Pressure determination in a fuel injection valve

Abstract

The invention provides a device and a method for determining a pressure of a fuel (19) which is to be injected into a combustion chamber (23) via a controllable closure element (11) of a solenoid valve (1), wherein the method comprises: generating a current flow (i) through a coil (3) of the solenoid valve (1) in order to generate a magnetic field, in order to generate a magnetic force acting on an armature (9), which magnetic force shifts the armature (9) in the direction of the opening of the closure element (11), determining a magnitude of a magnetic flux () of the magnetic field before or when a first state (I) at which the armature starts to shift the closure element is reached, and determining a magnitude of the pressure on the basis of the determined magnitude of the magnetic flux.

Claims

1. A method for determining a pressure of a fuel, which is to be injected into a combustion chamber via a controllable closure element of a solenoid valve, the method comprising: generating a current through a coil of the solenoid valve to generate a magnetic field, in order to generate a magnetic force acting on an armature, which magnetic force shifts the armature in the direction of the opening of the closure element; determining a magnitude of a magnetic flux of the magnetic field before or when a first state at which the armature starts to shift the closure element is reached; and determining a magnitude of the pressure on the basis of the determined magnitude of the magnetic flux, wherein a sensitivity of the magnitude of the magnetic flux as a function of the magnitude of the pressure is known from previous measurements on the solenoid valve; and wherein the determination of the magnitude of the pressure is carried out as a determination of a change in pressure on the basis of the determined magnitude of the magnetic flux and the known sensitivity.

2. The method of claim 1, wherein the magnitude of the pressure is also determined from reference data which contain at least one magnitude of the magnetic flux at a known pressure.

3. The method of claim 1, wherein the magnitude of the magnetic flux is determined when the first state is reached, and wherein the magnitude of the pressure is determined as being proportional to the square of the magnitude of the magnetic flux.

4. The method of claim 1, wherein the magnitude of the magnetic flux is determined before the first state is reached, and a magnitude of at least one of an idle stroke and a working stroke of the armature is determined from the magnitude of the magnetic flux, wherein a sensitivity of the magnitude of the magnetic flux is taken into account as a function of the magnitude of the at least one of the idle stroke and the working stroke.

5. The method of claim 1, wherein pairs of a magnitude of a current and a magnitude of the magnetic flux, which correspond to a state trajectory of the closure element during a closing process of the solenoid valve, are considered, and wherein the first state is associated with a pair in which a sign of a gradient changes along the state trajectory.

6. The method of claim 1, wherein in a graph in which the current through the coil is plotted on the abscissa, and the magnetic flux is plotted on an ordinate, the first state is identified as being assigned to one of a location at which a positive gradient changes into a negative gradient and a location between a section of a positive gradient and a section of a negative gradient.

7. The method of claim 1, wherein initially a boost voltage between about 3 V and about 65 V, and a holding voltage between about 6 V and about 14 V are used to generate the current flow through a coil; wherein the armature comprises a slotted ferromagnetic material and layers of ferromagnetic material which are electrically insulated from one another, in order to reduce Eddy currents.

8. A pressure measuring system, comprising: a solenoid valve having a controllable closure element, a coil and an armature, wherein a magnetic field is generated by current flow through the coil, in order to generate a magnetic force on the armature, which magnetic force shifts the armature in the direction of opening the closure element; and a fuel pressure determiner configured to determine the pressure of a fuel to be injected into a combustion chamber via the closure element of the solenoid valve, wherein the armature comprises, in particular, a slotted ferromagnetic material and/or layers of ferromagnetic material which are electrically insulated from one another, in order to reduce Eddy currents, wherein the fuel pressure determiner determines the pressure based on a magnitude of a magnetic flux of the magnetic field before or when a first state is reached in which the armature starts to move the closure element.

9. A control unit for determining a pressure of a fuel which is to be injected into a combustion chamber via a controllable closure element of a solenoid valve, the solenoid valve further comprising an armature and a coil, the control unit comprising: a driver circuit connected to the coil of the solenoid valve, the driver circuit generating a current flow through the coil in order to generate a magnetic field with a magnetic force that acts on the armature of the solenoid valve, which magnetic force shifts the armature in a direction for opening the closure element, wherein the control unit is configured to determine a magnitude of a magnetic flux of the magnetic field before or when a first state in which the armature starts to shift the closure element is reached, and determine a magnitude of the pressure on the basis of the determined magnitude of the magnetic flux, wherein the magnitude of the magnetic flux is determined before the first state is reached, and a magnitude of at least one of an idle stroke and a working stroke of the armature is determined from the magnitude of the magnetic flux, wherein a sensitivity of the magnitude of the magnetic flux is determined as a function of the magnitude of the at least one of the idle stroke and the working stroke.

10. The control unit of claim 9, wherein a sensitivity of the magnitude of the magnetic flux as a function of the magnitude of the pressure is known from previous measurements on the solenoid valve; and wherein the determination of the magnitude of the pressure is carried out by the control unit as a determination of a change in pressure on the basis of the determined magnitude of the magnetic flux and the known sensitivity.

11. The pressure measuring system of claim 8, wherein the fuel pressure determiner determines the pressure by determining a change in pressure on the basis of the determined magnitude of the magnetic flux and the known sensitivity.

12. The pressure measuring system of claim 8, wherein a magnitude of at least one of an idle stroke and a working stroke of the armature is determined by the fuel pressure determiner from the magnitude of the magnetic flux, wherein a sensitivity of the magnitude of the magnetic flux is determined as a function of the magnitude of the at least one of the idle stroke and the working stroke.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be explained with reference to the appended drawings. The invention is not restricted to the explained or illustrated embodiments.

(2) FIG. 1 illustrates, in a schematic sectional view, a solenoid valve for which the pressure of fuel can be determined according to a method, e.g. using a device for determining a pressure according to embodiments of the present invention;

(3) FIG. 2 illustrates graphs of reference data or state trajectories or measurement data of a solenoid valve according to embodiments of the present invention;

(4) FIG. 3 shows -I curves of a solenoid valve without an idle stroke for different needle strokes;

(5) FIG. 4 shows an enlarged view of a detail of the graph illustrated in FIG. 3;

(6) FIG. 5 illustrates graphs of state trajectories which are obtained by means of various actuation voltage profiles;

(7) FIG. 6 shows -I curves of a solenoid valve for various pressures;

(8) FIG. 7 shows an enlarged view of a detail of the curves illustrated in FIG. 6; and

(9) FIG. 8 illustrates a different enlarged detail of the curves illustrated in FIG. 6.

DETAILED DESCRIPTION

(10) The solenoid valve 1 illustrated in a schematic sectional view in FIG. 1 has a coil 3 to which a voltage can be applied, with the result that a current flows through the coil 3 in order to build up a magnetic field. In this context, the magnetic field extends essentially in a longitudinal direction 5 of a guide cylinder 7. The magnetic field acts on a ferromagnetic armature 9 which can be shifted within the guide cylinder 7. By shifting the armature 9, it is possible to shift a nozzle needle 11 or a closure element of the solenoid valve 1 in the longitudinal direction 5, in particular by forming contact between the armature 9 and an annular driver element 13, which is fixedly connected to the closure element 11.

(11) In the opened state illustrated in FIG. 1, a closure ball 15 composed of a conical seat 17 is pulled back, with the result that fuel 19 can pass through an opening 21 in the seat into a combustion chamber 23 for combustion. In the completely opened state, the armature 9 bears on the pole shoe 27, and therefore cannot be shifted further upward.

(12) In a closed state of the solenoid valve 1 (not illustrated in FIG. 1), the armature 9 is shifted downward by a restoring spring 25 when a current is not flowing through the coil 3, with the result that the driver element 13 is also shifted downward, together with the closure element 11, in such a way that the closure ball 15 bears in a seal-forming fashion against the conical seat 17, with the result that fuel 19 cannot pass into the combustion chamber 23. In this state of the armature 9, in which it is shifted downward, the driver element 13 and also the armature 9 have executed at least one working stroke 12 (during which the armature 9 and the driver element 13 are in contact) and optionally also an additional idle stroke 10 in which there is a gap between the armature 9 and the driver element 13.

(13) FIG. 1 also illustrates a device 2 for determining a pressure of a fuel 19. The device 2 comprises here a driver device 4 which can generate a current flow through the coil 3 (according in particular to an actuation profile). In addition, the device comprises a determining module 6 which is designed to determine a magnitude of a magnetic flux of the magnetic field before or when a first state in which the armature 9 starts to shift the closure element 11 (in particular together with the driver element 13) is reached, and which is also designed to determine a magnitude of the pressure on the basis of the determined magnitude of the magnetic flux. For this purpose, the device 2 can receive e.g. current and voltage via the control and data line 8 which is connected to the coil 3, and can calculate a magnetic flux therefrom.

(14) Embodiments of the present invention permit the pressure of fuel 19 to be determined by determining and evaluating the magnetic flux which passes through the armature 9 and partially through the pole shoe 27 and the driver element 13.

(15) The flux can be determined by means of the measurement and analysis of the concatenated magnetic flux . In this context, the concatenated magnetic flux can be calculated from the current which flows through the coil 3, the voltage which is applied to the coil 3, and the ohmic resistance of the coil 3. The measured voltage u(t) is composed of an ohmic component (i(t)*R) and an inductive component (u.sub.int(t)). The inductive voltage is calculated here from the derivative of the concatenated magnetic flux over time where is dependent on the change in current i(t) and the air gap x(t).

(16) $u\left(t\right)=i\left(t\right)R+u_{\mathrm{ind}}=i\left(t\right)R+\frac{d\left(i,x\right)}{\mathrm{dt}}=i\left(t\right)R+\left(\frac{d\left(i,x\right)}{\mathrm{di}}\frac{\mathrm{di}}{\mathrm{dt}}+\frac{d\left(i,x\right)}{\mathrm{dx}}\frac{\mathrm{dx}}{\mathrm{dt}}\right)$

(17) Given slow actuation, the magnetic component of the induction as a result of the change in current is small.

(18) $u_{\mathrm{ind}1}=\frac{d\left(i,x\right)}{\mathrm{di}}\frac{\mathrm{di}}{\mathrm{dt}}$

(19) The mechanical part of the induction as a result of the movement of the armature then describes the strokes (idle stroke and/or working stroke) of the solenoid valve

(20) $u_{\mathrm{ind}2}=\frac{d\left(i,x\right)}{\mathrm{dx}}\frac{\mathrm{dx}}{\mathrm{dt}}$

(21) The concatenated mechanical flux can be calculated in the following way by means of transposition and integration:
=(u(t)i(t)R)dt

(22) In order to determine the needle stroke or determine a stroke of a closure element 11 of a solenoid valve, the magnetic flux can be determined and subsequently evaluated.

(23) The determination of the stroke (e.g. idle stroke and/or working stroke) and also of the pressure can be carried out on the basis of -I diagrams, like the diagram illustrated in FIG. 2. In this context, the current i flowing through the coil 3 is calculated on an abscissa 30, and the magnetic flux calculated according to the above equation is plotted on the ordinate 32. FIG. 2 shows in this respect the trajectories (-I curves) 37 and 39 of a solenoid valve without an idle stroke. The state I corresponds to a state in which the armature 9 bears against the driver element 13 of the closure element 11 and just starts to shift the closure element 11 upward together with the driver element 13, for the purpose of opening. The state I can be determined e.g. by analysis of the graph 35 and, in particular, of the trajectory (or -I curve) 37 for example as an inflection point at which a gradient changes sign. The working stroke of 50 m to 0 m, i.e. the attraction of the armature 9 in the working stroke, takes place between the points I and II. A determination of a stroke and also a determination of a pressure can be carried out in a range before the state I by evaluating the magnetic flux .

(24) The state trajectory 37 is run through during an attraction process (that is to say during an opening process) and the trajectory 39 is run through during a release process (i.e. during a closing process) of the solenoid valve 1 (for the case without an idle stroke here). The pressure of the fuel can be determined from a comparison with reference data or reference trajectories which are not illustrated in FIG. 2.

(25) According to embodiments of the present invention, the range of the trajectory 37 before the point I is evaluated for a solenoid valve without an idle stroke. In the section between the points I and II the gradient of the curve 37 changes from a positive value to a negative value.

(26) FIG. 3 illustrates a graph 41, wherein the coil current is plotted on the abscissa 30, and the magnetic flux PSI on an ordinate 32. The trajectory or curves 43, 45 and 47 have been implemented by measuring one and the same solenoid valve at various positions of the pole shoe 27, in order to set various working strokes, in particular 77 m, 59 m and 52 m, respectively. As is apparent from FIG. 3, the -I curves 43, and 47 differ slightly from one another, which is illustrated in an enlarged illustration of a particular detail in FIG. 4. In this context, the measurements have been made at a constant fuel pressure. Reference data for determining a stroke from measurements of the magnetic flux can be determined from the curves 43, 45 and 47. For example, a relationship between the working stroke or pressure and a measured magnetic flux can be determined, e.g. in a range before the state I, or a sensitivity of the magnetic flux can be determined as a function of the working stroke or pressure. After measurement of a magnetic flux of a solenoid valve with an unknown working stroke or idle stroke or pressure, the desired unknown stroke (in particular working stroke, idle stroke) of the solenoid valve or pressure of the fuel can be determined from the sensitivity or from the relationship between the magnetic flux and stroke or the pressure.

(27) The form of the -I curve at various actuation voltages (3 V . . . 18 V) is illustrated in FIG. 5 by means of trajectories 48 (exciter voltage 18 V), 49 (exciter voltage 6 V), 51 (exciter voltage 12 V) and 53 (exciter voltage 3 V). As is apparent from FIG. 5, at relatively high voltages it becomes increasingly more difficult to detect the states I and II reliably, since only small changes in gradient occur. In the case of e.g. an exciter voltage of 18 V, it may be difficult to detect the state I reliably. Therefore, reference curves can be measured, or a measurement for determining a stroke at relatively low exciter voltages, e.g. between 3 V and 12 V, can be carried out.

(28) FIGS. 6, 7 and 8 illustrate -I curves 55, 57, 59 and 61 which have been recorded on one and the same solenoid valve at various pressures specifically 200 bar, 50 bar, 20 bar and 1 bar of a fuel, wherein the current through the coil 3 is plotted on the abscissa 30, and the magnetic flux is respectively plotted on the ordinate 32. FIGS. 7 and 8 show here specific details 63 and 64 of the curves 55, 57, 59 and 61 which are illustrated on a relatively small scale in FIG. 6. According to embodiments of the invention, a fuel pressure is determined by obtaining -I curves from magnet actuators, in particular solenoid valves or injectors, in injection systems. In -I curves it is possible to recognize air gaps or magnetic gap forces and magnetic movement forces which also change in the event of changes in pressure (possibly owing to mechanical deformations). Furthermore, the forces during which the actuator moves at different pressures can change, since different pressures can cause different opposing forces of the movement.

(29) FIGS. 6, 7 and 8 show -I curves of a solenoid valve or injector at different pressures. In this context, changed gaps/strokes are recognizable, along with the force which is to be applied at the start of the movement in the state I.

(30) According to one alternative of the pressure determining method, as illustrated in FIG. 7 the magnetic flux 65 is determined (precisely) in the state I, in order to calculate the fuel pressure therefrom. At this location or in this state, there can in fact be a force equilibrium between the force generated on the basis of the fuel pressure and the force generated on the basis of the magnetic field or the magnetic flux. The force which is generated by the magnetic flux is proportional here to the square of the magnetic flux. The pressure of the fuel should therefore be proportional to the square of the magnetic flux evaluated in the state I.

(31) Furthermore, a relationship between the magnetic flux in the state I (and/or before the state I) and the previously known pressure can be determined from the multiplicity of -I curves 55, 57, 59 and 61. This determined relationship can be used to evaluate a -I curve of a solenoid valve with a pressure which is to be determined, in order to carry out a pressure determination. Furthermore, a sensitivity (for example a difference quotient between the magnetic flux and the pressures or a reciprocal value of this difference quotient) can be formed from the differences between the magnetic flux at various pressures, in particular in the state I, and said sensor can be used for (relative) pressure determination of further measurements.

(32) FIG. 8 illustrates the range 64 of the curves 55, 57, 59 and 61 illustrated in FIG. 6. The range 64 occurs before the state I, i.e. in a range in which the armature bears against the driver element 13 or the closure element 11 and is in contact, but does not yet move the driver element and the closure element 13 to open. In one embodiment, this range can also be used to determine the fuel pressure. As is apparent, the magnetic fluxes of the curves 55, 57, 59 and 61 differ, wherein there is clearly no linear relationship between changes in a magnetic flux and changes in the pressure here. For this reason, various sensitivities can be determined and stored in various ranges of the magnetic flux and used later for the interpretation or evaluation of further measurement curves for pressure determination.

(33) A high level of accuracy of the method can be achieved if Eddy currents within the armature or other elements of the solenoid valve are relatively low. In order to ensure low Eddy currents, a relatively slow actuation for energizing the coil 3 can be used. In this context, a relatively low boost voltage such as e.g. between 3 V and 12 V can be used, as has also been mentioned in conjunction with FIG. 5. In any case, the state I can be reliably determined for these relatively low boost voltages. Alternatively or additionally, an actuator (in particular comprising the armature and the nozzle) can be used which is changed in its design in order to reduce Eddy currents. For this purpose, e.g. a slotted armature or an armature can be provided which is constructed from layers of ferromagnetic material which are each electrically insulated from one another. With such an armature, it is also possible to apply current to the coil of the solenoid valve by means of the standard actuation, since the curve profiles during the stroke movements are significantly more pronounced.

(34) Like the pressure determination, the stroke determination is also possible without measuring the complete curves. It can be sufficient e.g. to measure the curves only up to the state I in each case. It can be advantageous here that the determination of a stroke can be carried out without opening an injector (injection). Therefore, the measurement can be carried out without an adverse effect on emissions.

(35) Both the pressure determination and the determination of a stroke can be carried out here with or without reference data. A difference between pressures can be inferred from a difference in magnetic flux (under various pressure conditions). By means of reference data it is possible to carry out calibration, with the result that an absolute pressure determination is also possible. The method can be implemented e.g. in an engine control device.