DE10115956A1 - Multi-channel exhaust system for multicylinder engine has gas sensor per crossover point and at least one regulator for processing sensor signals and regulating an air-fuel ratio accordingly - Google Patents

Abstract

The system has at least two exhaust gas channels (24,24'), into each of which one or more cylinders (12,14,16,18) open, at least one crossover point (42) connecting two exhaust system channels near the engine, a first gas sensor (28) per crossover point and at least one regulator (32) for processing sensor signals and regulating an air-fuel ratio accordingly. An Independent claim is also included for a method of regulating an air-fuel ratio for a multicylinder engine with a multi-channel exhaust system.

Description

The invention relates to a multi-flow exhaust system of a multi-cylinder engine for Motor vehicles and a method for regulating an air-fuel ratio.

It is known to multi-cylinder engines of motor vehicles with exhaust systems Include at least two exhaust lines, in each of which one or more cylinders lead to equip. Usually there are more multi-flow in each exhaust line Exhaust systems arranged one or more catalysts to one To enable exhaust gas aftertreatment. Multi-flow exhaust systems can face single-flow systems achieve higher torques. Beyond that For reasons of installation space, the accommodation of several small-volume catalysts is common easier to implement than the arrangement of a single large-volume catalyst. This applies in particular to those who generally take up a lot of installation space Storage catalytic converters. Finally, there is a multi-flow exhaust system Possibility of a string or cylinder-selective engine control, in particular Lambda control to perform. This comes primarily to you Exhaust gas management benefits, for example, by targeting individual catalysts let it heat up or regenerate, resulting in a higher overall Pollutant conversion and lower fuel consumption can be achieved.

In contrast, a disadvantage of multi-flow exhaust systems is the high cost, which is caused in part by complex sensors. For example, increasingly stringent pollutant guidelines require extremely precise lambda control and constant monitoring of the catalysts. As a result, an extensive set of sensors, consisting, for example, of lambda sensors, NO _x sensors and temperature sensors, must be arranged in each individual exhaust line. In addition, there is an increased amount of cabling and control equipment for evaluating the signals from the sensors.

The invention is therefore based on the object of a multi-flow exhaust system for To provide multi-cylinder engines with a very accurate and fast  Lambda control is possible and yet with comparatively low costs connected is. A method for regulating an air-fuel ratio is also intended a multi-cylinder engine equipped with a corresponding exhaust system be proposed.

This task is accomplished with a multi-flow exhaust system with the characteristics of Claim 1 and a method according to claim 17 solved.

The multi-flow exhaust system according to the invention of a multi-cylinder engine for motor vehicles comprises

• At least two exhaust gas lines, each of which opens into one or more cylinders,
• - At least one, each connecting two exhaust lines, on one crosstalk located near the motor,
• - In each case a first gas sensor arranged in the crosstalk, and
• - At least one control device for processing by the first Gas sensor / s provided signals and regulation of one in the cylinder Air-fuel ratio to be fed in depending on the signals.

The procedure for controlling an air-fuel ratio provides for the following steps:

• - detecting close-coupled one dependent on a concentration of at least one exhaust gas component signal in at least one possible two exhaust lines interconnecting crosstalk point (42) by means of a first in the crosstalk point (42) arranged gas sensor (28)
• Assignment of the detected signal to one of the cylinders ( 12 , 14 , 16 , 18 ) of the multi-cylinder engine ( 10 ) or to an exhaust gas flowing out of this cylinder ( 12 , 14 , 16 , 18 ),
• - Control of the cylinder (12, 14, 16, 18) to be supplied to the air-fuel ratio as a function of the detected from the first gas sensor (28) and the cylinder (12, 14, 16, 18) associated signal.

According to the invention, a crosstalk is provided for two exhaust lines a first gas sensor installed in this. This eliminates the opposite conventional systems with one gas sensor in each exhaust line a gas sensor is required in a double-flow exhaust system its signal evaluation necessary cabling and evaluation device. The Lambda control of all cylinders connected to a crosstalk is carried out using of the gas sensor arranged in the crosstalk. This requires a temporal Correlation of the sensor signal with a cylinder or its exhaust gas respectively. This is made possible by the fact that not all cylinders are the same Time, but with a certain time offset according to a predetermined Ignite the ignition sequence and push the exhaust gas out.

Thus a temporal assignment of a sensor signal in a crosstalk arranged gas sensor to a cylinder connected to the crosstalk high reliability, the crosstalk should be suitable constructive Features. According to a preferred embodiment, a feed point has which connects an exhaust line with a crosstalk, a distance of maximum 100 mm, in particular maximum 30 mm, to that in the crosstalk arranged gas sensor. As a result and by the arrangement of the The crosstalk itself becomes short distances to be covered by the exhaust gas guaranteed. Furthermore, advantageously no more than four cylinders in one Feed in the crosstalk to ensure that only that at a time Exhaust gas from a cylinder is pushed out. A further embodiment provides that the cylinders are each assigned to an infeed point such that the one in the Gas sensor arranged at the cross-talk point flows alternately from both sides becomes. A crosstalk rate, that is the proportion of an exhaust gas flow in an exhaust line, that escapes through the crosstalk into the other exhaust line is preferably at most 5%, in particular it is below 1%.

It is preferably provided that the first arranged in a crosstalk Gas sensor is a broadband lambda sensor that is used in a large area of the air Fuel ratio can measure an oxygen content of the exhaust gas and thus can also determine lean and rich exhaust gas compositions.

According to an extremely advantageous embodiment of the invention is the downstream Crosstalk, especially downstream of a first catalyst or another Catalyst, a second gas sensor, preferably one, in each exhaust line  Step response lambda probe, and / or a temperature sensor arranged. Step response lambda sensors have the advantage over broadband lambda sensors significantly lower costs and greater stability of characteristics over their Lifespan. The latter feature enables calibration of the characteristic curve of the upstream broadband lambda probe by means of the downstream step response Lambda sensor.

In the case of the arrangement of the second gas sensor sees a particularly advantageous Embodiment of the invention provides that a fine control of the air-fuel Ratio of the cylinder / s assigned to an exhaust system as a function of the signal detected by the second gas sensor in the relevant exhaust line is carried out. In this version, too, the use of a step response Lambda probe as a second gas sensor is very advantageous, as this - at least in the relevant control range around λ = 1 - has a very high resolution, which the Broadband lambda probe not reached. The combination of broadband and Step response lambda probe enables accuracy of the lambda control in the Alcohol range.

According to another embodiment of the invention, the signal of the downstream a second gas sensor arranged to use a catalyst Monitor the catalyst condition of the catalyst in question. Doing so Time delay between a change in the cylinder supplied Air-fuel ratio and a response of the second gas sensor registered and tracked. The fact that a Oxygen storage activity of the catalyst correlated with its conversion activity. A different embodiment provides for the condition monitoring of the Catalyst based on a downstream of the catalyst, using a temperature sensor measured exhaust gas temperature. This is the context between conversion activity and an increase in exhaust gas temperature. The required knowledge of the exhaust gas temperature upstream of the catalyst either by suitably arranged temperature sensors or by Calculation done.

Further advantageous refinements of the invention result from the other, in the features mentioned in the subclaims.

The invention is described below in exemplary embodiments based on the associated Drawings explained in more detail. Show it:

Figure 1 shows a dual-flow exhaust system of a 4-cylinder engine according to the prior art.

Fig. 2 shows a preferred embodiment of a double-flow exhaust system according to the invention;

Fig. 3 temporal waveforms of gas sensors according to the embodiment shown in Fig. 2 and

Fig. 4 shows a further embodiment of a double-flow exhaust system.

Fig. 1 shows a double-flow exhaust system, as is obvious to a person skilled in the art from the prior art. A multi-cylinder engine 10 , preferably a direct-injection gasoline engine, comprises four cylinders 12 , 14 , 16 , 18 arranged in series. An air supply to the cylinders 12 , 14 , 16 , 18 is provided via a common suction system 20 with an actuating means 22 , for example a throttle valve, for regulating an air mass flow. The four cylinders 12 , 14 , 16 , 18 open into two exhaust lines 24 , 24 ', each of which houses a small-volume pre-catalytic converter 26 , 26 ', usually a 3-way catalytic converter. A broadband lambda probe 28 , 28 'is arranged as a first gas sensor at a position as close as possible to the engine upstream of the pre-catalysts 26 , 26 '. This serves for the rapid pre-regulation of an air-fuel mixture to be fed into the cylinders 12 , 14 , 16 , 18 . A second gas sensor, in particular a step response lambda probe 30 , 30 ', is arranged downstream of each precatalyst 26 , 26 '. The step response lambda probes 30 , 30 'serve on the one hand to regulate the lambda of the cylinders 12 , 14 , 16 , 18 assigned to the respective exhaust system 24 , 24 ' and on the other hand to monitor conversion activity of the catalysts 26 , 26 '. The signals of the broadband and step response lambda probes 28 , 28 ', 30 , 30 ' go into control devices 32 , 32 ', which evaluate the signals and the air-fuel ratio of the cylinders 12 , 14 , 16 , 18 . or adjust cylinder-selectively to a lambda target specification. For this purpose, it can in particular be provided that injection parameters of an injection system of the multi-cylinder engine 10 , not shown here, such as injection quantity, ignition angle, injection duration, an internal exhaust gas recirculation rate and / or post-injection parameters, are regulated. In addition, an external exhaust gas recirculation can also be provided, it being possible to influence an external exhaust gas recirculation rate. In the example shown, the two exhaust lines 24 , 24 'downstream of the step response lambda probes 30 , 30 ' combine to form a common exhaust line 34 . In a position remote from the engine, in particular at an underbody position of the motor vehicle, there is a large-volume NO _x storage catalytic converter 36 , its operation - in particular its regeneration intervals - in a known manner by means of a temperature sensor 38 arranged upstream of the catalytic converter and a downstream NO _x sensor 40 is monitored. In a departure from the example shown, the exhaust lines 24 , 24 'can also run completely multi-flow up to an exhaust outlet. In this case, a correspondingly dimensioned NO _x storage catalytic converter 36 with the associated temperature and NO _x sensors 38 , 40 are to be arranged in each line 24 , 24 '. It is also possible to provide one or more additional catalysts, for example a 3-way main catalyst, in addition to the NO _x storage catalyst 36 or in its place.

FIG. 2 shows a double-flow exhaust system that corresponds essentially to FIG. 1, but is designed according to a first preferred embodiment of the invention. According to the invention, a crosstalk 42 is arranged at a position close to the engine and connects the two exhaust lines 24 , 24 'to each other, which is connected on both sides to the exhaust lines 24 , 24 ' via a respective feed point 44 , 44 'and in which a gas sensor 28 , preferably one Broadband lambda probe is arranged. The two inner cylinders 14 , 16 of the motor 10 are assigned to the feed point 44 and the two outer cylinders 12 , 18 to the feed point 44 '. In a 1-3-4-2 ignition sequence typical for four-cylinder engines, this constellation causes the cross-talk point 42 to be alternately flowed through by the exhaust gas through the feed points 44 , 44 '. Assignment of a sensor signal to a specific cylinder is further facilitated by the smallest possible distance, preferably less than 30 mm, from an infeed point 44 , 44 'to the position of the lambda probe 28 . The signal from the probe 28 finds its way into the control device 32 , which also receives information about a current angle of rotation of a crankshaft (not shown) and can therefore correlate the sensor signal and the cylinder 12 , 14 , 16 , 18 . The control device 32 regulates the air-fuel ratios of the individual cylinders 12 , 14 , 16 , 18 to a desired target value in a known manner as a function of the lambda value detected in this manner. Of course, within the scope of the invention, lambda control of the cylinders 12 , 14 , 16 , 18 by means of a plurality of control devices, for example each associated with a cylinder 12 , 14 , 16 , 18 , is also conceivable. Furthermore, the invention also covers engines with a number and arrangement of cylinders which deviate from the illustration, as well as multi-part suction systems, in particular in the case of V-engines, a crosstalk with a gas sensor being provided for two exhaust gas lines. The lambda values of the cylinders 12 , 14 , 16 , 18 assigned to an exhaust system 24 , 24 'are fine-tuned by the downstream step response lambda probes 30 , 30 ' with an accuracy in the per mille range.

The sensor configuration shown in FIG. 2 not only enables precise and fast lambda control in both exhaust gas lines 24 , 24 ', but also continuous monitoring of the state of the pre-catalysts 26 , 26 '. This is explained in more detail by FIG. 3, in which a simplified time profile of a probe voltage U _{S of} a broadband lambda probe 28 (U _S ( 28 )) and a step response lambda probe 30 (U _S ( 30 )) during a slow linear enrichment of the air-fuel mixture is shown. The probe voltage U _S ( 28 ) of the broadband lambda probe 28 reflects the linear enrichment of the air-fuel mixture practically without a time delay. At a point in time t ₁ , the signal U _S ( 28 ) of the broadband lambda probe 28 corresponds to a lambda value of 1. The profile of the probe voltage U _S ( 30 ) of the downstream step response lambda probe 30 shows a typically sigmoidal profile with a sudden voltage change and a turning point at λ = 1. The step response lambda probe 30 shows a signal value U _S ( 30 ) which corresponds to λ = 1 only after a certain delay compared to the upstream broadband lambda probe 28 , namely at a time t ₂ . The time difference .DELTA.t that passes between the matching sensor signals depends on the one hand on the path length of the exhaust gas to be traveled between the two probes 28 , 30 . On the other hand, the time delay Δt is proportional to an oxygen storage capacity of the catalyst 26 . If this has stored oxygen during the previous lean phase, in which oxygen is present in a stoichiometric excess in the exhaust gas, this sorbed oxygen is released again during the lean-fat transition, so that for a certain period after the transition downstream of the catalyst 26 , 26 'is still detected an oxygen-containing, that is, lean atmosphere. Since the oxygen storage capacity of the catalyst 26 , 26 'in turn correlates with its conversion activity, the catalyst activity can be monitored with high sensitivity by registering and observing Δt. Alternatively, instead of the signal curve of the broadband lambda probe 28 , the point in time of an intervention in the air-fuel control of the relevant cylinders can also be used for the calculation of Δt.

FIG. 4 shows an alternative embodiment of a multi-strand exhaust system according to the invention. According to this embodiment, both step response lambda probes downstream of the catalysts 26 , 26 'of the embodiment shown in FIG. 2 are replaced by the temperature sensors 42 , 42 '. The control device 32 is not shown here. In this embodiment, the lambda control takes place in both exhaust lines 24 , 24 ′ exclusively as a function of the upstream lambda probe 28 . The condition of the catalytic converters 26 , 26 'is monitored on the basis of the exhaust gas temperatures behind the catalytic converters 26 , 26 ' recorded by the temperature measuring points 42 , 42 '. The exhaust gas temperatures determined by the sensors 42 , 42 'are compared with the exhaust gas temperatures present upstream of the catalysts 26 , 26 '. The latter can either be determined by further, correspondingly arranged temperature measuring points or - more cheaply - can be modeled with sufficient accuracy using known operating parameters of the engine 10 . In the constellation shown here, use is made of the fact that a conversion activity of a catalytic converter is always accompanied by an increase in the temperature of the exhaust gas. Accordingly, damage to the catalysts 26 , 26 'can be determined if no or only too slight temperature increases are measured behind the catalysts 26 , 26 '. Compared to the embodiment shown in FIG. 2, in which the catalyst is monitored by means of downstream lambda sensors 30 , 30 ', only relatively severe damage to the catalyst 26 , 26 ' can be detected by means of the temperature sensors 42 , 42 '. However, the arrangement has the advantage that a temperature sensor 38 (see FIG. 2) connected upstream of a NO _x storage catalytic converter 36 can be dispensed with.

REFERENCE SIGN LIST

10th

Multi-cylinder engine

12th

,

14

,

16

,

18th

cylinder

20th

Suction system

22

Positioning means

24th

,

24th

'' Exhaust system

26

,

26

'' First catalyst / pre-catalyst

28

first gas sensor / broadband lambda probe

30th

,

30th

'' second gas sensor / step response lambda probe

32

,

32

'' Control device

34

common exhaust system

36

second catalyst / NO _x

Storage catalytic converter

38

Temperature sensor

40

NO _x

-Sensor

42

Crosstalk

44

,

44

'Infeed point

46

Temperature sensor
U _S

Probe voltage
t time
Δt time difference

Claims (23)

1. Multi-flow exhaust system of a multi-cylinder engine for motor vehicles with

• at least two exhaust gas lines ( 24 , 24 '), into each of which one or more cylinders ( 12 , 14 , 16 , 18 ) open,
• at least one crosstalk ( 42 ), which connects two exhaust gas lines ( 24 , 24 ') to one another and is arranged at a position close to the engine,
• - In each case one in the crosstalk ( 42 ) arranged first gas sensor ( 28 ), and
• - at least one control device (32, 32) for processing the signals and control provided by the / the first gas sensors (28) of a fed into the cylinders (12, 14, 16, 18) air-fuel ratio as a function of the signals.

2. An exhaust system according to claim 1, characterized in that the crosstalk location downstream (42), in particular downstream of a first catalyst (26, 26 ') or of a further catalyst in each exhaust train (24, 24') each have a second gas sensor (30, 30 ) and / or a temperature sensor ( 42 , 42 ') is arranged. 3. Exhaust system according to claim 1 or 2, characterized in that the first gas sensor ( 28 ) arranged in a crosstalk ( 42 ) is a lambda probe, in particular a broadband lambda probe. 4. Exhaust system according to claim 2 or 3, characterized in that the second gas sensor ( 30 , 30 ') arranged downstream of the crosstalk ( 42 ) is a lambda probe, in particular a step response lambda probe. 5. Exhaust system according to one of the preceding claims, characterized in that a feed point ( 44 ), which connects an exhaust line ( 24 , 24 ') with a crosstalk ( 42 ), at most 100 mm, in particular at most 30 mm, of that in the crosstalk ( 42 ) arranged gas sensor ( 28 ) is removed. 6. Exhaust system according to one of the preceding claims, characterized in that a crosstalk ( 42 ) is assigned a maximum of four cylinders ( 12 , 14 , 16 , 18 ). 7. Exhaust system according to one of the preceding claims, characterized in that the cylinders ( 12 , 14 , 16 , 18 ) are assigned to a feed point ( 44 , 44 ') in such a way that the gas sensor ( 28 ) arranged in the crosstalk ( 42 ) is reciprocal is flowed from the feed points ( 44 , 44 '). 8. Exhaust system according to one of claims 1 to 4, characterized in that a crosstalk rate of an exhaust gas in a crosstalk ( 42 ) is less than 5%, in particular less than 1%. 9. Exhaust system according to claim 2, characterized in that the first catalytic converter ( 26 , 26 ') is a pre-catalyst, in particular a 3-way pre-catalyst. 10. Exhaust system according to one of the preceding claims, characterized in that downstream of the catalyst ( 26 , 26 '), in particular at an underbody position, at least one second catalyst ( 36 ), in particular a 3-way catalyst and / or a NO _x - Storage catalyst is arranged. 11. Exhaust system according to one of the preceding claims, characterized in that the exhaust lines ( 24 , 24 ') run completely multi-flow up to an exhaust outlet. 12. Exhaust system according to one of claims 1 to 10, characterized in that at least two exhaust lines ( 24 , 24 ) at a position upstream of the exhaust outlet, in particular immediately upstream of a common second catalytic converter ( 36 ), to one or more exhaust lines ( 34 ) unite. 13. Exhaust system according to one of the preceding claims, characterized in that the multi-cylinder engine ( 10 ) is a gasoline engine, in particular a direct-injection gasoline engine. 14. Exhaust system according to one of the preceding claims, characterized in that the air-fuel ratio to be fed into the cylinders ( 12 , 14 , 16 , 18 ) is line-selective, in particular cylinder-selective, controllable. 15. Exhaust system according to claim 14, characterized in that injection parameters of the cylinders ( 12 , 14 , 16 , 18 ), such as injection quantity, ignition angle, injection duration, internal exhaust gas recirculation rate and / or post-injection parameters, can be influenced in a line-specific or cylinder-selective manner. 16. Exhaust system according to claim 14 or 15, characterized in that a Exhaust gas recirculation is provided, with an external exhaust gas recirculation rate or can be influenced cylinder-selectively. 17. A method for regulating an air-fuel ratio of a multi-cylinder engine for motor vehicles with a multi-flow exhaust system with at least two exhaust lines, into which one or more cylinders each open, with the steps:

• - detecting close-coupled one dependent on a concentration of at least one exhaust gas component signal in at least one possible two exhaust lines interconnecting crosstalk point (42) by means of a first in the crosstalk point (42) arranged gas sensor (28)
• Assignment of the detected signal to one of the cylinders ( 12 , 14 , 16 , 18 ) of the multi-cylinder engine ( 10 ) or to an exhaust gas flowing out of this cylinder ( 12 , 14 , 16 , 18 ),
• - Control of the cylinder (12, 14, 16, 18) to be supplied to the air-fuel ratio as a function of the detected from the first gas sensor (28) and the cylinder (12, 14, 16, 18) associated signal.

18. The method according to claim 17, characterized in that the at least one first gas sensor ( 28 ) is a lambda probe, in particular a broadband lambda probe. 19. The method according to claim 17 to 18, characterized in that a fine control of the air-fuel ratio of the cylinder ( 12 , 14 , 16 , 18 ) as a function of one in a corresponding exhaust line ( 24 , 24 ') by means of one of the crosstalk ( 42 ) downstream, in particular downstream of a first catalytic converter ( 26 , 26 ') or a further catalytic converter arranged second gas sensor ( 30 , 30 ') which is dependent on the concentration of the at least one exhaust gas component. 20. The method according to claim 19, characterized in that the second gas sensor ( 30 , 30 ') is a lambda probe, in particular a step response lambda probe. 21. The method according to any one of claims 17 to 20, characterized in that as a function of a time delay (Δt) between a change in an air-fuel ratio, which the / the one of an exhaust system ( 24 , 24 ') associated cylinder ( 12 , 14 , 16 , 18 ) and a response from the second gas sensor ( 30 , 30 ') arranged downstream of the catalytic converter ( 26 , 26 ') in the exhaust line ( 24 , 24 '), condition monitoring of the catalytic converter ( 26 , 26 ') is carried out. 22. The method according to any one of claims 17 to 20, characterized in that a condition monitoring of the catalyst ( 26 , 26 ') is carried out as a function of an exhaust gas temperature measured downstream of the catalyst ( 26 , 26 '). 23. The method according to claim 18 and 20, characterized in that the broadband lambda probe ( 28 ) is calibrated by means of the step response lambda probe ( 30 ) arranged downstream thereof.