Method for operating an internal combustion engine with an exhaust-gas turbocharger having variable turbine geometry

Abstract

The invention relates to a method for operating an internal combustion engine (100) having an exhaust-gas turbocharger (5, 10, 15) for compressing the air fed to the internal combustion engine (100), wherein a drive power of a turbine (10) of the exhaust-gas turbocharger (5, 10, 15) in an exhaust tract (20) of the internal combustion engine (100) is changed through variation of a turbine geometry of the turbine (10), wherein, in a first control algorithm (I), a setpoint charge pressure (pL.sub.Soll) at the outlet of the compressor (5) of the exhaust-gas turbocharger (5, 10, 15) in the air feed tract (50) upstream of the combustion motor (55) is controlled in a manner dependent on a setpoint exhaust-gas back pressure (pT1.sub.Soll) to be set in an exhaust tract (20) downstream of the combustion motor (55) upstream of the turbine (10) of the internal combustion engine (100), wherein the setpoint charge pressure (pL.sub.Soll) is assigned an opening cross-sectional area of the turbine (10), which is controlled, by means of an actuating stroke of an actuating element (25) assigned to the turbine (10), in a manner dependent on a setpoint value (25.sub.Soll) assigned to the predefined setpoint charge pressure (pL.sub.Soll). According to the invention, provision is made for the actuating element (25), which is actuated by means of the first control algorithm (I), of the turbine (10) to be controlled by means of a second control algorithm (II), with predefinition of an upper threshold value of the setpoint exhaust-gas back pressure (pT.sub.1Soll) in the exhaust tract (20) upstream of the turbine (10) by intervention into the first control algorithm (I) with an adapted setpoint value (25′.sub.Soll), if, in a primary control path a) of the second control algorithm (II), a control deviation (ΔpT) upstream of the turbine (10) arises which is formed from an actual exhaust-gas back pressure (pT.sub.1lst) upstream of the turbine (10) and the predefined setpoint exhaust-gas back pressure (pT.sub.1Soll) upstream of the turbine (10), and, in a secondary control path b) of the second control algorithm (II), a control deviation (ΔpL) downstream of the compressor (5) arises which is formed from an actual charge pressure (pL.sub.lst) of the compressor (5) and the setpoint charge pressure (pL.sub.Soll) at the outlet of the compressor (5).

Claims

1. A method for operating an internal combustion engine having an exhaust gas turbo charger for compressing the air supplied to the internal combustion engine, comprising: altering a drive performance of a turbine of the exhaust gas turbocharger in an exhaust gas line of the internal combustion engine by varying a turbine geometry of the turbine, in a first control algorithm, controlling a target boost pressure at the output of the compressor of the exhaust gas turbo charger in the air supply line upstream of a combustion motor, depending on a target exhaust gas counterpressure to be set in an exhaust gas line downstream from the combustion motor before the turbine of the internal combustion engine, assigning to the target boost pressure an opening cross-section surface of the turbine, which is controlled via an adjusting stroke of an actuator assigned to the turbine depending on a target value assigned to the predetermined target boost pressure, controlling the actuator of the turbine, which is controlled via the first control algorithm, via a second control algorithm given an upper limit value of the target exhaust gas counterpressure in the exhaust gas line upstream from the turbine by intervening into the first control algorithm with an adapted target value, when in a primary control path a) of the second control algorithm, an exhaust gas back pressure control deviation occurs upstream from the turbine, which deviation is wherein the exhaust gas back pressure control deviation is determined by subtracting an actual exhaust gas counterpressure upstream from the turbine from the target exhaust gas counterpressure upstream from the turbine, and in a secondary control path b) of the second control algorithm, a boost pressure control deviation occurs downstream from the compressor, which deviation is formed from an actual boost pressure of the compressor and the target boost pressure at the output of the compressor, modifying the exhaust gas back pressure control deviation to be smoothed by a first characteristic curve provided with a gain factor and by a low-pass filter according to a second characteristic curve depending on an environmental pressure, such that a modified control deviation is transferred to the second subtract module at the intervention point, supplying the modified exhaust gas back pressure control deviation and the target value of the first control algorithm at an intervention point, and forming the corrected target value at the intervention point, outputting a corrected target value via a switch, correcting the adjusting stroke of the actuator of the turbine by taking into consideration dynamic states of the internal combustion engine only if the outputs of the primary control path a) and secondary control path b) are activated and the switch is closed.

2. The method according to claim 1, further including: actively switching and guiding the exhaust gas back pressure control deviation and the boost pressure control deviation to the switch of the intervention point after the exhaust gas back pressure control deviation and the boost pressure control deviation have in each case overshot a predeterminable threshold value of a hysteresis block, wherein the switch is only closed when both control deviations are active, such that an intervention of the second control algorithm into the first control algorithm at the intervention point takes place only when the switch is closed.

3. An internal combustion engine configured to perform the method according to claim 1, comprising: an exhaust gas turbo charger for compressing the air supplied to the internal combustion engine, a compressor, a combustion motor, a turbine having variable turbine geometry which is connected via a shaft to the compressor, and a control device, in which are stored a computer-readable program algorithm for carrying out the method of claim 1 and, where necessary, required characteristic diagrams.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained hereinafter with reference to the associated figures.

(2) FIG. 1 shows a schematic view of an internal combustion engine having the associated components for performing the method;

(3) FIG. 2 shows a function diagram for explaining the method according to the invention and the associated internal combustion engine having its associated components.

DETAILED DESCRIPTION OF THE INVENTION

(4) In FIG. 1, an internal combustion engine is referenced with the reference sign 100.

(5) The internal combustion engine 100 comprises a combustion motor 55, which can be for example in the form of a petrol motor or diesel motor. Fresh air is supplied in the direction of the arrow via an air supply line 50 to the combustion motor 55. Here, a compressor 5 of an exhaust gas turbo charger, for compressing the fresh air supplied to the combustion motor 55, is disposed in the air supply line 50. The exhaust gas turbo charger is driven via a shaft 15 by a turbine 10 which is disposed in an exhaust gas line 20 of the internal combustion engine 100. The exhaust gas turbo charger thus comprises the compressor 5, the shaft 15 and the turbine 10.

(6) The turbine 10 is driven by an exhaust gas mass flow {dot over (m)}.sub.ABG in the exhaust gas line 20. The flow direction of the exhaust gas and thus of the exhaust gas mass flow {dot over (m)}.sub.ABG is shown in FIG. 1 also using arrows.

(7) In flow direction of the exhaust gas, in the exhaust gas line 20 before the turbine 10 a first pressure pT.sub.1lst and a specified exhaust gas temperature T.sub.ABS prevail.

(8) In flow direction of the exhaust gas, in the exhaust gas line 20 after the turbine 10 a second pressure pT.sub.2 prevails.

(9) The exhaust gas mass flow {dot over (m)}.sub.ABG can be measured or modelled in a known manner by means of a mass flow meter 60 (not shown).

(10) The first pressure pT.sub.1lst can be measured in a known manner by means of a pressure sensor 65 or modelled in a different manner.

(11) The second pT.sub.2lst can be measured in a known manner by means of a pressure sensor 75 or modelled in a different manner.

(12) An adjusting member 25 of the turbine 10 is controlled for the realisation of a predetermined target boost pressure pL.sub.Soll in the air supply 50 in flow direction of the fresh air downstream from the charger. The adjusting member 25 adjusts in a known manner guide blades of the turbine 10 and thereby alters the turbine effectiveness and the effective opening cross-section surface of the turbine 10.

(13) The adjusting of the guide blades of the turbine 10 is carried out via an adjusting variable or an adjusting stroke of the adjusting member 25.

(14) In the conventional method, for realising the predetermined target boost pressure pL.sub.Soll of the charger a target value 25.sub.Soll is predetermined for the adjusting stroke of the adjusting member 25. The guide blades of the turbine 10 are then set on the basis of the realised target value 25.sub.Soll of the adjusting stroke such that the resulting turbine effectiveness results in the desired target boost pressure pL.sub.Soll of the charger.

(15) With the aid of the physical correlations between the first pressure pT.sub.1lst before the turbine 10, that is the exhaust gas counterpressure, the exhaust gas mass flow {dot over (m)}.sub.ABG in the exhaust gas line 20 and an actual value 25.sub.lst for the adjusting stroke of the adjusting member 25, a limit value can be determined for the adjusting stroke of the adjusting member 25 with respect to a maximum turbine performance from a predetermined pressure ratio pT.sub.1lst−pT.sub.2lst. The states taken into consideration in the case of this procedure are valid, however, only in the steady state of the internal combustion engine 100, as is also disclosed in the document EP 1 471 234 A2, wherein only the pressure ratio pT.sub.1lst−pT.sub.2lst is taken into consideration in the exhaust gas line 20.

(16) In order to improve this, the invention specifies a method which influences the exhaust gas counterpressure pressure pT.sub.1lst before the turbine 10 such that in an advantageous manner dynamic states are taken into consideration during the operation of the internal combustion engine 100, as will be further described hereinafter with reference to FIGS. 1 and 2 in comparison.

(17) The method according to the invention uses an exhaust gas counterpressure control algorithm I, which, in particular in the case of dynamic operational states, which occur and are recognised as a result of a control deviation ΔpL between the actual boost pressure pL.sub.lst of the charger and the target boost pressure pL.sub.Soll of the charger, is superimposed by a control algorithm II according to FIG. 2, which will be explained in more detail hereinafter.

(18) The exhaust gas counterpressure control algorithm I can be the already explained exhaust gas counterpressure control algorithm I or another exhaust gas counterpressure control algorithm known from the prior art.

(19) The control algorithm II according to the invention according to FIGS. 1 and 2 in detail uses the following input parameters.

(20) By means of a RPM sensor (not shown), an engine speed n of the combustion motor 55 is determined.

(21) By means of a pressure sensor (not shown), furthermore, an environmental pressure p.sub.U is provided.

(22) As already explained, the first pressure pT.sub.1lst (exhaust gas counterpressure (upstream) before the turbine 10) is measured by means of the pressure sensor 65 or modelled in a different manner and is made available for use as a model variable.

(23) In addition, by means of pressure sensors (not shown), the actual boost pressure pL.sub.lst of the charger and the target boost pressure pL.sub.Soll of the charger is measured, and in a secondary boost pressure control path b) the control deviation ΔpL=(pL.sub.Soll−pL.sub.lst) is determined, which in the same way is made available as an input parameter for the control algorithm II.

(24) If the control deviation ΔpL=0, the actual boost pressure pL.sub.lst has the desired target value, such that an intervention into the control algorithm I is not necessary, since the boost pressure control path b) with the control deviation ΔpL=0 is in a steady state.

(25) If the control deviation ΔpL>0, the actual boost pressure pL.sub.lst does not have the desired target value, such that an intervention into the hitherto existing control algorithm I is necessary, since the boost pressure control path b) in the case of a control deviation ΔpL>0 is not in a steady state.

(26) Finally, the target value 25.sub.Soll, known from the hitherto existing control algorithm I, for the adjusting stroke of the adjusting member 25 is made available to the new control algorithm.

(27) It is clear that the target value 25.sub.Soll for the adjusting stroke of the adjusting member 25 can be a target value determined according to the method of document EP 1 471 234 A2. It is however once more noted that the method according to the invention can be used in the same manner also for other known methods which determine the target value for the adjusting stroke of the adjusting member 25 in another manner than that described in document EP 1 471 234 A2.

(28) According to the invention, the already mentioned secondary boost pressure control path b) and a primary control path a) are followed within the new control algorithm II.

(29) The primary exhaust gas counterpressure control path a) concerns the control deviation ΔpL=(pL.sub.Soll−pL.sub.lst) of an actual exhaust gas counterpressure pT.sub.1lst before the turbine 10 (downstream from the combustion motor 55) with respect to a target exhaust gas counterpressure pT.sub.1Soll before the turbine 10.

(30) The target exhaust gas counterpressure pT.sub.1Soll is supplied as a value to be maintained, in particular as a predeterminable upper limit value, to the exhaust gas counterpressure control path a) of the control algorithm II) (compare FIG. 2) depending on the environmental pressure p.sub.U and depending on the engine speed n of the combustion motor 55 (compare characteristic curve K1) to a subtract module SB1 for determining the control deviation ΔpT=(pT.sub.1Soll−pT.sub.1lst).

(31) If the control deviation ΔpT of the exhaust gas counterpressure before the turbine 10=0, an intervention of the second control algorithm II onto the previously existing control algorithm I depending on the exhaust gas counterpressure control path a) is not necessary, since the exhaust gas counterpressure control in the case of a control deviation ΔpT=0 is in a desired steady state.

(32) If the control deviation ΔpT of the exhaust gas counterpressure before the turbine 10>0, an intervention of the second control algorithm II onto the previously existing control algorithm I depending on the exhaust gas counterpressure control path a) is necessary, since the exhaust gas counterpressure control in the case of a control deviation ΔpT>0 is not in a desired steady state.

(33) The determined control deviation ΔpT>0 of the exhaust gas counterpressure before the turbine 10 is guided onto a hysteresis block B1 which checks whether the control deviation ΔpT.sub.1lst−pT.sub.1Soll>0 is located in a first band having low control deviation or, by exceeding a predeterminable threshold value, in a second band having greater control deviation. Only if it is established that a greater control deviation is present, an output of the hysteresis block HB1 becomes active, i.e. is switched on. Thus, in an advantageous manner small control deviations ΔpT>0 of the exhaust gas counterpressure control path a) are not taken into consideration. The output of the hysteresis block B1 is switched to active when the determined control deviation ΔpT>0 overshoots the previously set limit value (the threshold value).

(34) Analogously thereto, the determined control deviation ΔpL=(pL.sub.Soll−pL.sub.lst)>0 of the actual boost pressure pL.sub.lst with respect to the target boost pressure pL.sub.Soll is guided in the same way onto a hysteresis block HB2 which checks whether the control deviation ΔpL>0 is located in a first band with small control deviation or in a second band with greater control deviation. Only if it is determined that a greater control deviation above a predeterminable threshold value is present in the second band does an output of the hysteresis block B2 become active, i.e. is switched on. Thus, in an advantageous manner, small control deviations ΔpL>0 of the boost pressure control path b) are not taken into consideration. The output of the hysteresis block B2 is switched to active when the determined control deviation ΔpT>0 overshoots the previously set limit value (the threshold value).

(35) By means of the hysteresis blocks HB1, HB2, rapid repetitions of switching-on and switching-off procedures, i.e. rapid activating and deactivating of the control paths a), b), are avoided.

(36) According to the invention, the new control algorithm II is only switched to active when both outputs, the output of the primary control path a) and of the secondary control path b) (&), are switched to active.

(37) Thereby it is recognised simultaneously whether an exhaust gas counterpressure control deviation ΔpT.sub.1Soll−pT.sub.1lst>0 of the exhaust gas counterpressure pT.sub.1lst is even present and whether a dynamic operational state in operating the internal combustion engine 100, i.e. a boost pressure control deviation ΔpL.sub.Soll−pL.sub.lst>0, is present. Only then is a release command also outputted, which is shown by the &-relation in FIG. 2.

(38) By means of the release command, the conventional target value 25.sub.Soll for the adjusting stroke of the adjusting member 25 is functionally released for an intervention point E by switching a switch S for a possible intervention. In other words, the switch S shown in FIG. 2 is switched, starting from the shown not-switched position, and the intervention according to the invention is possible.

(39) The switch S is then switched to the control deviation ΔpT=(ΔpT.sub.1lst−pT.sub.1Soll), shown in the intervention point E, of the exhaust gas counterpressure pT.sub.1lst before the turbine 10 onto a further subtract module SB2.

(40) Thus, now, depending on the control deviation ΔpT.sub.1lst−pT.sub.1Soll behind the first subtract module SB1 of the primary control path a), the conventional target value 25.sub.Soll by means of the subtract module SB2 as a correction value corresponding to the deviation present in the second subtract module SB2, a corrected target value 25′.sub.Soll can be outputted, i.e. the conventional target value 25.sub.Soll is altered depending on occurring dynamic states, in particular the boost pressure control deviation ΔpL>0 is altered according to the secondary control path b), but only when an exhaust gas counterpressure control deviation ΔpT>0 is even present in the primary control path a).

(41) In other words, the guide blades of the turbine 10 are then set on the basis of the target value 25′.sub.Soll according to the invention of the adjusting stroke such that the resulting turbine effectiveness, in addition to an optimum turbine performance of the turbine 10 depending on the desired target exhaust gas counterpressure ΔpT.sub.1Soll, and depending on dynamic states in the secondary control path b) of the new control algorithm II, results in a corresponding target boost pressure pL.sub.Soll of the charger before the combustion motor 55.

(42) In an advantageous manner, now the exhaust gas counterpressure pT.sub.1lst before the turbine 10 is actively controlled depending on the control deviation ΔpT>0 above a predeterminable band of the first hysteresis block HB1 of the exhaust gas counterpressure pT.sub.1Soll and depending on a boost pressure control deviation ΔpL>0 above a predeterminable band of the second hysteresis block HB2.

(43) In this regard, the exhaust gas counterpressure control deviation ΔpT is weighted before it is supplied to the second subtract module SB2 at the intervention point E.

(44) The weighting is carried out by modifying the exhaust gas counterpressure control deviation (ΔpT.sub.mod.)(pT.sub.1Soll−pT.sub.1lst).sub.mod., in that the exhaust gas counterpressure control deviation ΔpT=(pT.sub.1Soll−pT.sub.1lst) is smoothed according to the characteristic curve K2 via a low-pass filter and is equipped with an amplification factor according to the characteristic curve 3 depending on the environmental pressure p.sub.U.

(45) By means of the method, in an advantageous manner it is ensured that the controlling of the VTG-ATL is influenced by means of the determined or modelled exhaust gas counterpressure pT.sub.1lst to the effect that an accumulation of the exhaust gas counterpressure pT.sub.1lst which is too high is avoided. Thus, the effect is achieved that the residual gas content in a combustion chamber of a cylinder of the combustion motor 55 is effectively reduced.

(46) Moreover, an improvement in the engine smoothness and in the combustion effectiveness, and the controllability of the VTG-ATL are improved, since the method results in a reduction in boost pressure overshoots.

(47) The use of the exhaust gas counterpressure sensor for determining the exhaust gas counterpressure pT.sub.1lst or the use of a model value of the exhaust gas counterpressure pT.sub.1lst in combination with a petrol motor VTG-ATL or diesel VTG-ATL according to the method constitutes a new measure in controlling and regulating.

(48) In an advantageous manner, by means of the active regulation of the exhaust gas counterpressure pT.sub.1lst, all tolerances and component distributions of the combustion motor 55 and of the VTG-ATL of the exhaust gas system can be taken into consideration.

(49) In an advantageous manner, the drive dynamic of the vehicle is improved, since the motor control with respect to the torque generation is optimised via the active regulation, depending on the boost pressure pT.sub.1lst, of the exhaust gas counterpressure pT.sub.1lst, and not, as hitherto, exclusively via the exhaust gas counterpressure regulation. Thus, finally, the driving performance is improved, since the vehicle accelerates in a more harmonious manner when using the method, since dynamic states are taken into consideration.

(50) By means of the method, a maximum turbine performance of the turbine 10 can be generated while simultaneously maintaining the target value 25′.sub.Soll of the adjusting stroke for the guide blades of the turbine 10, wherein an optimisation of the exhaust gas counterpressure pT.sub.1lst also facilitates a maximisation of the exhaust gas mass flow {dot over (m)}.sub.ABG in the exhaust gas line 20.

LIST OF REFERENCE SIGNS

(51) 100 internal combustion engine

(52) 5 compressor

(53) 10 turbine

(54) 15 shaft

(55) 20 exhaust gas line

(56) 25 adjusting member

(57) 25.sub.Soll target value of the adjusting member

(58) 25′.sub.Soll corrected target value of the adjusting member 25

(59) 50 air supply line

(60) 55 combustion motor

(61) n engine speed

(62) 60 mass flow meter

(63) 65 pressure sensor

(64) 75 pressure sensor

(65) {dot over (m)}.sub.ABG exhaust gas mass flow in the exhaust gas line 20

(66) pT.sub.1 first pressure upstream from the turbine 10

(67) T.sub.ABG temperature of the exhaust gas upstream from the turbine 10

(68) pT.sub.2 second pressure downstream from the turbine 10

(69) pT.sub.1lst actual exhaust gas counterpressure upstream from the turbine 10

(70) pT.sub.1Soll target exhaust gas counterpressure upstream from the turbine 10

(71) ΔpT=Δ(pT.sub.1Soll−pT.sub.1lst) control difference ΔpT upstream from the turbine

(72) pL.sub.Soll target boost pressure downstream from the compressor 5

(73) pL.sub.lst actual boost pressure of the compressor 5

(74) ΔpL=Δ(pL.sub.Soll−pL.sub.lst) control difference ΔpL downstream from the compressor 5

(75) I conventional control algorithm

(76) II control algorithm according to the invention

(77) a) primary control path

(78) b) secondary control path

(79) p.sub.U environmental pressure

(80) SB1 first subtract module

(81) SB2 second subtract module

(82) HB1 hysteresis block

(83) HB2 hysteresis block

(84) E intervention point

(85) S switch

(86) K1, K2, K3 characteristic curves