DE102008063935A1 - Internal combustion engine i.e. Otto engine, operating method, involves subtracting output damper-pulse duty factor from actual servocontrol-duty factor and/or from hundred percentage-duty factor of servocontrol - Google Patents

Abstract

The method involves calculating exhaust gas dependent damper impulses when a predicted exhaust gas counter pressure is equal to or larger than a preset maximum pressure. Load pressure dependent damper impulses are calculated when a predicted load pressure is equal to larger than a preset target load pressure. Output damper impulses are calculated by addition of the damper impulses and converted into output damper-pulse duty factor. The duty factor is subtracted from an actual servocontrol-duty factor and/or from a 100 percentage-duty factor of a servocontrol.

Description

The The invention relates to a method for operating an internal combustion engine, in particular gasoline engine, with an exhaust gas turbocharger, a turbine and a compressor, wherein in the turbine an adjustable Turbine geometry (VTG) is arranged according to the Preamble of claim 1.

The Combination of VTG ATL (ATL turbocharger) and gasoline engine offers a high potential for increasing torque and performance and thus for an expansion of the downsizing potential d. H. the displacement reduction. When using a turbocharger with adjustable turbine geometry on a gasoline engine can the inpatient benefits are not necessarily synonymous be implemented in transient operation. Through a VTG ATL can significantly higher pressure ratios realized a rigid geometry ATL, the backpressure to very high at the cylinder exit lead. This can lead to high levels of residual gas, which adversely affect Otto engine combustion.

With the use of turbochargers with adjustable turbine geometry On a gasoline engine, torque and power can be significantly increased compared to a charge by means of rigid geometry ATL become. This results in further potential for downsizing Avoidance of relatively complex two-stage charging systems. This is additional to a rigid geometry ATL Potential arises mainly from the possibility of the Turbine throughput at high efficiencies for every full load point to optimize. A rigid geometry ATL is in contrast optimized only for one point of the full load curve. The im Compared to a rigid geometry ATL higher representable Low-end torque, d. H. Torque at low speeds, at one VTG ATL can be realized because a VTG ATL is closed Guide vanes even at low exhaust gas mass flows can build up very high pressure ratio. With this exhaust side very high pressure ratio can correspondingly a very high Pressure ratio on the fresh air compressor side being represented. In steady, stationary operation So there is a high pressure level above the combustion chambers of the engine, resulting in a high torque even at low engine speeds leads. Due to high overall ATL efficiencies can mostly on the fresh air side be provided a higher pressure, than on the exhaust side is necessary because the exhaust not only over the pressure ratio, but also about a cooling in the turbine energy is withdrawn. The residual gas from the combustion chambers So it can be rinsed out very well, so that optimal boundary conditions for the following combustion.

in the transient operation, which is characterized in that mostly From low loads very fast high engine torques provided but there is not enough time for that Exhaust back pressure and intake manifold pressure quasi-stationary in lockstep can increase. Rather, the VTG turbine mostly closed, so as quickly as possible high exhaust gas pressure ratio can be built up, with a high drive / acceleration energy for the Compressor is provided. Before the ATL but a significant Speed increase experiences and thus on the fresh air side Boost pressure builds up, the engine in the charge change already against push out the strongly closed turbine, without any noteworthy Boost pressure is available to support. hereby the charge change deteriorates and remains high Residual gas quantity in the combustion chambers. This residual gas quantity leads in the subsequent combustion to a deterioration combustion, resulting in less energy output to the piston. The torque build-up is therefore due to the high exhaust side obstruction slowed down. The exponentially increasing exhaust backpressure leads to a flattening of the momentum buildup, as despite increasing Boost pressure does not improve the scavenging gradient.

From the DE 40 25 901 C1 is a method for adjusting the boost pressure in a charged by means of an exhaust gas turbocharger with adjustable turbine engine internal combustion engine to a predetermined operating point-dependent boost pressure setpoint known. To improve the efficiency of the internal combustion engine in the unsteady operation, especially after a positive load change from low load and speed ranges out after a positive load change during the Instationärbetriebes below a predetermined setpoint for the exhaust back pressure upstream of the turbine, the boost pressure after a first, the instantaneous actual deviation Boost pressure actual value of the charge pressure setpoint corresponding characteristic and after exceeding this threshold value, the exhaust backpressure regulated by the charge pressure control circuit according to a special characteristic fictitious control errors are specified.

Of the Invention is based on the object, a method of o. G. kind in terms of torque increase and performance increase in particular to improve in terms of a downsizing potential.

This object is achieved by methods of the type mentioned above with the features characterized in claim 1. Advantageous embodiments of the invention are in the further on spells described.

• (a) Bestimmen eines prädizierten Abgasgegendrucks p_{3,prädiziert} und Bestimmen eines prädizierten Ladedruckes p_{2,prädiziert},
• (b) Vergleichen des prädizierten Abgasgegendrucks p_{3,prädiziert} mit einem vorbestimmten Maximaldruck des Abgasgegendruckes p_3,max und Vergleichen des prädizierten Ladedruckes p_{2,prädiziert} mit dem vorbestimmten Soll-Ladedruck p_2,soll,
• (c) Berechnen eines abgasgegendruckabhängigen Dämpferimpulses, wenn der prädizierte Abgasgegendruck p₃ gleich oder größer als der vorbestimmte Maximaldruck des Abgasgegendruckes p_3,max ist,
• (e) Berechnen eines ladedruckabhängigen Dämpferimpulses, wenn der prädizierte Ladedruck p_{2,prädiziert} gleich oder größer als der vorbestimmte Soll-Ladedruck p_2,soll ist,
• (f) Berechnen eines Ausgangsdämpferimpulses durch Addition des abgasgegendruckabhängigen Dämpferimpulses und des ladedruckabhängigen Dämpferimpulses,
• (g) Umrechnen des Ausgangsdämpferimpulses in ein Ausgangsdämpfer-Tastverhältnis,
• (h) Subtrahieren des Ausgangsdämpfer-Tastverhältnisses von dem aktuellen Vorsteuer-Tastverhältnis und/oder von 100%-Tastverhältnis der Vorsteuerung.

For this purpose, it is provided according to the invention in a method of the aforementioned type that following a positive load step from low load to high load, the following steps are carried out,

• (a) determining a predicted exhaust backpressure p _{3, predicating} and determining a predicted boost pressure p _{2, predicts}
• (b) comparing the predicted exhaust backpressure p _{3, predicted} with a predetermined maximum pressure of the exhaust _backpressure p _{3, max} and comparing the predicted boost pressure p _{2, predicted} with the predetermined target boost pressure p _{2, shall} ,
• (c) calculating an exhaust back pressure dependent damper pulse when the predicted exhaust back pressure p _{3 is} equal to or greater than the predetermined maximum pressure of the exhaust back pressure p _{3, max} ,
• (e) calculating a boost pressure dependent damper pulse when the predicted boost pressure p _{2 predicts} equal to or greater than the predetermined target boost pressure p _2, is,
• (f) calculating an output damper pulse by adding the exhaust backpressure dependent damper pulse and the boost pressure dependent damper pulse,
• (g) converting the output damper pulse into an output damper duty cycle,
• (h) subtracting the output damper duty cycle from the current pilot duty cycle and / or 100% duty cycle of the feedforward control.

This has the advantage that high exhaust back pressures over a corresponding control functionality especially in the transient Operation are limited so that an optimal response of the ATL is guaranteed to be negative without the combustion influence.

A rapid increase of the boost pressure in areas with not very rapidly increasing exhaust backpressure is ensured by additionally determining in step (a) an exhaust backpressure gradient dp _3, dt / dt, in step (b) the exhaust gas backpressure gradient dp3 _, / dt is compared with a predetermined threshold value and in step (h) before subtracting the output damper duty cycle is reduced by the amount of a predetermined negative duty cycle when the exhaust gas back pressure gradient dp _3, / dt falls below the predetermined threshold value.

In an advantageous embodiment, to determine the predicted exhaust backpressure p _{3, predicted} a product from the current gradient of the actual exhaust back pressure dp _{3, is} / dt and a predetermined prediction time T calculated and this product the current actual exhaust back pressure dp _{3, is} added.

Conveniently, is the Abgasgegendruckabhängige damper pulse independent of a boost pressure dependent damper pulse calculated.

In a preferred embodiment, the predetermined prediction time T is determined as a function of an engine speed, a boost pressure control deviation, a deviation from the maximum pressure of the exhaust backpressure p _{3, max} , a nominal charge, an ambient pressure, a boost pressure gradient and / or an exhaust backpressure gradient.

The Invention will be explained in more detail below.

According to the invention in an internal combustion engine with exhaust gas turbocharger having a turbine with adjustable turbine geometry (VTG) and having a compressor, an exhaust backpressure limitation in front of the turbine of the exhaust gas turbocharger in the form of a dynamic function according to the following Function Description.

To enable the dynamics function, the following is done. The limitation of the exhaust backpressure p ₃ is activated when a difference dpvdk_w of a setpoint pressure upstream of a throttle valve (DK) to an actual value of the pressure upstream of the DK is greater than a predetermined threshold FDPP3REGMX and thus a positive load step is detected, for which the boost pressure buildup is the VTG is closed and the exhaust back pressure upstream of the turbine increases rapidly. As a second condition, the exhaust gas back pressure p ₃ must exceed a predetermined maximum value (dpvtlim <0 mbar). If both conditions are present, an integrator is set to a starting value pvtregiiv, which can be applied via a factor FPVTREGIIV and the VTG precontrol value tvldvtg. If the actual boost pressure has approached the set boost pressure or the exhaust counterpressure falls below the maximum value, the exhaust backpressure limit is deactivated and the precontrol value tvldvtg is output. The deactivation via the boost pressure difference can be applied over a predetermined threshold FDPP3REGMN.

The following is done to calculate the controller value to reduce feedforward. A maximum exhaust back pressure upstream of the turbine pvtlim is predetermined via a speed-dependent characteristic curve KLPVTLIM and the difference dpvtlim to the exhaust back pressure pabgvt_w is formed. The difference dpvtlim serves as an input for an integrator of an I-controller component and as an input for a gain characteristic of the I- and a P-controller component. An amplification factor K of the integrator for the I-Reg can be applied via a map KFPVTREGIK depending on dpvtlim and the engine speed. The proportional part of the controller value can be applied via a map KFPVTREGP as a function of dpvtlim and the engine speed. The I-component of the controller value can be limited via DP3LIMIKMN and DP3LIMIKMX and amplified by the factor FPVTREGI. If the above release conditions are met, the then negative controller value pvtregtv and the VTG pilot value tvldvtg are added, thus reducing the control of the VTG until the predetermined maximum exhaust backpressure is reached.

To limit the pressure p ₃ , a VTG pilot control, which provides a duty cycle for driving a VTG actuator, is expanded by a p _3- dependent damper pulse. In order to limit the exhaust back pressure p ₃ , the damper taken over from a wastegate (WG) control and contained in the VTG pilot control is expanded by a p ₃ -dependent component. Parallel and analogous to the target charge pressure and control deviation contained in the pilot control damper p ₃ -dependent duty cycle is added to dampen the pressure build-up during the boost pressure build-up. This p ₃ -dependent damper portion can optionally be activated by codeword.

In a first part of the method, the calculation of a predicted pressure takes place and the release of the damper is linked to this. Analogous to the predicted boost pressure, a predicted exhaust backpressure is calculated. For this purpose, a product of the current p ₃ gradient and an applicable prediction time T to a current, real exhaust back pressure p _{3, is} added. The intersection of the predicted exhaust gas back-pressure p _3, with the _predicted administered over engine speed p ₃ -Maximaldruck or the point of intersection of the predicted boost pressure to the target boost pressure (whichever comes first) initializes the damper portion. In addition, the damper portion is initialized (in addition to the boost pressure control deviation already present in the damper) via the p ₃ maximum pressure deviation. A negative duty cycle component which prevents premature triggering of the VTG and can be applied via rotational speed can optionally be activated in addition to the boost pressure gradient threshold already present in the damper via an exhaust backpressure gradient threshold. This blocking of the damper portion by means of a negative duty cycle is excluded with active damper pulse. If the output duty cycle of this release function is negative, the I component of the controller is also reset.

In a second part, the calculation of the damper pulse takes place, for example, via a PT1 element. Here, the Abgasgegendruckabhängige damper pulse can be applied separately from the boost pressure-dependent damper pulse. While the initialization for the boost pressure-dependent part on the intersection of the predicted boost pressure with the target boost pressure and in dependence on the gradient of the boost pressure, this is for the Abgasgegendruckabhängigen part by the intersection of the predicted exhaust back pressure p _{3, pradiziert} with the p ₃ maximum pressure and in dependence started from the exhaust back pressure. The time parameter T can be applied via the engine speed and boost pressure control deviation or deviation from the maximum p ₃ pressure. The engagement depth can be applied in each case via engine speed, nominal charge, ambient pressure and boost pressure gradient or exhaust backpressure gradient. The output damper pulse of this functional part results from the addition of the boost pressure-dependent and exhaust back pressure-dependent damper pulse.

Switchable via a codeword then becomes either the (negative) duty cycle of the first functional part to the damper pulse of the second Partially added, then from the current duty cycle of the Pre-control to be deducted. Alternatively, the damper pulse deducted from 100% duty cycle of the pilot control.

In addition, a regulation of the exhaust back pressure p ₃ may be provided via a reduction of the target boost pressure. To limit the exhaust back pressure p ₃ is dependent on the gradient of the pressure p ₃ and the difference of p ₃ to an applicable maximum pressure, the target boost pressure for the boost pressure control reduced. The maximum pressure can be specified via a motor speed-dependent characteristic. The function is activated via the difference between this maximum pressure and the real exhaust backpressure. In this case, the set pressure reduction is scaled as a function of the pressure difference, that is to say the reduction is used by means of a pressure-difference-dependent characteristic with values from the set [0; 1] multiplied to obtain a steady transition between the reduced and the non-reduced target boost pressure. The specification of the amount of reduction takes place via a characteristic map and depending on the filtered gradient of the real exhaust backpressure and the engine speed. The output of this function is then the minimum of the given target supercharging pressure and the nominal supercharging pressure reduced by the value applicable here.

The dynamic function of the invention causes a limitation of the exhaust side back pressure p ₃ to a level that ensures a sufficiently good charge exchange and thus residual gas purging. This critical level of the exhaust side back pressure is engine-specific set. With such a limitation of the exhaust-side back pressure, a faster rise of the flushing gradient into the positive area is made possible. This, in turn, improves the charge cycle By itself or prevents an increasing deterioration of the charge exchange with exponentially increasing backpressure. Ultimately, hereby the flattening of the torque build-up is avoided.

Consequently is possible, especially in transient operation always the optimal compromise of optimal ATL acceleration and high combustion quality is ensured in the combustion chambers. The retraction of the VTG vanes is not delayed, but the VTG will maximally or as soon as possible closed to a previously applied maximum value. The result the turbine-side obstruction very rapidly increasing exhaust backpressure leads to the fastest possible construction of the ATL speed. As soon as the exhaust back pressure applied previously Threshold is reached, the VTG is opened so that the predetermined motor and speed specific applied maximum Exhaust back pressure is controlled as accurately as possible. Thus is ensured that the charge cycle can not collapse and the boundary conditions for combustion in one area remain, which allows efficient combustion and ultimately leads to steep moment gradients.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 4025901 C1 [0005]

Claims (5)

Method for operating an internal combustion engine, in particular gasoline engine, with an exhaust gas turbocharger having a turbine and a compressor, wherein in the turbine an adjustable turbine geometry (VTG) is arranged, wherein a boost pressure p ₂ by means of the position of the VTG in dependence on a difference of a predetermined target boost pressure p _{2, soll} and an actual boost pressure p _{2 is} controlled, wherein a pilot duty cycle of a feedforward control for driving an actuator of the VTG is determined, characterized in that at a positive load jump from low load to high Load following steps are performed, (a) determining a predicted exhaust back pressure p _{3, predicating} and determining a predicted boost pressure p _{2, predicts} (b) comparing the predicted exhaust back pressure p _{3, predicted} with a predetermined maximum pressure of the exhaust back pressure p _{3, max} and compare the predicted boost pressure p _{2, predicts} the predetermined n desired boost pressure p _{2, soll} , (c) calculating an exhaust back pressure dependent damper pulse when the predicted exhaust back pressure p _{3 is} equal to or greater than the predetermined maximum pressure of the exhaust back pressure p _{3, max} , (e) calculating a boost pressure dependent damper pulse when the predicted boost pressure p _{2, predicts} equal to or greater than the predetermined target boost pressure p _2, is, (f) calculating an output damper pulse by adding the exhaust backpressure dependent damper pulse and the boost pressure dependent damper pulse, (g) converting the output damper pulse to an output damper duty cycle, (h) Subtract the output damper duty cycle from the current pilot duty cycle and / or 100% duty cycle of the feedforward. A method according to claim 1, characterized in that additionally in step (a) a Abgasgegendruckgradienten dp _{3, is} / dt is determined, in step (b) the Abgasgegendruckgradienten dp _3, / dt is compared with a predetermined threshold and in step (h ) before subtracting the output damper duty cycle is decreased by the amount of a predetermined negative duty cycle when the exhaust backpressure gradient dp _{3 is} / dt falls below the predetermined threshold value. Method according to at least one of the preceding claims, characterized in that for determining the predicted exhaust back pressure p _{3, diniert predicted} a product of a current gradient of the actual exhaust back pressure dp _{3, is} calculated / dt and a predetermined prediction time T and this product is the current actual -Abgasgegendruck dp _{3, is} added. Method according to at least one of the preceding Claims, characterized in that the exhaust back pressure dependent Damper pulse independent of a boost pressure dependent damper pulse is calculated. Method according to at least one of the preceding claims, characterized in that the predetermined prediction time T as a function of an engine speed, a boost pressure control deviation, a deviation from the maximum pressure of the exhaust back pressure p _{3, max} , a desired filling, an ambient pressure, a boost pressure gradient and / or a Abgasgegendruckgradienten is determined.