DE10043366A1 - Process for heating catalysts in the exhaust gas of internal combustion engines - Google Patents

Abstract

The invention relates to a method for heating up a catalyst (15) in the exhaust gas of an internal combustion engine (1) which can be operated in different operating modes and which allows selection of at least one of a plurality of heating measures. According to the inventive method, first an estimation is made for the plurality of heating measures whether an individual heating measure can provide the desired heating effect. In a subsequent estimation step it is estimated whether an individual heating measure can be carried out in the actual operating mode regarding the exhaust gas values and the operating mode of the internal combustion engine required for said heating measure. The operating mode is requested in which these requirements can be best met. Depending on the actual operating mode at least one possible heating measure is then activated. The invention further relates to an electronic control device for carrying out said method.

Description

Need catalysts in the exhaust gas of internal combustion engines a certain minimum temperature (light off temperature) in order to develop their pollutant-converting effect. This should be reached as quickly as possible after a cold start. For engines with a lean fuel / air mixture are operated, for example in engines with Direct petrol injection and nitrogen oxide storage catalyst there are further and sometimes changing requirements to the catalyst temperature, for example from a necessary desulfation of the storage catalyst while driving. Desulfation required for example temporarily a higher one Catalyst temperature than in normal operation for the Storage of nitrogen oxides is required.

There are already various measures for heating Catalysts known.

For example, engine combustion can be so rich Mixture occur that the exhaust gas is still unburned Contains fuel. The supply of secondary air to the exhaust gas  creates a reactive mixture that the Catalyst heated up by an exothermic reaction.

Furthermore, engine combustion can be so lean Mixture occur that the exhaust gas is still unused Contains oxygen. In this case, a reactive Mixture generated by supplying fuel to the exhaust gas become.

It is also known to be the catalyst by the consequences a deterioration in the efficiency of the motor Heat up combustion. A deterioration in efficiency The engine combustion can, for example, by a Deviation of the ignition timing from the optimal timing can be brought about, the optimal time by the maximum efficiency is defined. Through the The loss of efficiency is hotter compared to Operation without loss of efficiency. It therefore unfolds one increased heating effect in the catalytic converter.

Allow for engines with gasoline direct injection different operating modes of the engine different Measures for heating the catalyst.

From DE 198 50 586 is an engine control program known that switching between shift operation and Controls homogeneous operation.

In shift operation, the engine becomes strong stratified cylinder charge and high excess air operated to keep fuel consumption as low as possible to reach. The stratified charge is replaced by a late Fuel injection achieved, which is ideal for The combustion chamber is divided into two zones: the first  Zone contains a combustible air-fuel mixture cloud on the spark plug. It is surrounded by the second zone, the consists of an insulating layer of air and residual gas. The potential for optimizing consumption results from the Possibility of avoiding the engine Charge exchange losses largely unthrottled operate. The shift operation is comparatively preferred low load.

At higher loads, when the performance optimization in The engine is more homogeneous Cylinder filling operated. The homogeneous cylinder filling results from early fuel injection during of the suction process. As a result stands up to the combustion a longer time for mixture formation. The Potential of this operating mode for performance optimization results for example from the exploitation of the whole Combustion chamber volume for filling with a combustible mixture.

For heating a NOx storage catalytic converter in the Homogeneous operation can set an exhaust gas composition be determined by the stoichiometric exhaust gas composition differs.

In the case of gasoline direct injection engines, this continues to exist Possibility when operating with excess air, so preferably in shift operation, targeted fuel in the Cylinder after engine combustion in the expansion stroke inject. Here the post-injected reacts Fuel with excess air from engine combustion in the catalyst. The one released during the exothermic reaction Heat heats up the catalytic converter.

The object of the invention is in everyone Operating state to choose an optimal heating strategy.

This object is achieved with the features of claim 1.

In particular, the catalyst according to the invention is heated in the exhaust gas of an internal combustion engine, which can be operated in different operating modes and in which at least one of a number of heating measures can be selected
such that it is initially estimated for several heating measures whether an individual heating measure can provide the desired heating effect
and that it is further estimated whether an individual heating measure can be carried out in the current operating state with a view to the exhaust gas values and the operating mode of the internal combustion engine required to carry out the heating measure
and that the operating mode in which the requirements can best be met is requested and that at least one possible heating measure is activated depending on the current operating mode.

Here, the current operating status is shown, for example Values for the catalyst temperature, the Vehicle speed and the current load characterized.

benefits

The different operating modes of the internal combustion engine with Direct petrol injection allows different measures for heating the catalyst. The assignment according to the invention of heating measures and operating modes enables a  Optimization of the heating strategy with a view to the Operating state of the vehicle, for example of Parameters such as catalyst temperature, Vehicle speed and torque requirement is determined.

The possible heating effects are advantageous different catalyst heating measures estimated and with compared to the heating effect requirement. The heating effect requirement leads to heating of a catalyst, for example physical requirements for quantity and temperature of the exhaust gas flow provided by the heating measure must become.

Furthermore, the operating limits for the individual Operating modes taken into account. This makes it possible to to choose an optimal heating strategy for every operating condition.

All requirements for active heating measures are considered Heat flow and temperature requirements formulated in the exhaust gas. As a result, all requirements can be treated uniformly become.

An exemplary embodiment of the invention is explained below with reference to the figure. Here, FIG. 1 shows the technical background of the invention. Fig. 2 shows an embodiment of the invention in the form of a flow chart.

The 1 in FIG. 1 represents the combustion chamber of a cylinder of an internal combustion engine. The inflow of air to the combustion chamber is controlled via an inlet valve 2 . The air is sucked in via a suction pipe 3 . The amount of intake air can be varied via a throttle valve 4 , which is controlled by a control unit 5 . The control unit receives signals about the driver's torque request, for example about the position of a driver. Accelerator pedal 6 , a signal about the engine speed n from a speed sensor 7 , a signal about the amount ml of the intake air from an air flow meter 8 and a signal Us via the exhaust gas composition and / or exhaust gas temperature from an exhaust gas sensor 12 . Exhaust gas sensor 12 can be, for example, a lambda probe, the Nernst voltage of which indicates the oxygen content in the exhaust gas and the internal resistance of which is used as a measure of the probe, exhaust gas and / or catalyst temperature. The exhaust gas is passed through at least one catalytic converter 15 , in which pollutants from the exhaust gas are converted and / or temporarily stored.

From these and possibly other input signals via further parameters of the internal combustion engine, such as intake air and coolant temperature and so on, the control unit 5 forms output signals for setting the throttle valve angle alpha by means of an actuator 9 and for controlling a fuel injection valve 10 , by means of which fuel is metered into the combustion chamber of the engine becomes. The control unit also controls the triggering of the ignition via an ignition device 11 .

The throttle valve angle alpha and the injection pulse width ti are essential, coordinated manipulated variables to realize the desired torque, the Exhaust gas composition and the exhaust gas temperature and thus the Catalyst temperature. Another essential control variable to influence these quantities is the angular position of the ignition relative to the piston movement. The determination of the manipulated variables to adjust the torque is the subject of DE 198 51 990, which are included in the disclosure to this extent should.  

Furthermore, the control unit controls further functions to achieve efficient combustion of the fuel / air mixture in the combustion chamber, for example exhaust gas recirculation and / or tank ventilation, not shown. The gas force resulting from the combustion is converted into a torque by pistons 13 and crank mechanism 14 .

In this technical environment, the catalyst temperature be measured or from the operating parameters of the engine be modeled. The modeling of temperatures in the Exhaust tract from internal combustion engines is off, for example US 5 590 521.

For heating by means of post-injection, the Motor control according to the invention minimum temperatures in the Catalysts. Until these are reached, for example as a first measure homogeneous operation with late ignition demanded and set. Are the necessary temperatures reached, the post-injection is a possible alternative allowed. Switching to shift operation takes place with Post-injection to generate a higher heat flow. The air flow is throttled so far that the required heat flow at a required temperature is achieved.

The throttling takes place in a first embodiment by controlled closing of the throttle valve by one predetermined angle or to a predetermined Opening angle. In other words, the throttling takes place unregulated in this example. The mixture composition should be close to lambda for maximum heat release be equal to 1. Through dynamic driving with changing Torque requests can be temporary  Mixture enrichments for lambda values less than one come. This can cause exhaust emissions to be undesirable - worsen way.

To avoid exhaust gas deterioration, the Post-injection advantageously with the help of existing exhaust gas probe regulated. This can be a breakthrough be prevented by rich exhaust gas. Inscribed Breakthrough the occurrence of HC emissions behind the Catalyst. Another advantage is the exothermic Maximum energy release used with lambda equal to 1.

In particular, due to the heating requirement amount of fuel required for post-injection at maximum possible throttling determined. In addition to the The air requirement for post-injection and the temperature increase due to throttling is taken into account become. The latter is particularly important to prevent overheating to prevent components in the exhaust system.

As an alternative to regulating the post-injected Fuel quantity over the measured exhaust gas lambda can Throttling can be controlled via the measured exhaust gas lambda.

Fig. 2 shows an embodiment in the form of a flow chart.

In step 2.1 it is checked whether there is a request for a catalyst heating measure. If this is the case, in step 2.2 an estimate is made for at least one heating measure X as to whether it can provide the desired heating effect and whether this heating measure with regard to the exhaust gas values and the operating mode of the internal combustion engine required to carry out the heating measure in the current operating state (catalyst temperature, vehicle speed , current load) is allowed.

The various heating measures are based on this physical requirements (heat flow and temperature) calculated and rated. Furthermore, the operating limits taken into account for the individual operating modes. This is it is possible to get an optimal one in any operating condition Heating strategy to choose. Next is for each heating measure checked whether they have a look at the exhaust gas values and the required operating mode in the current driving state, d. H. at current catalytic converter temperature, vehicle speed and Load is possible.

With this information, the individual heating measures depending on the operating status and a decision be taken for the best measure. The assessment a heating measure is carried out in the event of a request in a slow time grid for each heating measure. Only for the activated heating measure becomes the necessary interventions calculated in a fast time grid by computing time save up.

If necessary, the required optimal operating mode is requested in step 2.3 . For example, if the catalyst is still cold, post-injection in shift operation may not be optimal because a still cold catalyst cannot activate the exothermic reaction of the resulting mixture in the exhaust gas. In this case, a drop in efficiency due to late ignition would be appropriate to increase the exhaust gas temperature. This can preferably be carried out in the operating mode with homogeneous operation. Accordingly, a switchover to homogeneous operation can take place in step 2.3 .

The selected heating measure is then activated in step 2.4 .

If, on the other hand, the query in step 2.1 is answered in the negative, no heating measure is requested and any activated heating measures are deactivated.

Claims (6)

1. Method for heating a catalyst in the exhaust gas of an internal combustion engine,
which can be operated in different operating modes and
where at least one of several heating measures can be selected
whereby for several heating measures it is estimated whether an individual heating measure can provide the desired heating effect
and it is estimated whether an individual heating measure can be carried out in the current operating state (catalytic converter temperature, vehicle speed, current load) with a view to the exhaust gas values and the operating mode of the internal combustion engine required to carry out the heating measure
and requesting the mode of operation in which the requirements can best be met
and at least one possible heating measure is activated depending on the current operating mode. 2. The method according to claim 1, characterized in that as a measure a worsening of the Efficiency of engine combustion via a The ignition angle is changed. 3. The method according to claim 1, characterized in that as another measure using an engine with Gasoline direct injection after combustion one Fuel post-injection takes place. 4. The method according to claim 3, characterized in that the post-injection is combined with shift operation. 5. The method according to claim 4, characterized in that the amount of air drawn in by the internal combustion engine is throttled so far that the required heat flow is reached at a required temperature. 6. The method according to claim 1, characterized in that for heating a NOx storage catalytic converter in Homogeneous operation set an exhaust gas composition is that of the stoichiometric exhaust gas composition differs.