DE10221536B4 - Method for controlling a working mode of an internal combustion engine - Google Patents

Abstract

Method for controlling a working mode of an internal combustion engine,
In which the operating parameters of the internal combustion engine are determined by means of the engine control unit and the working mode is regulated by adjusting the air / fuel mixture (λ value),
- That for realizing a driver's desired torque when exceeding a specified limit catalyst temperature (T _limit ) at a set air / fuel mixture of λ = 1 and at an existing control potential of the internal combustion engine supplied air masses and / or throttle adjustment by the engine control unit, the air / fuel Mixture is adjusted by mixture leaning to a value of λ> 1 such that the catalyst temperature (T _actual ) is equal to or slightly lower than the _limit catalyst temperature (T _limit ),
A throttle valve adjustment takes place simultaneously with the lean mixture via the engine control unit in such a way that a larger amount of combustion air is supplied to equalize the torque loss of the internal combustion engine by opening the throttle valve,
- When the lean load is reached by the engine control unit, the air / fuel mixture is adjusted from λ> 1 to λ <1 (rich phase),
- and at the same time with the mixture greasing ...

Description

The invention relates to a method for controlling a working mode of an internal combustion engine with the features mentioned in the preamble of claim 1 and the dependent claim 2.

It is well known to control the working mode of an internal combustion engine by an engine control unit based on the current engine data such as driver's desired torque, engine speed, engine temperature, exhaust gas temperature, ratio of the air / fuel mixture supplied to the engine (λ value), and so on. It should be noted that when realizing a driver's desired torque by setting the working mode, the exhaust gas temperature of the combustion gases is not increased so much that it exceeds the allowable temperature limit for the downstream of the engine catalytic converter. Exceeding the allowable limit catalyst temperature would damage or destroy the catalyst.

From the DE 197 48 971 A1 a system for protecting a catalytic converter of an internal combustion engine from overheating is already known, in which upon reaching a temperature critical for the catalyst from the engine control unit, the fuel processing system is influenced so that the engine is fed to a leaner air-fuel mixture. By leaning the air-fuel mixture, the temperature of the exhaust gas is reduced. In order to reduce the nitrogen oxides in the exhaust gas, the hydrocarbon-rich and oxygen-rich exhaust gas is fed to a first catalyst without oxygen storage capability and then to a three-way catalyst.

A disadvantage of this system is that the reduction of the exhaust gas temperature for the protection of the catalyst results in a reduced performance of the engine.

• – Öffnen des Absperrventils in einem Umgehungskanal zum Katalysator,
• – Umlenken des Fahrtwindes auf den Abgaskanal oder den Katalysator,
• – Verringerung der Luftfüllung der Brennkraftmaschine,
• – Anfetten des Luft-Kraftstoff-Gemisches.

From the DE 43 44 137 A1 For example, a system for protecting a catalyst from overtemperature is previously known in which measures are taken to cool the catalyst depending on the maximum allowable catalyst temperature and the actual catalyst temperature. As measures for cooling the catalyst, inter alia:

• Opening the shut-off valve in a bypass channel to the catalytic converter,
• - diverting the airstream to the exhaust duct or the catalyst,
• Reduction of the air charge of the internal combustion engine,
• - enriching the air-fuel mixture.

These individual measures are used individually or in complex according to the actual catalyst temperature.

The disadvantage here is a high hardware cost for the complicated and expensive control for cooling the catalyst. In addition, the widespread measure of enriching the air-fuel mixture to lower the catalyst temperature has the disadvantage of increased fuel consumption.

From the DE 199 32 290 A1 a method for controlling a working mode of an internal combustion engine is previously known, in which the operating mode is regulated as a function of the catalyst temperature. When a first predetermined limit temperature of the catalyst is exceeded, a working mode with λ ≦ 1 is set by means of mixture enrichment. After a first exceeding of a second limit temperature of the catalyst, which is above the first limit temperature, and a subsequent drop in the catalyst temperature below the second limit temperature, a working mode with λ> 1 (lean operation) is set. The lean operation is thereby obtained so long as is necessary until a predetermined threshold value for an NO _x emission is exceeded on the catalyst.

This described control can only be used when using a NO _X storage calculator. Operating the catalyst in pure lean operation is therefore not possible. A lean operation can only be maintained until a threshold value for a NO _x emission is exceeded.

Furthermore, from the DE 197 28 926 C1 a control device for Nachstartverschiebung the λ control known, in which a reduction of the harmful nitrogen oxides in the Nachstartphase is made by changing a lean or rich shift of the fuel-air mixture. This regulation can be used only limited to the post-start phase. A regulation of the working mode during the regular operating period is not provided.

From the US 5 622 049 A a method is known in which set by a motor control unit at a catalyst temperature which is above the Grenzkatalysatortemperatur, a Gemischanfettung and thereby a possible torque surplus by closing the throttle or by reducing the amount of combustion air is compensated.

According to the US 5,473,887 A. the air / fuel mixture is controlled by means of an engine control unit such that a catalyst temperature remains smaller than or equal to a boundary catalyst temperature and thereby any deviations from the optimal engine operation by opening the throttle or by increasing the amount of combustion air can be compensated.

The invention has for its object to provide a generic method for controlling a working mode of an internal combustion engine, which prevents overheating of the catalyst in all load ranges even with the realization of a maximum engine torque, reduces the thermal load on the catalyst while fuel consumption in the upper load and Speed range reduced.

This object is achieved in a generic method according to the invention by the characterizing features of claim 1 and by the characterizing features of the independent claim 2.

By controlling the operating mode in response to a driver's desired torque request to the engine, the resulting catalyst _{temperature is} limited by leaning the air / fuel mixture to a predetermined _limit catalyst temperature T _limit . After reaching the lean full-load operating state takes place by mode change in the rich region with λ <1, a further moment structure while reducing the combustion air masses supplied. The advantage of this regulation of the working mode is that when a driver request torque is realized, a predetermined catalyst limit temperature is not exceeded and the catalyst temperature assumes an almost constant value during driving, which corresponds approximately to the limit catalyst temperature T _limit . By increasing the λ value to> 1, with a corresponding existing control potential of the internal combustion engine supplied air masses and / or the throttle position adjustment, the fuel consumption is reduced during operation.

Another advantage of the invention is that the regulation of the working mode of the internal combustion engine can also be adjusted such that at a desired driver torque and at a corresponding existing control potential of the internal combustion engine supplied air masses and / or the throttle adjustment on reaching the allowable limit catalyst temperature T _limit a Gemischabmagerung is made in such an order that the temperature T _{ist of} the catalyst is well below the limit temperature. As a result, on the one hand the thermal load of the catalyst and its wear is reduced and on the other hand there is a further minimization of fuel consumption.

With reference to a drawing, an embodiment of the invention will be described below. In the accompanying drawing, a flowchart of the control of a working mode of an internal combustion engine is shown schematically.

The regulation of the working mode of an internal combustion engine is carried out by means of an engine control unit which determines the operating parameters of the internal combustion engine and regulates the working mode, for example by adjusting the air / fuel mixture (λ value). According to the invention, the regulation of the working mode takes place as a function of a request torque made by the driver to the engine 1 that is needed to realize the driving conditions. For the realization of a driver request torque 1 will be included in a first step 2 Checked whether a specified _limit catalyst temperature T limit is exceeded at a set air / fuel mixture of λ = 1. If the limit temperature is not exceeded, the λ value of 1, corresponding to the step 3 , maintained as a realization of the desired moment 1 is possible.

When exceeding the specified _limit catalyst temperature T _limit is in a further step 4 Check if the driver's request torque 1 in lean operation M _{lean of} the engine is displayed. If this is not the case, that is, there is no additional control potential with respect to the air masses supplied to the internal combustion engine is more, is about the step 5 the fat content in the air / fuel mixture increases. The λ value is set from λ = 1 to λ <1. The temperature of the catalyst is lowered and the desired moment 1 can be realized.

Will in step 4 determined that a corresponding control potential is available to the driver's desired torque 1 In lean operation M to be able to realize _lean engine, takes place in accordance with step 7 , with existing air mass or throttle flap potential DK, by the engine control unit a Gemischabmagerung to a value of λ> 1 with the corresponding temperature reduction potential. (Step 8th The temperature of the catalyst is set to a value which is slightly below the _limiting catalyst temperature T _limit . With the Gemischabmagerung takes place simultaneously in the step 9 for torque-neutral compensation of the moment loss occurring thereby opening the throttle and thus a larger combustion air quantity supply.

Upon reaching the lean load, in which a complete de-throttling is achieved at maximum open throttle, the condition in step 4 , the driver's request moment 1 In lean operation M _lean engine to represent, can no longer be met. About the engine control unit is a mode change from λ> 1 to λ <1. (Step 6 ) The resulting torque surplus is compensated torque-neutral by simultaneously closing the throttle. The resulting torque potential can be exploited again until complete Entschrosselung and the achievement of full fat.

To ensure the reversibility of the processes filter and hysteresis come 6 for use.

A variant of the regulation of the working mode of the internal combustion engine according to the invention provides that in the case of a positive result in step 4 according to step 8th an additional Gemischabmagerung takes place. At the same time takes place with the Gemischabmagerung on the engine control unit, a throttle adjustment, so that by opening the throttle of the internal combustion engine, a larger amount of combustion air is supplied to compensate for the torque loss. Due to the additional Gemischabmagerung and thus a further increase in the λ value, the temperature of the catalyst drops well below the boundary catalyst temperature, resulting in an increase in life with simultaneous further fuel savings.

In the case of complete de-throttling and thus with a complete open throttle valve (DK = DK _max ), the driver's desired torque is increased further 1 in a first phase, the fat content in the mixture lean according to the step 10 elevated. However, the λ value set here is> 1. The mixture enrichment results in an increase in the temperature of the catalytic converter. With further increase of the driver's desired torque 1 the limit catalyst temperature T _{limit is} exceeded. The condition in step 4 is no longer satisfied and there is a mode change from λ> 1 to λ <1. The resulting torque surplus is compensated torque-neutral by simultaneously closing the throttle. The resulting torque potential can be exploited until the complete de-throttling once the full-fat load has been reached.

LIST OF REFERENCE NUMBERS

1

Driver input torque

2

catalyst temperature

3

Adjustment of the air / fuel mixture

4

Determination of the existing working mode

5

Adjustment of the air / fuel mixture

6

Hysteresenregelung

7

Determination of the existing air mass or throttle valve potential

8th

Adjustment of the air / fuel mixture

9

Regulation of the throttle valve adjustment

10

Adjustment of the air / fuel mixture Value of the air / fuel mixture

DK

throttle potential

DK _max

Maximum throttle potential

T _border

Limit catalyst temperature

M

Driver input torque

M _lean

Engine torque in lean operation

M _bold

Engine torque in rich operation

T

catalyst temperature

T _{λ = 1}

Catalyst temperature at λ = 1

T _is

Actual catalyst temperature

Claims (2)

Method for controlling a working mode of an internal combustion engine, - Determined in the means of the engine control unit, the operating parameters of the internal combustion engine and the working mode by adjusting the air / fuel mixture (λ value) is controlled, - to realize a driver's desired torque when exceeding a specified limit catalyst temperature (T _limit ) at a set air / fuel Mixture of λ = 1 and at an existing control potential of the internal combustion engine supplied air masses and / or the throttle adjustment by the engine control unit, the air / fuel mixture is adjusted by Gemischabmagerung to a value of λ> 1 such that the catalyst temperature (T _actual ) is equal to or slightly smaller than the limit catalyst temperature (T _limit ), - at the same time as the Gemischabmagerung via the engine control unit, a throttle adjustment is such that to compensate for the torque loss of the internal combustion engine by opening the throttle a grö ßere combustion air quantity is supplied, - when the lean load by the engine control unit, the air / fuel mixture from λ> 1 to λ <1 (fat phase) is set, - and simultaneously with the mixture enrichment via the engine control unit, a throttle adjustment is such that Balancing the resulting torque surplus of the internal combustion engine by closing the throttle valve, a smaller amount of combustion air is supplied. Method for controlling a working mode of an internal combustion engine, - determined by the engine control unit, the operating parameters of the internal combustion engine and the working mode by adjusting the air / fuel mixture (λ value) is controlled - to reduce the catalyst temperature and to minimize the fuel consumption when exceeded a fixed limit catalyst temperature (T _limit ) at a set air / fuel mixture of λ = 1 and at an existing control potential of the internal combustion engine air masses supplied and / or the throttle adjustment by the engine control unit, the air / fuel mixture by Gemischabmagerung to a value of λ > 1 is set such that the catalyst temperature (T _actual ) is much smaller than the specified _limit catalyst temperature (T _limit ), - at the same time as the Gemischabmagerung via the engine control unit such a throttle adjustment olgt, that for balancing the torque loss of the internal combustion engine by opening the throttle valve, a larger amount of combustion air is supplied to the achievement of lean load, in which no control potential of the internal combustion engine supplied air masses and / or the throttle adjustment is more available to achieve a further instantaneous structure by the The engine control unit sets an increased proportion of fat in the lean-burn air / fuel mixture of λ> 1, - after the set limit catalytic converter temperature (T _limit ) has been exceeded, set the air / fuel mixture from λ> 1 to λ <1 (rich phase) by the engine control unit is - and simultaneously with the Gemischanfettung on the engine control unit, a throttle adjustment is made such that to compensate for the resulting torque surplus of the internal combustion engine by closing the throttle valve, a smaller amount of combustion air is supplied.

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