DE102015219640A1 - Method for determining a property of a fuel - Google Patents

Abstract

The invention relates to a method for determining at least one property of a fuel which is carried out in an injector (10) of an injection system of an internal combustion engine, which has a solenoid valve (12), wherein at least one point in the injector (10) the pressure of the fuel is measured in a period during activation of the solenoid valve (12), and the at least one characteristic is derived from the course of the pressure.

Description

The invention relates to a method for determining at least one property of a fuel and to an arrangement for carrying out the method.

State of the art

In internal combustion engines, the chemical energy of a fuel is converted to mechanical work by burning the fuel. Injectors are used to inject the fuel into the combustion chambers, the cylinders of the internal combustion engine.

Injectors that operate on the servo principle, basically include a switching valve, a holding body, a nozzle body and a nozzle needle. In the non-activated state, the nozzle needle is pressed into its seat by the adjacent rail pressure, no fuel is injected. If the switching valve is moved by means of a control, the pressure in the control chamber is lowered, the nozzle needle lifts off and fuel is injected. The nozzle needle moves back to its rest position at the needle closing time point during injection from a closed position to the needle opening time point to a needle turning point or a stroke stop in which the nozzle needle is furthest from its rest position. The activation duration has an immediate effect on the injection quantity. The presented injector contains in addition to the above-mentioned components a sensor with which a characteristic pressure, for. B. the valve chamber pressure can be measured. From this pressure, the injection end, the closing of the nozzle can be determined and used for a control of the injection duration. Various effects can now lead to a change in the duration of injection in operation, but must be reacted differently in a regulated injection system. So the injection time, z. B. by a coking of the nozzle or a change in temperature of the fuel or its viscosity, to be changed. In the case of coking, a prolonged spraying time is deliberately aimed at, the setpoint value of the spraying time is raised in order to compensate for the reduced nozzle flow through a longer injection. This leads to a constant injection quantity. If a reduced fuel viscosity is the cause of a later jet, the reference value for the spray duration must be maintained. The setpoint remains.

However, it is not possible to determine from the splash signal alone which of the two named causes of the duration of the spray duration is the basis. In order to make a coking or temperature correction in the controlled injection system, therefore, the cause of a deviation from the injection duration or injection end setpoint must be known. This information is determined according to the invention by characteristic sizes of the valve, since these depend only on the fuel, but not on the Düsenverkokung. Thus, the cause of a spray duration change can be differentiated.

The injection quantity, and therefore the injection duration, of Common Rail Systems (CRS) will continue to depend on various fuel properties, which in turn depend on the type of fuel and the ambient conditions. For example, the viscosity of the fuel grade, for example. Winter diesel, Arctic diesel, biodiesel, mixtures of different fuel types, and in addition also on the temperature and the (rail) pressure dependent. As long as there is no possibility in the CRS, important fuel properties, eg. B. directly via a sensor to determine quantity effects of these properties can only be corrected insufficiently or not at all.

The behavior of the solenoid valve injectors used in injection systems depends to a great extent on the properties of the fuel used. Thus, fuel properties, such as viscosity and density, affect the amount of fuel injected. In particular, it should be noted that the viscosity varies greatly with temperature. It is therefore desirable to determine properties of the fuel in order to be able to adapt the entire injection system and in particular the injectors to these properties.

From the publication DE 10 2011 005 141 A1 For example, a method for determining at least one property of a fuel is known. In this case, a closing duration of an armature of a solenoid valve, which moves through the fuel, measured at least one driving duration. Due to the measured closing duration, a factor is determined which represents the at least one property. The method is used in particular for determining the viscosity of the fuel.

Disclosure of the invention

Against this background, a method according to claim 1 and an arrangement according to claim 13 are presented. Embodiments result from the dependent claims and from the description.

The present method is used to determine at least one property of a fuel and is performed in an injector of an injection system of an internal combustion engine, typically an injection system of an internal combustion engine in a motor vehicle. So, as a property the viscosity of the fuel derived and thus determined or the deviation are determined to a reference viscosity.

In particular, the method is to be carried out prior to a start of a motor vehicle in order to draw conclusions about the refueled fuel, since in this way the injection system can be adapted in good time to the present fuel properties. This is especially taken into account in the control. Thus, the method basically offers a cold start. Furthermore, the method can be carried out continuously or at intervals in operation.

The present method allows, at least in some of the embodiments, the determination of the fuel quantities relevant to the injection quantities of the fuel. In particular, the determination of the injection-relevant fuel properties from the valve behavior is made possible. In addition, a compensation of temperature influences can be made.

Previous injection systems include controlled functions that partially compensate for the above-described change in fuel properties, i. H. that is changed in the presence of certain temperatures in the fuel or the environment, the driving time of the injectors to obtain an approximately constant injection quantity. This correction intervention is usually taken back in time via a ramp and switched off. However, this procedure represents only a very rough compensation of the effects. This is especially the case, since it is unknown which fuel type was fueled. With the determination of relevant fuel properties described herein, in particular also in combination with a spray end / duration control, however, a more precise compensation of these effects and a more accurate fuel metering is possible. In this way, injection tolerances should also be reduced.

The presented arrangement serves to carry out the method described. As an arrangement is, for example, a control unit.

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.

Brief description of the drawings

1 shows a schematic representation of an injector.

2 shows in a graph a pressure curve.

3 shows in a graph the temperature dependence of the viscosity of different fuels.

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 injector, in total with the reference numeral 10 is designated, in a greatly simplified form. The illustration shows a solenoid valve 12 , which serves as a switching valve and an anchor 14 , an anchor bolt 16 and coils 18 for driving the anchor 14 includes. Furthermore, the illustration shows a valve chamber 20 and a control room 22 of the solenoid valve 12 over which a needle 24 is moved. This needle movement causes the actual injection. Thus, the solenoid valve controls 12 the needle movement via the servo principle.

The illustrated injector 10 , which is designed as a common rail injector, has a sensor 26 for detecting a pressure, z. B. the valve chamber pressure. Alternatively, the rail or control chamber pressure can be recorded. The illustrated sensor 26 captures the one from the control room 22 or the valve space 20 on the anchor bolts 16 applied pressure. This sensor 26 is, for example, designed as a piezoelectric sensor, which outputs an electrical voltage as output variable.

Will when operating the anchor 14 This moves up, so needs fuel, which is in a gap 28 is displaced.

The resistance of the medium, in this case of fuel, to the moving armature, in this case the armature 14 , when operating the solenoid valve 12 is proportional to the hydraulic forces, which in turn depends on the material properties and, among other things, the speed of the anchor 14 are dependent. The higher the viscosity of the fuel and the greater the density, the slower the anchor will open 14 , This in turn affects the pressure curve in the valve chamber 20 , in the control room 22 and in the high-pressure inlet, since the fuel is throttled at the valve seat stronger or longer.

From the course of z. B. valve space pressure (when opening the switching valve or solenoid valve 12 ) a conclusion on the fuel properties is possible. This can be done either by explicit times of opening or closing, z. B. characterized by the minimum of the pressure curve, or by the gradient of the pressure curve.

2 shows in a graph 50 , on the abscissa 52 the time [ms] and its ordinate 54 a voltage [V] is plotted, a first course U (T1) 56 and a second course U (T2) 58 , These two traces show the course of a sensor, like this one in 1 with reference number 26 is outputted at a first temperature T1 and a second temperature T2.

Furthermore, in the illustration, a minimum voltage of the first course U (Min1) 60 and a minimum voltage U (Min2) 62 displayed. The minimum Min1 of the first course 56 is with reference number 66 marked, reference numeral 68 indicates the minimum Min2 of the second course 58 ,

In a window 70 indicating a time range in which the switching valve is opened is a slope dU / dt1 by a first asymptote 72 and a slope dU / dt2 by a second asymptote 74 displayed. A second window 80 illustrates the period of closing the switching valve. An arrow 82 shows the time period t_Min1 until reaching Min2 66 at. An arrow 84 shows the time period t_Min2 until reaching Min2 68 at.

As a criterion for the evaluation of the switching behavior z. B. the absolute minimum of the pressure (Min1 / 2), ie the height of the signal U (Min1 / 2) are used, any filtering of the signal to eliminate interference, can be performed beforehand. Another criterion may be the time of reaching the minimum (t_Min1 / 2), measured from the current to the minimum, if necessary filtered signal.

Another embodiment is to determine the maximum gradient of the pressure signal when opening or closing the valve Max (dU / dt_1 / 2). Alternatively, the height of the signal reached in the second window 80 be used as a feature when closing the valve.

The measured characteristics can be set in relation to the corresponding values of a medium "ideal" injector. In order to eliminate component tolerances in the determination of the fuel properties, the deviation from the expected value of the respective measured variable during normal operation of the respective injector is determined individually for each injector individually. The normal operation is preferably described by the exceeding of a relevant temperature, for example. The engine oil, the cooling water, the fuel inlet and / or the environment described. This ensures that the changed times, gradients and / or values are due to a change in the fuel temperature or material properties. Tank monitoring is also possible to determine new learning values after refueling.

3 shows a diagram 102 with an abscissa 104 , along which a temperature in ° C is plotted, and an ordinate 106 , along which a kinematic viscosity of a fuel in mm ² / s is plotted. The diagram includes four curves 108 . 110 . 112 . 114 , It represents a first curve 108 a temperature-dependent kinematic viscosity of a first winter diesel fuel, a second curve 110 a temperature-dependent kinematic viscosity of a test diesel, a third curve 112 a temperature-dependent kinematic viscosity of a winter diesel fuel and a fourth curve 114 a temperature-dependent kinematic viscosity of a so-called Arctic diesel fuel. Thus, the diagram shows 102 From Figure a temperature dependence of kinematic viscosities for different types of winter diesel.

From this diagram shows that for determining the fuel properties of one of the features already described from the sensor signal and the simultaneous knowledge of the fuel temperature possibly other temperatures, eg. Of cooling water, engine oil, etc. is required.

The determination of the fuel properties at the cold engine start is performed, which is characterized by the presence of the characteristic temperatures, for example in fuel, cooling water, engine oil, environment, in a range of values, d. H. the difference of these temperatures should not exceed a certain value, so that the assumption of an approximately constant temperature is fulfilled.

The parameters which were determined from the valve behavior are now compared with the measured injection duration of the nozzle or its deviation from a reference value compared to differentiate whether the cause of the deviation of the injection end of a coking or a fuel property is due , After this differentiation, the setpoint for the injection duration or the injection end is adjusted or maintained, for example. With different maps to compensate for the corresponding effect on the injection quantity.

Furthermore, after this differentiation, any existing algorithm for Learning injector parameters, eg. As the coking, or the learned values are corrected.

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 [0007]

Claims (13)

Method for determining at least one property of a fuel that is contained in an injector ( 10 ) an injection system of an internal combustion engine, which via a solenoid valve ( 12 ) is performed, wherein at least one point in the injector ( 10 ) the pressure of the fuel in a period during activation of the solenoid valve ( 12 ) is measured and from the course of the pressure, the at least one properties is derived.  The method of claim 1, wherein the deviation of a fuel property from a reference is determined.  The method of claim 1 or 2, wherein the valve chamber pressure is measured.  The method of claim 1 or 2, wherein the control chamber pressure is measured. A method according to claim 3 or 4, wherein one of the pressures acting on an anchor bolt ( 16 ) of the solenoid valve ( 12 ) is measured.  The method of claim 1 or 2, wherein the pressure in the high-pressure inlet is measured.  Method according to one of claims 1 to 6, wherein the viscosity of the fuel is determined as a property.  Method according to one of claims 1 to 7, which is carried out before a cold start. Method according to one of claims 1 to 8, wherein the course during the opening of the solenoid valve ( 12 ) is evaluated. Method according to one of claims 1 to 7, wherein the course during the closing of the solenoid valve ( 12 ) is evaluated.  Method according to one of Claims 1 to 10, in which correction values for the activation duration are determined on the basis of the determined at least one property.  The method of claim 11 performed to reduce injection tolerances. Arrangement for determining at least one property of a fuel in an injector ( 10 ) an injection system of an internal combustion engine, which via a solenoid valve ( 12 ), in particular for carrying out a method according to one of claims 1 to 12, wherein the arrangement is set up at at least one point in the injector ( 10 ) the pressure of the fuel in a period during activation of the solenoid valve ( 12 ) and derive the at least one characteristic from the course of the pressure.

Images