Method for assembling and calibrating a fuel injector having a piezoelectric pressure sensor

Abstract

The invention relates to a method for assembling a fuel injector (10) having a piezoelectric pressure sensor (12), in which method, depending on a length (L) of a transmission element (16) acting on the piezoelectric pressure sensor (12), a preload force (Fv) is exerted on the pressure sensor (12) as a result of the assembly process, wherein the pressure sensor (12) generates a voltage or charge signal which is dependent on the preload force (Fv) and on a hydraulic pressure in a pressure chamber of the fuel injector (10), wherein, in a first step, the length (L) of the transmission element (16) for generating a defined preload force (Fv) acting on the pressure sensor (12) after the transmission element (16) has been installed in the fuel injector (10) is determined, and in a second step, a calibration line (KG), which is characteristic of the force curve, of the pressure sensor (12) provided for installation in the fuel injector (10) is determined.

Description

[0001] R.409558

[0002] - 1 -

[0003] Description

[0004] Method for mounting and calibrating a fuel injector having a piezoelectric pressure sensor

[0005] Technical field

[0006] The invention relates to a method for mounting and calibrating a fuel injector having a piezoelectric pressure sensor, which is characterized in particular by the fact that wear, especially in large diesel fuel injectors, can be reliably detected even after a longer period of operation and taken into account when controlling the fuel injectors.

[0007] State of the art

[0008] The detection of hydraulic pressure prevailing in a control chamber of a fuel injector using a piezoelectric pressure sensor is already known from the prior art (DE 10 2021 203 572 A1). In this process, the hydraulic pressure prevailing in the control chamber is transmitted to the piezoelectric element of the pressure sensor via a deformable diaphragm plate and a bolt-shaped transmission element. At least the transmission element is arranged in the region of a through-bore of a valve plate, which is clamped axially against a housing part of the fuel injector by means of a nozzle clamping nut, or is subjected to an axial force. Since the nozzle clamping nut and the housing parts interacting with the nozzle clamping nut have threads, the initial force applied to the valve plate during tightening is not exactly coaxial with the longitudinal axis of the fuel injector or the through-bore in the valve plate.Furthermore, both the valve plate and the transmission element are subject to manufacturing tolerances, which have an effect on the piezo element of the R.409558.

[0009] - 2 -

[0010] The pressure sensor is subject to a force resulting from the hydraulic pressure, as well as a preload force on the pressure sensor that is generated during the assembly of the fuel injector and is necessary to ensure the functionality of the pressure sensor.

[0011] Particularly with large diesel injectors, wear can become apparent after approximately 2000 operating hours, negatively impacting their injection behavior. This leads to a deterioration in both fuel consumption and emissions. Using the pressure sensor described in the aforementioned document, the movement of the nozzle needle can be recorded via the control chamber pressure and evaluated using algorithms within a control unit. This allows the timing of the fuel injector solenoid valve activation to be adjusted to compensate for the wear of the large diesel injector. It is also crucial that the piezoelectric pressure sensor is subjected to the correct preload. Overloading it can lead to mechanical failure and consequently, signal loss.If, however, the preload force is too low, the algorithms in the control unit cannot properly analyze the sensor signal from the pressure sensor from the outset.

[0012] Disclosure of the invention

[0013] Based on the aforementioned prior art, the inventive method for mounting and calibrating a fuel injector comprising a piezoelectric pressure sensor, with the features of claim 1, has the advantage that, on the one hand, the setting of the aforementioned length of the transmission element, which significantly influences the preload force on the piezoelectric pressure sensor during mounting, can be determined very precisely, and that, on the other hand, design-related tolerances of the piezoelectric pressure sensor are taken into account by individually recording the force / displacement characteristic of the piezoelectric pressure sensor. Together, these features enable accurate measurement of the control chamber pressure over the entire service life of the fuel injector and thus the possibility of mitigating any mechanical wear of components that may occur during the actuation of a solenoid valve for opening and closing (R.409558).

[0014] - 3 - to take into account or compensate for a nozzle needle in order to ensure advantageous exhaust emission and fuel consumption values.

[0015] In light of the above explanations, a method according to the invention for mounting a fuel injector comprising a piezoelectric pressure sensor with the features of claim 1 provides that a preload force is generated on the pressure sensor during mounting, depending on the length of a transmission element acting on the piezoelectric pressure sensor. Furthermore, the piezoelectric pressure sensor generates a voltage or charge signal that depends on the preload force and a hydraulic pressure in a control chamber of the fuel injector. The method is characterized in that, in a first step, the length of the transmission element is determined to generate a defined preload force acting on the piezoelectric pressure sensor after the transmission element has been mounted in the fuel injector.In a second step, a force / displacement characteristic curve is then determined for the piezoelectric pressure sensor intended for installation in the fuel injector. Finally, the transmission element, which is individually designed in its length, is mounted in a housing of the fuel injector together with the individually measured piezoelectric pressure sensor.

[0016] The first two steps thus enable, on the one hand, an individual determination of the length of the transmission element for generating a defined preload force on the piezoelectric pressure sensor, particularly due to manufacturing tolerances, and, on the other hand, take into account the individual behavior of the piezoelectric pressure sensor for detecting the control chamber pressure.

[0017] Advantageous further developments of the inventive method for the assembly and calibration of a fuel injector having a piezoelectric pressure sensor are listed in the dependent claims.

[0018] In a specific preferred embodiment of the method, it is provided that the first step for determining the length of the transmission element comprises at least the following steps: First, a pressure is applied to a device radially receiving the transmission element in a through-hole, R.409558

[0019] - 4 - a pre-assembled valve plate with an alignment force acting in the direction of the pressure sensor, without the transmission element, to determine a tilt height between the valve plate and the housing component in relation to a housing component serving the planar contact of the valve plate. Subsequently, the piezoelectric pressure sensor is subjected to the preload force by means of a reference transmission element that is different from the transmission element. Finally, the length of the transmission element is determined based on the length of the reference transmission element, the tilt height, and a fuel injector-specific geometric constant.

[0020] In order to potentially eliminate measurement errors and to allow for the setting of components in order to achieve more constant measured values, a preferred embodiment of the method described above provides that the tilting height of the valve plate is determined by repeatedly applying a force to the valve plate, whereby the force is varied each time between a minimum value and a maximum value, and that the tilting height is preferably determined during the last application of the force to the valve plate, using the preload force that lies between the minimum value and the maximum value.

[0021] It is further preferred that the preload force corresponds to a force at which the piezoelectric pressure sensor generates a voltage or charge signal that changes linearly with the force. This enables a particularly simple and accurate determination of the hydraulic pressure conditions prevailing in the control chamber using an algorithm that, based on a linear characteristic curve in the form of a calibration curve, can easily calculate the force transmitted from the hydraulic pressure to the piezoelectric pressure sensor via the linearly changing voltage or charge signal.

[0022] In a specific preferred embodiment regarding the second step of the method according to the invention, it is provided that in the second step the piezoelectric pressure sensor is subjected to at least two test forces of different magnitudes, and that on the basis of the voltage or charge signals generated by the piezoelectric pressure sensor during the test forces with the resulting sensor forces, a

[0023] - 5 -

[0024] A calibration curve is determined, on the basis of which the hydraulic pressure in the pressure chamber is determined.

[0025] In particular, the latter method provides that the different test forces are applied several times and that the voltage or charge signals generated, preferably during the last application of the test forces, are used to determine the calibration curve.

[0026] Furthermore, it is advantageous if the two test forces correspond to the preload force and are below a maximum force that can be detected by the piezoelectric pressure sensor without damaging it. This results in a large distance between the forces detectable by the piezoelectric pressure sensor and the calibration curve, so that at least the minimum and maximum forces acting on the piezoelectric pressure sensor, or their corresponding voltage and charge signals, can be determined in advance.

[0027] It is also advantageous if the calibration curve is determined using a reference transfer element, wherein the reference transfer element is preferably the same reference transfer element used in determining or carrying out the first step to determine the length of the transfer element.

[0028] Furthermore, it is preferred that the process be used in the production of fuel injectors for large diesel engines. A large diesel engine is generally understood to be either stationary diesel engines, e.g., for power generation, or large diesel engines in ships, vehicles such as dump trucks, locomotives, etc.

[0029] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments of the invention and from the drawings.

[0030] Brief description of the drawings R.409558

[0031] - 6 -

[0032] Fig. 1 shows in a longitudinal section components of a fuel injector with a valve plate and a transmission element in the form of a spacer bolt acting on a piezoelectric pressure sensor,

[0033] Fig. 2 is a force-displacement diagram to illustrate the behavior of the pressure sensor under pressure.

[0034] Fig. 3 to

[0035] Fig. 5 shows the alignment of a measuring plunger to a valve plate during different, successive time periods.

[0036] Fig. 6 and

[0037] Fig. 7 shows the arrangement according to Figs. 3 to 5 during the measurement of a misalignment of the valve plate in a side view,

[0038] Fig. 8 and

[0039] Fig. 9 shows the force measurement on a pressure sensor when using a reference spacer bolt as a transmission element.

[0040] Fig. 10 in diagram for determining a calibration curve of the pressure sensor and

[0041] Fig. 11 shows a calibration curve of a pressure sensor determined on the basis of the diagram in Fig. 11.

[0042] Embodiments of the invention

[0043] Identical elements or elements with the same function are provided with the same reference numbers in the figures.

[0044] The invention relates to a method for determining the dimensioning of components of a fuel injector 10 and the calibration of an R.409558

[0045] - 7 - piezoelectric pressure sensor 12 of the fuel injector 10 for a self-igniting internal combustion engine. Such a fuel injector 10 is known in principle from DE 102021 203 572 A1 of the applicant, the content of which, with regard to the basic structure of such a fuel injector 10 and its operation, is to be incorporated into this application.

[0046] The fuel injector 10, shown in partial view in Fig. 1, is characterized in particular by the fact that the hydraulic pressure of the fuel prevailing in a control chamber (not shown in Fig. 1) is transmitted, at least indirectly, via a diaphragm plate 14 and a spacer bolt 16 as a transmission element, to a pressure-sensitive element of the piezoelectric pressure sensor 12, which generates a voltage or charge signal. This signal allows the temporal profile of the hydraulic pressure in the control chamber to be determined. Based on this temporal profile, the temporal profile or current flow of a nozzle needle, which can be moved by an electromagnet or similar element, can in turn be determined and optimized in order to achieve the desired performance and exhaust emission values ​​of the internal combustion engine.

[0047] Figure 1 shows the installation state of the piezoelectric pressure sensor 12 in the area of ​​a recess 18 of a housing component 20 in the form of a valve body of the fuel injector 10. The housing component 20 is arranged in planar contact with a valve plate 22. The valve plate 22 has a through-hole 24 for receiving the spacer bolt 16, the diameter of which is matched to the diameter of the through-hole 24 such that the spacer bolt 16 is guided in the through-hole 24 with only minimal radial play, in order to transmit the force acting via the diaphragm plate 14 to the piezoelectric pressure sensor 12 with minimal loss.

[0048] The spacer bolt 16 has a longitudinal axis 26 that runs perpendicular to the plane of the valve plate 22. Furthermore, a guide bolt 28 is shown in Fig. 1, which serves, among other things, to position or align the diaphragm plate 14 with respect to the valve plate 22. Fig. 1 also shows that the end face 27 of the spacer bolt 16 facing the diaphragm plate 14 is connected to the R.409558

[0049] - 8 -

[0050] Membrane plate 14 rests against and is flush with the top surface 29 of the valve plate 22.

[0051] Figure 2 shows the basic course of a force F acting on the piezoelectric pressure sensor 12 in the direction of the longitudinal axis 26, as detected by the sensor, as a function of a tool distance a to a reference plane, with the tool acting on the spacer bolt 16 in the through-hole 24. In particular, it can be seen that the force-displacement characteristic KL of the piezoelectric pressure sensor 12 typically exhibits a linear course from a force F of 300 N or a correspondingly decreasing tool distance a, which continues up to at least approximately 700 N. Furthermore, it is explained that larger forces F acting on the piezoelectric pressure sensor 12 can lead to damage to the sensor, with the force range mentioned between 300 N and 700 N typically corresponding to the hydraulic pressures prevailing in the control chamber of the fuel injector 10 during operation.the forces thereby exerted on the piezoelectric pressure sensor 12 are adapted. In order to utilize the linear curve of the characteristic curve KL, it is therefore desirable that the spacer bolt 16 is preloaded with a preload force F in the unpressurized state of the control chamber or without fuel pressure. v is preloaded by 300 N, so that the hydraulic pressures prevailing in the control chamber during the operation of the fuel injector 10 can lead to a force of the spacer bolt 16 on the piezoelectric pressure sensor of up to 700 N.

[0052] It is also essential that the valve plate 22, when assembled with the housing component 20, does not initially rest flat on the top surface of the housing component 20, but rather exhibits an inclination with a tilt height s (Fig. 3). The tilt height s of the valve plate 22 relative to the housing component 20 results from the fact that, during assembly or axial clamping of the valve plate 22 against the housing component 20 using a nozzle clamping nut (not shown), the thread pitch of the nozzle clamping nut causes the valve plate 22 to only make full contact with the top surface of the housing component 20 once axial clamping is complete or a certain minimum force is applied. This condition is illustrated in Fig. 4. R.409558

[0053] - 9 - To determine the tilt height s in the pre-assembled valve plate 22, which is essentially unloaded by the aforementioned nozzle clamping nut, a measuring punch 30, whose diameter is larger than the diameter of the through-hole 24 in the valve plate 22, is first aligned perpendicular to the plane of the housing component 20, as shown in the sequence of figures 3 to 5, so that a longitudinal axis 32 of the measuring punch 30 runs coaxially to the through-hole 24 or perpendicular to the plane of the valve plate 22. This is achieved by pressing the measuring punch 30, which may initially be tilted, against the top of the valve plate 22 with an alignment force FA of 350 N ± 30 N, as shown in figure 4. Figure 5 shows the state after the measuring plunger 30 has been arranged at a distance from the valve plate 22, with the longitudinal axis 32 of the measuring plunger 30 then being aligned perpendicular to the upper surface 34 of the housing component 20 facing the valve plate 22.

[0054] Subsequently, a dimension f is recorded taking into account the misalignment s of the valve plate 22, when the valve plate 22 is subjected to the preload force F. v The valve plate is loaded with a force of 300 N. The dimension f takes into account both the tilting height s and the compression of the valve plate 22 resulting from its (elastic) deformation. The dimension f is measured as shown in Figures 6 and 7 by pressing the measuring plunger 30 against the valve plate 22 with a force FM during several successive measurement processes, particularly during a 10-fold repetition. The force FM is increased from 0 N to 1000 N, with the preload force F being adjusted accordingly. v The dimension f is recorded when a force of 300 N is applied. The final dimension f is recorded when the valve plate 22 is last struck with the measuring stamp 30.

[0055] Subsequently, to determine the length L of the spacer bolt 16, which is individually matched to the fuel injector 10, a reference spacer element in the form of a reference spacer bolt 36 is used. The reference spacer bolt 36 has a length L re f, which is typically slightly larger than the length L of the (final) spacer bolt 16, so that the reference spacer bolt 36 projects beyond the valve plate 22 on the side facing away from the housing component 20, in order to prevent contact between the measuring pin 30 and the valve plate 22. The reference spacer bolt 26 is R.409558

[0056] - 10 - using the measuring punch 30, the load is also applied ten times in succession with an increasing force F between 0 N and 700 N, in order to record the displacement y2 visible in Fig. 9 in comparison between Figs. 8 and 9, which occurs when the preload force F is applied. v The final measurement of 300 N will be recorded.

[0057] The length L of the spacer bolt 16 can then be determined according to the formula

[0058] L = L re The f-y2-f offset is determined. The offset value characterizes the deformation behavior of the other components of the fuel injector 10 that are essential during the screwing process and was determined experimentally beforehand.

[0059] After calculating the length L of the spacer bolt 16, it is essential to know the individual behavior of the signal curve of the piezoelectric pressure sensor 12 in order to accurately measure the pressures prevailing in the control chamber of the fuel injector 10 during operation. Reference is made to the illustration in Fig. 10. Fig. 10 shows the curve of a test force Pi and P2 and a sensor force Si and S2 detected by the piezoelectric pressure sensor 12 during an ascending and descending load on the piezoelectric pressure sensor 12 with a maximum sensor force Si and S2 of 300 N and 500 N, respectively. The measurement is preferably carried out according to the illustrations in Figs. 8 and 9 using the reference spacer bolt 36. The measurement is preferably performed such that the piezoelectric pressure sensor 12 is first loaded four times with the test force Pi of 300 N, the first load serving to settle the components.The piezoelectric pressure sensor 12 is then subjected to a test force P2 of 500 N. The curves shown in Fig. 10 for the last measurement series are subsequently converted into a calibration curve KG shown in Fig. 11 using an evaluation program. The calibration curve KG shows the linear relationship between the test force P and the sensor force S. It serves to convert the voltage or charge signal generated by the piezoelectric pressure sensor 12, or the sensor force S determined from it, into the actual test force P acting on the piezoelectric pressure sensor 12, R.409558.

[0060] - 11 - after the screwing process of the nozzle clamping nut acts on the piezoelectric pressure sensor 12. The calibration curve KG thus shows, using the spacer bolt 16 with length L, the sensor force S generated by the piezoelectric pressure sensor 12 under a load of test force P. The sensor force S can therefore be converted into the test force P acting on the piezoelectric pressure sensor 12 using the calibration curve KG and supplied as an input variable to a control device for controlling a solenoid valve for the required opening and closing of a nozzle needle of the fuel injector 10 with regard to performance and exhaust gas values, when the hydraulic pressure acts on the piezoelectric pressure sensor 12 via the pressure chamber during operation of the fuel injector 10.

[0061] After the individual dimension for the length L of its spacer bolt 16 for the fuel injector 10 has been determined and, in addition, the piezoelectric pressure sensor 12 used in the fuel injector 10 has been individually measured, the components of the fuel injector 10 are assembled in a manner known per se.

Claims

R.409558 - 12 - Claims 1. Method for mounting a fuel injector (10) having a piezoelectric pressure sensor (12), wherein, depending on the length (L) of a transmission element (16) acting on the piezoelectric pressure sensor (12), a preload force (F) is applied to the piezoelectric pressure sensor (12) by the mounting. v ) is generated, wherein the piezoelectric pressure sensor (12) is subjected to the preload force (F v ) and a hydraulic pressure in a pressure chamber of the fuel injector (10) generates a voltage or charge signal, wherein in a first step the length (L) of the transmission element (16) is used to generate the defined preload force (F) acting on the piezoelectric pressure sensor (12) after the transmission element (16) has been mounted in the fuel injector (10). v) is determined that in a second step a calibration curve (KG) characteristic for the force curve of the piezoelectric pressure sensor (12) provided for mounting in the fuel injector (10) is determined, and that finally the transmission element (16) individually designed in its length (L) with the individually measured piezoelectric pressure sensor (12) is mounted in a housing of the fuel injector (10).

2. Method according to claim 1, characterized in that the first step comprises at least the following steps: applying an alignment force (FA) acting in the direction of the piezoelectric pressure sensor (12) to a pre-assembled valve plate (22) radially receiving the transmission element (16) in a through-bore (24) without the transmission element (16) to determine a tilting height (s) between the valve plate (22) and the housing component (20) in relation to a housing component (20) serving as a surface contact point for the valve plate (22). R.409558 - 13 - Applying the preload force (F) to the piezoelectric pressure sensor (12) by means of a reference transmission element (36) that is different from the transmission element (16). v ), Determining a length (L) of the transmission element (16) based on a length (L ref) of the reference transfer element (36), the tilt height (s) and a fuel injector-specific geometric constant.

3. Method according to claim 2, characterized in that the determination of the length (L) of the transmission element (16) according to the formula L= L re f - y2 - offset is performed, where L re f is the length of the reference transmission element, y2 is a measure when the piezoelectric pressure sensor (12) is subjected to the reference force, and offset is the fuel injector-specific geometry constant.

4. Method according to claim 2 or 3, characterized in that the tilting height (s) of the valve plate (22) is determined by repeatedly applying a force (F) to the valve plate (22), wherein the force (F) is varied each time between a minimum value and a maximum value, and that the tilting height (s) is preferably determined during the last application of the force (F) to the valve plate (22) when applying the preload force (F) which lies between the minimum value and the maximum value. v ) is determined.

5. Method according to one of claims 1 to 4, characterized in that the preload force (F v ) corresponds to a force from which the piezoelectric pressure sensor (12) generates a voltage or charge signal that changes linearly with the force. R.409558 - 14 - 6. Method according to one of claims 1 to 5, characterized in that in the second step the piezoelectric pressure sensor (12) is subjected to at least two different test forces (Pi , P2), and that on the basis of the voltage or charge signals generated by the piezoelectric pressure sensor (12) at the test forces (Pi, P2) with the resulting sensor forces (Si , S2) the calibration curve (KG) is determined, on the basis of which the hydraulic pressure in the pressure chamber is determined.

7. Method according to claim 6, characterized in that the different test forces (Pi, P2) are applied several times and the voltage or charge signals generated preferably during the last application of the test forces (Pi, P2) are used to determine the calibration curve (KG).

8. Method according to claim 6 or 7, characterized in that the two test forces (Pi, P2) of the preload force (F v) and correspond to a maximum force that can be detected below by the piezoelectric pressure sensor (12) without damage.

9. Method according to one of claims 6 to 8, characterized in that the calibration line (KG) is determined by means of a reference transfer element (36), preferably the reference transfer element (36) used in the first step.

10. Method according to one of claims 1 to 9, characterized in that the method is used in the production of fuel injectors (10) for large diesel engines.

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