EP4352351A1

EP4352351A1 - Method for heating a catalytic converter

Info

Publication number: EP4352351A1
Application number: EP22738337.9A
Authority: EP
Inventors: Christopher Gessenhardt; Karsten Michels
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2021-06-09
Filing date: 2022-06-08
Publication date: 2024-04-17
Also published as: CN117255892A; WO2022258667A1; US20240102427A1; DE102021114777A1

Abstract

The invention relates to a method of heating a catalytic converter (40) of an internal combustion engine (1), the method comprising the steps of: igniting the gas charge in one of the cylinders (22, 24, 26, 28) in a range from 10°KW before the ignition dead centre ZOT to 20°KW after the ignition dead centre ZOT; and opening the exhaust valve of the cylinder exhaust (32, 34, 36, 38) of the cylinder (22, 24, 26, 28) in a range from 30°KW to 55°KW after the ignition dead centre ZOT. The method allows the catalytic converter of the combustion engine to quickly reach operating temperature and thus contributes to the reduction of pollutant emissions. The invention further relates to an internal combustion engine (1) which is designed to carry out the method according to the invention for heating a catalytic converter (40).

Description

description

Process for heating a catalytic converter

The invention relates to a method for heating a catalytic converter of an internal combustion engine and a device for carrying out such a method.

The current exhaust gas legislation and one that will become increasingly strict in the future places high demands on engine raw emissions and exhaust gas aftertreatment of combustion engines, especially 4-stroke gasoline engines.

Gasoline engines usually have a so-called "three-way catalytic converter". This is a vehicle catalytic converter for exhaust aftertreatment, in which carbon monoxide (CO), nitrogen oxides (NO _x ) and unburned hydrocarbons (HC) are converted into carbon dioxide (C0 ₂ ), nitrogen (N2) and water (H2O). The name of the catalyst is derived from the simultaneous conversion of these three air pollutants.

The measures known from the prior art are not yet entirely satisfactory. So far, when the catalytic converter is heated when the engine is idling, especially when the vehicle is stationary, the efficiency of the internal combustion engine has been reduced due to the ignition being retarded significantly after the piston TDC. The reduction in efficiency that can be achieved in this way is limited by the maximum ignition retard angle due to the smooth running of the engine, since retarding combustion is associated with poorer ignition and combustion boundary conditions. The known method is therefore unsatisfactory insofar as it is accompanied by a deterioration in the ignition conditions due to the late ignition point, which makes the use of passive prechamber spark plugs more difficult. Thus, processes for heating catalysts are described in US Pat. No. 5,904,902 A, US Pat. No. 9,810,167 B2 and US Pat. No. 8,402,757 B2.

The invention is now based on the object of providing a method which enables more efficient exhaust gas aftertreatment to the effect that carbon monoxide (CO), nitrogen oxides (NO _x ) or unburned hydrocarbons (HC) are converted even more efficiently into carbon dioxide (C0 ₂ ), nitrogen (N ₂ ) or water (H ₂ 0) are converted. According to the invention, this object is achieved by a method for heating a catalytic converter of an internal combustion engine with at least one engine block having a plurality of cylinders and an exhaust tract having a plurality of cylinder outlets, each of the plurality of cylinder outlets being opened and closed by an outlet valve of the cylinder can be. A cylinder can also have more than one cylinder outlet, for example two. According to the method, the gas charge in one of the cylinders is ignited in a range from 10° CA before ignition dead center, ZOT, to 20° CA after top dead center; and an outlet opening of the outlet valve of the cylinder outlet of the cylinder takes place in a range from 30° CA to 55° CA after the ignition top dead center, ZOT.

In the context of the present invention, the feature "exhaust opening of the exhaust valve of the cylinder exhaust of the cylinder" refers to the beginning of the opening process, ie the transition from a completely closed cylinder exhaust to an open cylinder exhaust. In particular, the term refers to achieving a valve lift deflection of 0.2 mm or more in relation to the fully closed position.

The process allows the combustion engine's catalytic converter to be brought up to operating temperature quickly, thus helping to reduce pollutant emissions. In particular, carbon monoxide (CO), nitrogen oxides (NO _x ) and/or unburned hydrocarbons (HC) are converted into carbon dioxide (CO ₂ ), nitrogen (N ₂ ) or water (H ₂ 0).

This achieves an improvement in catalyst heating through a significant increase in exhaust gas enthalpy, with both the exhaust gas mass flow and the exhaust gas temperature being increased. In contrast to what was previously the case when heating the catalytic converter when idling, especially when the vehicle is stationary, in which case the efficiency of the internal combustion engine is reduced by retarding the ignition significantly after the piston TDC, in the case of the method according to the invention the effectively usable expansion phase between ignition and exhaust opening is shortened. The method according to the invention therefore results overall in a significantly increased exhaust gas enthalpy and at the same time in good ignition conditions at the point of ignition, as a result of which the use of passive prechamber spark plugs is made possible. If numerical values are disclosed in connection with the present invention, a deviation of +/-10% from the respective value is included.

According to a preferred embodiment, the method is carried out at idle. Idling can occur when the vehicle is stationary. However, the method described here can also be carried out while driving, in particular in the case of hybrid-powered vehicles, while the engine is not doing any work and the vehicle is being driven electrically. Method according to claim 1, wherein the method is carried out with the vehicle idling and/or stationary.

According to a preferred embodiment, the internal combustion engine is a 4-stroke gasoline engine.

According to a preferred embodiment, a hook spark plug and/or a prechamber spark plug is used for igniting the gas charge. The method according to the invention results in a significantly increased exhaust gas enthalpy and, at the same time, good ignition conditions at the point of ignition, which in particular also enables the use of such passive prechamber spark plugs.

According to a preferred embodiment, the method also includes the step: outlet closing of the outlet valve of the cylinder outlet of the cylinder in a range from 300° CA to 390° CA after top dead center of ignition.

This embodiment is particularly preferred since it enables the outlet opening and closing times to be configured in an optimal manner for the operating point. In particular, disadvantages such as this embodiment having a high residual gas rate in the combustion chamber due to the inevitably very early closing of the outlet, with which a reduced air throughput associated with suboptimal ignition conditions in the combustion chamber, can be prevented.

According to a preferred embodiment, the exhaust valve lift curve is operated with a control width of 300° CA to 330° CA, preferably at 315° CA. The discrete value 315°CA includes a deviation of +/- 10%. According to a preferred embodiment, a valve lift cam switching mechanism is preferably used. This enables the use of different valve lift curves for conventional operation over the entire map and for catalyst heating operation.

According to an alternative specific embodiment, the method further includes the step: outlet closing of the outlet valve of the cylinder outlet of the cylinder in a range from 230° CA to 290° CA after the ignition top dead center.

In the context of the present invention, the feature "exhaust closing" of the exhaust valve of the cylinder exhaust of the cylinder refers to the end of the opening process, i.e. the transition from an open cylinder exhaust to a fully closed cylinder exhaust. In particular, the term refers to the achievement of a displacement of a valve lift of 0.2 mm or less with respect to the fully closed position.

According to a preferred embodiment, the ignition of the gas charge in a cylinder is shifted in the “retarded” direction (“retarded ignition”) compared to an efficiency-optimized ignition point during the catalytic converter heating as a further measure. The term "efficiency-optimized ignition timing" refers to an ignition point at which the combustion engine provides maximum torque. The ignition point is preferably retarded by at least 5° CA, in particular at least 10 CA, compared to the efficiency-optimized ignition point. The late ignition reduces the efficiency of the combustion, so that less work is done on the piston and more energy in the form of increased exhaust gas enthalpy is available for heating the catalytic converter.

According to a preferred embodiment, the gas charge in the cylinder is ignited approximately 10° CA before up to approximately 20° CA after the ignition top dead center, in particular approximately 8° CA up to about 16° CA after the ignition top dead center. This permits particularly good ignition conditions at the point of ignition, making it possible to use passive prechamber spark plugs. According to a preferred embodiment, the method is described, wherein the outlet opening of the outlet valve of the cylinder outlet of the cylinder takes place at approximately 45° CA after the ignition top dead center. The discrete value of about 45°CA includes a deviation of +/- 10%.

Insofar as method steps are listed in a specific order in connection with the invention described, this does not express the fact that these method steps must necessarily also be carried out in this order. However, the specified sequence of process steps is preferred. Furthermore, each method step can also be repeated if necessary in order to achieve the object on which the invention is based.

In connection with the present invention, the term "exhaust gas aftertreatment" and "exhaust gas aftertreatment device" is initially used generally as a designation for a method or for a corresponding device for its implementation, in which combustion gases are cleaned after they have left the combustion chamber or the combustion chamber, i.e. freed from pollutants that occur during combustion processes. This happens in particular mechanically and/or catalytically.

In particular, the term "exhaust aftertreatment" as well as

"Exhaust after-treatment device" is used as a designation for a process or a corresponding device in which combustion products such as nitrogen oxides _NOc are removed from combustion gases. The catalytic converter is the exhaust gas aftertreatment device or is part of this exhaust gas aftertreatment device if a particle filter is also used.

A method is described as a further preferred embodiment, in which the combined exhaust gases are fed to the exhaust gas aftertreatment device including the catalyst by means of a total outlet.

As a preferred embodiment, the exhaust gas aftertreatment device comprises a particle filter, in particular a so-called Otto particle filter. The chemical reactions taking place in the exhaust aftertreatment device require a correspondingly high temperature level. This applies in particular to the regeneration of a particle filter. Depending on the driving profile, however, the temperature level required for efficient operation of the exhaust aftertreatment cannot always be achieved. The measures according to the invention are therefore also suitable for the operation of particle filters in exhaust gas aftertreatment. The Otto particle filter is a device for reducing the particles present in the exhaust gas from Otto engines. Two functional types can be distinguished: wall-flow filters, in which the exhaust gas penetrates a porous wall in the filter, or bypass-flow filters, in which the exhaust gas penetrates the filter on its inner surface flows along.

Those skilled in the art know that dead centers are the positions of the crankshaft of an internal combustion engine in which the piston no longer moves in the axial direction. The position of the dead centers is clearly determined by the geometry of the crankshaft, connecting rod and piston. In four-stroke engines, a distinction is also made between the gas exchange TDC (LWOT, between exhaust and intake stroke) and the ignition TDC (ZOT, between compression and power stroke).

The dead center position of a crank mechanism is given when the three axes of rotation of the crankshaft axis and connecting rod bearing axis (connecting rod, connecting rod) and piston pin or crosshead axis are in one plane. A distinction is made between top dead center (OT), where the connecting rod (piston, crosshead) is the greatest distance from the crankshaft, and bottom dead center (UT), where the connecting rod is the shortest distance from the crankshaft. Since the connecting rod force is completely absorbed by the axle bearings at these positions and without developing lateral components, the crank drive cannot start from either position without assistance.

The top dead center serves as a reference for the crankshaft position. The ignition timing for petrol engines and the start of injection for diesel engines is given in degrees before TDC.

In a further aspect, the invention relates to an internal combustion engine comprising a catalytic converter and at least one engine block, having a plurality of cylinders and an exhaust tract having a plurality of cylinder outlets, each of the plurality of cylinder outlets being able to be opened and closed by an outlet valve. According to the invention, the internal combustion engine is designed to carry out the method according to the invention.

The various embodiments of the invention mentioned in this application can be combined with one another, unless stated otherwise in the individual case.

The invention is explained below in exemplary embodiments with reference to the associated drawing:

Figure 1 shows an embodiment of an internal combustion engine,

Figure 2a an ideal Otto cycle,

FIG. 2b shows a cylinder piston for such a cycle process,

Figure 3 shows a curve of cylinder pressure and exhaust valve according to a

embodiment,

FIG. 4 shows a profile of cylinder pressure and exhaust valve lift according to a particularly preferred embodiment.

FIG. 1 shows an embodiment of an internal combustion engine 1 schematically. The exhaust tract in turn has an exhaust manifold with a plurality of cylinder outlets 32, 34, 36, 38. Each cylinder exhaust is connected to one of the four cylinders. The cylinder outlets combine into a common outlet 39, first within the exhaust manifold and then an exhaust duct. Exhaust gases that are produced during combustion in the cylinders are first guided downstream through the cylinder outlets 32 , 34 , 36 , 38 and then combined in the overall outlet 39 .

An exhaust gas catalytic converter 40 is arranged in the exhaust gas duct, to which the exhaust gases are supplied via the overall outlet. In Otto engines, the catalytic converter 40 is preferably a “three-way catalytic converter” that converts the three pollutants carbon monoxide CO, nitrogen oxides NO _x and unburned hydrocarbons HC to carbon dioxide CO ₂ , nitrogen N ₂ and water H ₂ O.

The catalytic converter 40 can optionally be connected to further exhaust gas treatment devices, for example an Otto soot particle filter 50, by a feed line 52, through which the exhaust gases are passed on downstream.

The internal combustion engine 1, as shown schematically in FIG. 1, is suitable for carrying out the method according to the invention, as will now be described in two embodiments in the further FIGS.

FIG. 2a schematically shows an ideal Otto cycle, which provides a theoretical basis for the method according to the invention. FIG. 2b shows a schematic of a cylinder with a crank mechanism for such a cyclic process, with the compression volume V _K and the swept volume V _H . In such an ideal process, no dissipation losses, mechanical friction losses or the like are taken into account. Furthermore, the working gas has the same properties over the entire cycle and flow losses are not taken into account. Furthermore, no mixing of charge mixture with exhaust gas is assumed.

The invention preferably relates to a method for a 4-stroke gasoline engine. A stroke consists of one piston stroke or half a crankshaft revolution. In the case of the 4-stroke gasoline engine, the state changes can be assigned to the work cycles. This is described below with reference to FIG. 2a:

The first stroke, the intake stroke, includes induction where the piston moves to the right in Figure 2b and the cylinder fills with fresh air. This corresponds to the connecting line between points 0 and 1 in the diagram.

The second stroke, the compression or compression stroke, involves compressing the cylinder charge with the piston moving to the left in Figure 2b. In the diagram, this corresponds to the isentropic connecting line between points 1 and 2, and the isochoric heat supply qzu occurs through ignition and combustion of the gas charge, which corresponds to the connecting line between points 2 and 3 (equal-space combustion). The third stroke, the expansion or power stroke, involves isentropic expansion, moving the piston to the right again as a result of the exothermic combustion. This corresponds to the connecting line between points 3 and 4 in the diagram.

The fourth stroke is also referred to as the exhaust stroke (heat removal), where the piston moves to the left again as the exhaust valve opens, the exhaust gases at bottom dead center expand outwards without further work (connecting line between points 4 and 1) and the rest of the exhaust gases pushed outwards by the piston stroke (connecting line between points 1 and 0). The heat q _A b contained in the exhaust gas is given off to the environment. The ideal process does not take into account that the residual volume in the compression space does not reach the ambient condition.

FIG. 3 now shows the course of cylinder pressure and exhaust valve lift according to an embodiment of the invention and a conventional method for heating the catalytic converter.

The reference number 60 here shows the course of the cylinder pressure and the reference number 65 shows the course of the valve lift of the exhaust valve in the conventional catalytic converter heating operation from the prior art.

Furthermore, reference number 70 shows the profile of the cylinder pressure in catalyst heating operation according to the invention, while reference number 75 describes the profile of the valve lift of the exhaust valve in catalyst heating operation according to the invention.

In the known method for heating a catalytic converter of an Otto internal combustion engine, the ignition 61 of the gas charge in one of the cylinders takes place relatively late after ignition top dead center, while the outlet opening of the outlet valve of the cylinder outlet of the cylinder also takes place late.

In the method according to the invention for heating a catalytic converter of an Otto internal combustion engine with at least one engine block, the ignition 71 of the gas charge in the cylinders takes place early in comparison to the prior art, for example at top ignition dead center, while the outlet opening of the outlet valve of the cylinder outlet of the Cylinder also takes place relatively early, for example at about 45 ° CA after the ignition top dead center.

A representation of the early exhaust opening can be found here by a

Exhaust camshaft phase adjusters are made with a very wide adjustment range, with a crank angle of at least 120° being assumed, and a cam contour that is also used outside of the catalytic converter heating mode.

According to this embodiment, the exhaust valve of the cylinder is closed in a range from 230° CA to 290° CA after the ignition top dead center.

FIG. 4 shows the progression of piston pressure and exhaust valve lift according to a further particularly preferred embodiment.

The curves and the reference numbers correspond to those from FIG. 3. However, the outlet closing 75' of the outlet valve of the cylinder takes place later, which results in a larger outlet width. According to this particularly preferred embodiment, the exhaust valve lift curve is operated with a control width of 300° to 330° CA, preferably at approximately 315° CA.

This embodiment is particularly preferred since it enables the outlet opening and closing times to be configured in an optimal manner for the operating point. Compared to the embodiment according to FIG. 3, the associated disadvantages can be avoided in that this embodiment has a high residual gas rate in the engine block due to the inevitably very early exhaust closing, which results in reduced air throughput and suboptimal ignition conditions in the combustion chamber.

The method according to the invention results in a significantly increased exhaust gas enthalpy and, at the same time, good ignition conditions at the point of ignition, as a result of which the use of passive prechamber spark plugs is made possible. Reference List

combustion engine

intake tract

combustion chamber

cylinder

exhaust tract

cylinder exhaust

total outlet

catalyst

Supply of further components of the exhaust aftertreatment device

Conventional cylinder pressure curve

Ignition conventional

Conventional exhaust valve lift

Cylinder pressure curve according to the invention

Ignition according to the invention

Course exhaust valve according to the invention

Course exhaust valve according to the invention, preferred

Claims

Expectations:

1. A method for heating a catalytic converter (40) of an internal combustion engine (1) with at least one engine block (20) having a plurality of cylinders (22, 24, 26, 28) and an exhaust tract (30) having a plurality of cylinder outlets (32, 34, 36, 38), wherein each of the plurality of cylinder outlets (32, 34, 36, 38) can be opened and closed by an outlet valve, characterized in that the method comprises the steps of:

Ignition of the gas charge in one of the cylinders (22, 24, 26, 28) in a range from 10° CA before ignition top dead center (ZOT) to 20° CA after ignition top dead center (ZOT); and

Outlet opening of the outlet valve of the cylinder outlet (32, 34, 36, 38) of the cylinder (22, 24, 26, 28) in a range from 30° CA to 55° CA after top dead center (ZOT).

2. The method of claim 1, wherein the method is performed at idle.

3. The method according to any one of the preceding claims, wherein a hook spark plug and / or a pre-chamber spark plug is used for the ignition of the gas charge.

4. The method according to any one of the preceding claims 1 to 3, further comprising the step:

Outlet closing of the outlet valve of the cylinder outlet (32, 34, 36, 38) of the cylinder (22, 24, 26, 28) in a range from 300° CA to 390° CA after top dead center (ZOT).

5. The method according to any one of the preceding claims 1 to 3, further comprising the step:

Outlet closing of the outlet valve of the cylinder outlet (32, 34, 36, 38) of the cylinder (22, 24, 26, 28) in a range from 230° CA to 290° CA after top dead center (ZOT).

6. The method according to any one of the preceding claims, wherein the ignition of the gas charge in one of the cylinders (22, 24, 26, 28) compared to an efficiency-optimized ignition point in the "retarded" direction.

7. The method according to any one of the preceding claims, wherein the ignition of the gas charge in one of the cylinders (22, 24, 26, 28) takes place at ignition top dead center (TDC).

8. The method according to any one of the preceding claims, wherein the outlet opening of the outlet valve of the cylinder outlet (32, 34, 36, 38) of the cylinder (22, 24, 26, 28) at 45 ° CA after the ignition top dead center (TDC).

9. The method according to any one of the preceding claims, wherein the internal combustion engine (1) is an Otto engine.

10. Internal combustion engine (1) comprising a catalytic converter (40) with at least one engine block (20) having a plurality of cylinders (22, 24, 26, 28) and an exhaust tract (30) having a plurality of cylinder outlets (32, 34, 36, 38), wherein each of the plurality of cylinder outlets (32, 34, 36, 38) can be opened and closed by an outlet valve, characterized in that the internal combustion engine (1) is designed, the method according to any one of the preceding claims to execute.