METHOD FOR CYLINDER EQUALIZATION OF AN INTERNAL COMBUSTION ENGINE

Abstract

A method and control unit for cylinder equalization of an internal combustion engine having at least two cylinders, and includes the following steps: Determination of exhaust gas back pressure values of the individual cylinders over at least two operating cycles, correlation of the exhaust gas back pressure values with the camshaft position and/or the operating cycle, determination of the exhaust gas back pressure maxima for each cylinder, comparison of the exhaust gas back pressure maxima between the individual cylinders and detection of differences, adjustment of the cylinder-specific charge quantities of fresh air and/or fuel. In addition, the invention relates to a controller for carrying out the method and a motor vehicle having such a controller. The method improves the previously known methods and makes them more efficient, especially with regard to the efficiency of the combustion process and thus also of exhaust-gas aftertreatment.

Claims

1. A method for cylinder equalization of an internal combustion engine having at least two cylinders, the method comprising: determining exhaust gas back pressure values of individual cylinders over at least two operating cycles; correlating the exhaust gas back pressure values with a camshaft position and/or an operating cycle; determining an exhaust gas back pressure maxima for each cylinder; comparing the exhaust gas back pressure maxima between the individual cylinders and detecting differences; and adjusting the cylinder-specific charge quantities of fresh air and/or fuel.

2. The method according to claim 1, wherein the exhaust gas back pressure in the exhaust duct is measured adjacent to the exhaust valve by an exhaust back pressure sensor.

3. The method according to claim 1, further comprising: measuring the exhaust gas back pressure; correlating the measured values with time and/or the camshaft position and/or an operating cycle; determining the maxima of the correlation curve from the correlating step; associating the maxima with at least one or every individual cylinder; correlating the maxima with the individual cylinder charge; comparing the maxima and/or cylinder charge between the cylinders; and adjusting the cylinder-specific charge with fresh air and/or fuel.

4. The method according to claim 1, wherein a cylinder-specific ignition angle correction is carried out on the basis of the identified differences of the cylinders.

5. The method according to claim 4, wherein determination of exhaust gas back pressure values of the individual cylinders is accomplished via a high-resolution exhaust back pressure sensor.

6. The method according to claim 1, wherein a sampling rate of the exhaust back pressure sensor is in the range from 0.5 kHz to 3000 kHz, in particular in the range from 1 kHz to 1000 kHz.

7. The method according to claim 1, wherein a cylinder lambda equal to 1 and an exhaust lambda equal to 1 are specified in the adjustment of the cylinder-specific charge quantities of fresh air and/or fuel.

8. A control unit for cylinder equalization of an internal combustion engine, wherein the control unit is designed to carry out the method according to claim 1.

9. The control unit according to claim 8, wherein the control unit includes at least one exhaust back pressure sensor or is connectable to at least one exhaust back pressure sensor, and wherein the exhaust back pressure sensor is designed to output a sensor signal with a high sampling rate in terms of time that represents the exhaust gas back pressure for the relevant cylinder.

10. A motor vehicle comprising: an internal combustion engine that includes at least two cylinders, each with at least one intake valve by which the cylinders are connected to an air inlet, and each with at least one exhaust valve by which each cylinder is connected to an exhaust duct; and a control unit according to claim 8 for cylinder equalization of the internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0053] The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein the sole FIGURE is a highly schematic representation of a flowchart of a method according to the invention for cylinder equalization.

DETAILED DESCRIPTION

[0054] In the FIGURE a flowchart of a method for cylinder equalization of an internal combustion engine is shown in an exemplary embodiment.

[0055] At S1, a sensor signal that represents the exhaust gas back pressure is received from a high-resolution exhaust back pressure sensor. The exhaust back pressure sensor is designed to measure the exhaust gas back pressure with a high sampling rate in terms of time. The sensor signal thus provides values for the exhaust gas back pressure for multiple points in time of one, but preferably several, working cycles of the internal combustion engine.

[0056] At S2, a correlation of the measured values of the exhaust back pressure sensor with the time and/or the camshaft position and/or the operating cycle is carried out. The signal processing thus performed produces a curve of the exhaust gas back pressure, for example over the values of the crankshaft angle.

[0057] At S3, a determination of the extreme points is carried out, and the relevant maxima of the curves from S2 are determined. Preferably, the maxima are each determined directly after the opening of the exhaust valve for this purpose.

[0058] At S4, an association of the maxima to the individual cylinders is carried out. This can be accomplished on the basis of the crankshaft angle or in correlation with the camshaft positions, for example. A plausibility test of the association thus found with additional operating parameters can follow.

[0059] At S5, a correlation of the maxima of the exhaust gas back pressure of each cylinder with the individual cylinder charge in each case is carried out. This can be accomplished in a model-based manner. It can also be accomplished using a stored characteristic map that was measured beforehand, for example on a test stand.

[0060] Optionally, a normalization of the values thus processed can be carried out, for example with a residual gas quantity and/or the speed as the normalization quantity.

[0061] At S6, a comparison is optionally undertaken of the normalized or non-normalized values from step S5, which yields the cylinder-specific differences of either the maxima of the exhaust gas back pressure values, or especially preferably of the relevant cylinder charge quantities.

[0062] The identified cylinder-specific charge quantities can be used at S7 as a basis for adjusting the future cylinder-specific charge quantities of fresh air and/or fuel. Preferably, optimized charge quantities can now be introduced into the applicable cylinder with a requirement for minimum forced amplitude of the cylinder lambda value and of the exhaust lambda value.

[0063] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.