Method for operating an internal combustion engine

Abstract

A method and an arrangement for operating an internal combustion engine. According to the method, a load threshold is defined below which load control by a throttle valve is performed.

Claims

1. A method for operating an internal combustion engine with variable valve drive, wherein the internal combustion engine comprises at least one cylinder having at least one inlet valve, the method comprising the steps of: performing load regulation above a defined load threshold by opening a throttle valve and predefining, by a regulator, a valve timing for each cylinder as a control variable; and performing the load regulation below the load threshold, by way of the throttle valve and predefining a fixed value for the valve timing, wherein the step of performing the load regulation above the defined load threshold includes the regulator predefining, as the control variable, the valve timing for each cylinder, wherein the valve timing of each cylinder is adapted by adding a pilot-control value to the control variable.

2. The method according to claim 1, including setting the defined load threshold to a value of approximately of a maximum load.

3. The method according to claim 1, including fully opening the throttle valve above the defined load threshold.

4. The method according to claim 1, including using a single-loop regulator as the regulator.

5. The method according to claim 1, wherein the pilot-control value is determined from a load jump increase and a setpoint load.

6. An arrangement for operating an internal combustion engine with variable valve drive, wherein the internal combustion engine has at least one cylinder with at least one inlet valve, the arrangement comprising: a regulator that predefines, as a control variable, a valve timing for each cylinder; and a throttle valve provided for actuation in a manner dependent on load, the arrangement being configured to perform load regulation so that above a defined load threshold the throttle valve is opened and the regulator predefines the valve timing for each cylinder as a control variable by adapting the valve timing by adding a pilot-controlled value to the control variable.

7. The arrangement as claimed in claim 6, wherein the regulator is a single-loop regulator.

Description

BRIEF DESCRIPTION OF T DRAWING

(1) The invention is schematically illustrated on the basis of embodiments in the drawing and will be described in more detail below with reference to the drawing.

(2) FIG. 1 shows an embodiment of the described method.

(3) FIG. 2 shows the process of a supplementary method.

(4) FIG. 3 shows signal profiles in three graphs.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 illustrates the load regulation using a throttle flap. The illustration shows an arrow 100, on which the load is plotted from 0% to 100%. The illustration also shows a load threshold 102 which is indicated by a dashed line and which is also referred to as low-load threshold. Said load threshold lies, in this embodiment, at approximately 200 kW, which corresponds to of the maximum load.

(6) Below the load threshold 102, a throttle flap 104 is slightly open. The excursion of the inlet valve is illustrated in a graph 106, on the abscissa 108 of which an angle is plotted and on the ordinate 110 of which the excursion is plotted. The inlet valve closing angle s 112 is constant. The load regulation is performed by way of the throttle flap 104.

(7) Above the load threshold 102, a throttle flap 114 is open. The excursion of the inlet valve is illustrated in a graph 116, on the abscissa 118 of which an angle is plotted and on the ordinate 120 of which the excursion is plotted. The inlet valve closing angle s 122 changes in a manner dependent on the excursion. The load regulation is performed by way of the inlet valve closing angle s 122 and thus by way of a valve control management arrangement which predefines the valve timings. Thus, for the load regulation, a valve timing is predefined for each cylinder.

(8) FIG. 2 describes the principle of the valve pilot control in accordance with the supplementary method. This is used in the case of an internal combustion engine with variable valve drive which makes it possible for the valve timing of each individual cylinder to be predefined. The cylinders are thus individually controllable. It is to be noted that the method is used in the context of global regulation of the load or power of the internal combustion engine, wherein pilot control may be predefined for each cylinder individually.

(9) FIG. 2 shows a regulating loop which constitutes an embodiment of the described arrangement and which is denoted overall by the reference designation 10. The illustration shows a regulator 12, in this case a PI regulator, and an internal combustion engine 14. As input variable 16 of the regulating loop 10, use is made of the value Load Setpoint |.sup.t and thus the setpoint load of the internal combustion engine at the time t. A difference of said variable in relation to the regulating variable 18 Load Actual |.sup.t, the actual load at the time t, forms an input variable 20 of the regulator 12. The latter outputs a control variable 22, the valve timing for each individual cylinder. Before said control variable 22 is input into the internal combustion engine 14, a pilot-control value 24, specifically VCM=f ( Load Setpoint |.sup.t, Load Setpoint |.sup.t), is in this case added to said control variable, so as to give an adapted or increased control variable 26 for the redefinition of the valve timing of the individual cylinders, typically in relation to the dead centers of the individual cylinders.

(10) Said pilot-control value 24 is determined from the change in the setpoint load at the time t or the load jump magnitude at the time t and the setpoint load at the time t. For the adaptation of the control variable 22, an element 28 is provided which, in the case of the embodiment shown, is in the form of a summing element and which adds the pilot-control value 24 to the control variable 22 in order to thereby obtain the adapted control variable 26. The pilot-control value 24 may also alternatively or additionally be determined from a change in the setpoint rotational speed at the time t and the setpoint rotational speed at the time t.

(11) The value for the pilot-control value 24 may basically be calculated or else may be taken from a characteristic map. Said characteristic map may be determined for example by way of a simulation.

(12) Thus, pilot control in the case of an internal combustion engine 14 with variable valve control is performed with fast reaction, the regulator 12 can possibly be dimensioned to be of lower power, such that an excessive overshoot can be prevented. In the event of a load jump, the value for the valve control, specifically the control variable 22, is artificially increased, in a manner dependent on the load jump magnitude and the present load, in order that the internal combustion engine 14 reaches its operating point earlier. As control variable 22, and thus also as adapted control variable 26, it is the case here that the closing angle or the closing time of the inlet valve is predefined.

(13) FIG. 3 illustrates, in three graphs, the effects of the described method. The measurements on which the illustrated profiles are based show, in isolated operation, a considerable reduction of the drop in rotational speed. In a first graph 30, the time [s] is plotted on an abscissa 32 and the generator power [kW] is plotted on an ordinate 34. A curve 36 shows the profile, which increases abruptly, of the setpoint power. Said curve 36 exhibits a load increase from 200 kW to 700 kW at 21 s.

(14) In a second graph 50, the time [s] is plotted on an abscissa 52 and the valve control value [ CA] is plotted on an ordinate 54. A first curve 56 shows the profile of the valve control value without pilot control, and a second curve 58 shows the profile of the valve control value with pilot control. The pilot-control value 60 is indicated by a double arrow.

(15) It can be seen that, with the pilot control, the internal combustion engine settles significantly more quickly, and the overshoot is considerably reduced.

(16) In a third graph 70, the time is plotted on an abscissa 72, and the rotational speed [rpm] is plotted on an ordinate 74. A first curve 76 shows the profile of the setpoint rotational speed, a second curve 78 shows the rotational speed profile without pilot control, and a third curve 80 shows the rotational speed profile with pilot control. The pilot control thus yields a considerably reduced drop in rotational speed 82, as indicated by a double arrow.