DE102013218609A1 - Method for operating a fuel injection system of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating a fuel injection system (10) of an internal combustion engine, wherein a high pressure pump (18) delivers fuel from a low pressure region into a common rail (20), wherein a pressure in the common rail (20) via a pressure control valve (20). 24) is controlled and in the course of the control overflow (36) of fuel via the pressure control valve (24) is returned to the low pressure region and wherein an opening cross section of the pressure control valve (24) is determined and wherein by means of the specific opening cross section of the pressure control valve (24) the Overflow (36) is controlled or controlled.

Description

The present invention relates to methods of operating a fuel injection system of an internal combustion engine.

State of the art

Injection systems of an internal combustion engine are used to supply pressurized fuel to combustion. Thus, an injection system comprises two essential sections, namely the pressure generation and the actual injection. A well-known principle in injection systems is the so-called common rail injection. The common-rail injection is an injection for internal combustion engines in which a high-pressure pump brings the fuel to a high pressure level. The pressurized fuel fills a piping system, the common rail, which is constantly under pressure during operation of the internal combustion engine. In the injection, the complete separation of the pressure generation from the actual injection process is essential.

In the common-rail injection is intended to promote fuel from a tank by means of a low-pressure pump in a low pressure region. From this low-pressure region of the fuel is conveyed by means of a high-pressure pump in the high-pressure region and thus in the common rail. The delivery rate of the high pressure pump may be controlled by a valve located between the low pressure pump and the high pressure pump, e.g. the so-called metering unit (ZME). To regulate the pressure and a pressure control valve (DRV) may be provided on the common rail, which is integrated in a control loop, which also includes a controller. Controlled variable is the pressure in the common rail, manipulated variable is for example a current with which the pressure control valve is controlled. If the pressure is too high, fuel is returned to the tank via the pressure control valve. This recycled fuel is referred to as overflow. The controller gets, for example, from an engine control unit a target pressure specification, which is compared with the actual pressure in the common rail.

Current control concepts for common rail systems with pressure control valve and valve between low pressure pump and high pressure pump or other pump flow rate adjustments, such as an electric suction valve, see in regulated with pressure control valve operation for the pump either a full pumping or in operation with simultaneous control via pressure control valve and valve before High-pressure pump, which controls the flow rate, a pilot-operated pump delivery. In the latter case, all pump tolerances must be taken into account, so that even with a system with maximum permissible leakage and a minimum permissible pump delivery rate, there is still sufficient overflow available for the regulation of the pressure regulating valve. This, in turn, results in a system at the other end of the tolerance band, i. a minimal leakage and a pump with maximum flow, to an unnecessarily high flow rate at the pressure control valve.

Too high an overflow has several disadvantages. For example, an unnecessarily high system heating associated with a high power loss is the result. In addition, in case of short-circuit faults on the pressure control valve in the regulated with pressure control valve operation, high flow rates lead to critically fast pressure build-up with increased risk of system damage.

From the publication DE 197 31 994 A1 a method for controlling an internal combustion engine is known, in which promotes at least one high pressure pump fuel from a low pressure region in a common rail and the pressure in the common rail can be detected. In order to set the pressure in the common rail, a pressure control means releases a control quantity from the common rail into the low pressure range, wherein the control quantity can be regulated to a desired value. It can be provided that a first controller regulates the pressure in the common rail and a second controller regulates the control quantity. However, the rule set must be determined explicitly by means of a flow rate sensor.

It is therefore desirable to provide a way to keep an overflow of a pressure regulating valve as simple as possible in a simple manner.

Disclosure of the invention

According to the invention, methods are proposed for operating a fuel injection system of an internal combustion engine having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

In the course of the invention, in addition to the conventional regulation of the pressure in the common rail via the pressure control valve, a control or control of the overflow of the pressure control valve is performed. Thus, an excessive overflow and the associated disadvantages are avoided. An increased risk of system damage is avoided as well as high system heaters and power losses.

The regulation or control of the overflow quantity is preferably carried out via a delivery quantity of fuel. The flow rate is thus changed depending on the current overflow. Thus, ultimately, the amount of overflow is changed and is regulated in particular to the specific target value. This results in a closed loop for the excess flow.

In particular, the regulation or control of the overflow quantity is carried out with the aid of a metering unit ZME and / or an electric suction valve ESV. By means of the metering unit or the electric suction valve ESV, as known, the flow rate is influenced.

For determining the current overflow quantity (actual values), an effective opening cross section of the pressure regulating valve is preferably initially determined. This opening cross-section describes the degree of opening of the pressure regulating valve or how far the pressure regulating valve is open. The opening cross-section at the current rail pressure or the current pressure of the fuel correlates directly with the overflow amount recirculated via the pressure regulating valve. The rail pressure is detected anyway, especially in the train of pressure control in the common rail. Thus, the opening cross-section can be used as a measure of the actual Überstrommenge. By means of the specific opening cross-section can thus be carried out in a simple manner, a control or regulation of the excess current amount.

Advantageously, a current actual value of the overflow quantity is determined from the specific opening cross section. For the overflow quantity, therefore, no separate separate measuring sensor must be used. The amount of overflow is easily determined without additional hardware. By means of this specific actual value of the overflow quantity, the control or the regulation of the overflow quantity is carried out to a specific desired value.

Alternatively, the overflow amount can be indirectly controlled by controlling the opening area of the pressure regulating valve. For example, a desired value for the opening cross-section can be specified, which corresponds to the smallest possible amount of overflow. The desired value for the opening cross-section is determined in particular as a function of the known rail pressure. If the opening cross section is this setpoint value, the desired nominal value of the overflow quantity is established at the current rail pressure.

Advantageously, the overflow is regulated to a minimum value. In order to be able to regulate the pressure in the common rail, at least a certain minimum value of the overflow quantity must be available. In the course of the scheme, the overflow is preferably controlled to this minimum value. This ensures that the pressure in the common rail can be regulated to the desired value and that no excess overflow is returned, but that only the smallest possible overflow is returned. Thus, the amount of overflow can be adjusted via a closed loop using the flow rate, in particular by metering and / or electric suction valve to the, necessary for the common rail pressure control, minimum value.

In a preferred embodiment of the invention, an inductance of the pressure regulating valve is determined, and from this the opening cross section of the pressure regulating valve is determined. In particular, the pressure regulating valve has an electromagnetically actuated coil. By controlling the coil, an armature is set in motion and the opening degree or the opening cross section of the pressure regulating valve can be increased or decreased. Preferably, a position of the armature is determined from the determined inductance of the coil. From this position of the armature ultimately the opening cross section of the pressure regulating valve is determined. The inductance of the coil of the pressure regulating valve depends on the position of the armature. The knowledge of the armature position can be used particularly advantageously for the operation of such an actuator within a control, since now a return of the actual position of the armature and thus the actual opening cross-section is possible. In particular, at high dynamic range, the inert properties of the magnetic actuators come increasingly to bear, so that the actual position of the armature behind a desired position more or less behind. Therefore, a desired position to which the pressure control valve is to be set in the course of the pressure control of the common rail, for a precise control of the excess flow is only partially suitable. By determining the actual position of the armature from the specific inductance, otherwise resulting inaccuracies in the control loop of the excess current can be avoided.

In a further preferred embodiment of the invention, a PWM-synchronous current measurement is performed. A pulsed signal having a number of pulses is thereby output to the coil of the pressure regulating valve to open or close a circuit containing the coil in accordance with the pulses. In this case, a first measured current value in connection with a rising edge of a pulse of the pulsed signal and a second current measuring value in connection with a falling edge of the same pulse are detected. From these two measured current values, an actual value of a current through the coil of the pressure regulating valve is determined. It will in particular, an actual value of an effective value and / or an average value of the current flow through the coil of the pressure regulating valve is determined. In particular, the pulsed output signal may be a PWM signal, but also another pulsed signal, for example according to pulse width modulation (PDM) or pulse frequency modulation (PFM).

In particular, the first current measured value corresponds to a minimum current flow and the second current measured value corresponds in particular to a maximum current flow during the pulse of the pulsed signal. In the context of an edge means that the measurement can be triggered by the edge, or is in a fixed time relationship (for example, 5 ms before) to the edge. Using two current readings increases the accuracy of the calculation.

This method of measurement produces a strictly coupled relationship between the pulses of the pulsed signal and the current measurement. The current measurement is thus no longer dependent on e.g. from an operating system scheduler of the controller. Thus, the dynamics of the current control can be increased.

The inductance of the coil is preferably determined from the determined current through the coil, in particular from the determined actual value of the effective value and / or the mean value of the current flow through the coil of the pressure regulating valve. The use of two current measured values allows, in addition to the more accurate calculation of the effective value, in particular the calculation of the current inductance of the coil of the pressure regulating valve. Many electromagnetic actuators change their inductance in the control range by changing the reluctance. The inductance is determined by current measurements on a pulsed signal during operation.

According to a further aspect of the invention, the overflow quantity is set to a minimum value without the opening cross section of the pressure regulating valve being explicitly determined. In this case, a closing time of the pressure regulating valve is determined. In this case, the delivery rate of the high pressure pump is continuously reduced, in particular to certain operating points (certain pressure values of the rail pressure) until the closing time is detected. The set at the closing time flow rate represents a lower limit flow, the high pressure pump must deliver more than this limit flow, so that the pressure control valve is open at this value of the rail pressure. The flow rate of the high-pressure pump is set larger than this lower limit flow rate.

Preferably, this lower limit flow rate plus a specific offset is set as a delivery rate. The offset ensures that the pressure control valve is definitely open. The offset can be chosen to be much smaller than a conventional, mathematically necessary tolerance reserve. The overflow quantity is thus set to a minimum value. Thus, in particular a pilot control of the flow rate is realized.

An arithmetic unit according to the invention, e.g. a control device of a motor vehicle is, in particular programmatically, configured to perform a method according to the invention.

The implementation of the method in the form of software is also advantageous, since this causes particularly low costs, in particular if an executing control device is still used for further tasks and therefore exists anyway. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

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.

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

Brief description of the drawings

1 schematically shows a fuel injection system of an internal combustion engine, which is adapted to carry out a preferred embodiment of a method according to the invention.

2 schematically shows a pressure control valve, which is adapted to carry out a preferred embodiment of a method according to the invention.

3 schematically shows a diagram of a PWM signal and a current signal, which can be determined in the course of a preferred embodiment of a method according to the invention.

Embodiment (s) of the invention

1 shows an embodiment of a fuel injection system, the whole with the reference numeral 10 is designated. The illustration shows a tank 12 in which fuel is included, a low-pressure pump 14 , a valve 16 , which serves as a pump delivery rate regulator, a high-pressure pump 18 , a common rail 20 that has a pressure sensor 22 has one with the common rail 20 connected pressure control valve 24 and a regulator 26 that is an actual pressure value 28 from the sensor 22 read in and this with a specification for a target pressure value 30 coming from a control unit 32 provided compares. Based on this comparison, a manipulated variable is used as controller output 34 predetermined, for example, a current value for the pressure control valve 24 , Is the pressure in the common rail 20 too high, becomes an overflow 36 to fuel back into the tank 12 recycled. Through the regulator 26 , the pressure control valve 24 and the rail 20 is a loop 50 given.

In 2 is the pressure control valve 24 out 1 shown schematically. The pressure control valve 24 has a magnetic coil 111 and an armature movably mounted therein in an x-direction 112 on. The anchor 112 is with a sealing element 113 , eg a valve needle or the like, connected to a valve seat 114 cooperates to provide the valve functionality.

An opening degree or opening cross section is via a drive current through the magnetic coil 111 controlled. In particular, the current value for the pressure regulating valve 24 acting as a controller output 34 is specified as a manipulated variable, this drive current.

From the inductance L is on the position x of the armature 112 in the magnetic coil 111 closed. A magnetic force arises in the direction of decreasing magnetic resistance (reluctance force). At the minimum of the magnetic resistance the magnetic field reaches its desired energetic minimum. The magnetic force induced by the electric current changes the position of the armature 112 , With a large penetration depth of the armature into the magnet coil 111 reduces the magnetic resistance in the magnetic circuit. A reduction of the magnetic resistance is equal to the increase of the inductance L.

wobei N die Windungszahl, A der Flächeninhalt und l_m die Länge des Magnetkreises ist.The following applies:

where N is the number of turns, A is the area and l _{m is} the length of the magnetic circuit.

The following applies:

Thus it can be concluded from the inductance to the anchor position x.

The inductance L of the magnetic coil 111 is in accordance with a preferred embodiment of the invention from a measurement of the current through the magnetic coil 111 certainly. This is the solenoid 111 by means of a pulsed signal, in particular a PWM signal, driven.

In 3a is a PWM signal shown schematically, which thereby to control the solenoid coil 111 is used. In 3b is a current signal, which is called current flow through the solenoid coil 111 in a drive according to 3a results, shown schematically.

The control unit 32 is in particular set up to output a pulsed signal, in particular a PWM signal. In the example shown in FIG 3 it is a PWM signal with 50% duty cycle.

If a current I flows according to 3b by magnetic coil 111 , a voltage drop can be measured. If a voltage is applied (rising edge in 3a ), the current through the solenoid increases 111 on, the voltage is switched off (falling edge in 3a ), the current through the solenoid decreases 111 ,

For the inductance of the magnetic coil 111 results in a non-linear current profile, which is calculable. From the duty cycle and (known or measurable) physical parameters becomes an effective value of the current flow through the solenoid coil 111 certainly.

Determining the RMS value involves measuring two current values and calculating the RMS value from the two measurements. The control unit 32 is set up so that the current measurement is carried out both on the rising edges and on the falling edges of the PWM signal. After a certain settling time, a maximum value I _max and a minimum value I _{min are obtained} . The measuring points in the current signal are in 3b marked with circles. For this example, a programmable coupling between PWM output and ADC conversion (eg by interrupts or by internal timer of a microcontroller of the controller 32 initiated ADC conversion). The measured values are expediently in the control unit for further calculation 32 cached. To evaluate the current measurement, a current model is preferably used by means of which an effective value I _eff can be calculated from the measured maximum and minimum values. The calculation preferably has no fixed time reference to the measurement, but takes place according to an internal calculation grid of the control unit.

From the determined effective value I _{eff of} the current flow through the magnetic coil 111 becomes the inductance L of the magnetic coil 111 certainly. From this, the position x of the anchor 112 certainly. This in turn becomes the opening cross section of the pressure regulating valve 24 certainly. From the opening cross-section ultimately the Überstrommenge 36 or an actual value of the overflow quantity 36 certainly. As target value for the overflow quantity 36 a minimum value is preferably selected. This minimum value is the smallest possible value of overflow 36 , which is just enough to the operation of the pressure control valve 24 to ensure.

Does the specific actual value deviate from the overflow quantity? 36 From this target value, the high-pressure pump 18 through the control unit 32 driven accordingly and the flow rate of fuel from the high pressure pump 18 is conveyed from the low pressure area is increased or decreased accordingly.

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 19731994 A1 [0006]

Claims (13)

Method for operating a fuel injection system ( 10 ) of an internal combustion engine, - wherein a high-pressure pump ( 18 ) Fuel from a low pressure area into a common rail ( 20 ), - wherein a pressure in the common rail ( 20 ) via a pressure regulating valve ( 24 ) and, in the course of the scheme, an overflow ( 36 ) to fuel via the pressure regulating valve ( 24 ) is returned to the low pressure region and - wherein an opening cross section of the pressure regulating valve ( 24 ) and wherein by means of the specific opening cross section of the pressure regulating valve ( 24 ) the overflow ( 36 ) is regulated or controlled. The method of claim 1, wherein from the particular opening cross section of the pressure regulating valve ( 24 ) an actual value of the overflow ( 36 ) and the determined actual value of the overflow ( 36 ) for the control of the overflow ( 36 ) is used to a certain target value. Method according to claim 1 or 2, wherein the overflow quantity ( 36 ) indirectly via the opening cross-section of the pressure regulating valve ( 24 ) is controlled or controlled by the opening cross section of the pressure regulating valve ( 24 ) is controlled or controlled to a desired value. Method according to one of the preceding claims, wherein the overflow quantity ( 36 ) by means of one of the high-pressure pump ( 18 ) is controlled or controlled from the low pressure range conveyed flow as a manipulated variable. Method according to one of the preceding claims, wherein the overflow quantity ( 36 ) is controlled to a minimum value, this minimum value being a minimum value of the overflow ( 36 ), which is used for the regulation of the pressure in the common rail ( 20 ). Method according to one of the preceding claims, wherein an inductance of a coil ( 111 ) of the pressure regulating valve ( 24 ) is determined from the inductance, a position (x) of one of the coil ( 111 ) moving anchor ( 112 ) of the pressure regulating valve ( 24 ) is determined and from the opening cross-section of the pressure regulating valve ( 24 ) is determined. Method according to one of the preceding claims, wherein a pulsed signal (PWM) comprising a number of pulses to the coil ( 111 ) of the pressure regulating valve ( 24 ), whereby the current flow through the coil ( 111 ), wherein a first current value associated with a rising edge of a pulse of the pulsed signal (PWM) and a second current value associated with a falling edge of the pulse of the pulsed signal (PWM) are measured, the first and the second Current value an effective value (I _eff ) and / or an average value of a current flow through the coil ( 111 ) is determined. Method according to claim 7, wherein from the determined effective value (I _eff ) and / or average value of the current flow through a coil, the inductance of the coil ( 111 ) of the pressure regulating valve ( 24 ) is determined. Method for operating a fuel injection system ( 10 ) of an internal combustion engine, - wherein a high-pressure pump ( 18 ) Fuel from a low pressure area into a common rail ( 20 ), - wherein a pressure in the common rail ( 20 ) via a pressure regulating valve ( 24 ) and, in the course of the scheme, an overflow ( 36 ) to fuel via the pressure regulating valve ( 24 ) is returned to the low pressure region and - wherein a closing time of the pressure regulating valve ( 24 ) and one of the high pressure pump ( 18 ) conveyed from the low-pressure region flow rate at the closing time of the pressure control valve ( 24 ) is determined and - the overflow ( 36 ) is set to a minimum value by setting the delivery amount to a value larger than the delivery amount at the closing time. Method according to claim 9, wherein the overflow quantity ( 36 ) is set to a minimum value by adjusting the flow rate to the flow rate at the closing time plus an offset. Control unit ( 32 ), which is adapted to perform a method according to any one of the preceding claims. Computer program comprising a control unit ( 32 ) to perform a method according to any one of claims 1 to 10, when it on the control unit ( 32 ), in particular according to claim 11, is executed. A machine-readable storage medium having a computer program stored thereon according to claim 12.

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