EP1079079B1 - Engine control system for a diesel engine - Google Patents

Description

The invention relates to a motor control for a Diesel engine, in whose exhaust system a storage catalytic converter is arranged with the characteristics of the preamble of Claim 1.

From DE 197 50 226 Cl an operating method for a diesel engine is known, in which the diesel engine, in whose exhaust gas line a NO _x storage catalytic converter is arranged, in a superstoichiometric operation (lean operation) and in a substoichiometric operation (rich operation) can be operated. In lean operation of the diesel engine, the NO _x salts contained in its exhaust gases are stored in the NO _x storage catalyst by adsorption. In this adsorption or storage operation, a large part of the nitrogen oxides emitted by the diesel engine can be removed from the exhaust gas. In order to maintain the storage capacity of the NO _x storage catalytic converter, it is necessary to remove the stored nitrogen oxides again from the NO _x storage catalytic converter. For this purpose, the diesel engine is switched over to the rich operation for a certain time, in which the unburned diesel fuel acts as a reducing agent for the adsorbed in the NO _x storage NO _x salts, which reduces the nitrogen oxides for desorption from the NO _x storage catalytic converter , During this desorption operation or regeneration operation, the stored nitrogen oxides are removed from the NO _x storage catalyst.

In the case of sulfur-containing diesel fuels, during the lean operation of the diesel engine, in addition to the desired adsorption of nitrogen oxides, undesired adsorption of sulfur oxides (SO _x ) contained in the exhaust gas occurs. These sulfur oxides are formed by combustion of sulfur-containing hydrocarbons present in the diesel fuel and are stored in the storage catalyst as SO _x salts, in particular as sulfate. However, these SO _x salts (sulfates) are thermodynamically more stable and therefore have a higher chemical binding energy than the NO _x salts (nitrates), with the result that a regeneration process described above, although sufficient to desorb the adsorbed nitrogen oxides, but not sufficient to desorb the adsorbed sulfur oxides. In this way, it comes in the course of time to an accumulation of sulfur oxides in the NO _x storage catalytic converter, through which the storage capacity of the NO _x storage catalyst for nitrogen oxides gradually decreases. The increasing accumulation of sulfur oxides in the NO _x storage catalyst can lead to irreversible damage in this case and is generally referred to as "sulfur poisoning" of the NO _x storage catalyst.

From EP 0 580 389 A1 an engine control of the type mentioned is known which allows operation of a diesel engine in a storage mode in which NO _x salts and SO _x salts are absorbed in a storage catalytic converter from the exhaust gas of the diesel engine an exhaust line of the diesel engine is arranged. The known engine control also allows operation of the diesel engine in a regeneration mode in which a reducing exhaust gas is generated, whereby at least the NO _x salts are desorbed from the storage catalyst. Furthermore, the known engine control allows operation of the diesel engine in a desalting mode in which a higher temperature is generated in the storage catalyst than in the storage mode and regeneration mode and in which alternately a reducing exhaust gas and an oxidizing exhaust gas will be generated, whereby at least the SO _x Salts are desorbed from the storage catalyst.

Due to the elevated temperature, it is possible in conjunction with a reducing exhaust gas, salts with relatively high chemical binding energy, such. B. SO _x , desorb from the storage catalyst. By the oxidizing exhaust gas then the desorbed salt can be oxidized, so that on the one hand prevents re-adsorption in the storage catalyst and on the other hand, the formation of harmful secondary products such. B. H ₂ S, can be avoided. It has been found that an effective desulfating a NO _x storage catalytic converter is carried out with the aid of the desalting carried out mode so that sulfur poisoning of the NO _x storage catalytic converter can be prevented.

From EP 1 050 675 A1, EP 1 105 629 A0 and the EP 1 183 453 A0 are further generic motor controls However, according to Art. 54 (3) EPC, they are only for the question novelty for like-named Contracting States are.

The present invention deals with the problem for a motor control of the type mentioned a to provide improved embodiment, in particular a has increased efficiency and effectiveness.

According to the invention, this problem is solved by the subject matter of independent claim solved. Advantageous embodiments are the subject of the dependent claims.

For a diesel engine, which in storage mode is lean of stoichiometry with λ values> 1, the Inventive embodiment in which the λ-values in Desalting mode are always smaller than in the storage mode, as particularly advantageous. A lean operated Diesel engine usually operates with λ values of 1.3 to 10. In contrast, the inventive control causes in desalination mode, operation with λ values <1.3. Preferably, the inventively designed works Diesel engine in desalination mode with λ-values <1,1, in particular ≤ 1.05, e.g. λ = 1.03.

Additionally or alternatively, in a diesel engine operating in the Regeneration mode substoichiometric, d. H. with λ <1, is operated, according to the invention provided that the Engine control according to the invention the diesel engine in Desalting mode is operated so that the λ values are always greater are as in the regeneration mode of the diesel engine. to Denitratisierung work in the conventional diesel engines Regeneration mode with λ values of 0.75 to 0.85. in the In contrast to this, the control according to the invention actuates the Diesel engine so that this in desalting λ values which are always greater than 0.85. Preferably works according to the invention operated diesel engine in Desalting mode with λ values ≥ 0.88, in particular with λ ≥ 0.9, e.g. λ = 0.97.

When the control according to the invention the diesel engine in Desalting mode, thus preferably takes place permanent change of operating phases with about λ = 1.05 and about λ = 0.95. It has been shown that such an operation with λ jumps around the stoichiometric operating point (λ = 1) is particularly advantageous for the implementation of a Desalination, in particular desulfation.

A particularly advantageous embodiment is characterized formed that the diesel engine alternately in desalination mode superstoichiometric, d. H. with an air-fuel ratio λ> 1, and substoichiometric, d. H. with a Air-fuel ratio λ <1 is operated. By the Stoichiometric operation becomes the oxidizing Exhaust gas generated during the stoichiometric operation of the causing reducing exhaust gas.

Alternatively to the aforementioned development, the diesel engine Permanently stoichiometric in desalting mode, ie with λ <1, are operated, in which case one between the Diesel engine and the storage catalytic converter to the exhaust system connected secondary air supply alternately on and is turned off. With secondary air supply switched off is in the storage catalytic converter then from the diesel engine in substoichiometric operation produced, reducing acting Exhaust gas available while switched on Secondary air supply of the supplied oxygen to the exhaust gas in the Storage catalyst gives the desired oxidizing effect. In particular, this then points into the storage catalytic converter introduced exhaust gas secondary air mixture a superstoichiometric air-fuel ratio.

The temperature in the storage catalyst is during the Desalting mode preferably at least 500 to 600 ° C to the To support desalination. Preferably, the change takes place between reducing and oxidizing atmosphere in the Storage catalyst with a frequency of about 1 to 10 Hz instead of. An increase in temperature, for example, by a late fuel post-injection can be achieved.

It is particularly advantageous if the controller operates the diesel engine only following an operation in the regeneration mode in the desalting mode, ie, that a desorption of salts with relatively high chemical binding energy, such. B. SO _x , is only carried out when previously the salts with relatively low chemical binding energy, such as. B. NO _x , have been desorbed from the storage catalyst. This procedure allows a particularly efficient desorption of the salts with relatively high chemical binding energy.

Other important features and advantages of the invention Method emerge from the subclaims, from the Drawing and from the associated figure description based the drawing.

It is understood that the above and the hereinafter to be explained features not only in the each specified combination, but also in others Combinations or alone can be used without the To leave the scope of the present invention.

Fig. 1 zeigt eine schematische Prinzipdarstellung einer Brennkraftmaschine, die nach dem erfindungsgemäßen Verfahren betrieben werden kann.

Preferred embodiments of the invention are illustrated in the drawings and will be explained in more detail in the following description.

Fig. 1 shows a schematic diagram of an internal combustion engine, which can be operated by the method according to the invention.

According to FIG. 1, an exhaust gas turbocharger 1 sucks on its Compressor inlet side fresh air according to the arrow a on. Instead of an exhaust gas turbocharger 1 can also another Charger, z. B. a mechanical loader and / or a so-called "booster". The sucked Fresh air flows through at a correspondingly increased pressure Heat exchanger 2, which serves as intercooler, and reached a throttle point 3 in a suction line 4 a Diesel engine 10. In throttle 3 is a throttle 5 arranged, via an actuator 6 of a power-operated actuator 7 is actuated. After Throttle 3 first passes through the fresh air Suction pipe 16 and then reaches an air-collecting chamber 8, from where from them via separate inlet channels 9 the combustion areas of the Diesel engine 10 is supplied. In the inlet channels 9 are each individual throttle valves 11 are arranged, the according to the embodiment via a common Actuator 12 of a servo-operated actuator 13th are operable.

Downstream of the diesel engine 10 are those during combustion formed exhaust gases in an exhaust gas collection chamber 14 with a Exhaust gas recirculation line 15 in the intake manifold 16, d. H. here after the throttle 3 and in front of the air collection chamber 8 in the Air intake 4 opens. In another embodiment can the exhaust gas recirculation line 15 also upstream of the Throttle 3 to the intake of the diesel engine 10th be connected.

In the mouth region of the exhaust gas recirculation line 15 is in Intake manifold 16, an exhaust gas recirculation valve 17 is arranged, the via an actuator 18 of a power-operated Actuator 19 can be actuated. In the illustrated Embodiment is the exhaust gas recirculation line 15 with a heat exchanger 20 in the heat exchange, so that optionally achieved cooling of the recirculated exhaust gas can be.

The turbine inlet section and / or the turbine flowing exhaust gas flow is with the help of a Actuator 21 changeable, that of a power-operated Actuator 22 is actuated. After flowing through the Turbine of the exhaust gas turbocharger 1, the exhaust gas according to the Arrow b an exhaust purification device 28 fed, the in Fig. 1 by a dashed lines shown Frame is marked and described in more detail below becomes.

The diesel engine 10 is powered by a motor control or Motor control 23 controlled or regulated, what this over Lines with the corresponding units of the diesel engine 10 is connected. For example, in Fig. 1, a line 24th shown, which the engine control with a Injection 25 of the diesel engine 10 connects. Further Lines 34, 35, 36 and 37 connect the controller 23 with the Actuators 22, 13, 19 and 7.

The exhaust gas purification device 28 has an adsorber or storage catalytic converter 29, which is preferably designed as a NO _x storage catalytic converter. The exhaust gas purification device 28 further comprises an oxidation catalyst 30 arranged upstream or downstream of the NO _x storage catalytic converter 29. The two catalytic converters 29 and 30 are connected to one another by at least one possibly thermally insulated pipe 31 which is, for example, air-gap or mat-insulated. Downstream of the storage catalytic converter 29, a first λ probe 32 is arranged in the exhaust line of the diesel engine 10, which is connected via a corresponding signal line 33 to the controller 23. Furthermore, downstream of the storage catalytic converter 29, a first temperature sensor 38 is arranged, which is connected via a signal line 39 to the controller 23. In addition, upstream of the storage catalytic converter 29, a second λ probe 40 and a second temperature sensor 41 are arranged, which also communicate with the controller 23 in a corresponding manner. In addition, further, not shown λ probes and temperature sensors may be housed in the exhaust line of the diesel engine 10. In addition, at least one NO _x sensor 42 is provided which communicates downstream of the storage catalytic converter 29 with the exhaust line and is also connected to the controller 23.

Furthermore, a secondary air feed 43 may be provided be the fresh air over one to the exhaust system connected supply line 44 downstream of the diesel engine 10, here downstream of the turbocharger 1, and upstream of the Storage catalytic converter 29 introduces into the exhaust system. The Amount of the supplied secondary air is via a controllable Supply valve 45 adjustable via a corresponding Control line 46 is connected to the motor controller 23. The secondary air can, for example, from the pressure side of the Be exhausted exhaust gas turbocharger 1. Likewise, the Secondary air available in another suitable way be put.

The storage catalytic converter 29 may be provided with a heating device 27 be equipped in Fig. 1 by a in the Storage catalytic converter 29 symbolizes integrated heating coil is.

The control according to the invention operates as follows:

For normal operation of the diesel engine 10, the controller 23 operates the diesel engine 10 to operate in a storage mode in which the diesel engine 10 operates more than stoichiometrically. In such a lean operation thus prevails for the combustion of the diesel fuel, an excess of atmospheric oxygen, so that λ> 1 applies. The diesel engine 10 is operated in its storage mode with λ-values of 1.3 to 10, wherein the change of the λ-value can be realized by varying the injected amount of fuel. In the exhaust gases of the diesel engine 10 are mainly salts with relatively low chemical binding energy, usually NO _x , as well as significantly less salts with relatively high chemical binding energy, such as. Eg SO _x . As it flows through the NO _x storage catalytic converter 29, both the NO _x salts and the SO _x salts are adsorbed by the storage catalytic converter 29. Over time, the storage capacity of the storage catalytic converter 29 decreases, so that a regeneration of the storage catalytic converter 29 must be performed. The time at which such a regeneration must be performed can be determined by means of calculation models or, for example, with the aid of the NO _x sensor 42.

To perform a regeneration, the controller 23 switches the operation of the diesel engine 10 to a regeneration mode in which the diesel engine 10 operates at a substoichiometric ratio of atmospheric oxygen and fuel. In this "rich operation" no complete combustion of the injected fuel can be realized in the diesel engine 10, so that unburned fuel is still contained in the exhaust gas. The diesel engine 10 is operated in its regeneration mode, for example, with a λ value of 0.85. The unburned fuel in the exhaust gas serves as a reducing agent, so that the exhaust gas supplied to the storage catalytic converter 29 has a reducing effect. Due to this reducing atmosphere, the nitrates stored in the storage catalyst 29 can be desorbed and transported away. The regeneration mode is operated until the nitrates adsorbed in the storage catalyst 29 are almost completely desorbed. Since the sulfates have a higher chemical binding energy relative to the nitrates, they are thermodynamically more stable, so that during denitrification or denitration in the regeneration mode there is virtually no desorption of the SO _x salts. However, the occupied by the sulfates surface of the storage catalyst 29 is no longer available for storing the nitrates. Over time, the salts accumulate with relatively high chemical binding energy, so usually the sulfates in the storage catalytic converter 29 more and more, causing its NO _x storage capacity decreases more and more. From a certain threshold, the controller 23 decides that desulfurization or desulfation of the NO _x storage catalyst 29 must be performed.

Prior to such desulfation, the controller 23 causes First, a denitrification by the operation of the Diesel engine 10 is switched to the regeneration mode.

Upon completion of the denitration, the controller 23 switches the diesel engine operation either directly on one Desalting mode or initially back to the storage mode and then to the desalting mode. In this Desalting mode becomes the storage catalyst 29 alternately reducing exhaust gas and oxidizing exhaust gas fed.

In a first alternative, this alternating occurs Change between reduction and oxidation in that constant between a lean operation and a fat operation of the Diesel engine 10 is switched. Please note that the λ values in the fat operation of the desalting mode always are greater than the λ values in the rich mode of the Regeneration mode. For example, the diesel engine 10 is in a fat operating phase of desalting mode with λ = 0.88 or 0.90 or 0.97 operated. Furthermore, the λ values are in Lean operation of the desalting mode always smaller than the λ values in lean operation of the storage mode. For example the diesel engine 10 operates in the lean operating phases of the Desalting mode with λ = 1,1 or 1,05 or 1,03. In order to Storage catalyst 29 to increase the temperature can For example, the heating coil 27 are activated. Likewise is It is possible by a targeted late post-injection of Fuel a temperature increase in the exhaust line, in particular in the storage catalytic converter 29.

According to a second alternative, the alternating Change between oxidizing exhaust gas and reducing acting exhaust gas can be achieved in that the diesel engine 10 is permanently operated fat in desalting mode, wherein alternately the secondary air supply 43 is turned on and is switched off. With secondary air supply switched on 43 is then so much atmospheric oxygen in the rich exhaust introduced that upstream of the storage catalyst 29th gives a lean exhaust gas composition.

By means of this alternately reducing and oxidizing atmosphere at a generally elevated temperature in the storage catalyst 29, it is possible to reduce the salts in the reduction phases and to oxidize them in the oxidation phases. Harmful secondary emissions, such. B. H ₂ S, can be avoided. It is clear that the storage catalytic converter 29 to a certain extent also has an oxidation and reduction function or reducing and oxidizing properties for realizing the above-described reduction and oxidation processes.

Claims (8)

1. Engine control system, which enables operation of a diesel engine (10) in a storage mode in which, from the exhaust gas of the diesel engine (10), first salts with relatively lower chemical binding energy such as NO_x and second salts with relatively higher chemical binding energy such as SO_x are adsorbed in a storage catalyser (29), which is arranged in an exhaust gas conduit of the diesel engine (10),

   such that the engine control unit (23) enables the diesel engine (10) to be operated in a regeneration mode in which exhaust gas with a reducing action is produced, by virtue of which at least the first salts are desorbed from the storage catalyser (29),

   such that the engine control unit (23) enables the diesel engine (10) to be operated in a salt-release mode in which a higher temperature is produced in the storage catalyser (29) than during the storage mode and the regeneration mode, and in which, in alternation, exhaust gases with a reducing and with an oxidising action are produced, by virtue of which at least the second salts are desorbed from the storage catalyser (29),

   characterised in that

   in the storage mode the diesel engine (10) is operated above-stoichiometrically (with air-fuel ratio λ > 1) and the λ-values during the salt-release mode are always lower than during the storage mode, and/or

   in the regeneration mode the diesel engine (10) is operated below-stoichiometrically (with air-fuel ratio λ < 1) and the λ-values during the salt-release mode are always higher than during the regeneration mode.
2. Engine control system according to Claim 1,
   characterised in that
   in the salt-release mode the λ-values are always lower than 1.3.
3. Engine control system according to Claims 1 or 2,
   characterised in that
   in the salt-release mode the λ-values are always higher than 0.85.
4. Engine control system according to any of Claims 1 to 3,
   characterised in that
   in the salt-release mode, the diesel engine (10) is operated in alternation in the above-stoichiometric mode (with λ > 1) and in the below-stoichiometric mode (with λ < 1).
5. Engine control system according to any of Claims 1 to 3,
   characterised in that
   in the salt-release mode, the diesel engine (10) is operated in the below-stoichiometric mode (with λ < 1) and a secondary air inlet (43) connected to the exhaust conduit between the diesel engine (10) and the storage catalyser (29) is opened and closed in alternation.
6. Engine control system according to any of Claims 1 to 5,
   characterised in that
   in the salt-release mode, the change between exhaust gases with reducing and with oxidising actions takes place with a frequency of about 1 to 10 Hz.
7. Engine control system according to any of Claims 1 to 6,
   characterised in that
   the temperature in the storage catalyser (29) during the salt-release mode is higher than 500°C.
8. Engine control system according to any of Claims 1 to 7,
   characterised in that
   the diesel engine (10) is only operated in the salt-release mode after it has been operated in the regeneration mode.

Images