Method and apparatus for diagnosing a secondary air valve in an engine system having an internal combustion engine

Abstract

To provide a diagnostic method for a secondary air induction device.SOLUTION: The present invention relates to a diagnostic method for a secondary air induction device in an engine system (1) having an internal combustion engine (2), in which the secondary air induction device connects an air supply system (4) and an exhaust gas discharge system (5) at the upstream side of a lambda sensor (16) via a secondary air valve (12) to introduce fresh air into the exhaust gas discharge system (5) in a secondary air operation. The method executes in diagnosis operation: a step (S2, S5) of changing a position of the secondary air valve (12); a step (S3, S6) of detecting a progress change of a lambda signal of the lambda sensor (16) in response to the change of the position of the secondary air valve (12); and a step (S4, S7) of signaling an error of the secondary air induction device (10) when the progress change of the lambda signal is not detected.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an internal combustion engine, in particular for an engine having a so-called secondary air valve. Furthermore, the present invention relates to a method for diagnosing such a secondary air valve. [Background technology]

[0002] The secondary air valve is a component used in motorbikes to improve the quality of the exhaust. For certain operating conditions, the secondary air valve allows fresh air to be fed from the air supply system to the exhaust gas discharge system, so that additional oxygen can be supplied to the exhaust gas aftertreatment device. This allows for a more emission-friendly combustion.

[0003] A secondary air intake system error causes the intentionally controlled, emission-reducing fresh air supply to the exhaust gas discharge system to be interrupted, resulting in the emission limit being exceeded. Possible errors in the secondary air intake system include the secondary air valve being open or closed, or the secondary air valve being stuck in an intermediate position, or the supply between the secondary air valve and the intake to the exhaust gas discharge system being interrupted. Summary of the Invention

[0004] According to the invention there is provided a method for diagnosing a secondary air intake device in an engine system having an internal combustion engine according to claim 1 as well as an apparatus and an engine system according to the other independent claims.

[0005] Further configurations are set forth in the dependent claims. According to one aspect, a method for diagnosing a secondary air introduction device in an engine system having an internal combustion engine is contemplated, the secondary air introduction device connecting an air supply and an exhaust gas discharge via a secondary air valve upstream of a lambda sensor to introduce fresh air into the exhaust gas discharge in a secondary air operation, and in a diagnostic operation: - changing the position of a secondary air valve; - detecting a change in the course of a lambda signal of a lambda sensor as a function of a change in the position of the secondary air valve; - signalling an error in the secondary air intake system if no change in the course of the lambda signal is detected.

[0006] The above method contemplates a diagnostic means for a secondary air intake system that can be used in internal combustion engines, particularly for motorcycles. In particular, the diagnostic method is suitable for engine systems having a two-point lambda sensor, which is typically used in motorcycle systems.

[0007] The essence of the method is to evaluate the lambda signal of a lambda sensor arranged before the exhaust aftertreatment device as a reaction to an intentional change in the position of the secondary air valve. In particular, the time duration before the lambda signal reacts to an intentional change in the position of the secondary air valve is evaluated. For diagnosis, the secondary air valve is switched from closed to open or from open to closed under stationary operating conditions and the reaction of the lambda signal at the lambda sensor to this is evaluated. If the secondary air valve opens and closes normally, an excess of oxygen or hydrocarbons is indicated at the lambda sensor. If the lambda signal reacts too early after a change in the position of the secondary air valve, a malfunction of the secondary air intake system can be identified.

[0008] If the engine system is functioning without errors, a lambda signal of a defined duration indicates either a rich phase, i.e. combustion with excess fuel, or a lean phase, i.e. combustion with excess oxygen, if controlled by a two-point lambda sensor and the secondary air valve is not defective. If, after diagnostic adjustment of the secondary air valve, a change of state from a lean phase to a rich phase or vice versa is detected early, this is an indication of a malfunction of the secondary air intake system, especially the secondary air valve.

[0009] The idea of ​​the method is to evaluate the duration of the lambda signal change in comparison with a properly functioning system, in which there is a delay in the change in the level of the lambda signal during a position change, whereas in a faulty system there is no delay in the change in the level of the lambda signal.

[0010] If, within the scope of the diagnosis, the secondary air valve is closed, an error is detected if the lambda sensor signal indicates an early lean phase. The advantage of the above diagnostic method is that by deliberately changing the position of the secondary air valve and observing the effect on the lambda signal of the lambda sensor, maximum robustness against system error detection is ensured. Opening the secondary air valve at the appropriate operating point significantly increases the oxygen fraction of the combustion exhaust gases, which is immediately detectable by the lambda sensor due to the longer duration before the level of the lambda signal changes.

[0011] Additionally, diagnostic action may be performed only if one or more of the following operating conditions are determined to be met: - The lambda sensor is active. - The lambda control device is active. - The engine temperature exceeds a certain threshold. - There is a stationary operating point. - The control factors of the control device are stable and there exists a stationary control operating point. - The temperature of the exhaust aftertreatment device exceeds a predetermined temperature threshold. - Tank vent is not active or has been active for a minimum duration. - There are no electrical errors in the lambda sensor or secondary air valve.

[0012] Furthermore, when the secondary air valve is opened to perform two-point control of the air-fuel mixture, the lambda control may detect the change in the lambda signal of the lambda sensor over time by determining the extension of the lean phase due to the opening of the secondary air valve.

[0013] When the secondary air valve is closed and two-point control of the air-fuel mixture is performed, it may be intended to detect the change in the lambda signal of the lambda sensor over time by determining the extension of the rich phase due to the opening of the secondary air valve by the lambda control.

[0014] In particular, during diagnostic operation, when the secondary air valve is opened or closed, pilot control of the amount of additional fuel to supplement the fresh air supplied via the secondary air intake system is not possible. According to one embodiment, the opening or closing time of the secondary air valve may coincide with the start of a lean or rich phase, respectively.

[0015] An error in the secondary air intake system can be determined if the change in the lambda signal of the lambda sensor, in particular the duration until the level of the lambda signal changes in response to a change in the position of the secondary air valve, is decreasing or if a duration that is too short is determined multiple times.

[0016] According to an alternative embodiment, the change in the course of the lambda signal can be determined by a deviation from a control factor of the lambda control device, which is present before the start of the diagnostic operation and which influences the ratio of the duration of the rich and lean phases by means of the fuel distribution. The control factor defines the correction of the injected fuel quantity with respect to the injected fuel quantity preset by the pilot control in order to set the lambda value to 1. If the change in time of this factor is limited, then there is stability of the control factor.

[0017] According to an alternative embodiment, the course of the lambda signal can be determined by deviation from the lambda value present before the start of the diagnostic operation. According to another aspect, a diagnostic device for a secondary air introduction device in an engine system having an internal combustion engine is provided, the secondary air introduction device connecting an air supply and an exhaust gas discharge via a secondary air valve upstream of a lambda sensor to introduce fresh air into the exhaust gas discharge in a secondary air operation, the device comprising: - changing the position of a secondary air valve; - detecting a change in the course of a lambda signal of a lambda sensor as a function of a change in the position of the secondary air valve; - signalling an error in the secondary air induction device if no change in the course of the lambda signal is detected.

[0018] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic diagram of an engine system having a secondary air introduction device. [Diagram 2] FIG. 4 shows the time course of the lean and rich phases in a lambda control device with a jump-type lambda sensor; [Diagram 3] 4 is a flowchart illustrating a method for diagnosing a secondary air introduction device of an engine system having an internal combustion engine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] 1 shows a schematic diagram of an engine system including an internal combustion engine 2 having cylinders 3 (two cylinders in this embodiment). Air is supplied to the internal combustion engine 2 via an air supply system 4, and combustion exhaust gas is discharged via an exhaust gas discharge system 5.

[0021] The air supply system 4 is provided with a throttle valve 6 for each cylinder 3 of the internal combustion engine 2 in order to control the air supply to these cylinders 3. Alternatively, the cylinders 3 may be provided with only one common throttle valve.

[0022] Further, in order to generate an air-fuel mixture in the cylinder 3, an injection valve 7 (intake system injection or in-cylinder injection) associated with the cylinder 3 is provided. The volume of the air supply system 4 includes a secondary air supply introduction device 10. The secondary air introduction device 10 has a secondary air line 11 that connects the volume of the air supply system 4 with the exhaust gas discharge system 5 upstream of the exhaust aftertreatment device 13 via an inlet 14. Also, a check valve 18 is provided at the inlet 14 of the secondary air line 11 to the exhaust gas discharge system 5.

[0023] The secondary air line 11 is provided with a secondary air valve 12 for controlling the flow of gas through the secondary air line 11 from the air supply system 4 to the exhaust gas discharge system 5. Also provided upstream of the exhaust aftertreatment device 13 and downstream of the intake 14 of the secondary air line 11 to the exhaust gas discharge system 5 is a lambda sensor 16. The lambda sensor 16 can be provided as a continuous measuring lambda sensor (wideband lambda sensor or LSU) or as a two-point lambda sensor or a jump type sensor (LSF).

[0024] A control unit 20 is provided for controlling the internal combustion engine 3. For this purpose, a lambda control device is provided which increases the amount of fuel injected in the exhaust gas discharge system 5 in case of a detected lean combustion exhaust gas (resulting from burning an air-fuel mixture with excess air with respect to stoichiometric equilibrium) and decreases the amount of fuel injected in case of a detected rich combustion exhaust gas (hydrocarbon content in the combustion exhaust gas) (resulting from burning an air-fuel mixture with excess fuel with respect to stoichiometric equilibrium). The amount of fuel injected is increased or decreased in a conventional manner by adapting the injection amount provided to provide a predefined target torque.

[0025] In static operation of a conventional engine system, the use of a jump-type lambda sensor results in a course of the lambda signal L as shown in Figure 2. The lambda signal switches between a signal level indicative of a lean phase and a signal level indicative of a rich phase within an approximately constant phase duration.

[0026] Under certain operating conditions, the control unit 20 drives the secondary air valve 12 in secondary air operation to draw fresh air from the air supply system 4 into the exhaust gas discharge system 5 in case of temporary negative pressure in the exhaust gas discharge system 5. Also, the check valve 18 prevents the combustion exhaust gas from flowing back out of the exhaust gas discharge system 5. Opening the secondary air valve 12 provides additional oxygen to the exhaust gas discharge system 5, which allows for combustion with low emissions.

[0027] In the following, a method for diagnosing the secondary air intake device 10 is proposed. The method for diagnosing can be implemented as a software or hardware algorithm in the control unit 20. The method is based on a powered internal combustion engine with an active lambda control system, and an engine system 1 is provided with an exemplary two-point lambda sensor as lambda sensor 16 .

[0028] First, in step S1, it is checked whether an operating point of the engine system 1 suitable for diagnosis exists. If so (option: yes), the method continues with step S2, otherwise it returns to step S1. The operating conditions necessary to execute the diagnostic method may include one or more of the following criteria, which must be fulfilled together / simultaneously: - The lambda sensor must be active. - The lambda controller must be active. - the engine temperature exceeds a certain threshold to prevent the diagnostic method from being executed during cold operation. There is a stationary operating point, for example idling operation of the internal combustion engine 2. - The control factors of the control device are stable and there exists a stationary control operating point. It can be ensured that the temperature of the exhaust aftertreatment device 13 is above a predefined temperature threshold and therefore the diagnosis can only be carried out if the exhaust aftertreatment device 13 is functional. - The function of the secondary air introduction device 10 for the secondary air operation to prevent emissions is not controlled. - The tank ventilation system is not active or is active for a minimum duration, so that the influence of gas supplied by the tank system is adjusted. - there is no electrical error in the lambda sensor 16 or the secondary air valve 12.

[0029] In step S2, the secondary air valve 12 is opened for diagnosis. Now, fresh air from the air supply system 4 flows into the exhaust gas discharge system 5, so that the oxygen proportion there increases. Before the secondary air valve 12 is opened, a two-point control of the air-fuel mixture is performed so that the state changes evenly with a defined duration between the rich and lean phases. This process is disturbed by the opening of the secondary air valve 12 if there is no error in the secondary air introduction device 10 or a malfunction in the secondary air valve 12, so that the lean phase is extended.

[0030] When the secondary air valve is open, unlike the functional operation of the secondary air supply, there is no pilot control of the amount of additional fuel to supplement the fresh air supplied via the secondary air introduction device 10 during diagnostics.

[0031] Thus, in step S3, it is checked whether the duration of the lean phase exceeds the target duration of the lean phase. The target duration can correspond to the duration of the lean phase or depend on how it was set by the lambda controller just before the secondary air valve was opened. The duration of the lean phase is monitored by measuring the duration from the change of the lambda controller to the lean phase to the rich phase.

[0032] If the duration of the lean phase exceeds the target duration of the lean phase (option: yes), no error is detected and the method continues with step S5, otherwise (option: no), an error is detected and the method continues with step S4.

[0033] In step S4, the value of a first error counter for secondary air intake device opening errors is incremented and the method continues with step S5. In step S5, proper functioning is determined when the secondary air introduction device 10 is opened, and as a result, the secondary air valve 12 is closed.

[0034] In step S6, after closing the secondary air valve 12, it is checked whether the lambda signal indicates an early lean phase, i.e. the rich phase must be present for a minimum duration, since closing the secondary air valve 12 interrupts the additional supply of fresh air via the secondary air introduction device 10. If in step S6 it is determined that the lambda signal indicates an early lean phase (option: yes), the method continues with step S7. If not (option: no), the method continues with step S8.

[0035] In step S7, the value of a second error counter for an opening error of the secondary air introduction device 10 is incremented and the method continues with step S8. In step S8 it is checked whether a number of diagnostic loops have been performed. If it is determined that the abort condition is met (option: yes), the method ends in step S9, signaling an error if any of the error counters exceed a predefined value. If not (option: no), it returns to step S1 to check whether the operating conditions for performing diagnostics still exist.

[0036] According to the method described above, the diagnosis of the secondary air introduction device requires multiple openings and closings of the secondary air valve 12. In particular, the diagnosis method can be carried out as soon as an operating phase with an active secondary air introduction device has ended, i.e. immediately after the completion of an operating phase during which secondary air was actively supplied to the exhaust gas discharge system 5 in the sense of functionally improving emissions.

[0037] The intended target durations of the lean and rich phases are calculated from the average observed durations of the lean and rich phases as soon as possible before the start of the diagnostic method. For this purpose, the control unit 20 may have corresponding timers.

[0038] For increased robustness, the duration of each of the rich and lean phases can be increased in an acceptable range, for example by applying a factor greater than 1. In particular, the opening and closing times of the secondary air valve 12 preferably coincide with the start of the lean or rich phase, respectively.

[0039] That is, the request to open the secondary air valve 12 is triggered by an edge change of the lambda signal from rich to lean, thus ensuring a defined system state when additional secondary air is applied, and the request to close the secondary air valve 12 is triggered depending on the time of the edge change of the lambda signal from lean to rich, or after a minimum duration has elapsed after the edge change of the lambda signal from rich to lean.

[0040] Also, if the lean phase ends early or the rich phase starts early, the secondary air valve 12 closes early after it is opened to perform the diagnostics, thereby detecting an error.

[0041] As an alternative to the above method, instead of evaluating the duration of the lean and rich phases, a control factor can also be evaluated. The control factor indicates the ratio of the durations of the rich and lean phases. A first error counter increases in value if the control factor increases by more than a predefined threshold after opening the secondary air valve, thereby representing enrichment of the air-fuel mixture in response to the additional air supply to the lambda sensor. A second error counter increases in value if the control factor decreases by more than a predefined threshold after closing the secondary air valve, which is the reaction of the lambda controller to the omission of the additional air supply due to the leaning of the air-fuel mixture.

[0042] Also, in the case of using a lambda sensor with continuous measurement, the lambda signal can be evaluated for error detection. Instead of monitoring the duration of the lean and rich phases, a first error counter is incremented if the lambda signal increases on average above a predefined threshold after the secondary air valve opens (leaning). A second error counter is incremented accordingly if the lambda signal decreases on average below a predefined threshold after the secondary air valve 12 is closed.

Claims

1. A method for diagnosing a secondary air introduction device in an engine system (1) having an internal combustion engine (2), the secondary air introduction device comprising: connecting an air supply system (4) and an exhaust gas discharge system (5) via a secondary air valve (12) upstream of a lambda sensor (16) to introduce fresh air into the exhaust gas discharge system (5) in a secondary air operation; In the diagnostic operation, - changing the position of said secondary air valve (12) (S2, S5); - detecting (S3, S6) the change in the course of the lambda signal of the lambda sensor (16) as a function of changing the position of the secondary air valve (12); - carrying out a step (S4, S7) of signalling an error of the secondary air intake device (10) if no change in the course of the lambda signal is detected, a first process for opening the secondary air valve (12) in a step (S2) of changing a position of the secondary air valve (12) and determining whether the duration of a lean phase exceeds a first target duration in a step (S3) of detecting a change in the lambda signal; a second process of incrementing a first error counter if the duration of the lean phase does not exceed the first target duration; a third process for closing the secondary air valve (12) in a step (S5) of changing a position of the secondary air valve (12), and for determining whether the lambda signal indicates a lean phase after a rich phase has continued for a second target duration due to the closing of the secondary air valve (12) in a step (S6) of detecting a change over time of the lambda signal; a fourth step of increasing a value of a second error counter if the lambda signal does not indicate a lean phase after the rich phase has lasted for the second target duration; Repeated a predetermined number of times, The method of claim 1, wherein the opening or closing time of the secondary air valve (12) coincides with the start of a lean or rich phase, respectively.

2. The diagnostic operation includes: - said lambda sensor (16) is active; - the lambda controller is active, - the engine temperature exceeds a predetermined threshold; - there is a stationary operating point; the control factors of the control device are stable and there is a stationary control operating point; - the temperature of the exhaust aftertreatment device exceeds a predetermined temperature threshold; - there are no electrical errors in the lambda sensor or in the secondary air valve; The method of claim 1 , wherein the method can be performed when one or more of the operating conditions are determined to be satisfied.

3. 3. The method according to claim 1, wherein during diagnostic operation, when the secondary air valve (12) is opened or closed, no pilot control of an additional fuel quantity to supplement the fresh air supplied via the secondary air introduction device (10) is performed.

4. 3. The method according to claim 2, wherein the change in the lambda signal over time is determined by a deviation from a control factor of the lambda control device that exists before the start of the diagnostic operation and that influences the ratio of the duration of rich and lean phases by fuel distribution.

5. 3. The method according to claim 1, wherein the course of the lambda signal is determined by a deviation from a lambda value present before the start of the diagnostic operation.

6. A diagnostic device for a secondary air introduction device (10) in an engine system (1) having an internal combustion engine (2), the secondary air introduction device (10) connecting an air supply system (4) and an exhaust gas discharge system (5) via a secondary air valve (12) upstream of a lambda sensor (16) to introduce fresh air into the exhaust gas discharge system (5) in secondary air operation, The diagnostic device, in a diagnostic operation of the secondary air introduction device (10), - changing the position of said secondary air valve (12); - detecting the change in the course of the lambda signal of the lambda sensor (16) as a function of the change in position of the secondary air valve (12); - signalling an error in the secondary air intake device (10) if no change in the course of the lambda signal is detected, said diagnostic device further comprising: a first process for opening the secondary air valve (12) in a step of changing a position of the secondary air valve (12) and for determining whether the duration of a lean phase exceeds a first target duration in a step of detecting a change in the lambda signal; a second process of incrementing a first error counter if the duration of the lean phase does not exceed the first target duration; a third process for closing the secondary air valve (12) in the step of changing a position of the secondary air valve (12) and determining whether the lambda signal indicates a lean phase after a rich phase has continued for a second target duration due to the closure of the secondary air valve (12) in the step of detecting a change in the lambda signal over time; and a fourth step of increasing a value of a second error counter if the lambda signal does not indicate a lean phase after the rich phase has lasted for the second target duration. configured to repeat a predetermined number of times, The time when the secondary air valve (12) opens or closes corresponds to the start of a lean or rich phase, respectively.

7. A computer program arranged to carry out all the steps of the method according to any one of claims 1 to 5.

8. A machine-readable storage medium having stored thereon the computer program of claim 7.

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