EP0731876A1

EP0731876A1 - Process for checking a catalyst heating burner system

Info

Publication number: EP0731876A1
Application number: EP95932615A
Authority: EP
Inventors: Erwin Achleitner; Achim Koch
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1994-09-30
Filing date: 1995-09-22
Publication date: 1996-09-18
Also published as: US5634330A; JP2819068B2; DE4435196C1; KR960706602A; WO1996010685A1; JPH09503273A

Abstract

In order to check the air ratio in the burner, the fuel-air mixture of the internal combustion engine is made richer or poorer depending on the momentary state of the mixture during operation of the burner and the resulting states of signals generated by lambda probes arranged upstream and downstream of the catalyst are evaluated.

Description

description

Method for checking a burner system for catalyst heating

The invention relates to a method for checking a burner system for heating an exhaust gas catalytic converter according to the preamble of patent claim 1.

The pollutant emission of an internal combustion engine can be effectively reduced by catalytic aftertreatment with the aid of a three-way catalytic converter in connection with an ambda control device. An important prerequisite for this, however, is that both the lambda probe of the control device and the catalytic converter have reached their operating temperatures. In order to bring these two components of the exhaust gas purification system to their operating temperature quickly, various heating measures have already been proposed.

While the heating of the ambda probe, which has a low mass in relation to the catalytic converter, does not pose any technical problems by means of an electrical heating device, the provision of electrical energy from the vehicle electrical system of a motor vehicle is often necessary for the catalytic converter to be heated up in a short time beyond the capacity of the vehicle power system.

In order to nevertheless reduce the pollutant emissions during the cold start phase of the internal combustion engine, in which approximately 70 to 80% of the total pollutants are emitted by HC and CO, it is known from DE 41 32 814 A1 to enter the exhaust gas line to install an additional burner, which is fed with fuel from the internal combustion engine, for the catalytic converter and thereby quickly heat the catalytic converter to its operating temperature of approximately 300 ° C. (light-off temperature). to

To achieve the shortest possible heating-up time, the burner is arranged directly in front of the catalytic converter. The fuel will fed to the burner from the distributor rail of the fuel circuit of the internal combustion engine and the air necessary for combustion contributes to the secondary air blower, which is often already standard. Such a secondary air blower is conventionally used to blow air into the exhaust pipe of the internal combustion engine near the exhaust valves in order to achieve pre-oxidation of the exhaust gases.

Since such a burner is thus part of the entire exhaust system of the internal combustion engine and the burner also has its own emission, it must be monitored with regard to its functionality with regard to the limit values to be complied with for pollutant emissions. In addition to an intact ignition of the burner, the air ratio of the burner on the one hand influences this self-emission, and on the other hand the burner air ratio influences the heating behavior of the catalytic converter. So that the air ratio of the burner is exhaust gas and must be monitored by suitable measures.

The invention is therefore based on the object of specifying a checking method for an internal combustion engine with a burner system mentioned at the outset for heating an exhaust gas catalytic converter, which allows a simple statement to be made about the functionality of the burner in a simple manner.

This is solved with a method according to the features of claim 1. Advantageous further developments can be found in the subclaims.

Characterized in that the air ratio of the burner is used as a criterion for the functionality of the burner and this air ratio is derived from the signal positions of two lambda probes, one of which is arranged upstream of the catalytic converter in front of the burner and the other behind the catalytic converter and the anyway in modern internal combustion engines for on-board diagnosis of exhaust-relevant parts. are available, there is a low-cost and therefore inexpensive way of assessing the burner in terms of its proper function.

An embodiment of the invention is shown in the drawing and is explained in more detail with reference to the following description. Show:

1 shows a simplified block diagram of an internal combustion engine with a catalytic converter that can be heated by means of a burner and a lambda probe in front of and behind the catalytic converter, FIG. 2 shows a selection of time-dependent signal profiles when the method according to the invention is carried out.

In the simplified form shown in Figure 1

Block diagram shows only those parts that are necessary for understanding the method according to the invention.

The reference numeral 10 denotes an internal combustion engine with an intake line 11 and an exhaust line 12. An air mass meter 13 arranged in the intake line 11 measures the air mass drawn in by the internal combustion engine 10. The air mass meter can be implemented as a hot wire or hot film air mass meter. A first oxygen sensor in the form of a lambda probe LSI is inserted in the exhaust gas line 12 upstream of a three-way catalytic converter 14 used to convert the constituents HC, CO and NO _x contained in the exhaust gas of the internal combustion engine 10, which sensor outputs an output signal ULS1 as a function of the residual oxygen content in the exhaust gas outputs to an electronic control device 16 of the internal combustion engine 10. In addition, downstream of the three-way catalytic converter 14, a second lambda probe LS2 is provided in the further course of the exhaust line 12, which outputs an output signal ULS2 depending on the residual oxygen content of the exhaust gas after cleaning by the catalyst 14. So-called jump probes are preferably used as lambda probes, which have a jump in the output signal, for example the output voltage, from a high value (typically 900-1000 mV) at a rich one with a stoichiometric mixture composition of the fuel-air mixture of λ = 1.00 Have mixture composition (λ <1.00) to a low value (typically 100-200 mV) with a lean mixture composition (λ> 1.00) (ZrC> 2 probe).

In addition, jump probes can also be used in which the electrical resistance has a jump function at λ = 1.00 (TiO 2 probe).

The statement used for reasons of simplification "the lambda probe indicates a rich or lean mixture" in the following description of the exemplary embodiment is therefore equivalent to the fact that the output voltage of the lambda probe has a value assumes that represents a rich or a lean mixture composition.

While the lambda sensor LSI arranged in front of the catalytic converter 14 serves in a conventional manner as a control element for the lambda control of the fuel-air mixture of the internal combustion engine, it is possible to evaluate both the lambda sensor LSI in front of the catalytic converter 14 by evaluating the output signals ULS1 also the

Output signals ULS2 of the lambda probe LS2 after the catalyst 14 possible to check the functionality or the efficiency of the catalyst 14. For example, the difference between the output signals of the two probes (DE 38 30 515 AI) or the time delay between the output signals of the two probes for switching from rich to lean or vice versa can be used as a measure of the catalyst efficiency (DE 41 01 616 AI ).

Furthermore, a sensor 18 for detecting the engine speed and a coolant temperature sensor 19 are provided at suitable points of the internal combustion engine 10. The exits of the sensors mentioned are connected via interfaces to corresponding inputs of the electronic control device 16 for the internal combustion engine 10. Such electronic control devices for internal combustion engines which, in addition to fuel injection, can also take on a multitude of other tasks, including the on-board diagnosis of exhaust-gas-relevant components, are known per se, so that in the following only in connection with the structure and mode of operation of the present invention is dealt with.

The heart of the electronic control device 16 is a microcomputer which controls the required functions according to a defined program. In a so-called air mass-guided engine control system, the

Sensors (air mass meter 13 and speed sensor 18) supplied and processed in appropriate circuits signals air mass and speed calculates a basic injection time or basic injection time and depending on further operating parameters (for example pressure and temperature of the intake air, temperature of the coolant, Battery voltage, etc.) Corrections of this basic injection time are carried out in such a way that a fuel-air mixture which corresponds to the stoichiometric ratio (λ = 1.00) is achieved by using the lambda control. The fuel for the internal combustion engine 10 is then injected into the intake line 11 with the aid of one or more injection valves 20.

An electrically operated air pump 21, often referred to as a secondary air pump, draws in fresh air via an air line (not shown) and, if required, conveys this additional air both into the exhaust line 12 of the internal combustion engine 10 via a secondary air line 22 and via a burner air line 23 to one , for the external heating of the exhaust gas catalytic converter 14 serving burner 24. This burner 24, which via a line 26 having a fuel shut-off valve 25 with fuel of the internal combustion engine 10 is supplied consists essentially of a combustion chamber with a burner nozzle and an ignition device. The burner nozzle is supplied with the burner air conveyed by the secondary air pump 21, as well as the fuel made available from the fuel circuit of the internal combustion engine. The ignition device comprises ignition electrodes which extend into the combustion chamber and which are ignited by the electronic control device 16 with ignition pulses. Further components of the burner system, such as metering valves, air shut-off valves and pressure regulators, have been left out for reasons of clarity and are also not necessary for understanding the method according to the invention. The detailed structure of such a burner system and its control can be found, for example, in document DE 41 32 814 AI.

At the time to (FIG. 2, engine start), the internal combustion engine 10 is started and both the secondary air pump 21 and the ignition of the burner 24 are switched on via corresponding signals from the electronic control device 16. Since the secondary air pump 22 requires a certain start-up time until the air required for combustion is available in the combustion chamber of the burner 24, the fuel for the burner 24 is only available after the time delay T_BR at the time t1 (FIG. 2, burner start) by opening the fuel cut-off valve 25 released. During this time, the secondary air supply and the ignition device of the burner 24 are monitored in a manner known per se, for example by checking the secondary voltage of the ignition device. If this check reveals that there is faulty ignition or no or insufficient secondary air, then the fuel supply to the burner 24 remains interrupted. If both the ignition and the secondary air supply to the burner have been recognized as being in order, the fuel supply to the burner is switched on. After the fuel has been switched on, the combustion process is monitored with the aid of the ignition voltage on the spark plugs of the burner. In order to be able to carry out the diagnosis of the burner / air ratio already during the burner run, both La bda sensors LSI, LS2 are operated with maximum heating power from the engine start (time tO). If a clocked activation of the probe heaters is used, this means that the two lambda probes LSI, LS2 are activated with a 100% duty cycle. After a predefined time T_LD determined on the test bench and essentially dependent on the construction and installation location of the lambda probes, both lambda probes are heated to their operating temperature and are therefore ready to produce an output signal rich / lean according to the To discharge residual oxygen content in the exhaust gas before and after the three-way catalytic converter 14 of the internal combustion engine 10.

The diagnosis of the burner-air ratio is only started after the time T_LD at time t2, if in addition to the conditions already mentioned, no diagnosis errors of the two lambda probes, the lambda control device or the long-term adaptation are stored. For this purpose, the content of an error memory 27 contained in the electronic control device 16 is read out and evaluated accordingly.

At the beginning of the diagnosis (time t2) of the burner air ratio, hereinafter also referred to as burner lambda λgR, four different ones are used depending on the values of the output signals ULS1, ULS2 of the two lambda sensors LSI, LS2 Differentiated cases:

Case 1:

- The lambda probe LSI in front of the catalytic converter shows a lean mixture (air ratio λuLsι> -00) and

- the lambda probe LS2 after the catalytic converter also shows a lean mixture (air ratio λτLS2 l-00)

Case 2:

- The lambda sensor LSI in front of the catalytic converter shows fat - The lambda probe LSI in front of the catalytic converter shows a rich mixture (air ratio λu _J sι <l-00) and

- The lambda probe LS2 after the catalytic converter also shows a rich mixture (air ratio λu _J g ₂ <1.00)

Case 3:

- The lambda probe LSI in front of the catalytic converter shows a rich mixture (air ratio λτjLsι <1.00) and

- The lambda probe LS2 after the catalytic converter shows a lean mixture (air ratio λ-rι _J g2> l .00)

Case 4:

- The lambda probe LSI in front of the catalytic converter shows lean mixture (air ratio λuLgι> l.0) and - the lambda probe LS2 after the catalytic converter shows rich mixture (air ratio τjτ _J s2 ^<1 • 0) •

Since, in the conventional burner systems (for example: DE 41 32 814 AI), secondary air is additionally blown into the exhaust line in the flow direction in front of the burner and, moreover, the burner is to be operated with an air ratio of approximately λ = 1.05 Case 1 on. In this case, the fuel-air mixture of the internal combustion engine 10 is enriched from the time t2 for the purpose of diagnosing the burner lambda. Enrichment takes place via a factor TI_BR, which is gradually increased starting from the value 1.0 according to the following relationship:

TI_BR _new = TI_BR _old + TI_BR _IC .

The expression TI_BRJJJC represents a fixed amount by which the value of the enrichment factor is increased per specified time unit.

The enrichment is ended when either the output signals ULS1, ULS2 of the two lambda probes LSI, LS2 signal a rich mixture, or when a predetermined limit value TI_BR_MAX has been reached for the enrichment, regardless of whether the two lambda probes have already recognized a rich mixture or not. In both cases, the enrichment factor TI_BR is then reset to a value of 1.0.

If the output signal ULS2 of the lambda probe LS2 shows no rich mixture composition during the enrichment up to the maximum value TI_BR = TI_BR_MAX, although the output voltage ULS1 of the lambda probe LSI assumes a value that indicates a rich mixture due to the enrichment, this becomes Air ratio of the burner 24 classified as faulty.

If, on the other hand, the output signal ULS1 of the lambda probe LSI does not jump from its initial state, which signals a lean mixture, to a state which represents a rich mixture, it can be assumed that either an error in the air ratio of the engine supplied to the internal combustion engine There is a mixture or a fault in the La bda probe LSI. In this case, the diagnosis is aborted and repeated the next time the burner is started and no entry is made in the error memory 27.

The value for the enrichment factor TI_BR, at which the output signal ULS1 of the lambda probe LSI indicates a rich mixture (time t3), is referred to as TI_F1 and the value for the enrichment factor TI_BR, at which the output signal ULS2 of the lambda probe LS2 is rich Mixture indicates (time t4) is referred to as TI_F2 (Fig. 2). The values TI_F1, TI_F2 are temporarily stored in a memory 28 of the electronic control device 16.

In addition, the times t3 and t4 at which the output signals ULS1 and ULS2 signal a rich mixture are recorded, and the time period T_SU between the probe switchovers is calculated from this by forming a difference, and likewise in the memory 28 for further diagnosis of the burner lambda between cached. The time T_SU is positive if first the lambda probe LSI and then the lambda probe LS2 indicate rich mixture (example according to FIG. 2, case 1) and the time T_SU is negative if the lambda probe LS2 and only then does the LSI lambda probe display a rich mixture.

In order to take into account the runtime of the exhaust gas from the lambda probe LSI to the lambda probe LS2, the enrichment factor TI_F2, in which the lambda probe LS2 indicates a rich mixture, is corrected according to the following relationship:

TI_FK2 = TI_F2 - (TI_F2 - TI_F1) * TI_LS / TI_SU,

where the value TI_FK2 denotes the corrected enrichment factor and T_LS a dead time that takes the gas running time between the two probes into account.

With the help of the enrichment factor TI_F1 and the corrected enrichment factor TI_FK2, the air ratio of the burner (burner lambda) λg _R can be determined:

λ .. = ^ML - ^BKM + τi FAK2 * TI FK2 - TI FAK \ * TI l) +1 ^HR ML_ BR * \ 4.1 ^{~ ~ ~}}

With

ML_BKM Air mass flow that is supplied to the internal combustion engine during the diagnosis (determined by the air mass meter) ML_BR Air mass flow that is supplied to the burner during the diagnosis (fixed predetermined value)

TI_FAK1,2 Total of the other, applied in the electronic engine control for warming up the internal combustion engine

Enrichment factors at times t3 and t4 at which the output signals of the two lambda probes signal a rich mixture. In order to assess the functionality of the burner, the air ratio of the burner λβ _R calculated according to the formula given above is compared with previous limit values. If the air ratio of the burner λgR is outside the limits

^λ BR_MAX * ^ R * ^λ BR_MIN

⁽ Eg: λßR _^ MAX = ^'15 / λ _B R vjiN = 0.95),

then a safe function of the burner 24 is no longer guaranteed and a corresponding entry is made in the error memory 27 of the electronic control device 16. At the same time, the result of the check can be communicated acoustically and / or visually to the driver of the vehicle and when the internal combustion engine is started again 10 the heating of the catalyst can be suppressed by means of the burner.

If, on the other hand, both lambda probes LSI, LS2 show a rich mixture before the start of the diagnosis (case 2), the

For the purpose of diagnosing the burner lambda λgR, the fuel-air mixture of the internal combustion engine 10 is emaciated. The reduction is also carried out via the factor TI_BR, which is gradually reduced from the value 1.0 according to the following relationship:

TI_BR _new = TI_BR _old - TI_BR _INC .

The emaciation is ended when either both lambda probes have detected lean or when a predefined limit value is reached

TI_BR_MIN for the thinning is reached, regardless of whether the two lambda probes have already recognized a lean mixture or not. In both cases, the TI BR factor is then reset to a value of 1.0.

If the lambda probe LS2 does not reach a voltage jump during the leaning down to the limit value TI BR = TI BR MIN, although If the lambda probe LS2 does not reach a voltage jump during the leaning down to the limit value TI_BR = TI_BR_MIN, although the lambda probe LSI has already detected a lean mixture due to the leaning, the air ratio of the burner 24 is classified as faulty.

If, on the other hand, the lambda probe LSI does not reach a voltage jump during the thinning, it can be assumed that there is either an error in the air ratio of the mixture supplied to the internal combustion engine or an error in the lambda probe LSI. In this case the diagnosis is aborted and repeated the next time the burner is started. There is no entry in the error memory 27.

The values at which the lambda probes LSI, LS2 detect lean (thinning factors in the voltage jumps) are recorded, as is the time between the voltage jumps, and the further evaluation is carried out in a corresponding manner, as was shown in case 1.

If the lambda probes LSI, LS2 show different mixture compositions before the diagnosis begins, ie the lambda probe LSI shows a rich mixture, while the lambda probe LS2 shows lean mixture (case 3) or vice versa (case 4), Since the diagnosis described in case 1 can only be carried out with rectified probe signals, the state of the signal of the lambda sensor LSI can be changed by emaciation (case 3) or enrichment (case 4) of the fuel-air mixture of the internal combustion engine . This takes place with an accumulation or enrichment function, as was explained on the basis of the two cases 1 and 2. If the thinning factor or the enrichment factor reaches its limit value during this phase without a change of state occurring before the catalytic converter in the signal from the lambda probe LSI, the diagnosis is terminated. If the lambda probe LS 1 in front of the catalytic converter indicates the same mixture composition as the lambda probe LS 2 after the catalytic converter within the limit value by leaning or enriching, the further diagnosis is carried out as in the case of cases 1 and 2 described method.

Claims

claims

1. Method for checking the functionality of a burner arranged in the exhaust tract of an internal combustion engine and operated with a fuel-air mixture for heating an exhaust gas catalytic converter of the internal combustion engine, with a first and a second lambda probe upstream or downstream of the exhaust gas catalytic converter, which each emit an output signal corresponding to the respective residual oxygen content in the exhaust gas and whose signal positions represent either a rich or lean mixture composition,

characterized by ^'

- that the signal positions (rich / lean) of the output voltages (ULS1, ULS2) of both lambda probes (LSI, LS2) are recorded,

- depending on these signal positions, the fuel-air mixture of the internal combustion engine (lo) is enriched or thinned by means of an enrichment or thinning factor (TI_BR) until both lambda sensors (LSI, LS2) change their signal positions,

- The values that occur for the enrichment or thinning factor (TI_F1, TI_F2) are recorded

an air ratio (λg _{R) of} the burner (24) is determined from these values (TI_F1, TI_F2) and from the air masses (ML_BR, ML_BKM) supplied to the burner (24) and the internal combustion engine (10) during the check, and,

the air ratio (λg _{R) of} the burner (24) is compared with predetermined limit values (λβ _R IN '^ BR MAX ^ and the burner (24) is classified as not currently functional if the air ratio (λß _R ) of the burner (24) lies outside these limits.

2.The method according to claim 1, characterized in that the enrichment. or reduction factor (TI_BR) is changed step by step up to a limit value (TI_BR_MAX, TI_BR_MIN).

3.Procedure according to claim 1, characterized in that the enrichment. or Abmage¬ tion factor (TI_F2), in which the output signal (ULS2) of the lambda probe (LS2) changes its signal position after the catalyst (14) by a dead time (T_LS) is corrected, which is based on the running time of the exhaust gas between the two probes (LSI, LS2).

4.The method according to claim 1 or 3, characterized in that the enrichment. or reduction factors (TI_F1, TI_F2) are corrected with a warm-up factor (TI_FAK1, TI_FAK2) that takes the warm-up of the internal combustion engine (10) into account.

5. The method according to claim 1, characterized in that the method is terminated if within the limits (TI_BR_MAX, TI_BR_MIN) for the enrichment or emaciation factor (TI_F1, TI_F2) the output signal (ULS1) of the lambda probe (LSI) before the catalyst (14) does not change its signal position.

6. The method according to claim 1, characterized in that the lambda probes (LSI, LS2) are heated for a predetermined time period (T_LS) before the start of the check of the burner (24).