EP2084383A1

EP2084383A1 - Method for determining a characteristic map of the injection quantity against an electrical variable of an electrically activated injection valve

Info

Publication number: EP2084383A1
Application number: EP07803597A
Authority: EP
Inventors: Metin Gencbay
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2006-10-25
Filing date: 2007-09-25
Publication date: 2009-08-05
Also published as: CN101529070A; DE102006050171A1; JP2010507748A; US20110120420A1; WO2008049704A1

Abstract

The invention relates to a method for determining a characteristic map of the injection quantity (Q) against an electrical variable (UB) of an electrically activated injector. The electrical variable (UB) in operation of the internal combustion engine is varied from a starting value (U0), at which no injection is deposited, until a defined first injection quantity (Q-1) is injected, wherein the value (U1) which is set at the defined first injection quantity is assigned as a first value (U1) of the electrical variable (UB) of the defined first injection quantity (Q1).

Description

description

title

Method for determining a characteristic map of the injection quantity over an electrical variable of an electrically controlled injection valve

State of the art

The present invention relates to a method for determining a characteristic map of the injection quantity over an electrical variable of an electrically controlled injection valve.

From the prior art electrically controlled injection valves are known, which are used in connection with so-called common rail injection systems. Such injection valves are usually provided with a piezoelectric actuator which can move a valve needle via a hydraulic coupling element. Of the

Piezo actuator is located directly above the needle and completely surrounded by fuel under high pressure. Due to a long-term drift (aging and the like) of the electrical and mechanical property of the injector, it may happen that with the old injector the pre-injection or general injection with small amounts fail or be discontinued with altered amounts, since the applied values for a new injector , such as a bottom voltage and drive time for which aged (drifting) injectors are no longer sufficient to open, or the drift leads to a wrong injection quantity. This leads to an increase in the combustion noise, which can be disturbing especially when idling. In addition, an increase in the amount of pilot injection by a drift of the injector may cause a deterioration of the exhaust gas composition.

Disclosure of the invention An object of the present invention is therefore to detect and correct deviations of an injection valve (injector) from the desired state caused by aging or long-term drift.

This problem is solved by a method for determining a characteristic map of the injection quantity over an electrical variable of an electrically controlled injector, the electrical variable during operation of the internal combustion engine being changed from an initial value at which no injection is discontinued to a defined first injection quantity is, wherein the set at the defined first injection amount value is assigned as the first value of the electrical quantity of the defined injection quantity. Preferably, the method is carried out at a pre-injection. The associated main injection is carried out unchanged, with the injection quantity increasing as soon as the pre-injection is successfully completed. This ensures that the combustion takes place, but the torque contribution is less than in a pre-injection. It can thus be observed whether the pre-injection was discontinued or not discontinued by the torque contribution to the total torque of the internal combustion engine is determined at the respective observed injection. Preferably, it is provided that the method is carried out in towing mode of the internal combustion engine, since in this case the lack of torque contribution in case of failure of pre-injection has only a small effect on the ride comfort of a vehicle driven by the internal combustion engine. The electrical variable is preferably changed in a further method step so that a defined second injection quantity is injected, the value set in the defined second injection quantity being assigned as a second value to the electrical quantity of the defined second injection quantity. So two value pairs voltage stroke / injection quantity are determined. It is preferably provided that from the pair of values of the first injection quantity with the first electrical value and the value pair of the second injection quantity and the second electrical value by means of an extrapolation and interpolation function, a characteristic value electrical value is determined. In addition, additional value pairs can enter the extrapolation or interpolation, whereby the accuracy of the extrapolation or interpolation function formed can be improved. Preferably, the extrapolation and interpolation function is a linear one Function. The electrically controlled injection valve is preferably driven piezoelectrically, the electrical variable being the voltage swing between a holding voltage and a bottom voltage. In this case, to determine a characteristic map of the injection quantity over the voltage stroke of the piezoelectric injection valve, the voltage swing during operation of the internal combustion engine from the initial voltage, in which no injection is discontinued, increased until a defined injection quantity is injected, wherein the voltage set in the defined injection quantity of the assigned to defined injection quantity.

The actually injected injection quantity is preferably based on the temporal

History of the torque of the crankshaft of the internal combustion engine determined. It is preferably provided that the injection quantity is determined by means of a Schubgas- torque model of a cylinder of the internal combustion engine from the time course of the torque of the crankshaft of the internal combustion engine.

The problem mentioned at the outset is also solved by a device, in particular an internal combustion engine or control unit for an internal combustion engine, which is set up for determining a characteristic map of the injection quantity over an electrical variable of an electrically controlled injector, wherein the electrical variable during operation of the internal combustion engine is of an initial value , in which no injection is discontinued, is changed until a defined first injection quantity is discontinued, wherein the value set in the defined first injection quantity is assigned as the first value of the electrical quantity to the defined injection quantity. The problem mentioned at the outset is also solved by a computer program with program code for carrying out all steps according to a method according to the invention, if the

Program is running in a computer.

Hereinafter, an embodiment of the present invention will be explained in more detail with reference to the accompanying drawings. Showing:

1 shows the voltage profile across the piezoelectric actuator over time;

Fig. 2 is a graph of the injection amount over the bottom voltage; Fig. 3 is a flowchart of an embodiment of an inventive

Process.

Embodiment of the invention

In the following embodiments, it is assumed that an injector (injection valve) with piezoelectric actuator as a controller. Such an injector is provided with a piezoelectric actuator, which is controlled by a control unit. The piezoelectric actuator is connected to a valve needle via a hydraulic coupling element, wherein the valve needle can rest on a valve seat in the interior of the housing of the injection valve. In a valve needle lifted from the valve seat, the injection valve is opened and fuel is injected. If the valve needle is seated on the valve seat, the injection valve is closed. The transition from the closed to the open state is effected by means of the piezoelectric actuator. For this purpose, an electrical voltage is applied to the actuator, the one

Changes the length of a piezo stack causes, which in turn is exploited to open or close the injector. To the piezoelectric actuator to a so-called holding voltage is applied, which causes a certain length of the piezo stack. The hydraulic coupling element has the effect that the valve needle is seated on its valve seat when the tension is stationary and the injection valve is closed. A sufficiently rapid change of the voltage applied to the piezoelectric element can not be compensated by the hydraulic coupling element, a voltage change which causes a shortening of the piezoelectric element, thus causing an injection.

In Fig. 1, the voltage waveform of the voltage U is shown on the piezoelectric actuator over the time t. In the closed state of the injection valve, the so-called holding voltage U _{H is applied} . To settle an injection, the holding voltage U _{H is} lowered to a so-called bottom voltage U _B. The bottom voltage U ₆ can be kept for a suitable period of time, but can also be raised immediately to a suitable other voltage differing from the holding voltage. At the end of the injection, the holding voltage U _{H is again} applied to the piezoelectric actuator. In the exemplary embodiment of FIG. 1, the holding voltage U _{H is} initially set to the bottom chip to initiate an injection. UB lowered, then raised to an intermediate voltage Ui and kept constant for a holding time .DELTA.t _H and then raised again with a rising edge to the holding voltage U _H. If the holding voltage U _{H is} kept constant and the voltage curve and the holding time Δt _H are also kept constant, then the injection quantity essentially depends on the bottom voltage U _B. The difference

Holding voltage U _H to bottom voltage U _B is referred to as a voltage swing .DELTA.U. Thus, if only the bottom voltage U _{6 is} changed, only the voltage swing .DELTA.U is changed, so that the injection quantity P depends on the voltage swing .DELTA.U.

A change in the injection quantity P of a cylinder affects the torque m of the internal combustion engine. For the following illustration, it is assumed that the internal combustion engine is in overrun mode.

The voltage swing during a pilot injection of a cylinder in overrun operation of the internal combustion engine is now reduced according to the invention until guaranteed no pilot injection takes place. A reduction in the voltage swing means an increase in the bottom voltage for the same output voltage. This value of the bottom voltage U _B is referred to as UO in Fig. 1. Now the voltage swing in the pilot injection is gradually increased until a pilot injection takes place. This can easily be measured in overrun mode on the speed signal of the internal combustion engine, a pre-injection is carried out provides an additional torque of the internal combustion engine, thereby increasing the speed. About the speed increase, the additional gas torque of the cylinder in which the pilot injection was discontinued, are determined and thus the injection quantity can be determined using a model of combustion. The voltage swing on the cylinder is now adjusted so that a defined first injection quantity Qi is injected, for example one cubic millimeter per injection. The defined first injection quantity includes a voltage swing and thus a bottom voltage, these are designated U 'and U ₆ ' in FIG. One obtains a first value pair Ui / Qi. In a next step, the bottom voltage U _6, and thus the voltage is changed so .DELTA.U now until a defined second injection quantity Q ₂ bikmillimetern for example, three Ku is achieved per injection. This value is designated in FIG. 1 as a voltage swing ΔU "or as a bottom voltage U _B '. In particular, the holding voltage U _H and the holding time .DELTA.t _H remain unchanged. The presence of the second defined injection quantity Q ₂ from here, for example, three cubic miles per injection is again determined on the basis of the speed signal. This gives a second value pair U ₂ ZQ ₂ .

For further determination of a map of the relationship voltage swing or at a constant holding voltage of the bottom voltage U ₆ to the injection quantity Q is assumed that a linear relationship between the two. With the previously determined two value pairs bottom voltage / injection quantity, a straight line can now be determined with the help of which the further value pairs of the characteristic field are determined.

This relationship is sketched in FIG. A first point Pi is determined with a value pair O ₁ JQ ₁ and a second point P ₂ value pair O ₂ JQ ₂ as previously shown. Both are used to set an equalization line, all value pairs bottom voltage / injection quantity or voltage stroke / injection quantity lie on this straight line. Optionally, instead of two points, several points can be used to determine the extrapolation or interpolation line according to FIG. 2, in which case a suitable adaptation method should be selected, for example a least squares method or the like, in order to match the straight line through the set of points lay.

3 shows a flow chart of an exemplary embodiment of a method according to the invention. The method begins in step 101 with the transition of the internal combustion engine into the overrun mode. In step 102, the bottom pressure for pilot injection in a cylinder is reduced to a value (eg, a fixed value for the respective injector type) at which no injection is discontinued. Now, the bottom voltage is increased in a loop until a defined injection quantity, for example, 1 mm ^{3 is} injected. Based on the speed curve, the torque contributed by the pilot injection is determined in step 103 and the injection quantity is determined based on the torque. In step 104 it is checked whether the required injection quantity Qi has been reached. If this is the case (option J), the associated bottom voltage Ui is stored together with the injection quantity Qi as value pair Ui / Qi in step 105, otherwise (option N) the bottom voltage is increased in step 106 by a voltage amount ΔU. Is the value pair U ₁ JQ ₁ in the loop of the step te determined 103 to 106, then a similar loop of steps 107 to 110 follows to determine the value pair U ₂ / Q ₂ , wherein in step 107, the injection amount Q is determined, it is checked in step 108, whether this value Q ₂ has reached, in step 109, the bottom voltage is increased in a loop and in step 110, the value pair U ₂ / Q _{2 is} stored. In step 111, a straight-line equation is set up from the two value pairs Uj / Qi and U ₂ / Q ₂ , with which a characteristic map is determined in step 112 and stored in a control unit.

Claims

claims

1. A method for determining a characteristic map of the injection quantity (Q) over an electrical variable (U _B ) of an electrically controlled injector, characterized in that the electrical variable (U _B ) in the operation of the internal combustion engine of an initial value (UO), at the injection is discontinued, is changed until a defined first injection quantity (Qi) is injected, wherein the set at the defined first injection amount value (Ui) as the first value (Ui) of the electrical variable (U _B ) of the defined first injection quantity ( Qi) is assigned.

2. The method according to claim 1, characterized in that the electrical variable is changed in a further method step so that a defined second injection quantity (Q ₂ ) is injected, wherein the set at the defined second injection quantity (Q ₂ ) value as the second value (U ₂ ) of the electrical quantity (UB) of the defined second injection quantity (Q ₂ ) is assigned.

3. The method according to claim 2, characterized in that from the value pair (Ui, Qi) of the first injection quantity (Qi) and the first electrical value (Ui) and the value pair (U ₂ , Q ₂ ) of the second injection quantity (Q ₂ ) and the second electrical value (U ₂ ) by means of an extrapolation and interpolation function

Characteristic electric value to injection quantity is determined.

4. The method according to claim 3, characterized in that further value pairs enter into the extrapolation or interpolation.

5. The method according to any one of claims 1 to 4, characterized in that the extrapolation and interpolation function is a linear function.

6. The method according to any one of the preceding claims, characterized in that the electrically controlled injection valve is driven piezoelectrically and that the electrical size of the voltage swing (.DELTA.U) between a holding voltage (UH) and a bottom voltage (U _B ).

7. The method according to any one of the preceding claims, characterized in that the injection quantity is determined based on the time profile of the torque of the crankshaft of the internal combustion engine.

8. The method according to claim 7, characterized in that the injection quantity is determined by means of a Schubgasmomentenmodells a cylinder of the internal combustion engine from the time course of the torque of the crankshaft of the internal combustion engine.

9. Device, in particular internal combustion engine or control device for an internal combustion engine, which is adapted to determine a characteristic map of the injection quantity (Q) over an electrical variable (U _B ) of an electrically controlled injector, characterized in that the electrical variable (U _B ) in operation the internal combustion engine from an initial value (UO), in which no injection is discontinued, is changed until a defined first injection quantity (Qi) is injected, wherein the set at the defined first injection amount value (Ui) as the first value (Ui) the electrical quantity (U ₆ ) of the defined first injection quantity (Qi) is assigned.

A computer program with program code for performing all the steps according to one of claims 1 to 8, when the program is executed in a computer.