EP1250519B1 - Method for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine comprising several cylinders and gas exchange valves (5) which, with regard to the valve opening characteristics, can be variably adjusted directly and electromagnetically or by means of an electrohydraulic valve actuation system that is provided with several electromagnet valves (7). The electromagnet valves (7) are operated in a cylinder-selective manner and by means of variable control voltages and/or control currents (I1, I2, I3) for synchronising all the gas exchange valves (5) with the desired valve opening characteristics during operation of the internal combustion engine.

Description

The invention relates to a method for operating an internal combustion engine according to the preamble of patent claim 1.

In the magazine Auto Motor and Sport, Issue 17, 1999, on page 49 already an electro-hydraulic valve actuation system for an internal combustion engine is explained, which has a cam-operated ram, not directly, but by means of hydraulic oil (engine oil) to a gas exchange valve (inlet valve ) acts in the cylinder head of the internal combustion engine. The pressure of the hydraulic fluid propagates via a brake piston on the gas exchange valve, wherein depending on the valve switching position of an integrated in the cylinder head solenoid valve, this amount of hydraulic oil and thus the stroke of the gas exchange valve in the cylinder head can vary. As a result of manufacturing tolerances for the aforementioned components scattering of the valve opening times can not be excluded, so that just in view of the multi-cylinder design of the engine unequal cylinder fillings inevitably lead to a dispersion of exhaust emissions.

A method for operating a multi-cylinder internal combustion engine is already known from the generic US-A-5419301, the gas exchange valves are selectively adjustable by a cylinder selectively to a desired valve opening characteristic, for which the solenoid valves are actuated by means of electrical pulses of variable duration at different times selected.

The object of the present invention is to develop a method for operating a multi-cylinder internal combustion engine with which the cylinder fillings of all engine cylinders can be adjusted taking into account minimum exhaust gas values.

This object is achieved by a method having the features of claim 1.

Further features, advantages and possible applications of the invention will be apparent from the description of an exemplary embodiment explained with reference to several drawings.

Fig. 1

eine Prinzipdarstellung eines elektrohydraulischen Ventilbetätigungssystems,

Fig. 2

die aus dem Ventilbetätigungssystem nach Fig. 1 resultierende variable Ventilverstellung der Gaswechselventile, veranschaulicht durch mehrere Ventilhubkurven,

Fig: 3

eine Erläuterung einzelner Verfahrensschritte anhand eines Programmablaufplans, welche die Vergleichmäßigung bzw. Synchronisierung der Ventilsteuerzeiten aller Motorzylinder unter Berücksichtigung minimaler Abgaswerte ermöglichen,

Fig. 4

eine aus dem Programmablaufplan nach Fig. 3 repräsentative Strom-, Spannugsimpuls,- und Hubkennlinie für eines der Elektromagnetventile des Ventilbetätigungs- bzw. Einspritzsystems.

Show it:

Fig. 1

a schematic diagram of an electro-hydraulic valve actuation system,

Fig. 2

1 resulting from the valve actuation system of FIG. 1 variable valve timing of the gas exchange valves, illustrated by several valve lift curves,

Fig. 3

an explanation of individual method steps on the basis of a program flow chart, which allow the equalization or synchronization of the valve timing of all engine cylinders taking into account minimum exhaust gas values,

Fig. 4

a representative of the program flowchart of FIG. 3 current, Spannugsimpuls, - and stroke characteristic for one of the solenoid valves of Ventilbetätigungs- or injection system.

1 discloses a schematic diagram of an electro-hydraulic valve actuation system, with a valve train arranged in the cylinder head 1 of an internal combustion engine, consisting of a camshaft 2, a plunger assembly 3 and a gas exchange valve 5 extending into the intake passage 4 of the internal combustion engine as an intake valve. The gas exchange valve 5 is not actuated directly by the plunger assembly 3, but by means of a pressure medium volume provided by the engine oil pump 6 with respect to the movement sequence, for which purpose a solenoid valve 7 is inserted into the cylinder head 1 in order to be able to vary the pressure medium volume clamped between the tappet assembly 3 and the gas exchange valve 5. Since it is a multi-cylinder internal combustion engine, according to the number of gas exchange valves and the already mentioned above other components of the electro-hydraulic valve actuation system are several times available. The valve actuation system also has per engine cylinder to a buffer 8, which takes in case of need excess pressure fluid volume that is not needed to control the valve actuation system accommodates. In addition, in the intake passage 4, an injection valve 20 is arranged, which can also be operated as the solenoid valve 7 by means of variable drive voltage and / or variable drive current for balancing all engine cylinders to uniform injection quantities.

The illustration according to the principle of the electro-hydraulic valve actuation system is consequently designed for a multi-cylinder and multi-valve combustion engine, with the task to be able to influence the valve lift electro-hydraulically for each engine cylinder. At high engine speeds are only a few milliseconds to control the solenoid valves 7 available.

By a suitable method for operating the internal combustion engine, the system tolerances in the control, the magnetic circuit and the component tolerances within the valve train can no longer lead to unacceptable dispersion of the valve opening cross sections, since now each of the hydraulic control pressure between the plunger assembly 3 and the associated gas exchange valve 5 according to the invention is set individually for each engine cylinder by the control of the valve switching voltage applied to the solenoid valve 7 and the valve current as a function of the crank angle, so that the same valve strokes result for each gas cycle for all gas exchange valves 5. This would theoretically also be technically possible with the aid of displacement sensors in the area of the gas exchange valves. But this solution is eliminated for cost and construction cost reasons. It should also be noted that the exhaust emission is usually adjusted by means of a single lambda probe per cylinder bank.

FIG. 2 shows, by way of example, the valve lift curves which can be set in principle with the presented variable valve actuation system according to FIG. 1 and are also plotted for reduced valve opening clearances of 40 degrees, 80 degrees and 120 degrees camshaft angle starting from a maximum camshaft angle illustrated on the abscissa. Along the ordinate the possible valve lift for each camshaft angle is plotted, which inevitably has the smallest camshaft angle of 40 degrees and the smallest valve lift of about 3.8 mm.

According to the invention, FIG. 3 shows the individual method steps for equalizing the valve lifts and thus the valve opening times for all the gas exchange valves 5 of a multi-cylinder internal combustion engine, which is preferably connected to the from Fig. 1 known electro-hydraulic valve actuation system is equipped. Taking into account the program flow according to FIG. 3, the system-related uncertainties and tolerances in the control of the electromagnetic valves 7 and in the valve drive can be compensated such that each valve operating system is selectively tuned to an optimal exhaust emission while the internal combustion engine is running, the control parameters obtained for the Solenoid valves 7 are stored in a data memory. For this purpose, the internal combustion engine is preferably operated in the speed band in which unacceptable deviations of the exhaust emission of the individual engine cylinders result from each other. The exhaust emission is detected in a known per se via a lambda control circuit. The drive voltage or drive currents of each solenoid valve 7 are then varied according to the program flowchart and cylinder-selectively stored in the data memory and detected as a function of the engine speed parameter. Based on the parameter map thus defined from cylinder to cylinder, the entire actuation of the electromagnetic valves 7 takes place.

The method for determining the exactly synchronized valve timing will now be explained in detail with reference to the program flowchart of FIG.

In each operation of the internal combustion engine is carried out for the purpose of control and thus concretely for the adjustment of the gas exchange valves 5 with each other an initialization of the solenoid valves 7 all engine cylinders according to a first operation step 9. In a second operation step 10, the worst exhaust value is initiated and the number of iteration steps and the iteration increment established. In a third operation step according to the diamond 11 it is determined whether the engine speed is in a predetermined speed band. If this condition is not met, a renewed interrogation of the engine speed from the engine control unit takes place via a loop 11a. Only when the internal combustion engine is in the predetermined, in particular exhaust-gas-sensitive, speed band in which an adjustment process of the solenoid valves 7 is to take place is the call of a subroutine according to the operation step 12 in which a currently valid and stabilized exhaust gas value is read into a data memory of the engine control unit. which can be done by way of example via a link to a lambda control circuit of the engine management. Thereafter, it is checked according to the following rhombus 13, whether the current exhaust gas value is better than the previously stored exhaust gas value. If this requirement is met, the current activation value for the solenoid valve 7 to be activated is stored in the next step 14 as a function of the engine speed and the associated engine cylinder. However, if the requirement for an improved exhaust gas value after step 13 is not met, the iteration process and thus the valve adjustment for the currently affected engine cylinder is continued instead of step 14 via loop 14a. In operation step 16, it is checked whether all iteration steps have been completed. Unless all the iteration steps have been completed, the loop 16a is used to repeat the valve adjustment procedure beginning at the rhombus 2. If, however, all the iteration steps have been completed, the next solenoid valve 7 is detected according to the field 17. In step 18, it is checked whether the electromagnetic valves 7 of all engine cylinders are adapted. In the case of a negative then carried over the loop 18a a repetition of the flowchart starting with the operation step 10. However, is the adaptation of all engine cylinders completed, then the valve balancing method explained herewith is terminated with the step 19.

Capturing this valve timing process for the individual engine cylinders through a suitable algorithm comparatively simplifies the offset of the valve timing from a nominal, ie. determine only crankshaft rotation angle-determining specification to set the optimization parameter exhaust quality here.

In an extension of the basic idea, values for different speed ranges can be determined and stored in a data memory of the engine management or engine control unit. As a result, a characteristic field or a parameter set for a mathematical description can be determined.

To determine the parameters, the algorithm can be used in one measurement run. In addition, however, the algorithm can also be used in the normal operating mode of the internal combustion engine, for example to optimize the parameters, e.g. to counteract the influence of the aging of components. For this purpose, the operation step 2 of FIG. 3 would then have to be modified and the engine speed indicated as an index in the map.

In summary, therefore, a method for operating an internal combustion engine is shown, which by varying the Ansteuerzeitpunkte the solenoid valves 7 and thus the synchronous actuation of the gas exchange valves 5 (intake valves) allows optimization of the exhaust gas values by a certain extent by a described in Figure 3 search method, the control parameters of the solenoid valves be varied. This is for a quality criterion or achieved several quality criteria optimal valve control.

With reference to the program flowchart of FIG. 3 thus results for each engine cylinder an optimized current characteristic of FIG. 4 for each solenoid valve to be activated 7, wherein each determines the optimal current waveform as a function of time and thus proportional to the engine crank angle and by the trigger point T. becomes. From the balancing process according to the invention results in a sawtooth waveform characteristic that begins with a comparatively low quiescent current I1 (inrush), which simultaneously causes the magnet armature of the solenoid valve 7 in motion with the increase to the excitation current I2 and holds in the open position until by lowering the excitation current I2 to the holding current I3, which is slightly larger in magnitude than the quiescent current I1, the trigger point T is reached, so that the armature of the solenoid valve 7 moves back to its original rest position. The trigger point T is detected on the basis of the method shown in Fig. 3 for each solenoid valve 7 and thus for each gas exchange valve 5 in the engine cylinder in a data memory of the engine control unit. The time course of the current pulse as well as the movements of the armature are applied phase-identical below the current characteristic, whereby a direct assignment of the current pulse duration and the magnetic armature movement to the current characteristic is possible.

In summary, there results a valve control method in which the exhaust gas emissions are measured for each engine cylinder and then alternately the drive voltage or the drive current with the aim of optimized exhaust gas values is varied as a function of engine crank angle for each solenoid valve 7 and the optimal trigger point T is determined. The determined during the process optimum switching points of the solenoid valves 7 are thus detected individually for each engine cylinder and stored as a function of engine speed as a parameter field in the data memory of the engine control unit. Based on this set parameter field thus takes place a cylinder-selective valve control, which ultimately leads to the same valve strokes of the gas exchange valves 5 in the present example.

The valve lifts the solenoid valves 7 but need not necessarily be the same, but can be varied to meet the task rather needs and thus desired. After this valve control method, the tolerances of the injection quantity can be adjusted by cylinder-selective control of the injectors 20.

The invention is not limited to the structural embodiment of Figure 1, but also suitable for alternative valve train designs, for example, provide a direct electromagnetic actuation of the gas exchange valves and having either a Saugrohr- or direct injection.

LIST OF REFERENCE NUMBERS

1

cylinder head

2

camshaft

3

tappet assembly

4

intake port

5

Gas exchange valve

6

Engine oil pump

7

Solenoid valve

8th

cache

9-19

operation steps

20

Injector

Claims (2)

1. Method for operating a multi-cylinder internal combustion engine having gas exchange valves (5) which are variably adjustable with respect to the valve opening characteristics either directly electromagnetically or by means of an electrohydraulic valve actuation system which includes several electromagnetic valves (7), wherein the electromagnetic valves (7) for adaptation of all gas exchange valves (5) to a desired valve opening characteristics are operated cylinder-selectively in the operation of the internal combustion engine by means of variable actuating voltages and/or actuating currents (I1, I2, I3),
   characterized in that the adaptation of the valve opening characteristics of all gas exchange valves (5) is preferably effected in a data memory of an engine control device, namely, by the following process steps:

   a) initialize the number of the electromagnetic valves (7) and/or injection valves (20) of all engine cylinders,

   b) initialize the exhaust gas value with the highest degree of emission and define the number of iteration steps and the iteration step width,

   c) check whether the predetermined engine speed, especially the engine speed at a high exhaust emission, is maintained where an inadmissible cylinder-selective spreading of the exhaust gas values is to be expected, otherwise step c) shall be repeated,

   d) read the currently valid and stabilized exhaust gas value into the data memory,

   e) compare the current exhaust gas value with the exhaust gas value previously stored in the performance graph of the data memory,

   f) store the current exhaust gas value in the data memory, in case of need, in dependence on the engine speed, if the current exhaust gas value is better than the original exhaust gas value stored in the performance graph of the data memory,

   g) continue iteration steps and adjust electromagnetic valves (7),

   h) check whether further iteration steps shall follow,

   i) check whether the actuation parameters of all electromagnetic valves (7) have been gathered in the data memory, in the negative: select next electromagnetic valve (7) and continue operation in step b).
2. Method as claimed in claim 1,
   characterized in that the adaptation of all electromagnetic valves (7) is carried out in dependence on the cylinder-selective exhaust emissions of the internal combustion engine.

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