WO2021094112A1

WO2021094112A1 - Internal combustion engine having a secondary air system

Info

Publication number: WO2021094112A1
Application number: PCT/EP2020/080572
Authority: WO
Inventors: Michael Baeuerle
Original assignee: Robert Bosch Gmbh
Priority date: 2019-11-13
Filing date: 2020-10-30
Publication date: 2021-05-20
Also published as: DE102019217473A1

Abstract

The present invention relates to an internal combustion engine (10) comprising a primary air system (1) for providing fresh air, and a secondary air system (2) which is designed to divert secondary air from the primary air system (1) and to blow said air into an exhaust gas channel (7), wherein: the secondary air system (2) has a secondary air channel (8) which connects the primary air system (1) to the exhaust gas channel (7); the secondary air channel (8) has a return flow limiter (9) which can be passed through in a blow-in direction (A) and in a return flow direction (B) opposite to the blow-in direction (A); the return flow limiter (9) has a first flow resistance in the blow-in direction (A) and has a second flow resistance in the return flow direction (B); and the second flow resistance is greater than the first flow resistance.

Description

description

title

Internal combustion engine with secondary air system

State of the art

The present invention relates to an internal combustion engine which has a secondary air system with a backflow limiter.

For a cold start, a gasoline engine usually requires a “rich mixture”, that is, a fuel-air mixture with excess fuel. This creates large amounts of carbon monoxide and unburned hydrocarbons in the cold start phase. Since the catalytic converter has not yet reached its operating temperature in this phase, these harmful exhaust gas components can escape into the environment without any aftertreatment. To avoid this and to reduce the pollutants during the cold start phase, oxygen-rich ambient air is blown into the exhaust system in front of the catalytic converter with the help of a secondary air system. This leads to a post-oxidation of the pollutants to harmless carbon dioxide and water. The resulting heat also heats up the catalytic converter and shortens the time until the lambda control starts.

Disclosure of the invention

The internal combustion engine according to the invention with the features of claim 1 offers the advantage of a very simple and inexpensive secondary air injection, which is characterized by a particularly low energy requirement with high heating power in order to quickly heat a catalytic converter. According to the invention, this is achieved by an internal combustion engine which comprises a primary air system and a secondary air system. The primary air system provides fresh air, in particular for combustion in a combustion chamber of the internal combustion engine. The secondary air system is set up to divert secondary air from the primary air system. The secondary air system preferably comprises a secondary air pump which conveys the secondary air. The primary air system preferably comprises an air filter, the secondary air system being connected to the air filter in order to branch off the secondary air therefrom. The internal combustion engine is particularly preferably an Otto engine which has a catalytic converter for exhaust gas aftertreatment. The secondary air system is preferably provided for a cold start of the internal combustion engine in order to bring about a post-oxidation of unburned hydrocarbons present in the exhaust system, which arise during a cold start, upstream of the catalytic converter. As a result, the amount of harmful exhaust gas components can be reduced during a cold start, above all in that the catalytic converter is heated particularly quickly to operating temperature by the heat generated during post-oxidation.

Furthermore, the secondary air system comprises a secondary air duct which connects the primary air system with the exhaust gas duct, that is to say through which the secondary air is conducted to the exhaust gas duct. The secondary air duct has a backflow limiter through which the secondary air flows. That is, the backflow limiter is part of the, for example tubular, secondary air duct, so that the secondary air must inevitably flow through the backflow limiter in every operating state. The return flow limiter is designed so that it can flow through in the injection direction, that is, from the primary air system in the direction of the exhaust gas duct, and in a return flow direction opposite to the injection direction. The backflow limiter has a first flow resistance for the secondary air flow flowing through it in the injection direction. In the backflow direction, the backflow limiter has a second flow resistance. The second flow resistance is, in particular significantly, greater than the first flow resistance. The backflow limiter is preferably designed in such a way as to generate a second pressure loss when there is a flow in the backflow direction, which is significantly greater than a first pressure loss when there is flow in the injection direction. Due to the larger second flow resistance, the backflow limiter makes it more difficult to flow through the secondary air duct in the backflow direction. That is, an inflow of exhaust gases into the secondary air system is restricted by the backflow limiter, but in particular a slight backflow of exhaust gases into the secondary air system Backflow direction is possible. In particular, a complete closure of the secondary air channel by the backflow limiter is not provided in and against the direction of flow of the secondary air. That is to say, the backflow limiter preferably allows the secondary air to flow through in every operating state, which can be described with a continuous, in particular continuous, streamline in every operating state. The backflow limiter particularly preferably has a free, unclosed flow channel through which a flow can flow in any operating state. The backflow limiter is preferably designed as a passive component, particularly preferably without moving parts. The different flow resistances with regard to the two flow directions of the backflow limiter can be achieved constructively in a variety of ways. For example, corresponding cross-sectional transitions of pipelines are possible. A possible alternative is a so-called Teslav valve.

Thus, the internal combustion engine with the secondary air system offers a very simple and reliable construction which can efficiently reduce a backflow of exhaust gases into the secondary air system with little construction effort. In particular, the backflow limiter makes it possible, for example, to dispense with switchable valves for preventing backflow, which are expensive, complex and prone to errors. In addition, thanks to its passive functionality, the backflow limiter enables a secondary air flow that is very well adapted to the highly unsteady exhaust gas flow, since a back flow of exhaust gases into the secondary air system is efficiently avoided and a larger amount of secondary air can thus be blown in. As a result, a more homogeneous post-reaction of the exhaust gases can be achieved in order to directly obtain low concentrations of pollutants in the exhaust gas and, in addition, to achieve a high heating output for heating the catalytic converter through the resulting heat.

The subclaims show preferred developments of the invention.

The second flow resistance is preferably at least 10%, preferably at least 30%, preferably at least 50%, and particularly preferably at least 70%, greater than the first flow resistance. Thereby the backflow limiter reliably blocks a strong backflow in the backflow direction.

The backflow limiter particularly preferably has a nozzle-shaped plate washer which tapers in the direction of injection. The plate disc tapers in the direction of injection to a minimal flow cross-section. For example, the plate washer can be designed as a conically tapering nozzle. Alternatively, a trumpet-shaped nozzle with a curved profile can be used as a cup washer. The plate washer is particularly preferably designed like a sheet metal. Such a washer results in a particularly simple manner in which the flow resistance of the backflow limiter is dependent on the direction of the flow.

It is particularly advantageous if the backflow limiter has a plurality of cup washers arranged one behind the other in the injection direction. Such stacked cup washers offer an even better blocking effect, that is to say a higher second flow resistance in the return flow direction, the first flow resistance being kept low in order to obtain an efficient injection of the secondary air. The cup washers are preferably arranged one after the other at regular intervals along the blowing direction.

More preferably, the plurality of cup washers each have increasingly larger minimum flow cross-sections along the injection direction. The flow cross-sections preferably increase uniformly, in particular linearly. This results in a progressive inhibition of the return flow along the return flow direction, which has a particularly favorable effect on a high second flow resistance. In particular, this also avoids an excessive blocking effect of the backflow limiter in the injection direction, since the cup washers can preferably have a larger minimum flow cross-section, although a sufficiently large second flow resistance can still be achieved in the opposite direction in the backflow direction.

Advantageously, the plurality of cup washers have increasingly smaller axial lengths along the blowing direction. The axial lengths of the plurality of cup washers preferably take in the blowing direction evenly, especially linearly. As a result, effects and advantages analogous to those in the preceding paragraph can be achieved.

The return flow limiter preferably protrudes at least partially into the exhaust gas duct. As a result, the very hot exhaust gas flow from a combustion chamber of the internal combustion engine sweeps over and / or through the return flow limiter, for example if the return flow limiter has an open design. As a result, the backflow limiter can be burned free of possible deposits, for example soot deposits, as a result of which a particularly long service life and a uniform, reliable function of the secondary air system can be achieved.

The secondary air duct preferably opens into a valve shade of an exhaust valve of the internal combustion engine within the exhaust duct. That is, the secondary air duct, starting from an inner wall of the exhaust duct, protrudes into the exhaust duct and ends inside the valve shade. A projection of a valve disk of the exhaust valve facing away from the combustion chamber along an axial direction of the exhaust valve is regarded as a valve shadow. The axial direction is preferably oriented essentially parallel to an outflow direction along which the exhaust gas flows out of the combustion chamber. The secondary air channel thus preferably opens into the exhaust gas channel close to a valve stem of the exhaust valve and, viewed in the flow direction of the exhaust gas channel, behind the valve disk. In this area, there can be a backflow area, especially during the outflow of the exhaust gases from the combustion chamber, whereby a particularly good mixing of the exhaust gases with the secondary air can be achieved by strong turbulence in this backflow area.

More preferably, the injection direction at an outlet end of the secondary air duct is essentially opposite to a main exhaust gas flow direction. The main exhaust gas flow direction is the middle direction of the exhaust gas flowing through the exhaust gas duct, that is to say pointing away from the combustion chamber and in particular following a contour of the exhaust gas duct. As a result, the dynamic effects of the highly unsteady exhaust gas flow that occur when the flow around the exhaust valve is used can be optimally used for particularly good mixing of secondary air and exhaust gas. It is particularly favorable if the secondary air duct opens into the exhaust duct outside the valve shadow. That is to say, the secondary air duct opens in particular in a region of the exhaust gas duct within which a flow direction essentially follows the geometry of the exhaust gas duct and points away from the combustion chamber. The outlet end of the secondary air duct is particularly preferably located in a wall of the exhaust duct. Preferably, the injection direction at the outlet end of the secondary air duct is essentially in the exhaust gas flow direction, i.e. the injection direction and the exhaust gas flow direction are essentially parallel to one another at the outlet end, or form an acute angle between them and point in the same direction. As a result, dynamic effects of the highly unsteady exhaust gas flow can also be used, for example by the exhaust gas flow sweeping past the outlet end, in order to obtain a secondary air injection that is better synchronized with the exhaust gas flow.

The internal combustion engine particularly preferably comprises a plurality of cylinders, in particular at least two cylinders, each with a return flow limiter per cylinder. That is, for each cylinder there is a separate injection of secondary air into the corresponding exhaust duct leading away from the cylinder downstream. In this case, a backflow limiter is preferably provided per cylinder in order to avoid a backflow of exhaust gases into the secondary air system or to keep it as low as possible. Alternatively, more than one exhaust gas duct per cylinder can preferably also be provided, it being possible for a secondary air duct, each with a backflow limiter, to be provided for each exhaust gas duct. Downstream of the secondary air injection points, the exhaust gas ducts can preferably be brought together in an exhaust gas collector, with the single catalytic converter of the internal combustion engine preferably being provided even further downstream.

Brief description of the drawings

Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. Identical or functionally identical components are always provided with the same reference symbols. In the drawing is: Figure 1 is a simplified schematic view of a

Internal combustion engine according to a first embodiment of the invention,

Figure 2 is a detailed view of Figure 1,

Figure 3 is a simplified schematic detailed view of a

Internal combustion engine according to a second embodiment of the invention,

Figure 4 is a simplified schematic detailed view of a

Internal combustion engine according to a third embodiment of the invention, and

Figure 5 is a simplified schematic detailed view of a

Internal combustion engine according to a fourth embodiment of the invention.

Embodiments of the invention

FIG. 1 shows a greatly simplified schematic view of an internal combustion engine 10 according to a first exemplary embodiment of the invention. The internal combustion engine 10 comprises a primary air system 1 in order to provide fresh air to a combustion chamber 4. The primary air system 1 has an air filter 12, from which the fresh air is guided via a primary air duct 14 to the combustion chamber 4 and there is admitted into the combustion chamber 4 at an inlet valve 13. A throttle valve 15 is also provided in the primary air duct 14 to regulate the amount of fresh air.

The internal combustion engine 10 further comprises an exhaust gas duct 7, which leads downstream away from the combustion chamber 4 at an outlet valve 3 in order to divert exhaust gases from the combustion chamber 4. The outlet valve 3 can open and close a passage opening 5 on the combustion chamber 4 in order to open or prevent the exhaust gases from flowing out of the combustion chamber 4. A catalytic converter 71 is provided in the exhaust gas duct 7. In order to enable a post-reaction of unburned hydrocarbons during a cold start phase of the internal combustion engine 10 to reduce harmful exhaust gas components and to heat up the catalytic converter 71 as quickly as possible, the internal combustion engine 10 also includes a secondary air system 2. The secondary air system 2 branches off and conducts secondary air from the primary air system 1 during a cold start the secondary air into the exhaust gas duct 7. The secondary air is blown into the exhaust gas duct 7 upstream of the catalytic converter 71 with respect to an exhaust gas flow direction 75 of the exhaust gas duct 7.

The secondary air system 2 comprises a secondary air duct 8 with a backflow limiter 9. The secondary air duct 8 connects the air filter 12 to the exhaust duct 7 in order to blow the secondary air into the exhaust duct in the blow-in direction A. The backflow limiter 9 is directly on the exhaust duct

7 arranged adjacent and has an outlet end 81 of the secondary air duct

8 on. The backflow limiter 9 is designed in such a way that it has a first flow resistance for the secondary air flow flowing through it in the injection direction A. Compared to a flow opposite to the injection direction A in the return flow direction B, the return flow limiter 9 offers a second flow resistance which is at least 30% greater than the first flow resistance. This prevents, in a very simple and reliable manner, a larger volume of exhaust gases from being able to flow from the exhaust gas duct 7 into the secondary air duct 8.

In the first exemplary embodiment shown in FIG. 1, the secondary air system 2 has a very simple structure without a secondary air pump. The highly unsteady flow of exhaust gas in the exhaust gas duct 7 causes a passive injection of secondary air. In detail, this is achieved in that between the exhaust gas pulses exiting the combustion chamber 4, which have very high pressure peaks, a negative pressure prevails in the exhaust gas duct 7, which sucks the secondary air into the exhaust gas duct 7. The backflow limiter 9 prevents a larger amount of exhaust gases from flowing into the secondary air system 2 during the exhaust gas pulses. It should be noted, however, that a secondary air pump can advantageously also be used in the secondary air system 2 in order to be able to blow in a particularly large amount of secondary air. Such a secondary air pump would preferably be integrated into the secondary air duct 8. The structure and the mode of operation of the backflow limiter 9 is described in detail in connection with FIG. 2, which shows a detailed view of FIG. In order to achieve the second flow resistance, which is significantly higher than the first flow resistance, the backflow limiter 9 has a plurality of cup washers 91 arranged one behind the other in the injection direction A. The injection direction A is parallel to a channel axis 85, along which the return flow limiter 9 and an adjacent section of the secondary air channel 8 extend. The plate disks 91 are each designed in the form of a nozzle as metal sheets tapering in the shape of a trumpet, starting from an inner diameter 92 of the secondary air duct 8. These metal sheets taper towards a through opening with a minimal flow cross section 91a. The flow cross-sections 91a of the plurality of cup washers 91 increase along the injection direction A. In addition, the cup washers 91 each have decreasing axial lengths 91b along the blow-in direction A. The cup washers 91 thus each cause a constriction of the free flow channel through which the secondary air flow flows. The special alignment of the sheet-metal plate washers pointing in the direction of the exhaust gas duct 7 has the effect that the second flow resistance in the return flow direction B is significantly greater than the first flow resistance in the injection direction A.

FIG. 3 shows a simplified schematic detailed view of an internal combustion engine 10 according to a second exemplary embodiment of the invention. The second exemplary embodiment essentially corresponds to the first exemplary embodiment in FIG. 1, with the difference that the return flow limiter 9 protrudes completely into the exhaust gas duct 7. This has the effect that the very hot exhaust gas flow impinging on the backflow limiter 9 enables soot to burn off soot deposits on or within the backflow limiter 9.

FIG. 4 shows a simplified schematic detailed view of an internal combustion engine 10 according to a third exemplary embodiment of the invention. The third exemplary embodiment essentially corresponds to the second exemplary embodiment in FIG. 3, the secondary air duct 8 opening into a valve shade 31 of the outlet valve 3. The outlet end 81 of the secondary air duct 8 lies within the valve shade 31 and close to it a valve stem 33 of the outlet valve 3. The valve shade 31 is defined as a projection of an outer diameter of a valve disk 34 along a valve axis 35 and in the main exhaust gas flow direction 75 behind the valve element 34

Main exhaust gas flow direction 75 can flow, and in which there is a high degree of turbulence in the exhaust gas flow. The secondary air duct 8 is arranged in such a way that the injection direction A at the outlet end 81 is essentially opposite to the exhaust gas flow direction 75 of the exhaust gases emerging from the combustion chamber 4 in order to ensure optimal mixing of exhaust gases and

To get secondary air.

FIG. 5 shows a simplified schematic detailed view of an internal combustion engine according to a fourth exemplary embodiment of the invention. The fourth exemplary embodiment corresponds essentially to the second

Embodiment of Figure 3 with a further alternative design of the outlet end of the secondary air duct 8. In the fourth example, the outlet end 81 of the secondary air duct 8 is arranged outside the valve shade 31 and also oriented so that the injection direction A at the outlet end 80 essentially points in the exhaust gas flow direction 75. By sweeping past the exhaust gas flow essentially in the same direction, the dynamic effects of the unsteady flow can be used particularly well in order to blow in the largest possible amount of secondary air.

Claims

Expectations

1. Internal combustion engine, comprising: a primary air system (1) for providing fresh air, and a secondary air system (2) which is set up to branch off secondary air from the primary air system (1) and to blow it into an exhaust duct (7),

- wherein the secondary air system (2) has a secondary air duct (8) which connects the primary air system (1) with the exhaust gas duct (7),

- wherein the secondary air duct (8) has a backflow limiter (9) which can be flown through in the injection direction (A) and in the backflow direction (B) against the injection direction (A),

- wherein the backflow limiter (9) has a first flow resistance in the injection direction (A) and has a second flow resistance in the return flow direction (B), and

- The second flow resistance is greater than the first flow resistance.

2. Internal combustion engine according to claim 1, wherein the second flow resistance is greater than the first flow resistance by at least 10%, in particular at least 30%, preferably at least 50%, particularly preferably at least 70%.

3. Internal combustion engine according to one of the preceding claims, wherein the backflow limiter (9) has a nozzle-shaped plate disk (91) which tapers in the injection direction (A) to a minimum flow cross-section (91a).

4. Internal combustion engine according to claim 3, wherein the backflow limiter (9) has a plurality of cup washers (91) arranged one behind the other in the injection direction (A).

5. Internal combustion engine according to claim 4, wherein the plurality of cup washers (91) have increasingly larger minimum flow cross-sections (91a) in the injection direction (A).

6. Internal combustion engine according to claim 4 or 5, wherein the plurality of cup washers (91) in the injection direction (A) have increasingly smaller axial lengths (91b).

7. Internal combustion engine according to one of the preceding claims, wherein the backflow limiter (9) protrudes at least partially into the exhaust duct (7).

8. Internal combustion engine according to one of the preceding claims, wherein the secondary air duct (8) opens inside the exhaust gas duct (7) in a valve shade (31) of an outlet valve (3) of the internal combustion engine (10).

9. Internal combustion engine according to claim 8, wherein the injection direction (A) at an outlet end (81) of the secondary air duct (8) is essentially opposite to an exhaust gas flow direction (75) of exhaust gases exiting from a combustion chamber (4).

10. Internal combustion engine according to one of claims 1 to 7, wherein the secondary air duct (8) outside the valve shade (31) opens into the exhaust duct (7), and in particular wherein the injection direction (A) at the outlet end (81) of the secondary air duct (8) in the Is substantially in the exhaust gas flow direction (75).

11. Internal combustion engine, comprising a plurality of cylinders (15), each with a backflow limiter (9) per cylinder (15).