EP0864735A1 - Method of operating a combustion engine in an innocuous manner - Google Patents

Abstract

A procedure for operating an IC engine to be free of toxic emissions has at least one operating mode with a lean air/fuel ratio and one operating mode with a stoichiometric air/fuel ratio. Measures for reducing the NOx emissions are provided. The NOx reduction is effected during the operation in the stoichiometric mode in a previously given speed/torque range by timing adjustment from the point of optimum efficiency in the direction of retard. In the operating mode with a lean mixture, the timing is adjusted for optimum efficiency. The engine is run in a second speed/torque range with a lean mixture with a lower speed or torque than the first range and the two ranges are chosen so that the engine during normal operation is run more frequently in the second than in the first range.

Description

The invention relates to a method for low-pollution operation an internal combustion engine with at least one operating mode with a lean air / fuel ratio and one Operating mode with essentially stoichiometric air / fuel ratio, in the measures to reduce the Raw nitrogen oxide emissions are provided.

To comply with the legally prescribed emission limit values of motor vehicles, in particular the nitrogen oxide limit values, are a variety of measures, both for reduction nitrogen oxide formation during the combustion process (Raw nitrogen oxide emissions) as well as subsequent exhaust gas cleaning (e.g. by a three-way catalytic converter or a Nitrogen oxide trap).

A known measure to reduce raw nitrogen oxide emissions provides a device for exhaust gas recirculation (Exhaust Gas Recirculation) in certain engine operating areas some of the exhaust gases return to the combustion process is supplied, which leads to a reduction in the nitrogen oxide content comes in the exhaust.

The exhaust gas recirculation device is a relatively complex System that makes the engine / exhaust system more complicated, becomes more maintenance-intensive, more expensive and heavier.

The invention has for its object a method of type mentioned at the outset for reducing the nitrogen oxide raw emissions especially in the stoichiometric operating mode create, with the use of an exhaust gas recirculation device can be dispensed with.

According to the invention this object is achieved in that the Nitrogen oxide reduction during operation in the stoichiometric Mode in a specified speed / torque range an ignition timing adjustment from the most efficient time in the "late" direction, and in the operating mode with a lean mixture, the ignition timing is essentially optimal is set.

By the ignition timing in the direction of "late" affects the combustion process in the individual cylinders so that the nitrogen oxide raw emissions even without the use of a Exhaust gas recirculation device with regard to the exhaust gas limit values can be reduced sufficiently. This measure can be significantly compared to the exhaust gas retraction implement less effort since the ignition timing in the widespread electronic ignition systems can be freely determined by an electronic motor control can.

However, such a "late adjustment" of the Ignition point in principle to a deterioration of the Engine efficiency. Therefore, in an appropriate design the invention provide that the internal combustion engine in a compared to the first predetermined speed / torque range lower speeds and / or torques comprehensive second speed / torque range with a lean Mixture is operated and that the internal combustion engine during normal operation of the internal combustion engine having motor vehicle more often in this second than is operated in the first speed / torque range. In order to the measure according to the invention for nitrogen oxide reduction none has an adverse impact on fuel economy So be provided that the engine is as large as possible second speed / torque range with a lean mixture is operated so that the efficiency deterioration in the first area in terms of total fuel consumption hardly affects.

In addition to the speed / torque ranges mentioned Expediently, further speed / torque ranges are provided in which the engine e.g. with a fat mixture is operated to meet the speed or torque requirements e.g. to be sufficient in full load operation.

The invention is illustrated below with reference to the drawing explained in more detail.

The single figure shows a schematic speed / torque diagram for controlling a motor vehicle internal combustion engine according to the inventive method, the engine torque M being plotted on the Y axis compared to the engine speed n on the X axis.

A motor vehicle, not shown, has a known Have electronic engine control. The engine control determined from the input variables of various sensors the current engine speed and the currently requested torque. Depending on these sizes will be in a known manner on the basis of a predefined table memory or on the basis of predefined functional relationships different engine parameters determines, in particular the position of in the cylinder intake systems asymmetrical swirl flaps, a requirement for the composition of the air / fuel mixture (lean, stoichiometric or rich) and ignition timing default values for the individual cylinders.

With the swirl flaps (Swirl Control Valves) the flow conditions influenced in the cylinder intake port in such a way that the combustion stability especially in lean air / fuel ratios is improved so that the engine saves fuel with a lean air / fuel ratio can be operated. Through the flow resistance however, the swirl flap becomes the maximum Air / fuel throughput limited, which is why at higher speeds / torques the swirl flaps by means of an actuator brought from their operative position into a starting position will.

Bereich a:

Betrieb des Motors mit magerem Gemisch, wobei zur Gewährleistung einer stabilen Verbrennung mit möglichst magerem Gemisch die Drallklappe in ihre Wirkposition gebracht wird;

Bereich b:

Betrieb des Motors mit magerem Gemisch bei höheren Drehmomenten und/oder Drehzahlen, wobei die Drallklappe zur Verminderung von Strömungsverlusten in ihre Ausgangsposition gebracht wird;

Bereich c:

Betrieb des Motors mit im wesentlichen stöchiometrischem Luft-/Kraftstoffverhältnis und mit in der Ausgangsposition befindlicher Drallklappe;

Bereich c*:

Betrieb des Motors wie im Bereich c, wobei jedoch der Zündzeitpunkt zur Reduktion der Stickoxidemissionen vom wirkungsgradoptimalen Zündzeitpunkt in Richtung spät verstellt wird;

Bereich d:

stöchiometrischer Betrieb des Motors mit in Wirkposition befindlicher Drallklappe (Schiebebetrieb);

Bereich e:

Betrieb mit angereichertem (fettem) Gemisch und in der Ausgangsposition befindlicher Drallklappe (Vollastanreicherung).

According to the figure, six speed / torque ranges a, b, c, c *, d, e can be distinguished, the limit curves of which are denoted by 1, 3, 4, 5 and 6, respectively. The speed / torque ranges are explained in more detail below:

Area a:

Operation of the engine with a lean mixture, the swirl flap being brought into its active position to ensure stable combustion with a mixture that is as lean as possible;

Area b:

Operation of the engine with a lean mixture at higher torques and / or speeds, the swirl flap being brought into its starting position in order to reduce flow losses;

Area c:

Operating the engine with a substantially stoichiometric air / fuel ratio and with the swirl flap in the initial position;

Area c *:

Operation of the engine as in area c, but with the ignition timing for reducing the nitrogen oxide emissions being adjusted from the ignition timing which is optimal for efficiency;

Area d:

stoichiometric operation of the motor with the swirl flap in the active position (push operation);

Area e:

Operation with enriched (rich) mixture and in the starting position swirl flap (full load enrichment).

Except for the area c *, the internal combustion engine is in all remaining speed / torque ranges with essentially efficiency-optimized ignition timing operated. The area c * comprises, as can be seen from the figure, a relatively small one Speed / torque range. Within the comparatively large speed / torque ranges a, b, the engine is in lean mode operated in which no measures to reduce the Raw nitrogen oxide emissions are required. With conventional lean-burn engines can the area c * be approximately within a Windows between 3000 and 5000 revolutions per minute and a torque between 50 and 80 Nm. The optimal one Size depends on the specific design of the internal combustion engine and is preferably determined experimentally.

In conventional internal combustion engines that only use be operated stoichiometric or fat mixture, would need measures to reduce raw nitrogen oxide emissions also take place in parts of areas a and b. With a conventional one Engine would be a late adjustment as a measure to Nitrogen oxide reduction with a relatively large additional fuel consumption connected so that with these conventional Internal combustion engines use an exhaust gas recirculation device would be preferable.

As with the example curve 2, the driving resistance in fifth gear becomes clear, the engine becomes relative rarely operated in the c * range, namely only for certain Acceleration processes. As a result, affects the deterioration in efficiency in the c * range with regard hardly affect the total fuel consumption.

Claims (2)

Process for low-pollution operation of an internal combustion engine with at least one operating mode with a lean Air / fuel ratio and an operating mode with essentially stoichiometric air / fuel ratio, in the measures to reduce the Nitrogen oxide emissions are provided, characterized in that that the nitrogen oxide reduction during operation in stoichiometric mode in a given speed / torque range (c *) by an ignition timing adjustment from the optimum time in the direction of efficiency "late" is effected, and in the operating mode with a lean mixture the ignition timing is essentially optimal is set. A method according to claim 1, characterized in that the internal combustion engine in a predetermined compared to the first Speed / torque range (c *) lower Speeds and / or torques encompassing a second speed / torque range (a, b) with a lean mixture is operated and that the first and second speed / torque range are chosen so that the internal combustion engine during normal operation of the internal combustion engine having motor vehicle more often in this second operated as in the first torque / speed range becomes.

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