Method for controlling an internal combustion engine

Abstract

A method of controlling an internal combustion engine having a plurality of cylinders, in particular a stationary internal combustion engine, wherein actuators of the internal combustion engine are actuable in crank angle-dependent relationship and/or sensor signals of the internal combustion engine can be ascertained in crank angle-dependent relationship, for compensation of a torsion of a crankshaft, by which torsion deviations in the crank angle occur between a twisted and an untwisted condition of the crankshaft, wherein for at least two of the cylinders a cylinder-individual value of the angle deviation is ascertained and the crank angle-dependent actuator or sensor signals are corrected in dependence on the detected angle deviation.

Claims

1. A method of controlling an internal combustion engine, comprising: providing the internal combustion engine connected at a fixed drive output side of a crankshaft to a generator; connecting a plurality of cylinders to the crankshaft of the internal combustion engine via a plurality of connecting rods; measuring with a measuring device torsion deviations for each crank angle of a working cycle occurring between a twisted and an untwisted condition of the crankshaft to obtain measured angle deviations for each cylinder position along a longitudinal axis of the crankshaft; calculating in real time for each cylinder of at least two cylinders of the plurality of cylinders, a cylinder-individual and crank angle-resolved value of angle deviation for the respective cylinder based on a geometric spacing, a firing spacing, and the measured angle deviations effected instantaneously in the current engine cycle, wherein the geometrical spacing of each cylinder of the at least two cylinders of the plurality of cylinders comprises an axial distance along the longitudinal axis from the fixed drive output side of the crankshaft to the respective cylinder, wherein the fixed drive output side is assumed to be fixedly clamped, wherein the firing spacing of each cylinder of the at least two cylinders of the plurality of cylinders comprises an angular difference between successive firing events in cylinders of the plurality of cylinders; and correcting actuation of actuators of the internal combustion engine based on the cylinder-individual and crank angle-resolved value and transmitting signals from a sensor in the internal combustion engine based on the cylinder-individual and crank angle-resolved value to control the internal combustion engine.

2. The method as set forth in claim 1, wherein a curve representing a magnitude of the angle deviation oscillates with varying peaks relative to the crank angle over the working cycle, wherein the varying peaks generally align with the firing spacing, and the magnitude of the angle deviation varies at least partially based on the geometrical spacing.

3. The method as set forth in claim 1, wherein calculating the cylinder-individual and crank angle-resolved value is in dependence on operating conditions.

4. The method as set forth in claim 3, wherein calculating the cylinder-individual and crank angle-resolved value is by a model function.

5. The method as set forth in claim 1, wherein the cylinder-individual and crank angle-resolved values of angle deviation for the at least two cylinders of the plurality of cylinders is different based on different axial distances along the longitudinal axis from the fixed drive output side of the crankshaft to the at least two cylinders.

6. The method as set forth in claim 1, wherein the cylinder-individual and crank angle-resolved value of angle deviation is different for different angular differences between successive firing events in cylinders of the plurality of cylinders.

7. The method as set forth in claim 1, wherein calculating the cylinder-individual and crank angle-resolved value varies based on whether the firing spacing is a uniform or a non-uniform angular difference between the successive firing events in cylinders of the plurality of cylinders.

8. The method as set forth in claim 1, wherein at least one engine management parameter is adjusted based on at least one cylinder-individual and crank angle-resolved value.

9. The method as set forth in claim 1, wherein at least one engine measurement is adjusted based on at least one cylinder-individual and crank angle-resolved value.

10. The method as set forth in claim 9, wherein the adjusted engine measurement is a cylinder pressure measurement.

11. A stationary internal combustion engine operable according to the method as set forth in claim 1.

12. A method, comprising: calculating a cylinder-individual and crank angle-resolved value of angle deviation of a crankshaft of an internal combustion engine due to torsion of the crankshaft for each crank angle during a working cycle, wherein calculating the cylinder-individual and crank angle-resolved value of the angle deviation compensates at least for a geometric spacing and a firing spacing for each cylinder of a plurality of cylinders of the internal combustion engine, wherein the geometrical spacing of each cylinder of the plurality of cylinders comprises an axial distance along a longitudinal axis from a fixed drive output side of the crankshaft to the respective cylinder, wherein the fixed drive output side is assumed to be fixedly clamped, and wherein the firing spacing of each cylinder of the plurality of cylinders comprises an angular difference between successive firing events in the plurality of cylinders; and adjusting sensor feedback and/or control of the internal combustion engine based on the cylinder-individual and crank angle-resolved value.

13. The method as set forth in claim 12, wherein a curve representing a magnitude of the angle deviation oscillates with varying peaks relative to the crank angle over the working cycle, wherein the varying peaks generally align with the firing spacing, and the magnitude of the angle deviation varies at least partially based on the geometrical spacing.

Description

(1) The advantages of the invention are described more fully hereinafter with reference to the drawings in which:

(2) FIGS. 1a and 1b show a diagrammatic view of an internal combustion engine,

(3) FIG. 2 shows a view of the torsion-induced crankshaft angle deviation for a 90 firing spacing, and

(4) FIG. 3 shows a view of the torsion-induced crankshaft angle deviation for a 120/60 firing spacing.

(5) The detailed specific description now follows.

(6) FIG. 1a diagrammatically shows an internal combustion engine having eight cylinders, wherein counting will be begun at the drive output side (in this case marked by the generator G) on the left-hand cylinder bank. In the case of the V-engine cylinders Z1-Z4 are on the left-hand cylinder bank and cylinders Z5-Z8 are on the right-hand cylinder bank.

(7) The Figure also indicates the crankshaft K to which the cylinders Z1 through Z8 are connected by connecting rods. The cylinder Z1, that is to say the location at which force is introduced by the connecting rod of cylinder Z1, is quite close to the drive output side which is assumed to be fixed.

(8) FIG. 1b shows an internal combustion engine with eight cylinders in an in-line arrangement. In the in-line engine the cylinders are counted from Z1 through Z8.

(9) In these examples let the firing order be Z1.fwdarw.Z6.fwdarw.Z3.fwdarw.Z5.fwdarw.Z4.fwdarw.Z7.fwdarw.Z2.fwdarw.Z8.

(10) In FIG. 1b the firing spacing, expressed as the crank angle difference, is 90. After ignition in the cylinder Z8 the process begins again with cylinder Z1. For this example the firing spacing is therefore distributed in relation to the crank angle at equal spacings to the cylinders. A firing event takes place every 90 crank angle.

(11) FIG. 2 shows a graph in which the torsion-induced angle deviation of the crankshaft is plotted on the ordinate at the position of cylinder Z8, .sub.8, over an entire working cycle, that is to say 720 crank angle.

(12) When now the above-discussed firing order is implemented, that gives the illustrated angle deviation .sub.8 which is discussed hereinafter. For better understanding, those cylinders which fire at the respective crankshaft position have been plotted in a parallel-shifted auxiliary axis.

(13) Firstly cylinder Z1 fires at 0 crank angle. As cylinder Z1 is quite close to the drive output side which is assumed to be rigid the firing event of cylinder Z1 can cause as good as no twisting of the crankshaft with respect to the crankshaft position of cylinder Z8.

(14) The next firing event, 90 crankshaft angle later, occurs at the cylinder Z6. By virtue of the distance relative to the drive output side that causes the greater contribution to twisting of the crankshaft.

(15) Expressed in words, the peak of the curve .sub.6 corresponds at the crankshaft position 90 to the contribution of the crankshaft angle deviation caused by the cylinder Z6, at the position of the cylinder Z6.

(16) The next firing event, this is cylinder Z3, occurs at the 180 crankshaft angle. That cylinder (more precisely: the engagement point of the associated connecting rod with the crankshaft) is less far away from the drive output side than Z8 and can thus cause only a lesser contribution to the twist of the crankshaft at the position of cylinder Z8. The next firing event (cylinder Z5) occurs at the 270 crankshaft angle and, because of the even closer position to the drive output, produces a markedly lesser contribution to the twist at the crankshaft position of cylinder Z8 than for example the cylinders Z8 and Z3. Next the cylinder Z4 fires and causes a greater twist (comparable to the cylinder Z8) as it is similarly far away from the drive output as the cylinder Z8. The next firing event is the firing of cylinder Z7 at the 450 crankshaft angle. The subsequent firing event is the cylinder Z2 at 540 and Z8 at 630. The 720 again correspond to the beginning of the scale at 0, that is to say firing of cylinder Z1.

(17) If torsion-induced angle deviation for other cylinders is incorporated into the graph then the maxima are below the curve plotted for cylinder Z8, scaled by their respective spacing from the drive output side assumed to be rigidly fixed.

(18) It will be seen therefore that the cylinders make quite different contributions to the twist of the crankshaft at the cylinder position Z8, due to their different spacing from the drive output side. The resulting curve therefore describes the torsion-induced crankshaft twist, in crankshaft angle-resolved and cylinder-individual relationship (shown here for the crankshaft position of cylinder Z8). That characteristic of the angle deviation .sub.i (with i as the numerator of the respective cylinder) can now be extrapolated to any desired cylinder or to any desired axial position of the crankshaft as, as a further boundary condition, the angle deviation caused by torsion is known for the cylinder Z1 as zero.

(19) The equidistant choice of the firing spacings (every 90) affords the same spacing in respect of time in regard to the propagation of a torsional fluctuation for all cylinders, which means: the torsional fluctuation has to be propagated for all cylinders the same time. The level of the angle deviation .sub.i is therefore given purely by way of the axial position of the cylinders on the crankshaft.

(20) FIG. 3 is a graph similar to FIG. 2 showing the angle deviation .sub.8 for the cylinder Z8 of the eight-cylinder engine shown in FIG. 1, but with different firing spacings. The firing order was retained with Z1.fwdarw.Z6.fwdarw.Z3.fwdarw.Z5.fwdarw.Z4.fwdarw.Z7.fwdarw.Z2.fwdarw.Z8, but the firing spacings expressed in crank angle are 120, 60, 120, 60, 120, 60, 120 etc. Therefore, as described with reference to FIG. 2, there are again 180 crank angles between the firing events of the cylinders Z1, Z3, Z4 and Z2, but only 60 between the firing events between cylinders Z6.fwdarw.Z3, Z4.fwdarw.Z7 and Z8.fwdarw.Z1. The altered firing spacings influence the pattern of the angle deviation, which is here plotted for the crankshaft position at cylinder Z8. Again, firing of the cylinder Z1 at the 0 crankshaft angle has no influence worth mentioning on twist of the crankshaft at the position of the cylinder Z8. The contributions to twist occur proportionally to the firing spacings, for a firing spacing of 120 provides that a torsional fluctuation introduced can be propagated longer than is the case with a firing spacing of 60.

(21) While in the example of the firing spacings in FIG. 2 where all cylinders are fired at equal firing spacings and thus the resulting torsional fluctuation respectively has the same time for propagation, the example of the firing spacings 120/160 in FIG. 3 affords a different picture in respect of angle deviation. The contributions to the torsional fluctuation of those cylinders which are fired at the 120 firing spacing therefore occur as 2:1 in relation to those cylinders which are fired at the 60 firing spacing, therefore the ratio of the contributions, expressed as the weighting factor, occurs at 2/3 to 1/3.

(22) The weighting factor therefore takes account of how much later the next application of force occurs.

(23) Once again the resulting pattern in respect of angle deviation .sub.i can now be transferred to any desired axial position of the crankshaft as, as a boundary condition, it is again established that no twist occurs at cylinder Z1 at the drive output side.

(24) In accordance with the method it is therefore possible, without measurement and merely from knowledge of the firing spacings and the firing order, as well as the distance of the cylinders relative to each other, to determine the magnitude of the angle deviation caused by torsion or torsional fluctuation, in crankshaft angle-resolved relationship, for each cylinder. The invention therefore makes use of the realisation that a standing wave in respect of torsion or torsional fluctuation is implemented over a period of 720 crankshaft angle.

(25) By virtue of the weighting factor the method takes account of whether the firing order is harmonic (equal firing spacing over all cylinders) or whether the firing spacings occur at spacings of unequal size, expressed as a crank angle. The crank angle which is between two firing events is synonymous with the time that the fluctuation has to develop. Interpreted as waves a uniform firing spacing means that all firing events occur in phases, while with unequal firing spacings there are a plurality of waves (two waves in the case of two different firing spacings) which are in a shifted phase position relative to each other.

(26) Engine diagnostics can be particularly advantageously implemented with the method according to the invention as sensor signals can now always be associated with the correct crankshaft position. For example sensor signals of a cylinder pressure monitoring system can be corrected in relation to the torsional angle deviation. To sum up, a higher quality in terms of control over combustion and thereby a higher level of efficiency and higher power density can be achieved. The method is particularly advantageous due to the improved accuracy in firing times and measurements in the cylinder like for example cylinder pressure detection.