Method for compensating valve drift in an internal combustion engine

Abstract

A method for compensating valve drift in an internal combustion engine having a variable valve train; in the method, an actual value of the current operating state of the internal combustion engine is determined in an air expenditure map and compared to a desired value of the air expenditure map, whereupon the air expenditure map is corrected.

Claims

1. A method for compensating valve drift in an internal combustion engine having a variable valve drive, the method comprising the steps of: determining an actual value of an instantaneous operating state of the internal combustion engine in a volumetric efficiency characteristic diagram, which volumetric efficiency characteristic diagram provides an air consumption in dependence on a closing point in time of an inlet valve, using a mass flow sensor; comparing the actual valve with a setpoint value of the volumetric efficiency characteristic diagram to determine a difference; and compensating the valve drift by subsequently correcting the volumetric efficiency characteristic diagram based on the difference.

2. The method according to claim 1, wherein the step of correcting the volumetric efficiency characteristic diagram includes shifting the volumetric efficiency characteristic diagram.

3. The method according to claim 1, wherein the step of correcting the volumetric efficiency characteristic diagram includes adding a correction factor.

4. The method according to claim 1, including measuring air/gas mixture mass flow in an intake path using the mass flow sensor.

5. The method according to claim 1, including carrying out measurement by the mass flow sensor in an intake path adjacent to a gas feed into the intake path.

6. The method according to claim 1, including carrying out measurement by the mass flow sensor upstream of a compressor arranged in an intake path.

7. The method according to claim 1, including applying the method in a stationary gas engine.

8. The method according to claim 1, including carrying out the method during a stationary operating state of the internal combustion engine.

9. The method according to claim 8, including carrying out the method during a stationary mode which lasts over a time period of longer than 30 seconds.

10. The method according to claim 1, wherein during the step of correcting the volumetric efficiency characteristic diagram charge pressure and/or rotational speed of the internal combustion engine are changed.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be described below on the basis of an exemplary embodiment in conjunction with the drawing, in which:

(2) FIG. 1 shows a schematic illustration of a volumetric efficiency characteristic diagram,

(3) FIG. 2 shows a schematic illustration of the structural application of the method according to the invention, and

(4) FIG. 3 shows a flowchart of the method sequence according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows a volumetric efficiency characteristic diagram in which the closing time of an inlet valve is illustrated on the abscissa, while the ordinate represents the volumetric efficiency. The values for individual rotational speeds of the internal combustion engine are illustrated with a continuous line in the diagram. The dotted line shows a corrected characteristic diagram which has been corrected on the basis of the method according to the invention by shifting the characteristic diagram or by adding a correction factor. If, for example in the case of large inlet closure angles, the restoring force of the valve decreases, for example as a result of valve wear of the valve spring, an increase occurs in the volumetric efficiency. This increase can be determined with a comparison of the respective actual value with the setpoint value. As a result it becomes clear that the setpoint characteristic diagram is not being complied with. The correction provided according to the invention is therefore carried out.

(6) FIG. 2 shows a schematic illustration of a cylinder 5 of an internal combustion engine having a piston 6. Air 7 is fed in through an intake path 2. Gas is added to this air 7 by means of a gas feed 4, with the result that a gas/air mixture 8 is produced. This gas/air mixture 8 is fed to a mass flow sensor 1 which carries out the measurement according to the invention. The mass flow sensor 1 is arranged upstream of a compressor 3 in the intake path 2. A charge pressure p.sub.5 is present downstream of the compressor 3. The gas feed 4 or the air feed 7 is controlled for compensating valve drift as a function of the measured values of the mass flow sensor 1.

(7) FIG. 3 shows a simplified flow chart of the method according to the invention. Here, a characteristic diagram 9, to which the rotational speed of the internal combustion engine (RPM) and the closing angle of the inflow valve (t.sub.s(VCM)) are fed as input variables, is illustrated schematically. A volumetric efficiency .sub.a,nc, which is not yet corrected, is obtained from the characteristic diagram. This value for the volumetric efficiency is fed to an electronic circuit 10 which outputs a volumetric efficiency .sub.a which is corrected by the fed-in value .sub.a,nc. By using this value for the volumetric efficiency, an air mass flow m.sub.calc is calculated, which air mass flow m.sub.calc is fed to an electronic circuit 11, to which a value for the measured air mass flow m.sub.probe is also fed. The value for the measured air mass flow m.sub.probe is output by the mass flow sensor 1 and is considered to be correct. The deviation in the volumetric efficiency .sub.a is measured by means of a PI controller and is fed, on the one hand, to the electronic circuit 10 and, on the other, to the characteristic diagram for characteristic diagram correction.