DE10253613A1 - Operation of vehicle combustion engine involves using switching conditions between lean operating region and homogeneous operating region e.g. as function of fuel consumption value - Google Patents

Abstract

Process for operating a vehicle combustion engine involves using switching conditions between the lean operating region and the homogeneous operating region as a function of a fuel low consumption value in the lean operating region, as a function of fuel high consumption value for a discharge in the rich operating region, as a function of a lean time as lean operating period and as a function of a rich time as rich operating period.

Description

The invention relates to a method for operating an internal combustion engine of a vehicle, in particular of a motor vehicle according to the preamble of claim 1.

In today's automotive engineering Otto engines as internal combustion engines with gasoline direct injection preferred instead of conventional intake manifold injection, because such internal combustion engines over the conventional Otto engines have significantly more dynamics in terms of torque and performance are better while reducing consumption by up to 15%. Possible does this primarily a so-called stratified charge in the partial load range, at only in the area of the spark plug an ignitable mixture needed will while the rest Combustion chamber filled with air becomes. Because conventional Internal combustion engines that work on the intake manifold principle at one such a high excess of air, as it is with direct petrol injection, are no longer ignitable, in this stratified charging mode, the fuel mixture is central Spark plug positioned in the combustion chamber focused while there is pure air in the edge areas of the combustion chamber. Around the fuel mixture positioned around the central one in the combustion chamber spark plug to be able to center around is a targeted air flow required in the combustion chamber, a so-called tumble flow. To an intense, cylindrical flow is formed in the combustion chamber and the fuel injected only in the last third of the piston upward movement. By the combination of special air flow and targeted geometry the piston, the z. B. about a pronounced one Fuel flow trough features, becomes the particularly finely atomized fuel in a so-called "mixture bale" optimally around the spark plug concentrated and certainly kindled. For the optimal adjustment the injection parameter (injection timing, fuel pressure) ensures the engine control or the engine control unit.

Such internal combustion engines can therefore be operated in lean operation for a correspondingly long time, which, as has already been explained above, has a positive effect on the overall fuel consumption. However, this lean operation has the disadvantage of a considerably larger amount of nitrogen oxide in the exhaust gas, so that the nitrogen oxides (NOx) in the lean exhaust gas can no longer be completely reduced with a three-way catalytic converter. In order to reduce nitrogen oxide emissions within the prescribed limits, e.g. B. to keep the Euro IV limit, nitrogen oxide storage catalysts are used in connection with such internal combustion engines. These nitrogen oxide storage catalysts are operated in such a way that the large amounts of nitrogen oxides generated by the internal combustion engine are stored therein. With increasing amount of stored nitrogen oxide, a state of saturation is reached in the nitrogen oxide storage catalytic converter, so that the nitrogen oxide storage catalytic converter has to be discharged. For this purpose, for a so-called discharge phase, the engine control or the engine control unit briefly switches to sub-stoichiometric, rich engine operation, in which the internal combustion engine is operated with a rich, air-deficient mixture. At the beginning of this discharge phase, an oxygen store of the nitrogen oxide storage catalytic converter is regularly emptied, as a result of which the oxygen required for the withdrawal process is made available. The additional fuel consumption for the discharge of the nitrogen oxide storage catalytic converter is generally approximately constant, the main portion being used here for emptying the oxygen storage device of the nitrogen oxide storage catalytic converter. During this withdrawal process, the stored nitrogen oxide is reduced to nitrogen (N ₂ ), in particular by the hydrocarbons (HC) and carbon monoxides (CO) which are numerous in these rich operating conditions, which can then be released into the environment.

According to a well known generic method for operating an internal combustion engine of a motor vehicle a first operating area is provided as a lean operating area, in which the internal combustion engine with an excess air and thus an excess of oxygen having lean mixture is operated and in which the by the Internal combustion engine generated nitrogen oxides in a nitrogen oxide storage catalytic converter are stored, whereby to discharge the nitrogen oxide storage catalyst by means of an engine control unit switched from the lean operating area to a rich operating area is in which the internal combustion engine with a lack of air rich mixture is operated and in which during the lean operating range the nitrogen oxide storage catalyst stored nitrogen oxides the nitrogen oxide storage catalyst are stored. Further a second operating area is provided as a homogeneous operating area, in which the internal combustion engine with a substantially stoichiometric homogeneous mixture (Lamda = 1) is operated, the switching between the lean operating area and the homogeneous operating area from the engine control unit dependent on from an operational load and / or speed requirement Reaching a predetermined switchover condition is made and being from the engine control unit switching from the lean operating area to the homogeneous operating area first for a discharge of the nitrogen oxide storage catalyst in the rich Operating range is switched.

Specifically, the lean operating area here is a stratified lean operating area in which the lambda value is approximately 1.4. Especially in connection with a dynamic driving style, such as this z. B. is the case in city traffic, the engine control unit is regularly switched to the homogeneous operating range in which the internal combustion engine is operated essentially with a stoichiometric homogeneous mixture of lamda = 1 due to the operationally increased load and / or speed requirement. Before switching to the homogeneous operating range, the engine control unit first switches to the rich operating range in order to discharge the nitrogen oxide storage catalytic converter. Studies have shown that in spite of occasional lean operation, the theoretical lean fuel saving potential that is actually available is not fully exploited in this mode of operation.

The object of the invention is therefore a method for operating an internal combustion engine of a vehicle, to provide in particular a motor vehicle with which simple way an operating mode optimized in terms of fuel consumption the internal combustion engine, in particular through optimized lean operation, possible becomes.

This task is solved with the Features of claim 1.

According to claim 1, the switching condition between the lean operating area and the homogeneous operating area as a function of an operating point-dependent fuel consumption value stored in a map in the lean operating range, an operating point-dependent fuel consumption value stored in a map for one Unloading in the rich operating range, a lean period as the lean operating period and A fat time as the fat operation period determines that the engine control unit a switch to the lean operating area locks if the with each other related values for a certain predeterminable Operating range reveal that the fuel consumption amount for the Discharges in this operating range is equal to or greater than the fuel shortage due to lean operation in this operating area. It is also envisaged that the engine control unit a lean operation and thus switching between the lean operation area and releases the homogeneous operating area if the in each other in related values for a certain predeterminable operating range result in the additional fuel consumption for the discharges in this operating range is less than the fuel consumption quantity due to lean operation in this operating area.

It is advantageous with such Operating mode achieved that the engine control unit calculates here for each operating range, whether the lean operation including the associated rich operation for the Discharges compared to the homogeneous operating range a fuel saving brings with it or not. This means that - in relation to one certain operating range as an operating cycle - a sensible lean operation an internal combustion engine is only possible if the additional fuel consumption while the discharge is smaller than that during the lean operating range resulting fuel economy. As soon as according to the mode of operation according to the invention it is found that there is no fuel consumption advantage in a lean operation across from can be moved out of the homogeneous operating area from the engine control unit the homogeneous operating range selected and the lean operating area is blocked. Because of this procedure, thus a consumption-optimized mode of operation of lean-burn engines easily done be, which significantly improves the fuel saving potential exhausted is considered general in the mode of operation according to the generic known prior art. The individual maps or the individual map points, that span such a map can simply be empirical determined and the simplest in the on-board computer or the engine control device available for download.

According to a particularly preferred mode of operation according to claim 2, it is provided that the engine control unit enables lean operation and thus switching between the lean operating area and the homogeneous operating area if the following switching condition is fulfilled:
Low fuel consumption value * Lean time> Higher fuel consumption value * Fat time.

Such a switching condition is from the engine control unit relatively easy to calculate, so a simple determination of a meaningful lean operation is possible.

The lean period can be according to claim 3 preferred by the engine control unit as a function of one in one also simplest, e.g. B. empirically ascertainable characteristic diagram of stored operating point-dependent nitrogen oxide raw mass flow value and a currently recorded value about the nitrogen oxide storage capacity of the nitrogen oxide storage catalyst can be determined. An actual Detection of this last value is e.g. B. by described below activities possible. Alternatively, this value can also be modeled. The lean time is calculated in a particularly simple and preferred manner according to claim 4 specifically from the quotient of the nitrogen oxide storage capacity value and the nitrogen oxide raw mass flow value.

If these approaches are taken into account, the following preferred switching condition results according to claim 5:
Fuel consumption value> (fuel consumption value * rich time * nitrogen oxide raw mass flow value) / nitrogen oxide storage capacity

The fuel consumption value as well as the fuel consumption value and the nitrogen oxide storage capacity are given in grams, while the rich time in seconds and the nitrogen oxide raw mass flow value in grams per se customer is specified.

According to claim 6, the discharge time in fat mode for each of the discharges is roughly constant, so the fat time from the sum of the easily detectable number of discharges leaves. This approximately the same discharge time results from the fact that at a Discharge most of the amount of fuel to withdraw oxygen needed from the oxygen storage and only one against it Smaller amount of fuel to withdraw nitrogen oxides from the Nitric oxide storage catalyst is needed. Because the oxygen storage very early in lean operation Completely is loaded, it is always full when unloaded, so that fluctuations in the amount of nitrogen oxides stored, z. B. by aging of the nitrogen oxide storage catalyst, hardly the discharge time and the required Impact fuel quantity for unloading.

According to claim 7, the fuel consumption value and / or the additional fuel consumption value and / or the nitrogen oxide raw mass flow value depending on load and / or speed determined in a simple way. This means that e.g. B. up to the preferably current value to be recorded via the nitrogen oxide storage capacity the nitrogen oxide storage catalytic converter all other for the determination of Changeover condition required values from the engine control unit in the simplest way from predefined maps depending on certain operating points and ranges, preferably depending on a particular Load and / or speed can be determined.

Only the current value as a statement about the Nitrogen oxide storage capacity the nitrogen oxide storage catalyst is preferably learned depending on the operating point. For this purpose, it is provided according to claim 8 that the nitrogen oxide mass flow upstream of the nitrogen oxide storage catalytic converter and / or the nitrogen oxide mass flow after the nitrogen oxide storage catalytic converter in each case over an identical period of time be integrated, whereby to determine the switching time from the storage phase to the unloading phase and thus from the lean operating area to the rich operating range at least from the integral value of the Nitrogen oxide mass flow before and / or after the storage catalyst and / or the changeover time in each case when a predefinable discharge changeover condition is met in a first stage to determine the degree of aging of the storage catalytic converter a switchover operating point as a function of an instantaneous operating temperature is determined at the time of switching. Then the respective switchover operating point in a second stage to determine the degree of aging of the storage catalytic converter with an over a predeterminable temperature window, in particular with regard to storage catalytic converter capacity field optimized for fuel consumption, through a multitude of individual operating points for one new and an aged storage catalyst is formed, compared. This represents a within the storage catalyst capacity field changeover operating point is not below the minimum nitrogen oxide storage capacity but the change across from the previous operating point as a measure of the storage catalytic converter aging. A switchover operating point leaving the storage catalyst capacity field , on the other hand, is below the minimum nitrogen oxide storage capacity. With a procedure of this type, it is therefore particularly easy Way a current detection of the value of nitrogen oxide storage capacity of the nitrogen oxide storage catalytic converter depending on the operating point consideration the degree of aging and / or the sulfurization of the nitrogen oxide storage catalytic converter be determined.

After is particularly preferred Claim 9 provided that to determine the switching time a relative nitrogen oxide slip from the storage phase to the discharge phase as the difference between that in the nitrogen oxide storage catalyst flowed Nitrogen oxide mass flow and that from the nitrogen oxide storage catalyst emanated Nitrogen oxide mass flow determined based on the injection time is such that the quotient of the integral values of the nitrogen oxide mass flow before and after the nitrogen oxide storage catalyst also in a relative relationship with a specifiable degree of nitrogen oxide conversion derived from an exhaust gas limit value is brought so that when this predefinable switchover condition is present switching from the storage phase to the unloading phase optimized with regard to fuel consumption and storage potential Switching point carried out becomes.

According to claim 10 can further be provided that the storage catalyst capacity field related to the temperature window on the one hand by a boundary line for a new storage catalytic converter and on the other hand, by a borderline for a border aging state representing aged storage catalyst is limited. there the temperature window preferably comprises temperature values between in about 200 ° C and at about 450 ° C.

The invention is described below closer to a drawing explained.

Show it:

1 1 shows a schematic representation of a load and speed-dependent characteristic map from which a fuel consumption value in the lean operating range can be read at a specific operating point,

2 1 shows a schematic representation of a load and speed-dependent characteristic map from which the fuel consumption value for a discharge in the rich operating range can be read,

3 a schematic representation of a depending on the exhaust gas mass flow and the temperature The characteristic map from which a current value for the nitrogen oxide storage quantity can be read into a nitrogen oxide storage catalytic converter for a specific operating point, and

4 is a schematic representation of a load and speed-dependent map from which a nitrogen oxide raw mass flow value can be read at a certain operating point.

In 1 an empirically determined load and speed-dependent characteristic diagram is shown schematically, from which a fuel consumption value can be taken as a fuel consumption quantity for a specific operating point. Analogously to this, the 2 depending on the load and the speed at a certain operating point, an additional fuel consumption value can be read as an additional fuel consumption amount for a discharge. From the map of the 3 a current value of the nitrogen oxide storage capacity of a nitrogen oxide storage catalytic converter can be taken at a specific operating point, that is to say depending on its degree of aging and sulfurization, while the 4 a load and speed-dependent raw nitrogen oxide emission value can be taken from a specific operating point. These values, which can be derived from these characteristic fields at a specific operating point, are recorded by an engine control unit, with an approximately constant rich time being required for each of the discharges due to an essentially constant fuel consumption for a discharge. Based on the easily ascertainable number of discharges that took place during a certain operating range or operating cycle, the engine control unit can also easily calculate a rich time, whereby the discharges in an operating cycle also result in a certain additional fuel consumption due to the rich operation. These values, which are easily ascertainable by the engine control, are then used in the following equation:
Fuel consumption value> (fuel consumption value * rich time * nitrogen oxide raw mass flow value) / nitrogen oxide storage capacity

As soon as this changeover condition is met, there the engine control unit a lean operation and thus switching between the lean operation area and the homogeneous operating area as this ensures is that the additional fuel consumption during the discharge by the Saving fuel during exceeded the lean phase becomes. If, on the other hand, this changeover condition is not fulfilled, then locks the engine control unit the lean operating area, since this then leads to lean operation no fuel saving is achieved and therefore compared to homogeneous operating area where an essentially stoichiometric Implementation takes place, no consumption advantages are brought out can.

Claims (10)

Method for operating an internal combustion engine of a vehicle, in particular a motor vehicle, with a first operating area as a lean operating area, in which the internal combustion engine is operated with a lean mixture which has an excess of air and thus an excess of oxygen, and in which the nitrogen oxides generated by the internal combustion engine are placed in a nitrogen oxide storage catalytic converter are stored, in order to discharge the nitrogen oxide storage catalytic converter by means of an engine control unit from the lean operating area to a rich operating area, in which the internal combustion engine is operated with a rich mixture having a lack of air, and in which the nitrogen oxides stored in the nitrogen oxide storage catalytic converter during the lean operating area are discharged the nitrogen oxide storage catalytic converter are stored, and with a second operating area as a homogeneous operating area in which the internal combustion engine with an essentially stoic hiometric homogeneous mixture (lambda = 1) is operated, the switching between the lean operating range and the homogeneous operating range being carried out by the engine control unit as a function of an operational load and / or speed requirement when a predefinable changeover condition is reached, and wherein the engine control unit switches before Lean operating range is switched to the homogeneous operating range first for discharging the nitrogen oxide storage catalytic converter into the rich operating range, characterized in that the switchover condition between the lean operating range and the homogeneous operating range as a function of an operating point-dependent fuel consumption value stored in a map in the lean operating range, one in one Map stored operating point-dependent fuel consumption value for a discharge in the rich operating range, a lean period as a lean operating period and a rich period as F The operating period is determined in such a way that the engine control unit blocks a switchover to the lean operating range if the values related to one another for a specific predeterminable operating range show that the additional fuel consumption quantity for the discharges in this operating range is equal to or greater than the fuel -Minimum consumption amount due to lean operation in this operating range, and that the engine control unit enables lean operation and thus switching between the lean operating range and the homogeneous operating range if the values related to one another for a specific predefinable loading drive range result that the additional fuel consumption for the discharges in this operating area is smaller than the reduced fuel consumption amount due to lean operation in this operating area. A method according to claim 1, characterized in that the engine control unit a lean operation and thus switching between the lean operation area and releases the homogeneous operating range if the following switchover condition is met: Fuel under-value * Lean period> Fuel consumption value * Fat time A method according to claim 1 or 2, characterized in that that the lean time from the engine control unit as a function of one in one Map of stored operating point-dependent nitrogen oxide raw mass flow value and a preferably currently recorded value about the nitrogen oxide storage capacity of the Nitrogen oxide storage catalyst is determined. A method according to claim 3, characterized in that the lean period is calculated from the quotient of the nitrogen oxide storage capacity value and of the nitrogen oxide raw mass flow value. Method according to one of claims 2 to 4, characterized in that that the engine control unit has a Lean operation and thus switching between the lean operation area and releases the homogeneous operating range if the following switching condition Fulfills is: Fuel economy value> (fuel economy value * rich time * Nitrogen oxide raw mass flow value) / nitrogen oxide storage capacity Method according to one of claims 1 to 5, characterized in that that the discharge time in the fat mode for each of the discharges approximately is constant so that the fat time is the sum of the detectable Number of discharges calculated. Method according to one of claims 1 to 6, characterized in that that the fuel economy and / or the fuel economy and / or a nitrogen oxide raw mass flow value determined depending on the load and / or speed become. Method according to one of claims 4 to 7, characterized in that that the currently recorded value above the nitrogen oxide storage capacity of the nitrogen oxide storage catalytic converter depending on the operating point consideration the degree of aging and / or the sulfurization of the nitrogen oxide storage catalytic converter is determined in such a way that the nitrogen oxide mass flow before Nitrogen oxide storage catalyst and / or the nitrogen oxide mass flow after the nitrogen oxide storage catalyst each integrated over an equal period of time become, that to determine the time of switching from Injection phase to the discharge phase and thus from the lean operating area to the rich operating range at least from the integral value of the nitrogen oxide mass flow before and / or after the storage catalytic converter and / or the changeover time each time it is fulfilled a predeterminable discharge switchover condition in a first stage to determine the degree of aging of the storage catalytic converter Switchover operating point as a function of an instantaneous operating temperature is determined at the time of switching, and that the respective Switchover operating point in a second stage to determine the Degree of aging of the storage catalytic converter with an over Temperature window, predeterminable, in particular with regard storage catalytic converter capacity field optimized for fuel consumption, through a multitude of individual operating points for a new one and an aged storage catalyst is formed is so that one within the storage catalyst capacity field horizontal switchover operating point not below the minimum Nitrogen oxide Speichertähigkeit represents but the change compared to the previous operating point as a measure of the storage catalytic converter aging represents, and that a leaving the storage catalyst capacity field Shift operating point below the minimum nitrogen oxide storage capacity represents. A method according to claim 8, characterized in that to determine the switchover time from the injection phase a relative nitrogen oxide slip as the difference between the nitrogen oxide mass flow flowing into the nitrogen oxide storage catalytic converter and the nitrogen oxide mass flow flowing out of the nitrogen oxide storage catalyst is determined in each case based on the injection time, that the quotient of the integral values of the nitrogen oxide mass flow and after the nitrogen oxide storage catalyst also in a relative relationship with a specifiable degree of nitrogen oxide conversion derived from an exhaust gas limit value is brought so that when this predetermined switching condition is met Switching from the storage phase to the unloading phase with regard to Fuel consumption and storage potential optimized switching time carried out becomes. A method according to claim 8 or 9, characterized in that the storage catalyst capacity field based on the temperature window on the one hand by a boundary line for a new storage catalyst and on the other hand by a Grenzli is never limited for an aged storage catalytic converter which represents a limit aging state, the temperature window preferably comprising temperature values between approximately 200 ° C. and approximately 450 ° C.