DE102017216973A1 - Method for determining a fuel grade - Google Patents

Abstract

The invention relates to a method for determining a fuel grade, in which a temporal behavior of a switching valve (14) is detected and evaluated by the temporal behavior of one of the fuel types is assigned, in addition, a time of opening the switching valve (14) is taken into account and this Time is taken into account during the assignment.

Description

The invention relates to a method for determining a fuel grade and an arrangement for carrying out the method.

State of the art

The injection quantity of Common Rail Systems (CRS) depends, among other things, on different fuel properties, which in turn depend on the type of fuel and the ambient conditions. The viscosity of the fuel depends on the type of fuel, for example winter diesel, arctic diesel, biodiesel, mixtures of different types of fuel, and additionally also on the temperature. As long as there is no possibility in the CRS, important fuel properties, eg. B. via a sensor to determine quantity effects of these properties can be insufficient or not corrected at all.

Before the engine start and during the annealing phase, a reference value for the closing duration difference is determined in particular in a non-pressurized common rail system by means of several measurements, with which a fuel-specific control duration correction can be performed. This means that a drive duration correction is performed depending on the particular fuel grade or fuel class. The function for determining the fuel grade is also referred to as FDV function (FDV: Fuel Detection by Valve Closing).

The publication DE 10 2011 005 141 A1 shows a method for determining a property of a fuel, in which a closing duration of an armature of a solenoid valve, which moves through the fuel, is measured at least one drive duration. Based on the measured closing time, a factor is determined that represents the property.

The measured closing duration values at cold temperatures, for example below -10 ° C., which serve as a measure of the viscosity of the fuel, show a very viscous fuel, for example a summer diesel, and a low-viscosity fuel, eg. B. Arctic class 4 , a winter diesel, in the current injector generations a very small closing duration difference. However, a closing time difference which is too small can result in a misdetection of the fuel property to be determined, for example the fuel viscosity. This can lead to an erroneous determination of the fuel grade and have a large impact on the cold start behavior.

It should be noted that a fast switching valve dynamics is desirable from a functional point of view. By the changes made to the anchor geometry, in particular a new residual air gap disk and an optimized magnetic core, the armature dynamics has been greatly improved. However, these measures lead to a significant deterioration in the quality of the fuel detection. For a better distinction of the type of fuel, a slower switching valve dynamics is advantageous. However, this property is a contradiction to the functional requirements of the switching valve in injector operation.

Furthermore, it should be noted that the determination of the fuel grade takes place in the unpressurized state of the common rail system and therefore only a very limited period of time is available for this purpose.

Disclosure of the invention

Against this background, a method according to claim 1 and an arrangement according to claim 9 are presented. Embodiments result from the dependent claims and the description.

The method described is used to determine a fuel grade or fuel class, wherein a temporal behavior of a switching valve, for example. A solenoid valve, is detected and evaluated in an injector. Thus, for example, the closing duration of the switching valve can be determined. In addition, the method takes into account a point in time of opening the switching valve in the assignment of the time behavior to the fuel grade. This can be done by adjusting the assignment rules or by applying a correction function, which takes into account the detected particular measured time of opening of the switching valve.

Depending on the detected or determined time of opening of the switching valve now the assignment of dynamic behavior of the switching valve to fuel grade or fuel class is made. A correction function can be used or class boundaries can be shifted. It is on this 6 directed.

The correction function includes, for example, the steps: fuel detection, determination of the fuel correction requirement as a function of the temperature and the fuel grade and determination of the drive duration correction.

The presented method enables a better differentiation of the fuel grade by monitoring the switching valve dynamics of the injector over the entire lifetime in vehicle operation. Thus, a misdetection of the fuel grade can be avoided.

It should be noted that the current FDV rating with a nominal injector set, i. H. with a new injector set, wherein the magnetic force and valve spring force are set in the middle, is created. Investigations have shown that even a small deviation of the magnetic force from the nominal value can severely impair the fuel detection. The reason for this was the ballistic operation of the armature during the FDV measurement. In ballistic operation, in which the armature does not reach the stroke stop, while the closing duration difference between the fuel types is greatest, but the risk of misdetection is also increased by a deviation of the magnetic force from the target value. To minimize the risk of erroneous detection, magnetic force compensation can be performed during assembly at the factory. In this case, the magnet assembly is first measured alone. This is referred to as a 100% test, a test in which all assemblies are measured. In the event of a deviation from the setpoint, the magnetic force deviation is compensated via the valve spring force. This means that at a high magnetic force, the valve spring force is set higher. At a low magnetic force, a low valve spring force is set.

• resultierende Kraft am Schaltventil = Magnetkraft - Ventilfederkraft - Störkräfte

With the help of this compensation a misdetection in new condition can be largely avoided. It should be noted that over the life of the switching valve dynamics by disturbances, such as the lateral force, particles, the armature stroke, the wear, the friction, pads, etc., can change significantly. The reason for this is a change in the resulting force at the switching valve, where:

• resulting force at the switching valve = magnetic force - valve spring force - disturbing forces

This can lead to misdetection of the fuel grade. In view of the future high RDE requirements (RDE: Real Drive Emission), a correct detection of the fuel grade is essential even with changed switching valve dynamics over the service life. This is achieved with the presented method.

In the method, a temperature, for example. A return temperature can be considered as an alternative tank or cooling water temperature.

The presented arrangement is set up to carry out the method described and is implemented, for example, in a control unit of a motor vehicle or designed as such. The arrangement may include hardware and / or software components. Thus, this can be realized as a computer program that is executed on a computing unit, for example. A computing unit of a control unit, for execution. Furthermore, this computer program can be created in a machine-readable storage medium.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

list of figures

• 1 shows a schematic representation of an embodiment of a switching valve, which is designed as a solenoid valve.
• 2a and 2 B show possible current curves in the control of a solenoid valve.
• 3 shows in two graphs the switching valve dynamics from an NCS signal.
• 4 shows in a flow chart a flow of a possible execution of the presented method.
• 5 shows in a graph possible courses of the fuel viscosity as a function of the temperature.
• 6 shows in a graph an adjustment in the context of the FDV function.

Embodiments of the invention

The invention is schematically illustrated by means of embodiments in the drawings and will be described in detail below with reference to the drawings.

1 shows an embodiment of an electromagnetically actuated switching valve, the total with the reference numeral 14 is provided. This serves to control the lifting movement of a nozzle needle 19 a fuel injector in a fuel injection system. The switching valve 14 includes a valve closing element for this purpose 1 , which has a hollow cylindrical approach 2 a valve piece 3 is guided axially movable. The valve piece 3 forms within the hollow cylindrical approach 2 a valve seat 4 from, against the valve closing element 1 by means of a spring 5 is axially biased. The valve closing element 1 also has a through hole 6 on, in which a pen 7 is received axially movable.

To open the switching valve 14 becomes a magnetic coil 18 energized, so that a magnetic field is established, the magnetic force acts on an armature, in this case by a plate-shaped portion 16 the valve closing element 1 is formed. The magnetic force moves the valve closing element 1 against the spring force of the spring 5 in the direction of a magnetic core 22 , which is the magnetic coil 18 surrounds and a stroke stop for the valve closing element 1 formed. Opens the switching valve 14 , becomes a connection of a control room 21 with an annular valve space 9 made within the hollow cylindrical approach 2 of the valve piece 3 is arranged. The connection leads via an outlet throttle 20 , as well as the control room 21 , in the valve piece 3 is trained. The one in the control room 21 prevailing control pressure of the nozzle needle 19 loaded in the closing direction, decreases and the nozzle needle 19 can open.

The one from the control room 21 in the valve room 9 Expiring fuel must continue to be dissipated. The valve piece 3 in the 1 points in the hollow cylindrical approach 2 radial bores 8th on that a permanent connection of the valve space 9 with a low-pressure room 10 produce.

To the nozzle needle 19 to return to their seat, the tax pressure in the control room 21 be raised again. For this purpose, the energization of the magnetic coil 18 finished, leaving the spring 5 the valve closing element 1 returns to its original position and switching valve 14 closes.

It should be noted that in the case of injectors with a high excess of force, the switching valve opens sooner or faster than the injectors with a lower excess of force. A change in the valve dynamics can be detected at any time during operation with a needle closing sensor (NCS: Needle Closing Sensor).

In the 2a and 2 B in two graphs possible current curves are shown when controlling a solenoid valve. For this purpose, the current I (ordinate 180 ) in the magnetic coil against the time t (abscissa 182 ), each in arbitrary units.

In both graphs, a current waveform I ₁ 184 is shown, which has a pull-in current I _A 186 and a holding current I _H 188 includes, as in the control, ie. is common in the application of voltages, for opening and keeping open solenoid valves.

In 2 B is another current course I ₂ 190 showing a sensor or measuring current I _M 192. This can be used to determine a closing time or a closing time.

In 3 The NCS waveforms of injectors with maximum (F _max ) and minimum (F _min ) excess force at a system pressure of 300 bar can be seen, with a first graph 200 a complete shift and a second graph 202 represents a temporal portion of the period shown in the first graph. At an abscissa 210 is the time in μs, on a first ordinate 212 the NCS signal and at a second ordinate 214 the current is plotted in A. Furthermore, in the second graph is a time 216 an opening of the switching valve displayed. This time 216 can be detected with a measuring accuracy of +/- 1 μs.

The injectors with high excess force show here an earlier valve opening. At a system pressure of prail (rail pressure) ≤ 300 bar, the hydraulic forces acting on the switching valve in the idle state of the switching valve, ie the switching valve is seated, are so small that they can be neglected. This means: $${\text{F}}_{\text{hydr}}<1\text{N},$$

As a result, from the time 216 the valve opening conclusions are drawn on the total force at the switching valve, so follows z. B. from a small excess of force to open a later valve. In view of this fact, the fuel class in vehicle operation can be correctly recognized even when changing the switching valve dynamics.

4 shows a possible sequence of the presented method. In a first step 300 it is checked whether the rail pressure prail ≤ 300 bar. This is not the case 302 , so no learning mode. In addition, in one step 304 checks if the injector temperature is T> T_threshold, ie if the injector is warm. If this is not the case, no learning mode takes place 306 , Both queries are in 300 and 304 affirmed 308 . 310 , so in a further step 312 measuring the timing of the valve opening. It should be noted that the two queries in 300 and 304 optional.

Returns the measurement in 312 to open an early valve 320 so the FDV function becomes FDV map # 2 in step 330 customized. Returns the measurement in 312 a late valve opening 322 so the FDV function will be according to FDV map # 3 in step 332 customized. Corresponds to the measured time of the valve opening and so that the target time point of valve opening t _{SV-open target} a Istzeitpunkt of valve opening t _{SV-open (block} 324 ), the FDV function will use the basic FDV map (step 334 ) used. On the influence of the FDV function by the factor Map (Mapping), which means an adaptation, in particular in connection with 6 received.

The method is also based on the fact that with a hot injector the time "valve opening" is independent of the fuel grade. The reason for this is that from T> 50 ° C follows that the kinematic viscosity B0 ~ kinematic viscosity "Arctic 4", see 5 , It should also be noted that in warm operation, the temperature of the fuel in the armature space is about 80 to 150 ° C.

5 shows in a graph 400 the course of the fuel viscosity as a function of the temperature for different fuel types. In the graph 400 is at an abscissa 402 the temperature in ° C and at an ordinate 404 the kinematic viscosity is plotted in mm ² / s. A first turn 410 shows the course for winter diesel B0 and a second curve 414 the history for Diesel Arctic 4 ,

vorgenommen werden.The value for the time of valve opening can be checked over the entire injector life at specific time intervals. In the event of a deviation from the setpoint t _{SV-open nominal} , the fuel _detection can be performed according to the in 4 (FDV Map # 2, # 3, ..) are performed. Alternatively, instead of multiple FDV adjustments or FDV maps, a correction function for the base FDV map may be dependent on $$\mathrm{\Delta }\text{t}={\text{t}}_{\text{SV}-\text{open is}}-{\text{t}}_{\text{SV}-\text{open target}}$$

be made.

The measuring point for t _SV-open can typically be at the neutral point at 300 bar. As an alternative, it is also conceivable that the NCS measurement is carried out at a rail pressure of 100 <prail <200 bar shortly before switching off the engine, with the injectors being warm. In the de-pressurized state, the NCS sensor shows no voltage change, ie the valve chamber pressure is 0 bar. Therefore, an NCS measurement at prail <80 bar is inaccurate because the change in the valve chamber pressure is too low.

• Referenz Schließdauer (z. B. 140 µs) - Schließdauer-Ist in µs.

6 illustrated in a graph 500 the adaptation of the FDV function. It is on an abscissa 502 the cooling water temperature in ° C and at an ordinate 504 a measure of the closing time, namely FDV closing duration delta plotted in μs. The value for FDV closing duration delta results from:

• Reference Closing time (eg 140 μs) - Closing duration actual in μs.

In the graph is a class boundary 1 / 2 with a first turn 510 and a class boundary 0 / 1 with a second curve 512 entered. This results in areas for different fuel types or fuel classes, namely variety or class 0 (Reference number 520 ), Variety or class 1 (Reference number 522 ) and variety or class 2 (Reference number 524 ).

When adjusting the FDV function, ie when assigning the detected closing duration as a function of the temperature to a fuel class, now the class limits, by the two curves 510 and 512 are adjusted, depending on the timing of the opening of the valve, which has an effect on the detected closing duration, ie the two curves 510 and 512 and thus the class boundaries are moved.

A first arrow 540 illustrates the direction of the shift of the class boundaries at a larger armature stroke, which leads to a greater closing time and is characterized by an earlier opening of the valve. A second arrow 542 illustrates the shift of the class boundaries when the armature stroke is smaller, that is, the armature stroke is not achieved and it follows an early valve closing, which is characterized by a subsequent opening of the valve.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011005141 A1 [0004]

Claims (10)

Method for determining a fuel grade (520, 522, 524), in which a temporal behavior of a switching valve (14) is detected and evaluated by assigning the temporal behavior of one of the fuel types (520, 522, 524), wherein additionally a time ( 216) of an opening of the switching valve (14) is taken into account and this time (216) is taken into account in the assignment. Method according to Claim 1 in which class limits (510, 512) are adjusted for different fuel types. Method according to Claim 1 in which a correction function is applied. Method according to one of Claims 1 to 3 in which the switching valve (14) is designed as a solenoid valve and in which a closing duration of an armature of the solenoid valve, which moves through the fuel, is measured at least one activation duration, wherein a factor is determined depending on the measured closing duration, the allocation allows. Method according to Claim 4 , in which the closing time is determined by means of a signal of a needle-closing sensor (NCS). Method according to one of Claims 1 to 5 , in which a magnetic force compensation is made. Method according to one of Claims 1 to 6 in which a rail pressure is taken into account. Method according to one of Claims 1 to 7 in which a temperature is taken into account. Arrangement, which is adapted to a method according to one of Claims 1 to 8th perform. Arrangement according to Claim 9 , which is implemented in a control unit of a motor vehicle.

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