Method and device for monitoring secondary air supply in internal combustion engine
By using the throttling equation and exhaust gas λ value to determine the secondary air mass flow in the internal combustion engine and deducing the effective throttling surface, the problem of insensitive diagnosis of secondary air supply devices in the prior art is solved, and the accurate identification and early warning of faults are achieved.
Patent Information
- Application Number
- CN202411589993.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-11-10
- Filing Date
- 2024-11-08
- Publication Date
- 2025-05-13
AI Technical Summary
The prior art is not sensitive enough to diagnose secondary air supply devices in internal combustion engines, and it is difficult to accurately identify small leakages or faults.
By determining the secondary air mass flow with the throttling equation and exhaust gas λ value, and deriving the effective throttling surface, the effective throttling surface is monitored using at least one pre-designated threshold to identify potential failures.
Reliable diagnosis of secondary air systems is achieved, fault identification can be identified in advance, and the ability to identify small leaks is improved.
Smart Images
Figure CN119982168A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for monitoring a secondary air supply in an internal combustion engine. The invention also relates to a diagnostic system for a secondary air supply in an internal combustion engine. Background Art
[0002] In the past few years, the emissions of modern internal combustion engines have been significantly reduced by numerous measures. The continuous tightening of existing exhaust gas limit values and the regulation of additional pollutant components such as NH 3 in various markets have led to an ever-increasing complexity of exhaust gas aftertreatment systems.
[0003] One measure for increasing the temperature in the exhaust gas aftertreatment system is the secondary air injection. Here, an external air mass flow is introduced into the exhaust manifold at the exhaust valve of the engine, which reacts exothermically with the enriched combustion chamber lambda at the hot surfaces of the manifold and the turbocharger.
[0004] For example, the target values for the secondary air injection can be predetermined for the combustion chamber lambda (untreated emissions of the internal combustion engine) and the exhaust gas lambda (catalytic conversion capacity). ). From the ratio of the two lambda target values and the current exhaust gas mass flow, for example, the required secondary air quantity can then be determined.
[0005] In the diagnosis of the secondary air system, the actual secondary air mass flow determined from the measured pressure in the secondary air system is monitored. When the secondary air mass flow is actively conveyed to the closed secondary air valve, the pressure in the secondary air system must increase, whereby the modeled actual secondary air mass flow should decrease due to the reduced scavenging difference. If the secondary air valve is open, a positive secondary air mass flow can be expected to occur depending on the scavenging difference.
[0006] However, currently used diagnostics of secondary air systems are in part not sensitive enough to be robust enough to identify, for example, a small leak in the secondary air system as a fault. Summary of the invention
[0007] The object of the present invention is therefore to provide a method for monitoring a secondary air supply device and a diagnostic system for the secondary air supply device which allow reliable diagnosis of faults in the secondary air system / improve the diagnosis of possible faults in the secondary air system.
[0008] According to the invention, a method for monitoring a secondary air supply in an internal combustion engine is provided according to claim 1 , and a corresponding diagnostic system is provided according to the independent claim.
[0009] Further refinements are described in the dependent claims.
[0010] According to a first aspect, a method for monitoring a secondary air supply in an internal combustion engine is provided, wherein the internal combustion engine has a secondary air supply, a device for determining a pressure in the secondary air supply, and an exhaust gas lambda sensor for determining a current exhaust gas lambda value, wherein the method comprises the following steps:
[0011] a) determining a first secondary air mass flow associated with the effective throttle surface by means of a throttling equation and as a function of the pressure in the secondary air supply;
[0012] b) determining a second secondary air mass flow taking the measured exhaust gas lambda value as a starting point and taking into account the primary air mass flow of the internal combustion engine and the supplied fuel mass flow;
[0013] c) deriving an effective throttle surface from the first secondary air mass flow determined in step a) and the second secondary air mass flow determined in step b);
[0014] d) Monitoring the effective throttle surface thus obtained using at least one predefined threshold value.
[0015] In a method for monitoring a secondary air supply device, a secondary air mass flow is determined in two different ways. First, a first secondary air mass flow associated with an effective throttle surface is determined based on a pressure relationship in an exhaust device by means of a throttling equation. Second, a second secondary air mass flow is determined based on a measured exhaust gas lambda value. An effective throttle surface is derived from these two secondary air mass flows obtained in different ways. Based on this effective throttle surface, it is possible to track whether the first secondary air mass flow and the second secondary air mass flow are in a coordinated ratio relative to each other. The effective throttle surface thus obtained is therefore suitable for diagnosing a secondary air system. Here, it is possible to monitor whether the effective throttle surface fluctuates within an expected range by means of at least one predetermined threshold value. If the effective throttle surface leaves the expected range, it can be inferred, for example, that there is a fault, such as a leak, in the secondary air system. Monitoring of the effective throttle surface enables accurate monitoring of the secondary air system during operation and enables early identification of faults.
[0016] The invention further relates to a diagnostic system for a secondary air supply in an internal combustion engine, wherein the internal combustion engine has a secondary air supply for supplying secondary air, a device for determining a pressure in the secondary air supply, an exhaust gas lambda sensor for determining a current exhaust gas lambda value, and an evaluation device which is designed to:
[0017] a) determining a first secondary air mass flow associated with the effective throttle surface by means of a throttling equation and as a function of the pressure in the secondary air supply;
[0018] b) determining a second secondary air mass flow starting from the measured exhaust gas lambda value and taking into account the primary air mass flow of the internal combustion engine and the supplied fuel mass flow;
[0019] c) deriving an effective throttle surface from the first secondary air mass flow determined in step a) and the second secondary air mass flow determined in step b);
[0020] d) Monitoring the effective throttle surface thus obtained using at least one predefined threshold value.
[0021] Advantageously, in step a), the first secondary air mass flow is determined with the aid of a throttle equation which relates the first secondary air mass flow to the pressure in the secondary air supply device and to the effective throttle surface.
[0022] Preferably, in step c), the effective throttle surface is derived with the aid of a mass flow balance as a function of the exhaust gas lambda value.
[0023] Furthermore, preferably in step c), the effective throttle surface is derived taking into account the time dynamics of the exhaust gas lambda sensor.
[0024] According to a preferred embodiment, in step c), the effective throttle surface is derived using a recursive least mean square method (LMS) or a recursive normalized least mean square method (NLMS). Using such a recursive method allows an accurate determination of the effective throttle surface.
[0025] Preferably, the difference between the secondary air mass flow derived from the pressure and the secondary air mass flow derived from the exhaust gas lambda value is used as the error term of the recursive least mean square method (LMS) or the recursive normalized least mean square method (NLMS).
[0026] According to a preferred specific embodiment, for monitoring purposes, a leakage is detected if the effective throttle surface is greater than a predefined first threshold value.
[0027] According to a preferred specific embodiment, a stuck or blocked secondary air valve is detected if the effective throttle surface is smaller than a predefined second threshold value.
[0028] According to a further aspect, a diagnostic system for a secondary air supply device in an internal combustion engine is provided, wherein the internal combustion engine has:
[0029] - a secondary air supply device for supplying secondary air;
[0030] - means for determining the pressure in the secondary air supply;
[0031] - an exhaust gas lambda sensor for determining the current exhaust gas lambda value;
[0032] - an evaluation device designed to:
[0033] a) determining a first secondary air mass flow associated with the effective throttle surface by means of a throttling equation and as a function of the pressure in the secondary air supply;
[0034] b) determining a second secondary air mass flow starting from the measured exhaust gas lambda value and taking into account the primary air mass flow of the internal combustion engine and the supplied fuel mass flow;
[0035] c) deriving an effective throttle surface from the first secondary air mass flow determined in step a) and the second secondary air mass flow determined in step b);
[0036] d) Monitoring the effective throttle surface thus obtained using at least one predefined threshold value. BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The following is a more detailed explanation of the embodiments with the aid of the accompanying drawings, wherein:
[0038] Figure 1 An overview of the exhaust equipment is shown;
[0039] Figure 2 A physical model of a secondary air supply is shown;
[0040] Figure 3 A schematic diagram of an estimation algorithm for obtaining the effective throttle surface is shown. DETAILED DESCRIPTION
[0041] One measure for increasing the temperature in the exhaust gas aftertreatment system is the secondary air injection. Here, an external air mass flow is introduced into the exhaust manifold at the exhaust valve of the engine, which reacts exothermically with the enriched combustion chamber lambda at the hot surfaces of the manifold and the turbocharger.
[0042] The diagnostic method and diagnostic system described below for a secondary air system are based on a physical model that describes the secondary air supply device. Figure 1 To illustrate the model. Figure 1 FIG. 1 shows an internal combustion engine 1 together with an exhaust system 2 and a secondary air supply 3. In the combustion chamber of the internal combustion engine 1, the supplied fuel mass flow Together with the supplied primary air mass flow The secondary air mass flow is supplied to the exhaust gas mass flow in the exhaust system 2 via the secondary air supply device 3. In this case, the unburned fuel reacts exothermically with the supplied secondary air in the exhaust gas tract 2. An exhaust gas lambda sensor 4 is arranged in the exhaust gas tract 2, which is designed to determine the exhaust gas lambda value λ sens .
[0043] The secondary air supply device 3 can be regarded as a throttle valve. A pressure sensor 5 is arranged in the secondary air supply device 3 , which is designed to determine the pressure p in the secondary air supply device 3 . S Secondary air mass flow Based on the modeled pressure p3 in the exhaust gas train 2 and the measured pressure p in the secondary air supply device 3 S The pressure difference between the two can be set and can be controlled by the effective throttle surface A eff (called the effective opening cross section), the effective throttling surface is also Figure 1 Drawn in.
[0044] The above-mentioned physical model describes the pressure p in the secondary air supply 3 S The measured exhaust gas lambda value sens The relationship between Figure 2 After the secondary air supply device 3 can behave as a throttle valve, in step 6 the pressure p in the secondary air supply device 3 can be adjusted. S , the temperature T in the secondary air supply device 3 S and the pressure p3 in the exhaust system 2 and the effective throttle surface A eff Determine the secondary air mass flow with the aid of the throttling equation Based on the secondary air mass flow thus determined Primary air mass flow and fuel mass flow A lambda calculation 7 can then be carried out in order to obtain the calculated lambda value lambda sum Then, by using the lambda dynamics 8 , ie by taking into account the exhaust gas lambda sensor 4 with the aid of the parameter τ sens and σ sens The dynamic and static times represented by the calculated λ value λ sum is converted into the exhaust gas lambda value lambda actually measured by the exhaust gas lambda sensor 4 sens (t).
[0045] Described below Figure 2 The calculations on which the physical model shown in FIG. is based. The secondary air mass flow through the secondary air supply device 3 which can be described as a throttle valve The throttling equation
[0046]
[0047] To indicate that, represents the pressure p3 in the exhaust system 2 and the pressure p in the secondary air supply device 3 S Here, A eff is the effective throttling surface, p S is the pressure in the secondary air supply 3, and T S is the temperature of the secondary air. S ) indicates that it depends on the pressure ratio Π S The flow function
[0048]
[0049] Among them, crit =0.528 and Ψ crit =0.484.
[0050] exist Figure 2 The subsequent λ calculation of the model shown in 7 is based on the total air supply As the starting point, the calculated λλ sum Calculated as
[0051]
[0052] Among them, λ sto =14.7 represents the stoichiometric ratio of fuel and air during the conversion. In the subsequent lambda dynamics 8, taking into account the dynamics and the static time of the exhaust gas lambda sensor 4, the following differential equation is used:
[0053]
[0054] The dynamic characteristics of the lambda segment are modeled, where lambda sum represents the λ,τ obtained by calculation sens and σ sens represents the parameters used to model the dynamics of λ, and λ sens (t) represents the exhaust gas lambda value detected by the exhaust gas lambda sensor 4 .
[0055] Now, based on the Figure 2 The model equations of the physical model shown in are used to construct the effective throttling surface A eff Schematically, in Figure 3 The method for obtaining the effective throttle surface A is shown in eff The goal is to obtain the effective throttle surface A effAnd according to the obtained effective throttle surface A eff The secondary air supply device is monitored in order to be able to detect and diagnose possible problems in the secondary air supply device as early as possible in this way.
[0056] First, we describe the method for estimating the effective throttle surface A. eff in Figure 3 In the lower path, the exhaust gas lambda value λ measured by the exhaust gas lambda sensor 4 is used. sens (t) as a starting point, with the aid of the inverted λ calculation 9 and using the primary air mass flow and fuel mass flow The associated secondary air mass flow is calculated in the case of To determine Using the formula
[0057]
[0058] This formula is obtained from the definition of λ, where λ sto Represents the stoichiometric ratio of air to fuel, represents the fuel mass flow supplied, λ sens represents the measured exhaust gas lambda value, and represents the primary air mass flow.
[0059] exist Figure 3 In the upper path of the schematic diagram shown in FIG. , in a first step 10, with the aid of the throttling equation (without an effective throttling surface)
[0060]
[0061] To determine the effective throttle surface A eff Related secondary air mass flows Here, S Indicates pressure ratio p S represents the pressure in the secondary air supply device 3, T S p3 denotes the temperature in the secondary air supply device 3 and p4 denotes the pressure in the exhaust gas line 2 .
[0062] With the aid of the subsequent lambda dynamics 11, the flow parameter τ of the exhaust gas lambda sensor 4 is converted to sens and σ sens The described dynamic and static times apply to the secondary air mass flow thus determined in relation to the effective throttle surface. In this way, the time-dependent secondary air mass flow is obtained in relation to the effective throttle surface. The secondary air mass flow is related to the measured exhaust gas lambda value λ sens(t) Determined secondary air mass flow Synchronous. The following differential equation
[0063]
[0064] For applying the lambda dynamics to the time-dependent secondary air mass flow in relation to the effective throttle surface superior.
[0065] Then, the secondary air mass flow is determined in the following path and the secondary air mass flow associated with the effective throttle surface determined in the upper path As a starting point, determine the effective throttle surface A eff This step is Figure 3 Step 12 is shown in FIG.
[0066] In order to determine the effective throttle surface A eff The parameters can be Divide by parameter However, it has been shown that such a quotient formation can lead to inaccurate results. In particular, if the secondary air mass flow becomes very small or even tends to zero, it is possible to obtain an inaccurate result for the effective throttle surface A. eff inaccurate numerical value.
[0067] For this reason, it is advantageous to recursively determine the effective throttle surface A eff Instead, a recursive least squares method is used, in the present case for example the LMS (least mean square) algorithm or more preferably the NLMS (normalized least mean square) algorithm.
[0068]
[0069] The starting point for recursively determining the effective throttle surface is formed by the equation establishing the secondary air mass flow rate determined from the effective throttle surface with the aid of the throttle equation. The secondary air mass flow rate determined by means of the exhaust gas lambda sensor 4 The relationship between.
[0070] For the case where the LMS (least mean square) algorithm is used as the adaptation algorithm, the adaptation factor is obtained in the derivation: And in the scalar case we get Here, w denotes the regression number, k denotes the proportionality constant, and error denotes the error. The regression number w is in the present case the secondary air mass flow obtained from the throttle equation without an effective throttle surface. However, if the secondary air mass flow tends towards zero, the problem may arise, for example in the LMS algorithm, that the adaptation factor becomes infinite.
[0071] To avoid this problem, it is advantageous to use the NLMS (Normalized Least Mean Square) algorithm in an embodiment. The adaptation factor for the NLSM algorithm is This gives in the scalar case To recursively estimate the effective throttle surface, using the modified NLMS algorithm, we obtain
[0072]
[0073] Here, K id is the adjustment parameter for the estimated speed. This differential equation is repeated at each time step. The estimated value A thus obtained is then effEst，k Compare with the pre-set threshold. Therefore, if A effEst，k becomes too large, a leak can be identified. effEst，k If it becomes too small, a stuck or clogged secondary air valve can be detected.
[0074] The invention can also be extended to other exhaust topologies. For example, it is possible to have multiple valves in the secondary air supply device, instead of p S Instead, other reference variables, such as, for example, the exhaust gas back pressure or the boost pressure, are used for modeling the throttle valve. Instead of a pressure sensor, a modeled variable can also be used.
[0075] The features disclosed in the preceding description, the claims and the drawings may be essential for the realization of the invention in its various embodiments both individually and also in any desired combination.
Claims
1. A method for monitoring a secondary air supply (3) in an internal combustion engine (1), wherein: The internal combustion engine (1) has a secondary air supply device (3), a pressure sensor (1) for determining a pressure (p) in the secondary air supply device (3). S ) and a device for determining a current exhaust gas lambda value (λ sens ) of an exhaust gas lambda sensor (4), wherein the method comprises the following steps: a) by means of the throttling equation and depending on the pressure (p S ) to determine the effective throttling surface (A eff )The first secondary air mass flow b) The measured exhaust gas lambda value (λ sens ) as a starting point and taking into account the primary air mass flow of the internal combustion engine (1) and the supplied fuel mass flow Determine the second secondary air mass flow rate c) from the first secondary air mass flow determined in step a) and the second secondary air mass flow determined in step b) The effective throttling surface (A eff ); d) the effective throttle surface (A) thus obtained, using at least one predetermined threshold value eff ) for monitoring.
2. The method according to claim 1, characterized in that In step a), the first secondary air mass flow is determined with the aid of a throttling equation The throttling equation converts the first secondary air mass flow and the pressure in the secondary air supply (p S ) and the effective throttling surface (A eff ) association.
3. The method according to claim 1 or claim 2, characterized in that: In step c), the effective throttle surface is derived with the aid of a mass flow balance as a function of the exhaust gas lambda value.
4. The method according to any one of the preceding claims, characterized in that In step c), the effective throttle surface is derived taking into account the time dynamics of the exhaust gas lambda sensor (4).
5. The method according to any one of the preceding claims, characterized in that In step c), the effective throttle surface (A) is derived using a recursive least mean square method (LMS) or a recursive normalized least mean square method (NLMS). eff ).
6. The method according to claim 5, characterized in that The pressure (p) is used as the error term of the recursive least mean square method (LMS) or the recursive normalized least mean square method (NLMS). S ) and the secondary air mass flow derived from the exhaust gas lambda value The difference.
7. The method according to any one of the preceding claims, characterized in that For the effective throttling surface (A eff ) is greater than a predetermined first threshold value, a leak is detected.
8. The method according to any one of the preceding claims, characterized in that For the effective throttling surface (A eff ) is less than a predetermined second threshold value, a stuck or clogged secondary air valve is detected.
9. A diagnostic system for a secondary air supply device (3) in an internal combustion engine (1), wherein: The internal combustion engine (1) comprises: - a secondary air supply device (3) for supplying secondary air; - for determining the pressure (p S ) - used to determine the current exhaust gas lambda value (λ sens ) of an exhaust gas lambda sensor (4); - Evaluation devices designed to: a) by means of the throttling equation and depending on the pressure (p S ) to determine the effective throttling surface (A eff )The first secondary air mass flow b) The measured exhaust gas lambda value (λ sens ) as a starting point and taking into account the primary air mass flow of the internal combustion engine (1) and the supplied fuel mass flow Determine the second secondary air mass flow rate c) from the first secondary air mass flow determined in step a) and the second secondary air mass flow determined in step b) The effective throttling surface (A eff ); d) the effective throttle surface (A) thus obtained, using at least one predetermined threshold value eff ) for monitoring.
10. An exhaust system of an internal combustion engine (1) having a diagnostic system according to claim 9.
11. Computer program product comprising instructions which, when the program is executed by at least one data processing device, cause the data processing device to perform the steps of the method according to any one of claims 1 to 8.
12. A machine-readable storage medium comprising instructions which, when executed by at least one data processing device, cause the data processing device to perform the steps of the method according to any one of claims 1 to 8.