DE10154151A1 - Process for operating an internal combustion engine with an exhaust gas turbocharger comprises producing and carrying out a boost pressure reduction mode - Google Patents

Abstract

Process for operating an internal combustion engine with an exhaust gas turbocharger comprises the following measures to produce and carry out a boost pressure reduction mode in the event that the quantity of fuel injected within a defined period is reduced so that the amount of change in the fuel quantity exceeds a reference value: adjusting a variable turbine geometry (8) of the exhaust gas turbine (3) in the direction of an open position extending the free flow cross-section to the turbine wheel, and opening the exhaust gas return valve (12). Preferred Features: Additional conditions for adjusting the boost pressure reduction are that the engine speed and the quantity of fuel injected per unit time fall below a reference value.

Description

The invention relates to a method for operating a Internal combustion engine with turbocharger and Exhaust gas recirculation device according to the preamble of claim 1.

From the publication AT 002 540 U1 is an internal combustion engine known with an exhaust gas turbocharger with an exhaust gas turbine equipped in the exhaust system and a compressor in the intake system is and also has an exhaust gas recirculation device. The exhaust gas turbine is from the exhaust gases under pressure driven and transmits over a wave the working movement on the compressor, the intake of combustion air to one increased boost pressure compressed, under which the combustion air the cylinder inlet of the internal combustion engine is supplied. to Reduction of nitrogen emissions can be certain Operating modes of the internal combustion engine, especially at high Load and speed, via the exhaust gas recirculation device Partial flow of the exhaust gas from the exhaust system back into the Intake tract be routed. The exhaust gas recirculation line branches upstream of the exhaust gas turbine from the exhaust line and opens downstream of the compressor in the intake system.

To an operation of the compressor in the area of the surge limit or exceeding the surge limit at which the flow in Compressor breaks off and a periodic pulsation of the flow can arise, can prevent, in certain situations the boost pressure downstream of the compressor can be reduced by About the exhaust gas recirculation device part of the compressed Combustion air from the intake tract downstream of the compressor in the Exhaust line upstream of the exhaust gas turbine is transferred. The Exhaust gas recirculation device has for this purpose two parallel Lines each with a valve, one of which as Recirculation valve and one is executed as a blow-off valve. The Blow-off valve is designed as a pressure-controlled valve, which a flow path from the intake side to the exhaust side only for Releases the case that the pressure difference is a minimum value exceeds.

But this is especially true in dynamic transition areas with sudden drop in injection, for example at broken starts on the mountain, not always safe ensures that inertia delays in the dismantling of the Exhaust counterpressure must be considered, the one positive pressure drop from boost pressure to exhaust back pressure conflict. In such situations, therefore, an unfavorable Pressure ratio across the compressor arise, the one to Operation of the compressor in the area of the surge line leads.

Another disadvantage is the comparatively expensive designed exhaust gas recirculation device, which in addition to the wiring harness for the exhaust gas recirculation and the therein arranged exhaust gas recirculation valve a parallel wiring harness for the boost pressure reduction and the blow-off valve arranged therein contains.

The invention is based on the problem in a charged internal combustion engine over a long period of operation ensure trouble-free operation. It should in particular Damage to the turbocharger, which indicates an operation of the compressor are due to the surge line, avoided become.

This problem is inventively with the features of Claim 1 solved.

The procedure differs from the state of the art Technique known operations charged Internal combustion engines with exhaust gas recirculation through a number of features. To the one becomes a conventional, but independent of the Pressure conditions in the intake tract and in the exhaust system controllable Exhaust gas recirculation device used to increased boost pressure blow off, resulting in the design effort for the Abblasungseinrichtung significantly reduced, since on one already existing valve device can be used, the for the blow-off only in a new mode is used.

On the other hand, the exhaust back pressure basically in one large operating area are dismantled by a variable Turbine geometry of the exhaust gas turbine - or a bypass in the case a flapper turbine - in the direction of the opening position is offset, whereby the free flow cross-section to Turbine wheel extended and increased in a short time Exhaust gas mass flow can be derived. This can be a one Boost pressure enabling pressure drop from intake side into Direction exhaust side be adjusted.

Finally, the triggering conditions for switching precisely defined in the boost pressure reduction mode, causing the Detecting situations where blowdown is indicated is relieved. The internal combustion engine is in case in the boost pressure mode transfers that into the combustion chambers injected fuel quantity within a defined Period is reduced in such a way that the amount of Change in fuel quantity exceeds a reference value. With This is to be met for the boost pressure reduction condition ensures that transient deceleration processes of the Vehicle - rapid transition from train operation in the Overrun at relatively low engine speed, z. B. triggered by a broken start on the mountain with a Automatic vehicle - an air mass congestion in the intake tract over the Exhaust gas recirculation device is degraded, so that in particular at the under these conditions prevailing low speeds and critical pressure conditions on the compressor Compressor pumps can be avoided.

Another advantage of the criterion of change of injected fuel amount is that this criterion in itself already sufficient to be critical Recognize compressor state in the area of the surge line. A Pressure measurement upstream and / or downstream of the compressor and / or in contrast, in the exhaust gas countercurrent upstream of the exhaust gas turbine is not required. The information about the exhaust back pressure is especially unnecessary for the reason that the exhaust back pressure through an opening of the variable turbine geometry - possibly by a discharge via a bypass to the turbine - is reduced, thereby reliably reducing a pressure gradient from intake to exhaust side is adjustable.

The knowledge about the boost pressure downstream of the compressor is While not mandatory, it may be helpful to those operating conditions in which a blowdown of the Boost pressure on the exhaust gas recirculation takes place, too specified. In particular, it is checked whether the boost pressure exceeds an assigned reference value. Furthermore It may be appropriate as an additional condition for the Transfer to the boost pressure mode to check if the injected fuel quantity falls below a reference value and the exhaust back pressure upstream of the exhaust turbine also falls below an assigned reference value.

Advantageously, the opening duration and the opening stroke of the Return valve in the boost pressure reduction mode according to a predetermined opening function performed, preferably a differential function with first order lag is which is characterized by a high initial stroke, which with a Applicable time constant drops. The over the time constant selectable opening time is chosen so that the valve on the one hand for a sufficient charge pressure reduction long enough is open, on the other hand, the boost pressure reduction but limited to after a return to normal mode in a short time sufficiently high pressure level in the intake tract and in the exhaust gas system to be able to produce, which is a rapid acceleration allows.

The boost pressure reduction mode is advantageously left again and the normal mode resumed when the injected Fuel quantity within a defined period in the Way that increases the amount of fuel one Reference value is exceeded. This corresponds to the Tripping criterion for the transfer to the boost pressure reduction mode, but with opposite sign, since now the increase of the Fuel quantity injection as a criterion for the termination of Boost pressure reduction mode and transfer to normal mode is used.

It is useful as exhaust gas recirculation valve in the Exhaust gas recirculation device a highly dynamic valve with short Reaction times used, which in particular less than 50 ms be sure to ensure that the return valve is within the required short times are opened and closed can.

Further advantages and expedient designs are the further Claims, the description of the figures and the drawings remove. Show it:

Fig. 1 is a schematic representation of a supercharged internal combustion engine with exhaust gas recirculation device, which can be operated via a control and control unit depending on the current operating condition of the internal combustion engine either in a normal mode in which an exhaust gas recirculation from the exhaust gas side takes place in the intake, or in a boost pressure reduction Mode can be operated in which charge pressure is passed from the intake side via the exhaust gas recirculation into the exhaust line,

Fig. 2 is a flow chart showing the individual steps for transferring the operating mode of the internal combustion engine from the normal mode to the boost pressure reduction mode and vice versa.

The internal combustion engine shown in FIG. 1 1, which is in particular a diesel internal combustion engine, but optionally also is a spark-ignition internal combustion engine, comprising an exhaust gas turbocharger 2 with an exhaust gas turbine 3 in the exhaust line 4 of the internal combustion engine and a compressor 5 in the intake duct 6 , wherein the compressor 5 is driven via a shaft 7 of the exhaust gas turbine 3 . The turbine wheel of the exhaust gas turbine 3 is acted upon by the exhaust gases under the exhaust backpressure p ₃ in the exhaust line between the cylinder outlet of the internal combustion engine 1 and the exhaust gas turbine 3 and transmits its rotary motion via the shaft 7 to a compressor wheel which draws in combustion air which is below the atmospheric pressure p ₁ stands, and compressed to an increased pressure p ₂ . After flowing through the exhaust gas turbine 3 , the exhaust gas assumes a relaxed pressure p ₄ , under which the exhaust gas is fed to a catalytic purification unit and subsequently discharged into the atmosphere.

On the air side, the combustion air under the increased pressure p ₂ downstream of the compressor 5 is supplied to a charge air cooler 9 , in which the combustion air is cooled, and then supplied to the cylinder inlets of the internal combustion engine 1 with the boost pressure P _2S .

The exhaust gas turbine 3 is equipped with a variable turbine geometry 8 , which allows a variable setting of the effective flow inlet cross section to the turbine wheel of the exhaust gas turbine during operation of the internal combustion engine - both in the fired drive mode and in engine braking. The variable turbine geometry 8 is to be adjusted between an open position with a maximum flow inlet cross section and a closed position with a minimum flow inlet cross section. The variable turbine geometry is designed, for example, as an adjustable guide grid, which can be inserted axially into the free flow inlet cross section or has adjustable guide vanes.

Furthermore, an exhaust gas recirculation device 10 is provided which comprises a return line 11 between the exhaust line 4 upstream of the exhaust gas turbine 3 and the intake 6 downstream of the charge air cooler 9 and an adjustable return valve 12 and optionally a cooler 13 .

In a control and control unit 14 , control signals for adjusting the return valve 12 in the exhaust gas recirculation device 10 and the variable turbine geometry 8 of the exhaust gas turbine 3 can be generated as a function of state and operating variables of the internal combustion engine 1 . The control and control unit 14 communicates via signal lines 15 , 16 and 17 with the internal combustion engine, the return valve and the variable turbine geometry.

In the normal operating mode, the exhaust gas recirculation device 10 is opened in the fired drive mode for returning a partial flow of the exhaust gas from the exhaust line 4 in the intake manifold 6 , if the exhaust back pressure p ₃ exceeds the boost pressure p _2S . The recirculation of exhaust gas takes place in particular at higher loads and speeds with the purpose of reducing nitrogen oxides in the exhaust gas.

In order to prevent a compressor pumps at critical pressure conditions between the atmospheric intake pressure p ₁ and the increased compression pressure p ₂ , which leads to flow separations on the compressor, which are associated with an unpleasant, pulsating noise and a high mechanical load on the compressor, can in certain Operating conditions of the internal combustion engine, in particular in a sudden withdrawal of the accelerator pedal operation, the exhaust gas recirculation device 10 are opened to reduce boost pressure P _2S or p ₂ by a partial mass flow of the combustion air downstream of the charge air cooler 9 and upstream of the cylinder inlet of the internal combustion engine via the exhaust gas recirculation device 10 in the exhaust system 4 is derived. This boost pressure reduction mode is in particular taken during deceleration processes of the vehicle, for example in the case of a rapid transition from the traction mode to the overrun mode and at the same time a low engine speed.

At the same time, the variable turbine geometry 8 is transferred to its open position, in which the flow inlet cross section to the turbine wheel assumes a maximum in order to lower the exhaust backpressure and to set a positive pressure ratio from the intake tract 6 to the exhaust tract 4 , which discharges compressed combustion air from the intake tract via the exhaust gas recirculation device 10 allows. Both the return valve 12 and the variable turbine geometry 8 are here set via control signals of the control and control unit 14 . This applies equally to the termination of the boost pressure reduction mode.

In Fig. 2 is a flow chart for switching from the normal operating mode in the boost pressure reduction mode and shown vice versa. Starting from the normal operating mode according to method block 2.1 , in which the exhaust gas recirculation valve ("EGR valve") and the variable turbine geometry are set by the control unit ("EGR controller") of the internal combustion engine according to internal combustion engine aspects or for generating braking power are prior to transfer to the boost pressure reduction mode according to method step 2.5, three conditions in the process steps 2.2 to 2.4 are queried, which must be cumulatively fulfilled in order to set the boost pressure reduction mode.

In method step 2.2 , it is first queried whether the amount of change in the injected fuel quantity | ≙ _K | is greater than an associated reference value ≙ _{K, Rn} , which represents a reference value for the negative gradient of the amount of fuel. About this condition, the condition is to be detected that the accelerator pedal operation by the driver has been withdrawn within a short time. If this condition is not met, the no-branching is correspondingly returned to the normal operating mode according to method step 2.1 ; the internal combustion engine remains in the normal operating mode until a renewed query of conditions 2.2 to 2.4 .

In the event that the query in step 2.2 is met, a sudden withdrawal of the accelerator pedal operation has been determined by the driver and it is the branching Ya continued according to the following query in Veraßhrensschritt 2.3 , in which it is queried whether the engine speed n _Mot an associated reference value n _{Mot, R falls} below. This query is to ensure that the boost pressure reduction mode is only achieved in low speed ranges. If the condition is not met, the no-branch is again returned to method step 2.1 . Otherwise, the yes branch is continued according to the following query for method step 2.4 .

In method step 2.4 , a further condition is queried as to whether the absolute quantity of fuel m _K which has been injected over a given injection period falls below an assigned reference value m _{K, R} , whereby it is to be ensured via this interrogation that the internal combustion engine is in a low load condition located. If the condition is not met, the no-branch is again returned to method step 1 accordingly. If the condition is met, the yes branch is continued according to the following step 2.5 and the boost pressure reduction mode is set.

In the boost pressure reduction mode, first the variable Turbine geometry opened to reduce the exhaust back pressure and between intake and exhaust system a positive pressure gradient manufacture. At an opening of the exhaust gas recirculation valve is a part of the supercharged combustion air from the Intake tract transferred to the exhaust system and accordingly Boost pressure reduced. It may be appropriate, the Opening function of the exhaust gas recirculation valve both in terms of the opening time as well as with regard to the opening stroke to control according to a predetermined function.

The boost pressure reduction mode can either be left after a regular closure of the exhaust gas recirculation valve in accordance with the predetermined function and the normal operation mode can be resumed as shown in FIG. 2.1 or, as shown in method step 2.6 , be left for the case that an additional condition is fulfilled. This additional condition shown in method step 2.6 relates to an increase in the injected fuel quantity ≙ _K within a defined period of time, which is compared with a reference value ≙ _{K, Rp} . If the fuel quantity increase exceeds the reference value, the yes branch is correspondingly returned to the normal operating mode according to method step 2.1 . Otherwise, the condition for returning to the normal operating mode is not met and the no branch is maintained according to the boost pressure reduction mode.

As further conditions necessary for a setting of the Boost pressure reduction mode can be met, if necessary, too a query of the pressure values for the boost pressure and the Exhaust back pressure done. It can be checked if the boost pressure exceeds an assigned reference value and / or the Exhaust back pressure falls below a reference value or a positive pressure ratio of boost pressure to exhaust back pressure prevails.

Claims (8)

1. A method for operating an internal combustion engine with exhaust gas turbocharger, comprising an exhaust gas turbine ( 3 ) and a compressor ( 5 ), and with an exhaust gas recirculation device ( 10 ), comprising a return line ( 11 ) between the exhaust line ( 4 ) upstream of the exhaust gas turbine ( 3 ) and the intake tract ( 6 ) downstream of the compressor ( 5 ) and an adjustable return valve ( 12 ), characterized
that, in the event that the injected fuel quantity is reduced within a defined period of time in such a manner that the amount of change of the fuel quantity (| ≙ _K |) exceeds a reference value (≙ _{K, Rn} ), the following action is taken a boost pressure reduction mode are taken:
a variable turbine geometry ( 8 ) of the exhaust gas turbine ( 3 ) is adjusted in the direction of an open position widening the free flow cross section to the turbine wheel,
the exhaust gas recirculation valve ( 12 ) is opened. 2. The method according to claim 1, characterized in that is taken into account as an additional condition for adjusting the boost pressure reduction, that the engine speed (n _Mot ) _falls below a reference value (n _{Mot, R} ). 3. The method of claim 1 or 2, characterized in that is taken into account as an additional condition for adjusting the boost pressure reduction, that the fuel quantity injected per unit time (m _K ) falls below a reference value (m _{K, R} ). 4. A method according to any one of claims 1 to 3, characterized in that is taken into account as an additional condition for adjusting the charge pressure reduction that the boost pressure (P _2S ) exceeds a reference value. 5. The method according to any one of claims 1 to 4, characterized in that is taken into account as an additional condition for adjusting the boost pressure reduction, that the exhaust gas backpressure (p ₃ ) upstream of the exhaust gas turbine ( 3 ) falls below a reference value. 6. The method according to any one of claims 1 to 5, characterized in that the opening duration and the opening stroke of the return valve ( 12 ) follows a predetermined function. A method according to claim 6, characterized in that the opening function of the recirculation valve ( 12 ) is a DT ₁ function (differential function with first order delay). 8. The method according to any one of claims 1 to 7, characterized in that the boost pressure reduction mode is left again when the injected fuel amount is increased within a defined period of time in such a way that the change in the amount of fuel (≙ _K ) is a reference value (≙ _{K, Rp} ).