Detection of coking in the intake tract of an internal combustion engine

Abstract

A method for detecting coking in the intake tract of an internal combustion engine having direct fuel injection is provided. The internal combustion engine has variable intake valve control. The variable intake valve control makes it possible to change the open time of the intake valves in relation to the crank angle of the crankshaft. In the method, the internal combustion engine is operated in idling mode at an idling rotational speed that is elevated in comparison with the normal idling operation. In order to perform the measurement, the open time of the intake valves is also shifted in an advanced direction. An uneven-running characteristic value of the internal combustion engine that is characteristic of the uneven running of the internal combustion engine is determined, and the presence of coking in the intake tract can be detected on the basis of the uneven-running characteristic value.

Claims

1. A method for detecting coking in an intake tract of an internal combustion engine having direct fuel injection and variable intake valve control, the method comprising the acts of: operating the internal combustion engine in idle at an idle speed that is increased compared to normal idle operation; controlling an opening time of the intake valves to achieve an early timing event; determining a rough running characteristic of the internal combustion engine which is typical of rough operation of the internal combustion engine, wherein presence of coking in the intake tract is detectable based on the determined rough running characteristic; and issuing a notice based on the determined rough running characteristic, the notice including at least one of notice of the presence of the rough running characteristic, notice of the presence of coking, and notice of a need for intake tract cleaning, wherein the notice is issued to at least one of an operator of the internal combustion engine, a user operating an engine testing device, a controller fault memory for storage and subsequent retrieval, and a controller configured to initiate automatic intake tract cleaning.

2. The method according to claim 1, wherein the increased idle speed is greater than 1200 rpm.

3. The method according to claim 1, wherein the increased idle speed is approximately 1500 rpm.

4. The method according claim 1, wherein the act of determining the rough running characteristic further comprises: determining, for each cylinder, a cylinder-based rough running characteristic that is typical of the rough operation of a cylinder, the rough running characteristic of the internal combustion engine being determined based on the cylinder-based rough running characteristics.

5. The method according to claim 4, wherein the rough running characteristic of the internal combustion engine is determined from the cylinder-based rough running characteristic by averaging.

6. The method according to claim 5, wherein the cylinder-based rough running characteristic of every cylinder is determined as a function of multiple rough running values that are based on the particular cylinder and describe a rough operation of the internal combustion engine in cycles of the particular cylinder.

7. The method according to claim 6, further comprising the act of: detecting the presence of coking by comparing the rough running characteristic to a comparison value.

8. The method according to claim 7, further comprising the act of: checking whether an engine temperature is lower than or lower than/equal to a threshold temperature.

9. The method according to claim 4, wherein the cylinder-based rough running characteristic of every cylinder is determined as a function of multiple rough running values that are based on the particular cylinder and describe a rough operation of the internal combustion engine in cycles of the particular cylinder.

10. The method according to claim 1, further comprising the act of: detecting the presence of coking by comparing the rough running characteristic to a comparison value.

11. The method according to claim 10, wherein cleaning or a replacement of an engine component in question is carried out, or is not carried out, as a function of the comparison.

12. The method according to claim 10, further comprising the act of: checking whether an engine temperature is lower than or lower than/equal to a threshold temperature.

13. The method according to claim 1, further comprising the act of: checking whether an engine temperature is lower than or lower than/equal to a threshold temperature.

14. An engine testing device for detecting coking in an intake tract of an internal combustion engine of a motor vehicle having direct fuel injection and variable intake valve control, comprising: a test unit connectable to a motor vehicle for controlling operation of the vehicle and for receiving vehicle-internal measurement values, the test unit being operatively configured to: operate the internal combustion engine in idle at an idle speed that is increased compared to normal idle operation; control an opening time of the intake valves to achieve an early timing event; determine a rough running characteristic of the internal combustion engine which is typical of rough operation of the internal combustion engine, wherein presence of coking in the intake tract is detectable based on the rough running characteristic; issue a notice based on the determined rough running characteristic, the notice including at least one of notice of the presence of the rough running characteristic, notice of the presence of coking, and notice of a need for intake tract cleaning, wherein the notice is issued to at least one of an operator of the internal combustion engine, a user operating an engine testing device, a controller fault memory for storage and subsequent retrieval, and a controller configured to initiate automatic intake tract cleaning.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an exemplary flow chart for a method according to the invention for detecting coking in the intact tract of an internal combustion engine;

(2) FIG. 2 is a graphical illustration for the definition of the intake spread value;

(3) FIG. 3 is a graphical illustration of measured rough running values for four different cylinders Z1, Z2, Z3 and Z4 plotted over the spread angle SW; and

(4) FIG. 4 shows measurement results for the rough running characteristic lutmwdiff before and after cleaning of the intake tract.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIG. 1 shows an exemplary flow chart for a method according to the invention for detecting coking in the intact tract of an internal combustion engine. In step 90, it is checked whether the engine temperature is below a threshold value, for example below 40 C. If this is not the case, a rapid cool-down of the engine is carried out by way of the electric fan, so that the engine temperature has been lowered to a value below 40 C. before starting the measurement.

(6) After it has been ensured that the temperature is below the threshold value, the idle speed is increased in step 100 from an idle speed that is typical in normal idle operation (for example 750 rpm) to an increased idle speed (for example 1500 rpm).

(7) Furthermore, the opening time of the intake valves is controlled to achieve an early timing event (see step 110) by advancing the intake camshaft. Here, what is known as the spread value SW is reduced. The spread value SW describes the angle in CS (crankshaft) between top dead center and the crest of the valve lift curve of the intake valve. This is shown in FIG. 2. Curve 200 describes an exemplary valve lift curve for a center position of the intake camshaft. Dotted curve 210 describes an exemplary valve lift curve after an advance of the curve 200, wherein the opening time Z (which is to say the time period between opening and closing of the intake valve) for curve 200 is chronologically before that for curve 210. FIG. 2 shows the spread value SW for curve 200 at the center position, which corresponds to the angle between top dead center and the crest of the valve lift curve.

(8) The control of the opening time Z to achieve an early timing event according to step 110 is carried out, for example, in that the opening time Z is passed through multiple times from early to late by varying the spread value SW, and that measurement values are recorded during each passage of the opening time Z. As an alternative, the opening time Z could of course be fixed to an early position (which is to say the spread value SW could be set to a fixed value, for example a value in the range of 50 CS to 85 CS), and the measurement could be carried out in this position.

(9) For passing through the opening time from late to early, the spread value SW is reduced, proceeding from a spread value SW.sub.4 (corresponds to a late opening time Z), to a spread value SW.sub.1 that is lower (corresponds to an early opening time Z). The spread value SW.sub.4, for example, corresponds to the latest possible position of the opening time Z that can be set with the intake valve gear of the engine, while the spread value SW.sub.1, for example, corresponds to the earliest possible position of the opening time that can be set with the intake valve gear of the engine. For example, proceeding from SW.sub.4=120 CS, the spread value SW is reduced to a spread value SW.sub.1=50 CS, wherein a control range of 70 CS is obtained. The passed-through value range of the spread value SW from SW.sub.1 to SW.sub.4 is shown as the x-axis in FIG. 3.

(10) The spread value SW is preferably passed through in step 110 not only once, but multiple times from SW.sub.4 to SW.sub.1.

(11) When passing through, so-called segment times are recorded by way of transducer wheel measurement. A segment time corresponds to the time at which the crankshaft exceeds a predetermined crankshaft angle range. Here, for example, a crankshaft angle range, in which the cylinder fires and which is referred to as a segment, is assigned to every cylinder. Based on the segment times, rough running values can be calculated for the individual cylinders (see step 120 in FIG. 1). The calculation of rough running values is described in the published prior art DE 198 14 732 A1, for example, the disclosure of which is hereby incorporated by reference herein

(12) Rough running values lut(n) can be calculated in the following manner, for example:

(13) $\mathrm{lut}\left(n\right)=\frac{\mathrm{ts}\left(n+1\right)-\mathrm{ts}\left(n\right)}{{\mathrm{ts}\left(n\right)}^3}-K$

(14) Here, lut(n) describes a rough running value for the firing cycle n of a four-cylinder engine, for example. The variable ts(n) describes the segment time at the firing cycle n; ts(n+1) describes the segment at the firing cycle n+1. The variable K corresponds to a correction value K, in particular for dynamic compensation.

(15) Every rough running value lut(n) is assigned to the cycle of a particular cylinder, and thus to a particular cylinder, as a function of the firing order of the cylinders. FIG. 3 shows exemplary rough running values for cylinders Z1, Z2, Z3 and Z4 of a four-cylinder internal combustion engine over the spread value SW, which is to say over the camshaft position. The rough running values lut(n) can assume either positive or negative values. A rough running value of zero corresponds to a smooth engine operation. At a positive value lut(n), the engine rotates too slowly in the assigned segment n; at a negative value lut(n), the engine rotates too quickly in the assigned segment n.

(16) The rough running values lut(n) shown in FIG. 3 are determined by passing through the spread value SW from SW.sub.4 to SW.sub.1 multiple times and are stored individually for each cylinder.

(17) The rough running values lut(n) form a funnel shape, wherein the amount and thus the funnel width tends to become smaller as the spread value SW increases (which is to say as the shift in the opening time toward late increases), and tends to become larger as the spread value SW decreases (which is to say as the shift in the opening time toward early increases). The rough running of the internal combustion engine also tends to increase when the opening time is shifted toward early. The use of rough running values lut(n) having a more advanced position of the camshaft, for example up to 85 CS, is suitable for the method according to the invention for detecting coking, since with a more advanced position of the camshaft the difference in the rough running of the internal combustion engine is greater between the case where the intake tract is coked and the case where it is not coked, whereby a distinction between coking and non-coking is easier. This increases the robustness of the measuring method.

(18) In the following steps, only the rough running values lut(n) in an evaluation window from SW.sub.2 to SW.sub.3 are taken into consideration, for example from SW.sub.2=60 CS to SW.sub.3=85 CS, for determining a rough running characteristic. The focus of the evaluation window is preferably on the early half of the maximum control range, and preferably the entire evaluation window is in the early half of the maximal control range. In the example of FIG. 3, the early half of the maximal control range extends from SW=50 CS to SW=85 CS, and the late half of the maximal control value extends from 85 CS to 120 CS, wherein in the case of an evaluation window of SW.sub.2=60 CS to SW.sub.3=85 CS the entire evaluation window is in the early half of the maximal control range.

(19) So as to calculate a rough running characteristic of the engine, a cylinder-based average value mwlutZipos is calculated for all rough running values of a cylinder Zi in the evaluation window which are greater than 0 (see step 130 in FIG. 1). This happens in each case for all cylinders Zi where i=1, 2, 3, and 4, for example.

(20) Similarly, the cylinder-based average value mwlutZi_neg is calculated for all rough running values of a cylinder Zi in the evaluation window which are smaller than 0. This is also done for every cylinder Zi.

(21) Based on the average values, it is possible to calculate, individually for every cylinder Zi, the difference difflutZi between the positive average value mwlutZi_pos of the cylinder Zi and the negative average value mwlutZi_neg of the cylinder Zi (see step 140 in FIG. 1). The difference difflutZi is also calculated in each case for all cylinders Zi. The difference value difflutZi indicates how wide the funnel in FIG. 3 is on average for the particular cylinder Zi in the selected evaluation window.

(22) In step 150, a rough running characteristic lutmwdiff of the internal combustion engine is determined by averaging the cylinder-based values difflutZi across all the cylinders Zi.

(23) Optionally, it is possible to determine multiple measurement values in consecutive measurements for the rough running characteristic lutmwdiff (for example, by carrying out steps 110 to 150 multiple times) and to average the multiple measurement values, wherein then the averaged variable is used as the rough running characteristic for detecting the coking in the intake tract.

(24) Based on the rough running characteristic lutmwdiff (or the averaged rough running characteristic), it is then possible to detect coking in the intake tract. If the rough running characteristic lutmwdiff (or the averaged rough running characteristic) is greater than a critical value, this indicates coking of the intake tract, and cleaning of the intake tract is necessary. If the rough running characteristic lutmwdiff (or the averaged rough running characteristic) is smaller than a critical value, the intake tract is not significantly coked, and cleaning is not necessary.

(25) The critical value can be obtained based on an empirical measurement of a sufficiently large number of vehicles.

(26) FIG. 4 shows in each case four measurement values for the rough running characteristic lutmwdiff before and after cleaning of the intake tract. The dotted lines in each case identify the average value of the respective four measurement values. As can be seen based on FIG. 4, the average value of lutmwdiff before cleaning of the intake tract is almost twice as high as after cleaning of the intake tract. It is further apparent that the measurement values for the rough running characteristic become increasingly smaller before cleaning and thereby lose meaningfulness. The cause for this is the increased engine temperature, since the engine temperature was below the threshold temperature of 40 C., for example, only before the start of the measurement of the first measurement value, while during subsequent measurements the temperature rose due to slow heating of the engine. The values for lutmwdiff are therefore a function of the temperature. When starting the first measurement, it should preferably be ensured that the starting temperature is below the threshold temperature of 40 C., for example. The measurements are then particularly meaningful.

(27) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.