Method for operating an exhaust gas purification system and exhaust gas purification system

Abstract

A method for operating an exhaust gas purification system arranged in the exhaust gas line of an internal combustion engine and an exhaust gas purification system are described. In the method, a combination of electric catalytic converter heating measures and combustion engine catalytic converter heating measures is performed, thereby achieving particularly fast and cost-effective heating of the catalytic converter (3). The corresponding exhaust gas system preferably first has an auxiliary catalytic converter (1) and then a heating catalytic converter (2) in the exhaust gas flow direction.

Description

Technical Field

[0001] The invention relates to a method for operating an exhaust gas purification system arranged in the exhaust tract of an internal combustion engine, the exhaust gas purification system having a heating catalytic converter for preheating the catalytic converter in order to bring the catalytic converter to its light-off temperature before starting the internal combustion engine. Background Art

[0002] It is known that catalytic converters arranged in the exhaust system of an internal combustion engine only achieve their full functional capacity starting from a certain temperature, the so-called light-off temperature. Therefore, below this temperature, the desired conversion of pollutants in the exhaust gas does not occur to a complete extent. However, in order to achieve sufficient conversion of pollutants even when starting the internal combustion engine from a cold state, it is known to use so-called heating catalytic converters, which are electrically heated and preheat the associated catalytic converter before the actual start of the internal combustion engine. In this case, the heating catalytic converter is switched on before the actual start of the internal combustion engine, for example 15 seconds before starting the internal combustion engine, in order to bring the temperature of the catalytic converter above the light-off temperature, which can be, for example, 300°C.

[0003] In order to accelerate the heating of the catalytic converter during a cold start, it is known to operate the internal combustion engine as an air pump before starting the internal combustion engine, in order to achieve particularly good heat transfer from the heated catalytic converter to the catalytic converter. Thus, it is known to heat up a larger E-Kat volume by means of the internal combustion engine operating as an air pump in addition to electrical heating. Summary of the Invention

[0004] The object of the present invention is to provide a method of the type described in the introduction which allows particularly rapid heating of the exhaust gas purification system before starting the internal combustion engine.

[0005] According to the invention, this object is achieved by a method for operating an exhaust gas purification system arranged in the exhaust line of an internal combustion engine. The method comprises the following steps:

[0006] Electrically heating the catalytic converter before starting the internal combustion engine;

[0007] operating the internal combustion engine as an air pump before starting the internal combustion engine;

[0008] Thereafter, the internal combustion engine is started;

[0009] Before starting the internal combustion engine, the catalytic converter is brought above its light-off temperature by being controlled during operation of its air pump in such a way that air is sucked back into the combustion chamber and / or drawn out into the intake tract.

[0010] In the method according to the invention, the measures for heating the electric catalytic converter are combined with the measures for heating the catalytic converter of the combustion engine. This allows for particularly rapid and cost-effective heating of the catalytic converter, so that the emitted pollutants, in particular NO, are reduced. x When starting the internal combustion engine from cold, the following is achieved: The required warm-up time of the catalytic converter is shortened.

[0011] According to the present invention, before starting the internal combustion engine, for example, before starting injection, the catalytic converter is brought to a light-off temperature, for example, above 300°C. When injection is switched on, the highest possible temperature is reached at the heated catalytic converter. In addition to electrically heating the heated catalytic converter, a corresponding temperature increase is achieved by additional measures during the control of the internal combustion engine in air pump operation. This allows the electrical heating power to be limited.

[0012] The catalytic converter heating measures implemented according to the present invention for combustion engines involve sucking air back into the combustion chamber and / or extracting air into the intake tract. These measures are preferably implemented by controlling the internal combustion engine during air pump operation in such a way that an increased valve overlap is achieved between the exhaust valves and the intake valves.

[0013] Modern internal combustion engines are now equipped with variable valve timing for the intake and exhaust camshafts. This allows for adjusting valve overlap during catalytic converter warm-up. This valve overlap results in exhaust gas recirculation and, consequently, faster warm-up during cold warm-up. During engine operation, valve overlap is limited due to the quiet operation of the combustion engine.

[0014] Upstream of the catalytic converter, the ambient pressure is practically constant. The pressure in the intake manifold is adjusted via the engine's throttle valve. During valve overlap, the intake and exhaust systems are connected. If the engine is operated as an air pump, the exhaust and intake camshafts can be brought to their maximum adjustment position. Furthermore, the throttle valve can be adjusted (throttled) so that a specific absolute pressure is set in the intake manifold. Due to the negative pressure in the intake manifold, air is sucked back into the intake duct via the combustion chamber. A lower intake duct pressure increases throttling losses and thus increases driving power, but also increases the amount of air sucked back into the combustion chamber (intake manifold).

[0015] The amount of air drawn back depends on the volume of the intake system (from the throttle valve to the intake valve), the negative pressure in the intake manifold, the valve overlap area, and the throttling losses at the intake and exhaust valves, as well as the exhaust turbine if necessary. The higher the negative pressure in the intake manifold, the higher the flow rate of the air drawn back. This results in better heat transfer to the heated catalytic converter.

[0016] Thus, by appropriately controlling the camshaft and the throttle valve, a portion of the air can be directed three times through the heated catalytic converter. This results in a temperature increase overall, which can be, for example, 30%, at the same heating power.

[0017] In order to achieve the above-mentioned object, the throttle valve of the internal combustion engine can therefore be further closed during operation of the air pump and / or the intake manifold pressure can be reduced during operation of the air pump.

[0018] Another variant consists in reducing the speed of the internal combustion engine during operation of the air pump.

[0019] The good heat transfer achieved at the heating catalytic converter during the re-induction of air also enables a very high electrical power at the heating catalytic converter without the risk of local overheating.

[0020] Therefore, the following combustion engine catalytic converter heating measures can be carried out individually or together in order to achieve particularly rapid heating: a lower rotational speed of the combustion engine at the start, for example 600-800 rpm instead of 1,000 rpm during the first 15 seconds;

[0021] By closing the throttle valve further, the intake manifold pressure is smaller;

[0022] greater valve overlap;

[0023] sucking air back into the combustion chamber;

[0024] pumping air out into the intake duct;

[0025] Adjust the throttle valve to reduce the intake manifold pressure to increase the amount of air sucked back.

[0026] The method according to the invention is preferably carried out using an exhaust gas purification system which, in the direction of exhaust gas flow, first has an auxiliary catalytic converter and then has a heating catalytic converter. The heating catalytic converter is preferably used to preheat the three-way catalytic converter.

[0027] The use of such an auxiliary catalytic converter in combination with a heating catalytic converter (heating disk) is known. The auxiliary catalytic converter and the heating catalytic converter are respective honeycomb bodies through which the exhaust gas flows. It is known to arrange the heating catalytic converter so that the exhaust gas first flows through it and then passes through the auxiliary catalytic converter.

[0028] In the method according to the invention, an arrangement is now preferred in which the exhaust gas flows first into the auxiliary catalytic converter and then into the heating catalytic converter. Although this arrangement has the disadvantage that the auxiliary catalytic converter acts as a heat sink, thus reaching the light-off temperature later and, therefore, starting the conversion of pollutants later, it offers the advantage over the prior art that the catalytic converter system can be heated at two points. The internal combustion engine heats the auxiliary catalytic converter, while the heating catalytic converter heats the downstream catalytic converter (the three-way catalytic converter).

[0029] In the method according to the invention, improved heating is achieved both at the auxiliary catalytic converter and at the heating catalytic converter. In particular, by means of combined measures (electrical heating and combustion engine heating measures), both the auxiliary catalytic converter and the heating catalytic converter are brought above the light-off temperature of, for example, 300° C. before starting the combustion engine. When the internal combustion engine is started (injection begins), particularly high temperatures are reached at the heating catalytic converter.

[0030] The invention further relates to an exhaust gas purification system for carrying out the method described above. The exhaust gas purification system preferably comprises, in the exhaust gas flow direction, first an auxiliary catalytic converter and then a heating catalytic converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be described in detail below based on embodiments in conjunction with the accompanying drawings.

[0032] Figure 1 a greatly schematic illustration showing an exhaust gas purification system; and

[0033] Figure 2 Shown is a largely schematic block diagram of an internal combustion engine with an exhaust gas purification system. DETAILED DESCRIPTION

[0034] In this case, the problem involves the rapid heating of a catalytic converter 3, which can be, for example, a three-way catalytic converter arranged in the exhaust tract 4 of an internal combustion engine 6. A heating catalytic converter 2, designed as an electrically heated honeycomb body, is used to rapidly heat the catalytic converter 3. The system also has an auxiliary catalytic converter 1, which is also designed as a honeycomb body.

[0035] In contrast to the prior art, in which the heating catalytic converter is arranged first in the direction of exhaust gas flow and then the auxiliary catalytic converter, the solution described here places the auxiliary catalytic converter 1 first in the direction of exhaust gas flow and then the heating catalytic converter 2, which has electrical connections 7. Thus, the exhaust gas flows first into the auxiliary catalytic converter 1 and then into the heating catalytic converter 2. This arrangement offers the advantage that the catalytic converter system can be heated at two points. The internal combustion engine heats up the auxiliary catalytic converter 1, while the heating catalytic converter 2 heats up the downstream catalytic converter (three-way catalytic converter).

[0036] In this case, the goal is to bring the catalytic converter to its light-off temperature as quickly as possible so that when the internal combustion engine is started, the catalytic converter can already carry out the desired conversion of pollutants. To this end, the electrocatalytic converter heating measures (by means of heating the catalytic converter 2) are combined with the combustion engine catalytic converter heating measures. The corresponding operating procedures are described in detail in the following sections. Figure 2 It is shown schematically in FIG.

[0037] This action causes the internal combustion engine to operate as an air pump until it starts. To this end, with injection turned off, the internal combustion engine is driven by an electric motor, such as a belt starter generator, or, in a P1-P4 hybrid configuration, by an electric motor. In addition to electrically heating the catalytic converter 2, the internal combustion engine 6 is controlled during its air pump operation so that air is drawn back into the combustion chamber and / or extracted into the intake tract. This can be achieved through various measures, either individually or collectively, such as further closing the throttle valve in the intake tract 5, adjusting the exhaust and intake valves accordingly to increase valve overlap, and / or reducing the speed of the internal combustion engine 6 during its air pump operation. Regardless, this results in a temperature increase, which overall allows for rapid and cost-effective heating of the catalytic converter.

[0038] If it is assumed in the present exemplary embodiment that the catalytic converter has a light-off temperature of 300° C., this light-off temperature is reached even before the internal combustion engine is started, for example within 15 seconds before starting, wherein the internal combustion engine is operated as an air pump during this time interval.

Claims

1. A method for operating an exhaust gas purification system arranged in an exhaust gas line (4) of an internal combustion engine (6), wherein the exhaust gas purification system has an auxiliary catalytic converter (1), a heating catalytic converter (2) and a catalytic converter (3) in the exhaust gas flow direction, wherein the heating catalytic converter (2) is used to preheat the catalytic converter (3) so that the catalytic converter reaches its light-off temperature before starting the internal combustion engine (6), the method comprising the following steps: Electrically heating the heated catalytic converter (2) before starting the internal combustion engine (6); operating the internal combustion engine (6) as an air pump before starting the internal combustion engine (6); Thereafter starting the internal combustion engine (6); The catalytic converter (3) is brought above the ignition temperature of the catalytic converter (3) before starting the internal combustion engine (6), by combining electric catalytic converter heating measures with combustion engine catalytic converter heating measures, wherein the internal combustion engine (6) is controlled during air pump operation of the internal combustion engine (6) so that an increased valve overlap is obtained between the exhaust valve and the intake valve and air is sucked back into the combustion chamber and / or air is extracted into the intake duct (5).

2. The method according to claim 1, characterized in that The intake manifold pressure of the internal combustion engine (6) and during operation of the air pump is reduced.

3. The method according to claim 1 or 2, characterized in that: The rotational speed of the internal combustion engine (6) is reduced during operation of the air pump.

4. The method according to claim 1 or 2, characterized in that: The throttle valve of the internal combustion engine (6) is further closed during the operation of the air pump.

5. The method according to claim 1 or 2, characterized in that: The method is carried out with an exhaust gas purification system which, in the exhaust gas flow direction, first has an auxiliary catalytic converter (1) and then has a heating catalytic converter (2).

6. The method according to claim 1 or 2, characterized in that: The heating catalytic converter (2) is used to preheat the three-way catalytic converter.

7. An exhaust gas purification system for carrying out the method according to any one of the preceding claims 1 to 6.

8. The exhaust gas purification system according to claim 7, characterized in that: The exhaust gas purification system comprises, in the exhaust gas flow direction, first an auxiliary catalytic converter (1) and then a heating catalytic converter (2).

Images