale of the part indicated by the arrow III in FIG. 2,

[0036] FIG. 4 is an enlarged detail of the part indicated by the arrow IV in FIG. 3,

[0037] FIG. 5 is a diagram illustrating an injector monitoring system,

[0038] FIG. 6 is a graph illustrating theoretical injection diagrams of an injector,

[0039] FIG. 7 is a diagram illustrating the trend of the supply current of the control valve of an injector, and

[0040] FIG. 8 is a diagram illustrating the trend of a monitoring signal of the injector together with an injection diagram created by the injector.

DETAILED DESCRIPTION

[0041] In FIG. 1, an injector for a common-rail injection system is indicated by 10. The injector 10 comprises a pulverizer 12 having a fuel delivery chamber 14 having a valve seat 16. An injector needle 18 extends into the delivery chamber 14 and has a sealing surface 20 that cooperates with the valve seat 16. The injector needle 18 is movable along its longitudinal axis A between a closed position in which the sealing surface 20 abuts against the valve seat 16, and an open position in which the sealing surface 20 is spaced apart from the valve seat 16. A spring 22 tends to push the injector needle 18 towards the closed position. The pulverizer 12 has a plurality of injection holes 24 through which the pressurized fuel located in the delivery chamber 14 is pulverized when the injector needle 18 is in the open position.

[0042] The injector 10 comprises a storage volume 26 which, together with similar storage volumes of other injectors of the same engine, constitutes a distributed common-rail. The storage volume 26 is filled with pressurized fuel coming from a high-pressure pump. The storage volume 26 is connected to a supply duct 28 having a first branch 30 connected to the delivery chamber 14 of the pulverizer 12 and a second branch 32 connected to a control chamber 34 through a first calibrated orifice 36. The control chamber 34 is connected to a discharge line 38 which leads to a tank 40. A control valve 42 is arranged on the discharge line 38. The control valve 42 is an electrically-controlled two-position valve whichin the open positionconnects the control chamber 34 to the discharge line 38 andin the closed positionisolates the control chamber 34 from the discharge line 38. A second calibrated orifice 44 is arranged upstream of the control valve 42.

[0043] When the control valve 42 is closed, the pressure in the control chamber 34 is equal to the pressure in the delivery chamber 14 whichin turnis equal to the pressure in the storage volume 26. In the closed position of the injector needle 18, the surface of influence of the injector needle 18 exposed in the control chamber 34 is greater than the surface of influence of the injector needle 18 exposed in the delivery chamber 14, so that a hydraulic force is generated on the injector needle 18 which pushes the injector needle 18 into the closed position. When the control valve 42 is opened, the pressure in the control chamber 34 is reduced and the injector needle 18 is subjected to a resulting hydraulic force which moves the injector needle 18 towards the open position.

[0044] FIGS. 2, 3 and 4 illustrate an embodiment of an injector according to the present invention which operates on the basis of the operating principle described with reference to FIG. 1. The elements corresponding to those previously described are indicated with the same numerical references.

[0045] With reference to FIG. 2, a flow rate limiting valve can be provided on the fuel supply line 28, which extends from the storage volume 26 to the delivery chamber of the pulverizer 12. The control valve 42 can be housed inside the injector 10, and is connected to an electric line 48 which gives the control valve 42 an electric opening command.

[0046] With reference to FIGS. 3 and 4, the injector 10 comprises a head plate 50 arranged in hydraulic sealing contact with a head surface 52 of the pulverizer 12.

[0047] In the head plate 50 the calibrated orifices 36, 44 are formed, which are connected to the control chamber through respective holes 54, 56 which are also formed in the head plate 50. The holes 54, 56 are open on a reaction surface 58 of the head plate 50 facing the control chamber 34. The reaction surface 58 of the head plate 50 can be formed in a seat 60 open towards the delivery chamber 14 of the pulverizer 12. A bushing 62 is partially housed inside the seat 60 and has a hole 64 in which a head portion of the injector needle 18 slides. The control chamber 34 is delimited by the reaction surface 58 of the head plate 50, by a head surface 66 of the injector needle 18 and by an annular portion 68 of the guide bushing 62.

[0048] In the open position of the injector needle 18, the head surface 66 of the injector needle 18 comes into contact with the reaction surface 58.

[0049] With reference to FIG. 4, the head plate 50 comprises an integral diaphragm 120 formed by a portion of the head plate 50 with reduced thickness. The diaphragm 120 has a first surface in direct contact with the pressurized fluid contained in the hydraulic chamber 34. The first surface of the diaphragm 120 may consist of a portion of the reaction surface 58. The diaphragm 120 has a second surface opposite the first surface, which is not in contact with the pressurized fluid contained in the hydraulic chamber 34. In the illustrated embodiment, the diaphragm 120 is located at the bottom of a blind hole 72 formed in the head plate 50. The blind hole 72 has a side surface 74 and a bottom surface 76 forming the second surface of the diaphragm 120.

[0050] With reference to FIGS. 3 and 4, the injector 10 comprises a sensor 70 which provides an electrical signal for monitoring the operation of the injector 10.

[0051] The sensor 70 can be a piezoelectric pressure transducer that provides an electrical signal related to the pressure acting on the reaction surface 58 of the head plate 50 in the direction of the longitudinal axis A. The electrical signal supplied by the sensor 70 is indicative of the deformations of the diaphragm 120 generated by the variations in fluid pressure in the control chamber 34 and by the variation in the force with which the injector needle 18 comes into contact with the reaction surface 58.

[0052] The sensor 70 may comprise two piezoelectric elements 78, 80 each of which has two flat faces parallel to each other and orthogonal to the axis A. The use of a piezoelectric sensor 70 allows withstanding much higher operating temperatures than those permitted by other types of sensitive materials.

[0053] Each of the two piezoelectric elements 78, 80 generates an accumulation of positive charges on a first face and negative charges on the second face opposite to the first. The amount of electric charges generates a potential difference that increases proportionally to the deformation of the piezoelectric element 78, 80 in the direction of the A axis.

[0054] Between the two piezoelectric elements 78, 80 there is an electrode 82 formed by a sheet of conductive material arranged in contact with the first faces of the two piezoelectric elements 78, 80, having a positive polarization under load.

[0055] The sensor 70 also comprises two supporting elements 84, 86 of metal material arranged in contact with the second faces of the piezoelectric elements 78, 80, having a negative polarization under load.

[0056] The electrode 82 arranged between the two piezoelectric elements 78, 80 constitutes the positive pole of the sensor 70. The negative pole consists of the supports 84, 86 electrically-connected to ground through the head plate 50. The electrode 82 is connected to an electric cable on which an analogue electrical signal is generated, proportional to the force acting between the two supports 84, 86 in the direction of the longitudinal axis A.

[0057] An annular element 88 of insulating material is arranged outside the electrode 82. The annular element 88 allows the centering between the piezoelectric elements 78, 80 and the electrode 82 and guarantees the isolation of the electrode 82 from the negative pole consisting of the metal components of the injector.

[0058] The sensor 70 is housed in the hole 72 and is compressed axially between the bottom surface 76 of the hole 72 and a surface 89 of a body portion 90 of the injector 10. An elastic element 92, formed for example by a cup spring, can be arranged between the support 84 and the bottom surface 76 of the hole 72. The elastic element allows adjustment of the force transmitted to the piezoelectric elements 78, 80 according to the deformation of the reaction surface 58 of the head plate 50 under the action of the pressure acting in the control chamber 34. In this way, it is possible to guarantee an adequate thickness of the wall arranged between the surfaces 58 and 76 and, therefore, the structural strength of the head plate 50 under the action of the pressure in the control chamber 34, and at the same time to ensure that the deformation of the reaction surface 58 does not generate excessive loads on the piezoelectric elements 78, 80.

[0059] By an appropriate choice of the dimensions and geometry of the elastic element 92, its rigidity is adapted to the compression force and, consequently, the overall rigidity of the components of the sensor 70 is modified so that the deformation of these components imposed by the displacement of the surface 76 generates a force compatible with the working field of the at least one piezoelectric element 78, 80.

[0060] The facing and opposite arrangement of the piezoelectric elements 78, 80 doubles the sensitivity of the sensor 70 with respect to a sensor that uses a single piezoelectric element and simplifies its construction since it uses the same piezoelectric elements 78, 80 as electrical insulation elements between the positive pole and the negative pole and avoids the introduction of further elements of insulating material into the stack of elements that support the load to which the sensor 70 is subject.

[0061] The sensor 70 has very small dimensions and can be easily housed between the calibrated orifices 36, 44 of the head plate 50.

[0062] The sensor 70 is capable of providing an indirect measurement of the hydraulic pressure in the control chamber 34 without any contact with the fuel. In fact, the pressure of the fuel in the control chamber 34 causes deformations of the diaphragm 120 which are detected by the sensor 70 with an excellent signal/noise ratio.

[0063] In the operation diagnostics of an injector for large naval engines, detection of the moments in which the injector needle 18 comes into contact with, or detaches from, the reaction surface 58, which implements the mechanical stop of the injector needle 18 during its opening path, is particularly important. A particularly advantageous feature of the method and the apparatus according to the invention is that the injector needle 18 in the open position enters directly into contact with the diaphragm 120. The sensor 70 is mechanically coupled to the diaphragm 120 and detectswith high precisionthe instant in which the injector needle 18 comes into contact with the reaction surface 58 (which is the instant in which the opening stroke of the injector needle 18 ends) and the instant in which the injector needle 18 detaches from the reaction surface 58 (which is the instant in which the closing stroke of the injector needle 18 begins).

[0064] The sensor 70, therefore, provides a signal that is directly related, without delay or disturbance, to the pressure existing in the control chamber and to the force with which the injector needle 18 rests against the reaction surface 58. The measurement is not invasive, as the hydraulic circuit that performs the injector control by modulating the pressure in the control chamber is not altered (standard injector and one equipped with diagnostic instrumentation behave identically).

[0065] With reference to FIG. 5, each injector 10 comprises an electronic board 94 which can be mounted on the end of the injector 10 opposite the pulverizer 12. The electronic board 94 receives analog signals coming from the pressure sensor 70 and, possibly, from a temperature sensor 95 and from a current sensor 96, which indicates the value of the driving current of the control valve 42. The analog signals from the sensors 70, 95, 96 can be sent to an analog/digital converter 98 which can be connected to a microprocessor 100. The microprocessor 100 may contain an identification number of the injector 10, data indicative of the number of operating hours, an identification code of the customer, as well as any other information. The electronic board 94 of the injector 10 receives the driving current of the control valve 42 from an engine control unit 102 and sends the driving current to the control valve 42 via the electric line 48 located inside the injector 10.

[0066] The microprocessor 100 of the electronic board 94 can be connected to a communication channel 104, which can be implemented by means of a BUS, for example, of the RS485 type, to which other injectors 10 of the same engine can be connected. The communication channel 104 can be connected to an interface circuit 106 which can interface communication lines with different communication protocols. The interface circuit 106 can be connected to a processing system 108, for example, via an Ethernet line 110. The interface circuit 106 can also be connected to the engine control unit 102 via a CAN line 112.

[0067] The processing system 108 receives the signals coming from the electronic boards 94 of all the injectors 10 of the same engine and processes them to obtain, for example, the following information: opening time of the control valve, start time of injection, end time of the injector needle opening, start time of injector needle closure, end time of injection, maximum value of the injected flow rate. The information processed by the processing system 108 can be stored locally or transferred to a remote server 114. A user interface 116 allows access to the information stored in the processing system 108 and/or in the remote server 114.

[0068] FIG. 6 illustrates an injection diagram of an injector 10 which shows the flow rate G of fuel injected in time t for four values of duration of the electric control to the control valve 42. The injectors 10 should create the injection diagrams envisaged by the design respecting the injection start times, the speed of variation of the flow rate in the opening and closing steps, and the maximum level of flow dispensed.

[0069] FIG. 7 shows the value of the driving current I of the control valve 42 as a function of the time t during an injection cycle. FIG. 8 reports the signal V provided by the sensor 70, indicative of the deformation of the head plate 50 under the action of the hydraulic pressure in the control chamber 34. The signal V is also indicative of the force that the injector needle 18 transfers to the head plate 50 when the head surface 66 of the injector needle 18 abuts against the reaction surface 58 of the head plate 50, since the head plate 50 also acts as an opening stroke-end regarding the injector needle 18.

[0070] FIGS. 6, 7, 8 report real values which are specific of a given injector. The numerical values indicated in these figures are given only by way of example and it is intended that the present invention can be applied to different injector models operating with different timing and signal amplitudes.

[0071] Analyzing the variation of the signal V allows the most significant instants of the injector operating cycle to be clearly distinguished. The same diagram in FIG. 8 reports the curve G that indicates the injection diagram (flow rate of fuel injected as a function of time) measured at the test bench simultaneously with the monitoring signal V. From the trend of the signal V it is possible to identify the following steps of the injector cycle: [0072] t1: opening of the control valve, [0073] t2: opening of the injector needle, [0074] t3: start of delivery of the maximum flow rate, [0075] t4: injector needle at the opening stroke-end, [0076] t5: start of closing of the injector needle, [0077] t6: end of delivery of the maximum flow rate, [0078] t7: closing the injector.

[0079] From the example shown in FIG. 8 it can be seen that the deformation signal V shows significant variations during the injection cycle and has a very low noise. Therefore, the signal V allows extraction of significant data in a robust way. Using artificial intelligence techniques on the basis of the signal V, it is possible to extrapolate the maximum flow rate delivered during the injection cycle, thus obtaining all the elements necessary to reconstruct the actual injection diagram of the injector.

[0080] The diaphragm 120 of the head plate 50 is deformed both by the pressure existing in the control chamber 34 and by the force transmitted by the injector needle 18 when it is in contact with the diaphragm 120. The resulting signal is, therefore, both sensitive to pressure and to the position of the needle, in a direct manner. As can be easily deduced from the analysis of the signal reported in FIG. 8, when the injector needle reaches (or leaves) the reaction surface, significant variations of the signal are measured, allowing development of a simple and robust automatic recognition algorithm for these moments.

[0081] The information provided by the signal V allows constant monitoring of the injector operating parameters in order to estimate the shape of the actual injection diagram. This allows the engine makers to modify the electrical control generated by the engine control unit 102 to restore the injector operation to the optimal operating conditions and/or to suggest maintenance interventions.

[0082] Of course, without prejudice to the principle of the invention, the details of construction and the embodiments can be widely varied with respect to those described and illustrated, without thereby departing from the scope of the invention as defined by the claims that follow.