Method and system for air fuel ratio control and detecting cylinder imbalance

A technology of air-fuel ratio and exhaust air-fuel ratio, which is applied in the direction of fuel injection control, electrical control, automatic control, etc., and can solve problems such as cylinder air/fuel imbalance

Active Publication Date: 2016-05-04
FORD GLOBAL TECH LLC
7 Cites 4 Cited by

AI-Extracted Technical Summary

Problems solved by technology

[0005] In one example, the problems described above may be addressed by a meth...
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Method used

[0069] A technical effect of the counting method includes counting samples below a threshold normalized to a total number of peak-to-peak oscillations and comparing this value to an imbalance threshold for better control of the operation of th...
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Abstract

Air/fuel imbalance monitoring systems and methods for monitoring air/fuel ratio imbalance of an internal combustion engine are disclosed. In one embodiment, adjusting engine operation responsive to cylinder air/fuel imbalance based on a determined total number of instances where sensed peak-to-peak exhaust air-fuel ratios differentials are less than a threshold normalized to a total number of peak-to-peak oscillations. The approach can be used to indicate air/fuel ratio imbalances between engine cylinders.

Application Domain

Electrical controlInternal combustion piston engines +6

Technology Topic

Air–fuel ratioMonitoring system +1

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  • Method and system for air fuel ratio control and detecting cylinder imbalance
  • Method and system for air fuel ratio control and detecting cylinder imbalance
  • Method and system for air fuel ratio control and detecting cylinder imbalance

Examples

  • Experimental program(1)

Example Embodiment

[0015] Hereinafter, the diagnosis method and diagnosis system of the engine system will be described in more detail with reference to the drawings. Note that the embodiment described below is an illustrative example, and various alternative embodiments may also be used.
[0016] figure 1 The illustration shows a schematic diagram of an engine system 100 including one cylinder of the multi-cylinder engine 10, and the engine system 100 may be included in the propulsion system of an automobile. The engine 10 may be controlled at least in part by a control system including the controller 12 and by input from a vehicle operator 132 via an input device 130. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The combustion chamber (ie, the cylinder 30) of the engine 10 may include a combustion chamber wall 32 in which the piston 36 is positioned. The piston 36 may be coupled to the crankshaft 40 such that the rotational movement of the piston is converted into the rotational movement of the crankshaft. The crankshaft 40 may be coupled to at least one drive wheel of the vehicle via an intermediate transmission system. Further, the starter motor may be coupled to the crankshaft 40 via a flywheel to ensure the starting operation of the engine 10.
[0017] The combustion chamber 30 may receive intake air from the intake manifold 44 via the intake passage 42 and may exhaust combustion gas via the exhaust passage 48. The intake manifold 44 and the exhaust manifold 48 can selectively communicate with the combustion chamber 30 via the corresponding intake valve 52 and exhaust valve 54. In some embodiments, the combustion chamber 30 may include two or more intake valves and/or two or more exhaust valves. In this example, the intake valve 52 and the exhaust valve 54 may be controlled by cam actuation via one or more cams and may utilize cam profile transformation (CPS), variable cam timing, which can be operated by the controller 12 One or more of (VCT), variable valve timing (VVT), and/or variable valve lift (VVL) systems to change valve operation. The positions of intake valve 52 and exhaust valve 54 may be determined by position sensors 55 and 57, respectively. In alternative embodiments, intake valve 52 and/or exhaust valve 54 may be controlled by electric valve actuation. For example, the cylinder 30 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including a CPS and/or VCT system.
[0018] In some embodiments, each cylinder of the engine 10 may be configured with one or more fuel injectors for supplying fuel thereto. As a non-limiting example, the cylinder 30 is shown as including one fuel injector 66 and the fuel injector 66 is supplied with fuel from the fuel system 172. The fuel injector 66 is shown as being directly coupled to the cylinder 30 for directly injecting fuel therein in proportion to the pulse width of the signal EPW received from the controller 12 via the electronic driver 68. In this way, the fuel injector 66 provides so-called direct injection (hereinafter also referred to as “DI”) of fuel into the combustion chamber 30.
[0019] It should be appreciated that in an alternative embodiment, injector 66 may be a port injector that provides fuel into the intake port upstream of cylinder 30. It should also be appreciated that cylinder 30 may receive fuel from multiple injectors, such as multiple port injectors, multiple direct injectors, or a combination thereof.
[0020] carry on figure 1 , The intake passage 42 may include a throttle 62 having a throttle plate 64. In this particular example, the position of the throttle plate 64 may be provided by the controller 12 via a signal provided to an electric motor or an electric actuator including the throttle 62 (a configuration commonly referred to as electronic throttle control (ETC)). To change. In this manner, the throttle 62 may be operated to change the intake air provided to the combustion chamber 30 and other engine cylinders. The position of the throttle plate 64 may be provided to the controller 12 through the throttle position signal TP. The intake passage 42 may include a mass air flow sensor 120 and a manifold air pressure sensor 122 for providing corresponding signals MAF and MAP to the controller 12.
[0021] In the selected operating mode, in response to the spark advance signal SA from the controller 12, the ignition system 88 can provide an ignition spark to the combustion chamber 30 via the spark plug 92. Although a spark ignition assembly is shown, in some embodiments, the combustion chamber 30 or one or more other combustion chambers of the engine 10 may be operated in a compression ignition mode with or without an ignition spark.
[0022] The upstream exhaust gas sensor 126 is shown as being coupled to the exhaust passage 48 upstream of the emission control device 70. The upstream sensor 126 may be any suitable sensor for providing an indication of the exhaust air-fuel ratio, such as a linear broadband oxygen sensor or UEGO (universal or wide-area exhaust oxygen), a two-state narrow-band oxygen sensor or EGO, HEGO (heated EGO) ), NO x , HC or CO sensor. In one embodiment, the upstream exhaust gas sensor 126 is a UEGO, which is configured to provide an output proportional to the oxygen content present in the exhaust gas, such as a voltage signal. The controller 12 uses this output to determine the exhaust air-fuel ratio.
[0023] The emission control device 70 is shown as being arranged downstream of the exhaust gas sensor 126 along the exhaust passage 48. The device 70 may be a three-way catalyst (TWC), which is configured to reduce NO x And oxidize CO and unburned hydrocarbons. In some embodiments, the device 70 may be NO x Trap, various other emission control devices, or combinations thereof.
[0024] The second downstream exhaust gas sensor 128 is shown as being coupled to the exhaust passage 48 downstream of the emission control device 70. The downstream sensor 128 may be any suitable sensor for providing an indication of the exhaust air-fuel ratio, such as UEGO, EGO, HEGO, etc. In one embodiment, the downstream sensor 128 is a HEGO, which is configured to indicate the relative enrichment or leanness of exhaust gas after passing through the catalyst. Therefore, HEGO can provide an output in the form of a voltage signal at the switching point or the point where the exhaust gas switches from lean to enriched.
[0025] The third downstream exhaust gas sensor 129 is shown as being coupled to the exhaust passage 48 downstream of the emission control device 70 and symmetrically opposed to the HEGO sensor 128. The downstream sensor 129 may be any suitable sensor for providing an indication of the exhaust air-fuel ratio, such as UEGO, EGO, HEGO, etc. In one embodiment, the downstream sensor 129 is a HEGO, which is configured to indicate the relative enrichment or leanness of the exhaust gas after passing through the catalyst. Therefore, HEGO can provide an output in the form of a voltage signal at the switching point or the point where the exhaust gas switches from lean to enriched.
[0026] Further, in the disclosed embodiment, an exhaust gas recirculation (EGR) system may deliver a desired portion of exhaust gas from the exhaust passage 48 to the intake passage 42 via the EGR passage 140. The amount of EGR provided to the intake passage 42 may be changed by the controller 12 via the EGR valve 142. Further, the EGR sensor 144 may be disposed in the EGR passage and may provide an indication of one or more of the pressure, temperature, and concentration of the exhaust gas. Under certain conditions, the EGR system can be used to regulate the temperature of the air and fuel mixture in the combustion chamber.
[0027] Controller 12 in figure 1 Is shown as a microcomputer, which includes: a microprocessor unit 102, an input/output port 104, an electronic storage medium for executable programs and calibration values ​​(shown as a read-only memory chip 106 in this particular example), Random access memory 108, keep-alive memory 110 and data bus. The controller 12 can receive various signals from sensors coupled to the engine 10, in addition to the signals discussed above, it also includes: the incoming mass air flow (MAF) measurement value from the mass air flow sensor 120; The engine coolant temperature (ECT) of the temperature sensor 112 of the cooling jacket 114; the surface ignition sensing signal (PIP) from the Hall-effect sensor 118 (or other type) coupled to the crankshaft 40; the signal from the throttle position sensor Throttle position (TP); and absolute manifold pressure signal (MAP) from sensor 122. The engine speed RPM can be generated by the controller 12 from the signal PIP.
[0028] The storage medium read-only memory 106 can be programmed with computer-readable data representing non-transitory instructions executable by the processor 102 for performing the methods described below and other variants that are expected but not specifically listed.
[0029] As mentioned above, figure 1 Only one cylinder in a multi-cylinder engine is shown, and each cylinder may similarly include its own set of intake/exhaust valves, fuel injectors, spark plugs, etc.
[0030] As will be recognized by those skilled in the art, the specific procedures described in the flowchart below may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and so on. Therefore, various actions or functions shown may be executed in the order shown, executed in parallel, or omitted in some cases. Likewise, the order of processing is not necessary to realize the features and advantages, but is provided for ease of explanation and description. Although not explicitly stated, depending on the particular strategy used, one or more of the actions or functions shown may be repeatedly performed. Further, these graphics graphically represent codes programmed into the computer-readable storage medium in the controller 12 and implemented by the controller and engine hardware, such as figure 1 Shown.
[0031] figure 2 It is a high-level flowchart illustrating an example method 200 for identifying an air/fuel imbalance fault using a counting method according to the present disclosure. In particular, the method 200 involves using the number of signals to identify an air/fuel imbalance fault associated with a cylinder. This article will refer to figure 1 The components and systems described in this section describe the method 200, but it should be understood that the method can be applied to other systems without departing from the scope of the present disclosure. The method 200 may be implemented by the controller 12 and includes calculating an air-fuel ratio based on an exhaust gas sensor, such as a sensor 126 located upstream of the catalyst.
[0032] Method 200 can be figure 1 The system 100 is implemented. For example, the controller 12 may include one or more of hardware and/or software configured to combine with the illustrated engine hardware (such as various sensors and actuators) to implement the method 200.
[0033] At 202, the method includes determining engine operating parameters. Engine operating parameters may include, but are not limited to, engine speed, engine load, commanded air-fuel ratio, exhaust air-fuel ratio measured by exhaust gas sensors (such as sensor 126), and other parameters. At 204, the method includes performing engine air/fuel control. Air/fuel control may include determining the commanded (e.g., target) engine air-fuel ratio (e.g., based on engine speed and load), determining the current exhaust air-fuel ratio based on feedback from the exhaust gas sensor, and determining the difference between the target air-fuel ratio and the current air-fuel ratio. The difference between them adjusts one or more engine operating parameters (such as fuel injection amount). For example, the exhaust gas sensor used in air/fuel control may be a UEGO sensor positioned upstream of the catalyst.
[0034] During air/fuel control, exhaust gas can be delivered from a group of cylinders to an exhaust gas sensor. The exhaust gas sensor may be positioned in such a way that exhaust gas is transmitted to the exhaust gas sensor from a group of cylinders, such as a group of cylinders in an engine bank upstream of the exhaust gas sensor. In one example, exhaust gas is only delivered to the sensor from a subset of engine cylinders. For example, the exhaust gas sensor may be positioned at or downstream of the confluence point of the exhaust gas, where the sub-branch of the exhaust manifold derived from a single cylinder of the corresponding engine cylinder bank of the internal combustion engine gathers and is located in the exhaust manifold Upstream of the confluence point where the branches of the exhaust manifold leading from a single engine cylinder bank gather. In this way, exhaust gas can only be delivered to the exhaust gas sensor from the corresponding set of cylinders.
[0035] At 205, method 200 may initiate cylinder imbalance monitoring. Simply put, the cylinder imbalance monitoring collects and analyzes the output of the exhaust gas sensor to determine whether there is a cylinder air/fuel imbalance, which will be explained below. In addition, a single gas sensor can be used to monitor the air/fuel ratio imbalance due to air/fuel changes between cylinders and provide air/fuel feedback control for multiple engine cylinders. The cylinder imbalance monitoring can be activated at any time during engine operation, or it can be activated only under certain operating conditions. For example, imbalance monitoring may only start during steady state operating conditions and/or only when the engine has reached the optimal operating temperature. This may be because the temperature of the exhaust gas sensor is too low to operate accurately. In some examples, cylinder imbalance monitoring may be performed at all times during engine operation, or it may be performed only periodically.
[0036] At 206, the method includes detecting and/or receiving a signal from an exhaust gas sensor. For each exhaust gas sensor, the detected signal may include a voltage output indicating the oxygen concentration of the exhaust gas, which may be converted into an air-fuel ratio. However, such a detected air-fuel ratio may indicate the total exhaust air-fuel ratio, and thus may be difficult to correlate with a specific cylinder of the engine. As explained below, in order to distinguish the individual air-fuel ratio of each cylinder, the exhaust gas sensor signal may be sampled using a frequency at or above the ignition frequency of the engine.
[0037] The example method of sampling exhaust gas sensor signals performed at 206 may involve sampling the exhaust gas sensor by the controller at a half PIP interval or a full PIP interval. The controller may then perform calculations to determine the air-fuel ratio difference (referred to as LAMDIF) value based on the exhaust gas sensor samples during the continuous PIP signal. The method can then proceed to 208 and compare the LAMDIF value to the threshold. In this example, the threshold can be used to utilize data that might otherwise be misunderstood as signal noise. For example, the threshold value may be an appropriate threshold value that eliminates the limitation of fault separation while maintaining samples counted to a large sample size, so as to reliably determine the diagnosis. This provides improved fault separation. In one example, the threshold may be in the range of 0.1-0.175. in image 3 with Image 6 This example is discussed in more detail in.
[0038] The second example method of sampling the exhaust gas sensor signal performed at 206 may include sampling the peak-to-peak difference from the exhaust gas sensor for a given duration (eg, multiple engine cycles). The amplitude of the peak-to-peak oscillation can be calculated and measured in comparison with the threshold value. The threshold may be the same threshold discussed above (for example, fixed in the range of 0.1-0.175), or it may be changed based on operating parameters. In one example, the threshold may vary with changes in engine speed and/or load, for example, the threshold may increase as the engine speed increases. In this example, the reason for using this threshold may be the same as the reason described above. in Figure 4 , Figure 7 with Figure 8 This example is discussed in more detail in.
[0039] As below about Figure 5 Described in more detail, two sampling/counting methods may be performed at the same time, or only one sampling/counting method may be performed. By performing only one sampling method, the processing load of the controller can be reduced. In contrast, by performing two sampling methods and indicating cylinder imbalance when one or both of the sampling methods indicate imbalance, a more sensitive and/or robust imbalance detection can be provided.
[0040] At 208, the method includes determining whether to count samples received during the sampling window based on whether the samples are less than the aforementioned threshold. If the answer is no, then the method proceeds to 210 and the sample is not counted. If the answer is yes, the sample is less than the threshold and is counted. The two procedures proceed to 214 (because non-count samples will be included in the total possible number of samples described below). At 214, the controller proceeds to method 200, repeating 206 to 212 for all samples for a given duration set by the controller.
[0041] At 216, the method may include comparing the number of counted samples normalized to the total number of samples for a given duration with a second threshold indicating whether there is a cylinder imbalance. For example, the second threshold may be a fixed threshold, such as in the range of 80%-90%, or it may be changed based on the engine speed and/or load. In one example, the second threshold may increase as the engine speed increases.
[0042] If the sample count does not exceed the second threshold, the method may indicate an imbalance 218, and the controller may perform an engine operation adjustment 222 in response to the indicated cylinder imbalance. As an example, adjustments may include limiting engine torque, lowering boost pressure, adjusting spark timing, and/or feeding back changes in fueling to maintain a desired air-fuel ratio (eg, limiting adjustments to feedback fueling adjustments). After performing engine operation adjustments, the method may proceed to 226. At 226, the controller may notify the operator of the imbalance via lighting a fault indicator and/or the controller may set a diagnostic code stored in the memory of the controller. If the sample count does exceed the second threshold, no indication of imbalance is indicated at 220 and current engine operation is maintained at 224. After 224 or 226, the method 200 exits.
[0043] Therefore, the method 200 described above samples the exhaust gas sensor signal at a frequency corresponding to, for example, the ignition frequency (or half of the ignition frequency) of the engine, so as to obtain the air-fuel ratio data of the individual cylinder. The difference between successive air-fuel ratios can be determined and compared with the failure threshold. The difference below this threshold shows a relatively small deviation from one sample to the next, and therefore does not indicate a cylinder air-fuel ratio failure. However, a difference value above this threshold shows a relatively large amount of deviation and can indicate a cylinder air-fuel ratio failure. All differences (e.g., non-faulty samples) that are less than this threshold are counted, normalized with respect to the total number of samples analyzed, and compared with the imbalance threshold. If the normalized no-fault sample count is less than the imbalance threshold, the cylinder imbalance is indicated and engine operation can be adjusted.
[0044] This method uses the variability of the upstream exhaust gas oxygen sensor (UEGO) during unstable combustion as an indicator of imbalance. The UEGO sensor is essentially a very rough sine wave. For the purpose of this method, the UEGO sensor voltage (converted to air-fuel ratio (lambse)) is sampled at every PIP (or half of the PIP). The sampled signal is then evaluated to determine the peak value (change in direction) of the signal and the differential signal length is calculated as the absolute value between successive peaks. This difference in air-fuel ratio may be referred to as a peak difference (peakdif).
[0045] Generally, when there is no cylinder imbalance, the peak difference is small. As more cylinder imbalance is introduced, the peak difference increases. Due to these differences in signal values, the peak difference can be used as an indicator of imbalance. Based on the test results, the magnitude of the peak difference (or, for that matter, any difference sampling of the air-fuel ratio (lambse) signal) is not always the same, because integrating the magnitude of the peak difference over a certain period of time may lead to inconsistencies The summation results and detection difficulties. However, "counting" these quantities tends to standardize the results. When there is an imbalance, the number of "peak difference counts below the threshold" will be reduced, resulting in a larger failure count. In some examples, the number of peak difference counts above the threshold can also be used to determine whether there is an imbalance.
[0046] In addition, according to the current speed/load, the monitoring can be operated in a wide speed/load range as the threshold value of the peak difference changes, or it can be "binned" counting in various speed/load ranges to allow data weighting. This can allow monitoring to operate in the optimal speed/load region and appropriately weight the results based on detection capabilities.
[0047] Therefore, the above method provides an engine method including: adjusting engine operation in response to cylinder air/fuel imbalance. The imbalance is determined based on the total number of instances in which the sensed peak-to-peak exhaust air-fuel ratio difference is smaller than the threshold normalized to the total number of peak-to-peak oscillations.
[0048] In one example, the adjustment of engine operation includes adjustments that limit feedback fuel addition adjustments to maintain a desired air-fuel ratio. The method may further include indicating the determined cylinder imbalance via a diagnostic code stored in the memory.
[0049] Each sensed peak-to-peak exhaust air-fuel ratio difference may contain the corresponding peak-to-peak amplitude of the sampled exhaust gas sensor signal. The exhaust gas sensor signal may be sampled at least once in each cylinder ignition event.
[0050] In order to determine the total number of instances in which the sensed peak-to-peak exhaust air-fuel ratio difference is less than a threshold, the method may include determining each peak-to-peak amplitude of the exhaust gas sensor signal sampled within a given duration, and combining the instance’s The total number is set to the number of peak-to-peak amplitudes less than the threshold determined within a given duration.
[0051] In order to normalize the total number of instances where the sensed peak-to-peak exhaust air-fuel ratio difference is less than the threshold, the method may include dividing the number of peak-to-peak amplitudes less than the threshold by the total peak-to-peak amplitude determined within a given duration. Quantity in order to determine the normalized number of peak-to-peak amplitudes less than the threshold.
[0052] In some examples, the threshold is a first threshold, and if the normalized number of peak-to-peak amplitudes less than the first threshold is less than the second threshold, it indicates an imbalance. In some examples, the first threshold is based on engine speed and/or engine load; for example, as engine speed increases, the first threshold may increase.
[0053] image 3 Is a flowchart of a more detailed exemplary method 300 of counting using LAMDIF that uses an exhaust gas sensor positioned in the exhaust path of an internal combustion engine and a PIP sensor attached to a crankshaft (e.g., crankshaft 40) to monitor the engine (e.g. , The air-fuel ratio of the engine 10) is unbalanced. Method 300 can be figure 1 The system 100 is implemented.
[0054] The method 300 may be implemented as part of the method 200 (eg, being activated in response to starting cylinder imbalance monitoring) to sample exhaust gas sensor signals. At 302, the method includes sampling the exhaust gas sensor signal at a certain frequency for a given duration. The frequency at which the exhaust gas sensor signal is sampled may be a suitable frequency and may be timed to correspond to individual cylinder firing events. In one example, the signal can be sampled every time the controller receives a PIP signal. Whenever a specific tooth (or missing tooth) of the runner coupled to the crankshaft passes the Hall effect sensor, a PIP signal may be sent from the crankshaft sensor (such as the Hall effect sensor 118). In other examples, the exhaust gas sensor signal may be sampled twice for each PIP signal, once for every two PIP signals, or sampled at other suitable frequencies. For example, the given duration may be a suitable sampling window, and may be a given number of engine cycles (for example, 50), a given number of sampled sensor signals (for example, 50 or 100), or a given The duration of time.
[0055] At 304, the controller calculates multiple exhaust air-fuel ratio differences. This can include converting the sampled exhaust gas sensor signal into an air-fuel ratio (e.g., lambda) and calculating the difference between the air-fuel ratio of the first sample and the air-fuel ratio of the subsequent second sample (also known as LAMDIF) , As indicated at 306. Additional details on calculating LAMDIF will be described below with reference to the drawings.
[0056] At 308, the method includes determining whether the LAMDIF is less than a first predetermined threshold for a given calculated LAMDIF. The threshold value may represent a value determined by the controller based on the current engine operation, including data within a cumulative percentage of 90%-95%. That is, samples below and above the limit can be counted because their fault separation meets the standard to accurately determine the deviation from the stoichiometric air-fuel ratio. As an example, the first predetermined threshold may include a value in the range of 0.1-0.175, which may cover 90%-95% of the total samples collected. If the answer is yes, the method proceeds to 310. At 310, the method includes counting LAMDIF values ​​below a first threshold. If the answer at 308 is no, then the method 300 proceeds to 312, where the method does not count samples at 312. Both 310 and 312 proceed to 314, where the comparison of LAMDIF with the first threshold is repeated for each calculated LAMDIF for a given duration. Then the method 300 ends.
[0057] Figure 4 It is a flowchart of the method 400, which calculates the air-fuel ratio difference based on the peak-to-peak exhaust gas sensor signal analysis. The method 400 may be implemented during execution of the method 200, for example, in response to a cylinder air/fuel imbalance monitoring being initiated. Similar to methods 200 and 300, method 400 uses an exhaust gas sensor (e.g., sensor 126) located in an exhaust passage (e.g., exhaust passage 48) of an internal combustion engine (e.g., engine 10) to monitor the engine's air-fuel ratio imbalance . Method 400 can be figure 1 The system 100 is implemented. For example, the controller 12 may include instructions stored on the controller that are executed to implement the method 400.
[0058] At 402, the controller receives the output from the exhaust gas sensor and stores it on the memory, which output may be illustrated as a graph of air-fuel ratio measured over time. Depending on the engine speed, the length of time may be associated with a given number of engine cycles (for example, 50) or other suitable durations. At 404, the controller calculates the peak-to-peak difference based on the sample output from 402. The output shows the peak value based on the gas sensor output, and the peak-to-peak difference is calculated based on the amplitude of the peak value. reference Figure 7 , Further illustrate further details of 402 and 404.
[0059] At 406, the method includes determining whether the peak-to-peak difference is less than a predetermined first threshold. The first predetermined threshold may be similar to the above regarding figure 2 with image 3 Describe the first threshold. If the answer is yes, the method proceeds to 408. At 408, the method includes counting peak-to-peak differences that are less than a first threshold. If the answer at 406 is no, then the method proceeds to 410 and does not count the peak-to-peak difference. Method 400 can exit.
[0060] Therefore, as above about Figure 3-4 As described, the exhaust gas sensor signal can be sampled at a desired frequency for a given duration and processed to determine whether each sample indicates a cylinder failure. The number of samples that do not indicate cylinder failure can be compared with an imbalance threshold to determine whether there is a cylinder air/fuel imbalance. The exhaust gas sensor signal can be sampled and processed into LAMDIF value or peak-to-peak difference. In some examples, it may be advantageous to only process the sampled signal according to the method 300 or the method 400 described above. However, in other examples, it may be advantageous to process the exhaust gas sensor signal according to these two methods, and indicate cylinder imbalance in the case where one or two sampling/counting methods indicate cylinder imbalance, as described below Figure 5 Described.
[0061] Figure 5 It is a flowchart describing the method 500 including the elements of the methods 300 and 400 in detail. Method 500 may be implemented during execution of method 200, for example, in response to cylinder air/fuel imbalance monitoring being initiated. Similar to methods 200, 300, and 400, method 500 uses an exhaust gas sensor (e.g., sensor 126) located in an exhaust passage (e.g., exhaust passage 48) of an internal combustion engine (e.g., engine 10) to monitor the air-fuel ratio of the engine unbalanced. Method 500 can be figure 1 The system 100 is implemented. For example, the controller 12 may include instructions stored on the controller that are executed to implement the method 500. Method 500 utilizes the above about image 3 with Figure 4 Two exhaust gas sensor sampling methods are described (for example, LAMDIF method 300 and peak-to-peak method 400) to perform cylinder air-fuel ratio imbalance diagnosis. Running both methods at the same time can show many benefits, including but not limited to greater sensitivity to cylinder imbalance, larger data settings, and backup counts in the event of a failure in one method.
[0062] At 502, the method includes comparing data counts from methods 300 and 400. At 504, the method includes determining whether the method 300 or 400 has a count less than a second predetermined threshold. As an example, at 504, if one or more of the method counts are less than the second threshold, the method continues to 506 and indicates an imbalance and continues to 510. If both counts are greater than the second threshold, no imbalance is indicated at 508. At 510, the controller may perform engine adjustments to diagnose air-fuel ratio imbalance. At 512, the controller may choose to maintain current engine operation. The benefit of running two methods to measure air-fuel ratio imbalance may be to provide better cylinder imbalance detection. Methods 300 and 400 evaluate the same data differently, and if one method meets its second threshold and the other does not, this can help detect air/fuel imbalances that may not be calculated in only one method.
[0063] As a second example, at 504, only if both methods 300 and 400 have counts less than the second threshold, does the method continue to 508 to indicate imbalance. As mentioned above, there can be many benefits to indicating imbalance when running both methods simultaneously and only when one method provides a count greater than the second threshold. As an example, given engine operation, one method may be more reliable than another (for example, one method may be more reliable at high speeds and loads, and another method may be more reliable at low speeds and loads. more reliable). Then even if only one of the two methods exceeds the second threshold, the controller can indicate imbalance. However, in some examples, in order to indicate imbalance, both sampling methods may have to have counts that exceed the second threshold. This can ensure a robust detection method that avoids false positive indications of cylinder imbalance. Method 500 can exit.
[0064] Therefore, the method 500 described above may sample the exhaust gas sensor signal to determine both the LAMDIF value and the peak-to-peak difference value and compare each corresponding value to a first threshold value. For each of the LAMDIF value and the peak-to-peak value, the value smaller than the first threshold is counted (for example, stored in the no-failure group) and normalized with respect to the total number of samples analyzed. Each standardized non-failure group is compared with the second threshold. In one example, if any normalized failure-free group (eg, a group including LAMDIF values ​​or a group including peak-to-peak values) is less than the second threshold, it may indicate cylinder imbalance. In another example, only when the two normalized no-fault groups are both smaller than the second threshold, can cylinder imbalance be indicated.
[0065] Image 6 Shows an illustration of an example engine system (such as figure 1 A graph 602 of example results of vehicle data of the system 100). The system 100 may be configured to sample (for example, take a "snapshot") the signal sent by the sensor 126 with the controller 12 at a time corresponding to a surface ignition sensing (PIP) event in order to monitor a multi-cylinder internal combustion engine The air-fuel ratio is not balanced. The sampled signal can be converted to the air-fuel ratio at the PIP, and can be used to calculate the air-fuel ratio difference (LAM_DIF). This can be achieved by finding the difference between the air-fuel ratio at a given PIP and the air-fuel ratio of the previous PIP event. Image 6 The 604 represents the graphic value of LAMDIF.
[0066] Figure 7 The curve 700 illustrates the graph 702 of the air-fuel ratio as a function of time. 704 refers to the peak-to-peak difference described in the method 400. The peak-to-peak difference is calculated by finding the length difference between two adjacent peaks on the curve, also known as the peak amplitude. 704 is just one example of this calculation. As above about figure 2 with Figure 4 As described, within a given sample duration, the difference between each peak is calculated and compared with the imbalance threshold.
[0067] As previously explained, the air-fuel ratio difference can be compared with a threshold value in order to determine whether the air-fuel ratio difference indicates a potential cylinder air-fuel ratio failure or whether it indicates a no-failure condition (for example, a value below the threshold is considered a no-failure value ). The threshold may be set at a level that provides a preferred separation between air-fuel ratios that deviate by a larger amount and a smaller amount from the stoichiometric ratio. Figure 8 A curve 800 describing the separation percentage from the stoichiometric ratio, which is used to change the level of rich or lean air-fuel ratio. 802 represents an example threshold range that provides reliable fault separation. The threshold range represents 90%-95% of the total calculated air-fuel ratio difference (for example, from the method 300 or 400 described above) that is less than the threshold. That is, the threshold is selected such that 90%-95% of the total calculated difference is lower than the threshold. As shown by 804A-D, fault separation represents the difference between the engine being 25% lean or rich and the engine being 7% lean and/or rich. The greater the separation percentage from the stoichiometric ratio between 25% and 7% lean and/or rich, the better the fault separation value. 806-812 represent graphs where engine cylinders are operating at 25% rich, 25% lean, 7% rich, and 7% lean, respectively.
[0068] In this way, the counting method can allow the engine controller to accurately diagnose cylinder air-fuel ratio imbalance. By counting samples below the threshold normalized to the total number of peak-to-peak oscillations, the data can be more consistent than a summation method that relies on counting only samples above the threshold.
[0069] The technical effect of the counting method includes counting samples below the threshold value normalized to the total number of peak-to-peak oscillations and comparing the value with the imbalance threshold value in order to better control the operation of the engine. If the number is below the threshold, it can be inferred that there is a relatively large number of samples that exceed the threshold and there is an air/fuel imbalance, and then the control system can take appropriate actions.
[0070] Therefore, the system and method described herein provide a method that includes: determining a peak-to-peak engine exhaust sensor signal difference; counting each determined peak difference that is below a first predetermined threshold; When a predetermined threshold value of the determined peak difference count decreases below a second predetermined threshold value, a cylinder imbalance is indicated via the vehicle display element.
[0071] The determined peak-to-peak exhaust gas sensor signal difference may include the corresponding peak-to-peak amplitude of the exhaust gas sensor signal. In one example, the first predetermined threshold varies with the engine speed. The method may further include adjusting engine operation in response to the indication of cylinder imbalance. Adjusting engine operation may include lowering the engine torque limit.
[0072] Another embodiment relates to a system including: an engine having a plurality of cylinders; an exhaust gas sensor; and a controller having instructions for adjusting engine operation in response to cylinder air/fuel imbalance, The imbalance is determined based on the number of counted air-fuel ratio differences normalized to the total number of air-fuel ratio differences calculated from feedback from the exhaust gas sensor within a given duration.
[0073] In one example, the controller has instructions for determining the air-fuel ratio difference as the peak-to-peak amplitude of the signal from the exhaust gas sensor, and if the peak-to-peak amplitude is less than the threshold, determining that the air-fuel ratio difference is the counted air Difference in fuel ratio.
[0074] The total number of air-fuel ratio differences may include the number of counted air-fuel ratio differences and the number of uncounted air-fuel ratio differences, and the uncounted air-fuel ratio differences include a peak-to-peak amplitude greater than a threshold.
[0075] The system may further include an engine speed sensor, and the controller may include instructions for determining the air-fuel ratio difference as the first output and the exhaust gas sensor sampled when the engine speed sensor sends the first signal to the controller The difference between the second output of the exhaust gas sensor sampled when the engine speed sensor sends the second signal to the controller, and if the difference between the first output and the second output is less than the threshold, it is determined that the air-fuel ratio difference is a count The difference in air-fuel ratio.
[0076] Note that the example control and estimation routines included in this article can be used with various engine and/or vehicle system configurations. The control method and program disclosed herein can be stored as executable instructions in a non-transitory memory. The specific programs described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and so on. Therefore, the various behaviors, operations and/or functions shown may be executed in the order shown, executed in parallel, or omitted in some cases. Likewise, the order of processing is not necessary to realize the features and advantages of the embodiments described herein, but is provided for ease of illustration and description. Depending on the particular strategy used, one or more of the actions, operations, and/or functions shown may be repeatedly performed. In addition, the described behaviors, operations, and/or functions may be graphically programmed into codes in the non-transitory memory of the computer-readable storage medium of the engine control system. It should be recognized that the configurations and procedures disclosed herein are exemplary in nature, and these specific embodiments should not be considered as having a limiting meaning, as many variations are possible. For example, the above technology can be used in V-6, I-4, I-6, V-12, opposed 4 cylinders and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and/or properties disclosed herein.
[0077] The following claims specifically point out certain combinations and sub-combinations that are regarded as novel and non-obvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include a combination of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendments to this application or through new claims appearing in this related application. Such claims, whether broader, narrower, equivalent or different in scope than the original claims, are deemed to be included in the subject matter of the present disclosure.

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