Torque estimation in engine control

Abstract

Method for performing diagnostic measures on a skip fire engine control system, wherein the skip fire engine control system comprises an engine with multiple working chambers, the method comprising: Calculating an engine operating torque; Operating an engine with skip fire to provide engine operating torque; Calculating a motor reference torque using a torque model, wherein the torque model includes the individual estimation of the torque for each working chamber; comparing the engine reference torque with the engine operating torque to assess the accuracy of the calculation of the engine operating torque; Identifying a potential error if a discrepancy between the calculated engine reference torque and the calculated engine operating torque exceeds a threshold; and Implementing a measure in response to the identification of the potential error, where the engine reference torque is calculated at least in part based on a skip fire ignition component used to operate the engine.

Description

CROSS-REFERENCE TO RELATED REGISTRATIONS

[0001] The present application claims priority over US patent application no. 15 / 171,931, filed on June 2, 2016, which is hereby incorporated by reference. AREA OF INVENTION

[0002] The present invention relates to an engine control system for an internal combustion engine. In particular, the present invention relates to systems and methods for estimating the torque output of an engine in skip fire (cylinder deactivation / activation) or ignition height modulation operation. BACKGROUND

[0003] In various conventional engine systems, when a demand for engine torque is detected (e.g., using an accelerator pedal sensor), the vehicle's electronic control unit (ECU) calculates an engine operating torque that would meet the torque demand. The engine is then operated to deliver the target torque.

[0004] Several motor systems also include a torque monitoring device. This device is designed to ensure the accuracy of the calculated motor operating torque. Generally, the torque monitoring device calculates the motor operating torque separately based on the settings used to operate the motor. If the motor torque calculated by the torque monitoring device differs significantly from the initial calculation, the device may indicate a problem with the calculation process, the motor settings, and / or the motor control.

[0005] The fuel efficiency of internal combustion engines can be greatly improved by varying the engine's displacement. This allows the full torque to be available when needed, but can also significantly reduce pumping losses and improve thermal efficiency by utilizing a smaller displacement when full torque is not required. The most common method of implementing a variable-displacement engine today is to deactivate a group of cylinders essentially simultaneously. In this approach, the intake and exhaust valves belonging to the deactivated cylinders are kept closed, and no fuel is supplied to the deactivated cylinders.

[0006] Another engine control approach that varies an engine's effective displacement is known as "skip-fire" engine control. Generally, skip-fire engine control involves selectively omitting the ignition of certain cylinders during selected firing opportunities. Thus, a particular cylinder may fire during one engine cycle, then be skipped during the next, and then selectively skipped or fired during the following cycle. Skip-fire engine operation differs from conventional variable-displacement engine control, where a fixed set of cylinders is essentially deactivated simultaneously and remains deactivated as long as the engine remains in the same variable-displacement mode.This means that in conventional variable displacement operation, the sequence of specific cylinder firings for each engine cycle is always exactly the same, as long as the engine remains in the same displacement mode, whereas this is often not the case during skip-fire operation. For example, an eight-cylinder variable displacement engine can deactivate half of its cylinders (i.e., four cylinders), so that it operates using only the remaining four. Currently available commercially available variable displacement engines typically support only two, or at most three, constant displacement modes.

[0007] In general, skip-fire engine operation allows for finer control of the effective engine displacement than is possible using a conventional variable-displacement approach. For example, firing every third cylinder in a four-cylinder engine results in an effective displacement that is one-third of the total engine displacement, a proportionate displacement that cannot be achieved by simply deactivating a set of cylinders. Theoretically, almost any effective displacement can be achieved using skip-fire control, although in practice most implementations restrict operation to a set of available firing proportions, sequences, or patterns. One of the applicants, Tula Technology, has filed a number of patents describing various approaches to skip-fire control. For example, U.S. Patent No.US 8,099,224 B2; US 8,464,690 B2; US 8,651,091 B2; US 8,839,766 B2; US 8,869,773 B2; US 9,020,735 B2; US 9,086,020 B2; US 9,120,478 B2; US 9,175,613 B2; US 9,200,575 B2; US 9,200,587 B2; US 9,291,106 B2; US 9,399,964 B2 and a variety of engine control systems that enable the practical operation of a wide variety of internal combustion engines in a dynamic skip-fire operating mode. Reference is made to each of these patents herein. Many of these patents relate to dynamic skip fire control, where ignition decisions on whether to skip or fire a particular cylinder during a given work cycle are made in real time - often just before the start of the work cycle and often on a case-by-case basis for a single cylinder.

[0008] In some applications referred to as multi-altitude skip fire, individual firing cycles during skip fire operation can be intentionally run at different cylinder delivery altitudes—that is, using intentionally different air charge and corresponding fuel delivery altitudes. In multi-altitude skip fire, the different firing altitudes are distributed across at least some effective firing portions during operation. For example, U.S. Patent No. 9,399,964, hereby incorporated by reference, describes some such approaches. The concept of individual cylinder control used in dynamic skip fire can also be applied to dynamic multi-altitude engine operation, in which all cylinders fire, but individual firing cycles are intentionally distributed across different cylinder delivery altitudes.Dynamic skip fire, dynamic multi-altitude skip fire, and dynamic multi-charge-altitude engine operation can be collectively viewed as different types of engine operation with dynamic ignition altitude modulation, in which the output of each duty cycle (e.g., skip / fire, high / low, skip / high / low, etc.) during engine operation is dynamically determined, usually on a duty cycle-to-duty-cycle (ignition opportunity-to-ignition opportunity) basis for a single cylinder.

[0009] DE 11 2014 001 465 T5 concerns powertrain diagnostics carried out during the control of intermittent ignition of an internal combustion engine.

[0010] DE 11 2015 002 437 T5 relates to methods and arrangements for monitoring the valve operation in an engine and in particular to identifying valve actuation faults during cylinder shutdown operation of an internal combustion engine. BRIEF SUMMARY OF THE INVENTION

[0011] A selection of methods and arrangements for estimating engine torque in a skip-fire engine control system suitable as a torque monitoring device are described. In one aspect, a method is described. An engine operating torque is calculated. The engine is operated with skip-fire or ignition altitude modulation to provide the engine operating torque. An engine reference torque is calculated using a torque model. The torque model includes estimating the torque at a working chamber plane. The engine reference torque is compared with the calculated engine operating torque to assess the accuracy of the engine operating torque calculation. Various embodiments of the present invention incorporate software, devices, systems, and engine controls related to one or more of the above operations.The present invention is defined by the attached claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention and its advantages are best understood by reference to the following description in conjunction with the accompanying drawings; the drawings show: Fig. 1 a block diagram of an engine control system according to an embodiment of the present invention.

[0013] The drawings occasionally use the same reference symbols to denote identical structural elements. It should be understood that the representations in the figures are schematic and not to scale. DETAILED DESCRIPTION

[0014] The present invention relates to skip-fire and ignition-level modulation engine control systems. In particular, the present invention relates to controls, systems, and methods for estimating the engine torque for an engine with skip-fire or ignition-level modulation operation, suitable for use in a torque-control monitoring device.

[0015] In various existing vehicle designs, when a driver presses the accelerator pedal, the vehicle's engine control unit estimates how much engine torque will be required to meet the driver's demands. Various engine settings (e.g., air charge, air / fuel ratio, ignition timing advance, etc.) are selected based on this estimated engine torque. Based on these settings, the engine is then operated to deliver the estimated engine torque.

[0016] Several vehicle designs also include a torque monitoring device. This device is a diagnostic tool that calculates an engine reference torque based on the selected engine settings. The torque monitoring device uses this reference torque to verify the accuracy of the initial engine torque estimate. If the difference between the engine operating torque and the reference torque is too large, the torque monitoring device may indicate a problem with the engine, its settings, or its control system.

[0017] In conventional engine control designs, when the torque-securing monitoring device calculates the engine reference torque, the calculation is generally performed at the engine level rather than at the individual cylinder level. This means that differences in conditions and settings for individual cylinders are not taken into account, and the torque output for a single or average cylinder is not modulated. This approach generally works well in a conventional, all-cylinder engine system and reflects the fact that all cylinders in such a system operate essentially the same and have the same characteristics; that is, each cylinder fires during each engine cycle using similar settings. Thus, there is little reason for the torque-securing monitoring device to consider the characteristics of individual cylinders.

[0018] However, it has been determined that such approaches may not be optimal when applied to skip-fire engine control systems. This is because the combustion chambers in a skip-fire engine control system can operate differently. For example, one combustion chamber may switch between exhaust and ignition more often than another at any given time. Unlike conventional all-cylinder ignition engines, where each combustion chamber fires during each power cycle, different combustion chambers in a skip-fire engine control system can have different ignition histories. Similar problems arise when the cylinders can operate at different ignition timings.

[0019] These differences in ignition history can lead to different combustion chambers in a skip-fire engine control system exhibiting different operating parameters and conditions, e.g., different temperatures, air mass charge, ignition timing settings, air / fuel ratios, etc. Various embodiments of the present invention take these differences into account when determining a reference engine torque. For example, in some approaches, the engine torque is estimated by first estimating the torque at the level of a combustion chamber. This allows the engine torque for a skip-fire engine control system to be determined more accurately.

[0020] Tula Technologies has previously described a selection of Skip Fire controllers. Fig. Figure 1 shows a functional representation of a suitable skip-fire controller 10. The skip-fire controller 10 shown comprises a torque calculation device 20 (also occasionally referred to as an engine torque determination unit 20), an ignition timing and powertrain setting determination unit 30, a transition setting unit 40, an ignition timing determination unit 50, and a diagnostic module 165. For illustrative purposes, the skip-fire controller 10 is shown separately from the engine control unit (ECU) 70, which implements the controlled ignitions and provides the precise component controls. However, it is understood that in many embodiments, the functionality of the skip-fire controller 10 can be integrated into the ECU 70. Indeed, integration of the skip-fire controller into an ECU or powertrain control unit is expected to be the most common implementation.

[0021] The torque calculation device 20 is configured to determine the target engine torque at a given time based on a number of inputs. The torque calculation device outputs a requested torque 21 to the ignition fraction and powertrain setting determination unit 30. In various embodiments, the requested torque 21 can be specified as an engine torque fraction (ETF), which is the desired proportion of the potentially available engine torque rather than an absolute torque value. The ignition fraction and powertrain setting determination unit 30 is configured to determine an ignition fraction suitable for providing the target torque based on the current operating conditions and outputs a target operating ignition fraction 33 appropriate for providing the target torque.Unit 30 further determines selected engine operating settings (e.g. manifold pressure 31, cam control (CAM) 32, torque converter slip, etc.) that are appropriate for providing the target torque at the specified ignition fraction.

[0022] The ignition ratio and powertrain setting determination unit 30 can employ a wide variety of approaches to determine the appropriate engine settings for any given operating conditions. One suitable approach is briefly described below as an example, although it is understood that a wide variety of other approaches could also be used. In the described approach, a fuel-efficient base ignition ratio (FF) is first determined. Basis) is determined based on the engine torque fraction (ETF) signal 21. In many implementations, the ignition fraction and engine and powertrain setting determination unit selects from a set of predefined ignition fractions for which relatively good NVH behavior has been determined.

[0023] Once the base ignition fraction has been determined, a cylinder torque fraction (CTF) can be calculated by dividing EFT by FF. Basis be determined. That is: CTF=EFT / FFBasis

[0024] The CTF (cylinder timing force) and engine speed can then be used as input for a lookup table that indicates the most efficient camshaft setting. Based on the camshaft setting and engine speed, a target manifold absolute pressure (MAP) can be determined. The cylinder mass air charge (MAC) can be determined based on the camshaft settings, manifold pressure, and engine speed. A target fuel mixture can then be determined based on the MAC and stoichiometric considerations, and any necessary ignition timing settings can be established.

[0025] When the ignition timing and engine and drivetrain setting determination unit selects from a set of predefined ignition timings, there are intermittent transitions between target operating ignition timings. Observations have shown that transitions between operating ignition timings are the cause of undesirable NVH (noise, vibration, and harshness). The transition setting unit 40 is designed to adjust the targeted ignition timing and certain engine settings (e.g., camshaft angle, throttle position, intake manifold pressure, torque converter slip, etc.) during transitions to help mitigate some of the transition-related NVH.

[0026] The ignition timing determination unit 50 is responsible for determining the specific ignition timing required to provide the desired ignition fraction. The ignition sequence can be determined using a suitable approach. In some preferred implementations, ignition decisions are made dynamically on a firing-chance basis for a single cylinder, allowing for very rapid implementation of desired changes. A selection of ignition timing determination units well suited for determining appropriate firing sequences based on a potentially time-varying requested ignition fraction or engine power has been previously described by Tula. Many such ignition timing determination units are based on a sigma-delta converter, which is well suited for making ignition decisions on a firing-chance basis.In other implementations, pattern generators or predefined patterns can be used to enable the provision of the desired ignition component.

[0027] The torque calculation device 20 receives a number of inputs that can influence or specify the target engine torque at any given time. In automotive applications, one of the main inputs to the torque calculation device is the accelerator pedal position (APP) signal 24, which indicates the position of the accelerator pedal. In some implementations, the accelerator pedal position signal is received directly from an accelerator pedal position sensor (not shown), whereas in others, an optional preprocessor 22 can modify the accelerator pedal signal before it is transmitted to the skip fire controller 10. Other main inputs can come from other function blocks, such as a vehicle speed controller (CCS command 26), the transmission control unit (AT command 27), a traction control unit (TCU command 28), and so on. There are also a number of factors, such as engine speed, that can influence the torque calculation.When such factors are used in the torque calculations, the appropriate inputs, such as engine speed (RPM signal 29), are also provided or can be obtained from the torque calculation device as required.

[0028] Furthermore, in some embodiments it may be desirable to take into account energy / torque losses in the drivetrain and / or the energy / torque required to drive engine ancillary components, such as the air conditioning system, alternator / generator, power steering pump, water pumps, vacuum pumps, and / or any combination of these and other components. In such embodiments, the torque calculation device may be configured either to calculate such values ​​or to receive information on the associated losses so that they can be appropriately considered during the calculation of the target torque.

[0029] The method of torque calculation varies depending on the vehicle's operating state. For example, during normal operation, the target torque may be primarily based on driver input, which can be reflected by the accelerator pedal position signal 24. When operating with cruise control, the target torque may be primarily based on input from a cruise control unit. If a transmission shift is imminent, a transmission shift torque calculation may be used to determine the target torque during the shift. If a traction control system or similar indicates a potential loss of traction event, a traction control algorithm may be used to appropriately determine the target torque to manage the event. In some circumstances, depressing a brake pedal may trigger a specific engine torque control.If other events occur that require measured control of the engine power, appropriate control algorithms or logic can be used to determine the target torque during such events. In any of these situations, the required torque determinations can be made in a manner appropriate to the specific situation. For example, the appropriate torque determinations can be made algorithmically, using appropriate logic, using predefined values, using stored profiles, using any combination of the foregoing, and / or using any other suitable approach.Torque calculations for special applications can be performed by the torque calculation device itself, or they can be performed by other components (inside or outside the ECU) and simply passed to the torque calculation device for implementation.

[0030] The ignition ratio and powertrain setting determination unit 30 receives a signal 21 of the requested torque from the torque calculation device 20 and other inputs, such as the engine speed 29 and various powertrain operating parameters and / or environmental conditions, which are useful for determining an operating ignition ratio 33 appropriate for providing the requested torque under the current conditions. Powertrain parameters include, but are not limited to, the throttle position, cam phase angle, fuel injection timing, ignition timing, torque converter slip, transmission gear, etc. The ignition ratio indicates the proportion or percentage of ignitions to be used to provide the target power. In some embodiments, the ignition ratio can be considered an analog input to a sigma-delta converter.Often, the ignition timing determination unit is limited to a specific set of available ignition components, patterns, or sequences, selected at least in part based on their comparatively more desirable NVH characteristics (here occasionally referred to collectively as the set of available ignition components). A number of factors can influence the set of available ignition components. These typically include the requested torque, cylinder load, engine speed (e.g., rpm), and current transmission gear. They may also include various environmental conditions, such as ambient pressure or temperature, and / or other selected powertrain parameters.The ignition timing determination aspect of unit 30 is designed to select the target operating ignition fraction 33 based on such factors and / or any other factors that the designer of the skip fire control system may consider important. For example, some suitable ignition fraction determination units are described in US Patent Nos. 9,086,020 and 9,528,446 and US Patent Applications Nos. 13 / 963,686, 14 / 638,908 and 62 / 296,451, to which reference is made herein.

[0031] The number of available ignition components / patterns and the operating conditions during which they can be used can vary greatly based on different design goals and NVH considerations. In a specific example, the ignition fraction determination unit may be designed to limit available ignition fractions to a set of 29 possible operating ignition fractions—each fraction having a denominator of 9 or less—i.e., 0, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 1 / 5, 2 / 9, 1 / 4, 2 / 7, 1 / 3, 3 / 8, 2 / 5, 3 / 7, 4 / 9, 1 / 2, 5 / 9, 4 / 7, 3 / 5, 5 / 8, 2 / 3, 5 / 7, 3 / 4, 7 / 9, 4 / 5, 5 / 6, 6 / 7, 7 / 8, 8 / 9, and 1. However, under certain (indeed, most) operating conditions, the set of available ignition fractions may be reduced, and sometimes the available set is greatly reduced.In general, the set of available ignition timings tends to be smaller in lower gears and at lower engine speeds. For example, there may be operating ranges (e.g., near idle and / or in first gear) where the set of available ignition timings is limited to only two (e.g., 1 / 2 or 1) or to only four possible ignition timings (e.g., 1 / 3, 1 / 2, 2 / 3, and 1). Of course, the permissible ignition timings / patterns for different operating conditions may vary considerably in other designs.

[0032] When the available set of ignition components is limited, various powertrain operating parameters, such as mass airflow (MAC) and / or ignition timing control, typically need to be varied to ensure that the actual engine power matches the target power output. In the case of the Fig. In the embodiment shown in Figure 1, this functionality is integrated into the powertrain settings component of unit 30. In other embodiments, it may be implemented in the form of a powertrain parameter setting module (not shown) that interacts with an ignition timing calculation device. In each case, the powertrain settings component of unit 30 or the powertrain parameter setting module determines selected powertrain parameters that are appropriate to ensure that the actual engine power substantially matches the requested engine power at the controlled ignition timing and that the wheels receive the target braking torque. Torque converter slip can be included in the determination of appropriate powertrain parameters, since an increase in torque converter slip generally reduces perceived NVH.Depending on the engine's design, the air charge can be controlled in many ways. The most common method is controlling the air charge by adjusting the intake manifold pressure and / or the camshaft phase (if the engine has a camshaft adjuster or another mechanism for controlling valve timing). However, where available, other mechanisms such as valve lifters, boost-increasing devices like turbochargers or superchargers, air dilution mechanisms like exhaust gas recirculation, or other mechanisms can be used to assist in adjusting the air charge. In the illustrated embodiment, the target air charge is specified in relation to a target intake manifold pressure (MAP) 31 and a desired camshaft setting 32. Of course, if other components are used to assist in regulating the air charge, values ​​for those components can also be specified.

[0033] The ignition timing control module 50 is designed to output a sequence of ignition commands 52 that cause the engine to provide the percentage of ignitions specified by a controlled ignition component 48. The ignition timing control module 50 can be implemented in many different forms. For example, sigma-delta converters function well as the ignition timing control module 50. A number of Tula's patents and patent applications describe various suitable ignition timing control modules, including a wide variety of different sigma-delta converters that function well as the ignition timing control module. See, for example, [reference to patent application]. B. US Patent Nos. 7,577,511, 7,849,835, 7,886,715, 7,954,474, 8,099,224, 8,131,445, 8,131,447, 8,839,766 and 9,200,587.The sequence of ignition commands (occasionally referred to as a control pulse signal 52) output by the ignition timing control module 50 can be sent to an engine control unit (ECU) 70 or another module, such as a combustion control unit (in . Fig. (1 not shown), which directs the actual ignitions. A significant advantage of using a sigma-delta converter or an analog structure is that it inherently includes an accumulator function that tracks the portion of an ignition that has been requested but not yet provided. Such an arrangement supports smooth transitions by taking into account the effects of previous ignition / non-ignition decisions.

[0034] When a change in ignition timing is controlled by unit 30, it will often (indeed, usually) be desirable to simultaneously control a change in the cylinder's mass airflow (MAC). As discussed above, changes in airflow tend to be implemented more slowly than changes in ignition timing, due to the waiting times associated with filling or emptying the intake manifold and / or adjusting the cam phase. The transition control unit 40 is designed to adjust the controlled ignition timing, as well as various operating parameters, such as the controlled cam phase and the controlled manifold pressure, during transitions in such a way as to mitigate unintended sudden increases or decreases in torque during the transition.This means that the transition timing unit takes care of at least the target cam phase, manifold pressure, and ignition timing during the transitions between controlled ignition timings. It can also control other powertrain parameters, such as torque converter slip.

[0035] The diagnostic module 165 is designed to perform a range of skip fire-related diagnostic tests. These may include misfire-related diagnostic tests, cylinder valve actuation-related diagnostic tests, exhaust-related diagnostic tests, etc.

[0036] The desired settings for many of the powertrain operating parameters are interrelated and are partly determined based on the expected engine operating torque output. Thus, the operating torque fraction determined by the torque calculation device 20 is used by the ignition fraction and powertrain setting determination unit 30 in determining the various operating parameters used during skip fire operation. However, there is always the possibility that the operating torque calculation could be incorrect. If the torque calculation is incorrect for any reason, the various powertrain settings would likely not be optimal. Therefore, it is desirable to provide an independent reference estimate / calculation of the engine torque that can be used to verify the main calculation.For maximum efficiency, the engine torque reference calculation preferably uses a different methodology for estimating engine torque than the main torque calculation used by the torque calculation device 20 or the ignition timing and / or powertrain setting determination unit 30. The independent estimation can be performed by a diagnostic module 165, the torque calculation device 20, the ECU 70, or any other suitable module.

[0037] In some embodiments (such as the one described above), the ignition timing and powertrain setting determination unit uses 30 engine-level torque estimates as the basis for determining various engine settings. In such cases, it may be desirable (but not necessary) to determine the engine reference torque at the working chamber level rather than solely at the engine level. In other embodiments, the reference torque calculation could be performed on an engine cycle basis or within a time-dependent window deemed relevant for maintaining safety, such as every 500 ms.It is understood that the appropriate reference torque calculation for the torque safeguard function will vary with both (a) the nature of the operating torque calculation (since it is desirable to use a reference torque calculation approach that differs from the operating torque calculation approach); and (b) torque safeguard function design considerations. The reference torque calculation can be performed in several ways. In various embodiments, for example, the diagnostic module 165 uses an algorithm, formula, or model to determine the torque of a single or average working chamber and then scales or modifies the determined working chamber output (e.g., based on a firing rate) to calculate a torque output for the engine as a whole.In various implementations, the model / algorithm is based on different operating parameters, including MAC, air / fuel ratio, ignition timing advance, and engine speed. In other implementations, the torque of each combustion chamber is calculated separately, and then the calculated torque outputs for the combustion chambers are summed to determine a reference engine torque. This means that the different operating parameters (e.g., different MAC, different ignition timing advance, different air / fuel ratio, etc.) used to operate the engine can be monitored and applied to determine the torque output of each combustion chamber. Such approaches allow the diagnostic module 165 to account for the different ignition histories and conditions of different combustion chambers in a skip-fire engine control system.

[0038] Different ignition histories can affect the operating parameters and conditions in individual working chambers in various ways. For example, consider an instance where the ignition proportion determination unit 30 determines that an ignition proportion of 4 / 7 would provide the target torque. In this example, the ignition timing determination module 50 uses a sigma-delta converter to generate a skip-fire firing sequence, in which ignitions and skips occur at substantially uniform intervals, although the sequence can also be generated using other methods. Over time, different working chambers will be fired and skipped using different patterns than other working chambers. For example, for a given period, one working chamber might be fired more times consecutively before a skip than another working chamber.

[0039] When a combustion chamber is fired repeatedly, its internal temperature tends to be higher. This can affect the settings and operating parameters for the combustion chamber. For example, if the combustion chamber temperature is higher, air will not be drawn into the chamber as easily as if the temperature were lower. This can result in a lower air mass charge for that particular combustion chamber compared to other combustion chambers.

[0040] Differences can also arise in a variety of other operating parameters. For example, advanceping the ignition timing generally allows a combustion chamber to generate more energy. However, if the ignition timing is advanced too far, the probability of detonation can increase. Detonations are generally greater when the pressures and temperatures in a combustion chamber are high. Thus, if a combustion chamber becomes hotter due to multiple consecutive ignitions, the ignition timing can be advanced less than in a combustion chamber with a different ignition history, i.e., one with fewer consecutive ignitions between ejections.

[0041] Diagnostic module 165 can be configured to account for the aforementioned differences in ignition histories, combustion chamber operating parameters, and conditions when determining the combustion chamber reference torque. For example, in some implementations, different ignition histories and combustion chamber operating parameters are known based on the ignition fraction. This means that for different ignition fractions, the extent to which parameters such as ignition timing advance and MAC differ between various combustion chambers is known. To account for this, the diagnostic module calculates a torque output for each combustion chamber. The calculation assumes operating parameters (e.g., ignition timing advance, MAC, etc.) that are the average of the various known parameters for multiple combustion chambers, and then adjustments are made for each combustion chamber.Alternatively, individual operating parameters can be determined for each individual combustion chamber. These parameters can vary with the ignition history of the combustion chamber and also with other engine parameters, such as the ignition timing.

[0042] To reiterate, it is understood that the torque output of a given combustion chamber during skip-fire operation can vary between different engine cycles, even during steady-state operation. This is partly because the ignition history of each cylinder is often different from one engine cycle to the next. For example, if a four- or eight-cylinder engine is operating at a steady state with a 2 / 3 firing rate, each cylinder will typically have a firing order that corresponds to FFSFFSFFSFFS... (where F = ignition and S = exhaust), although the timing of the sequences varies for the different cylinders. In this sequence, the cylinder's torque output is greater on the ignition immediately following the exhaust than on the ignition immediately following a previous ignition. These differences can easily be accounted for in the torque output calculations for individual combustion chambers.

[0043] The torque and operating parameters of the working chamber can be determined using a suitable method, model, algorithm, or formula. For example, in some embodiments, the air mass charge is calculated using input from an air flow meter and / or using velocity density calculations. As described in pending U.S. Patent Application No. 13 / 794,157, skip-fire operation can compromise the accuracy of these well-known MAC determination methods. In some embodiments, the MAC determination methods described in U.S. Patent Application No. 13 / 794,157, incorporated herein by reference in its entirety, can be used. One or more operating parameters can also be based on the engine parameters actually used to operate the engine, e.g.,based on an input from the powertrain setting determination unit 30. The following are some examples of the formulas used to calculate the operating parameters and the working chamber reference torque.

[0044] Once the combustion chamber reference torque has been determined, the diagnostic module 165 uses the combustion chamber reference torque to determine the engine reference torque. In some embodiments, the diagnostic module 165 determines a net engine torque (e.g., the total torque applied to the engine, including torque lost due to friction or pumping losses) and an engine braking torque (e.g., torque produced by the engine after accounting for pumping losses and friction). To estimate the engine braking torque, the diagnostic module 165 determines the effects of friction / pump losses (e.g., torque losses caused by friction). In various embodiments, the diagnostic module 165 determines the effects of friction based on the skip-fire ignition component.

[0045] The diagnostic module 165 is designed to compare the calculated engine reference braking torque with the operating torque calculated by the engine torque determination unit 20. In various embodiments, the diagnostic module 165 determines that if the discrepancy between two values ​​exceeds a certain threshold, a fault may be present, for example, in the engine or the engine control unit. In some embodiments, the diagnostic module 165 sends a signal that causes a warning or indicator to be displayed, for example, on the dashboard of a vehicle, to indicate that the problem should be addressed. This warning signal can also be integrated into the vehicle's OBD system.

[0046] The engine torque determination unit 20, the ignition timing and drivetrain setting determination unit 30, the ignition timing determination module 50, the diagnostic module 165 and the other components shown of Fig. 1. Functional blocks can exist in a wide variety of forms, and their functionalities can be integrated as an alternative within an ECU or provided by other, more highly integrated components, sub-component groups, or through a wide variety of alternative approaches. In various alternative implementations, these functional blocks can be achieved algorithmically using a microprocessor, ECU, or other computing device; using analog or digital components; using programmable logic; using combinations of the foregoing; and / or in any other suitable manner.

[0047] The Skip Fire control unit 70 and the ECU work together to enable skip-fire operation of the engine. A wide variety of skip-fire engine control methods can be used. Generally, skip-fire engine control involves selectively excluding the ignition of certain cylinders during selected firing opportunities. Thus, a particular cylinder can be fired during one engine cycle, then excluded during the next, and then selectively excluded or fired during the following cycle. In this way, even finer control of the effective engine displacement is possible. For example, firing every third cylinder in a four-cylinder engine results in an effective displacement that is one-third of the total engine displacement, a proportional displacement that cannot be achieved by simply deactivating a set of cylinders.Similarly, firing every other cylinder in a three-cylinder engine results in an effective displacement of 1 / 2, a partial displacement that cannot be achieved by simply deactivating a set of cylinders. U.S. Patent No. 8,131,445 (filed by the successor in title to the present application and incorporated herein by reference in its entirety) teaches various skip-fire engine control implementations.

[0048] As discussed above, the diagnostic module 165 (or another suitable component) is designed to provide one or more independent reference estimates / calculations indicating engine torque, which can be used to verify the main calculation. If the difference between the two values ​​exceeds a threshold, an appropriate fault indicator can be set in the OBD systems. If the difference is high enough, the driver can be warned by activating an engine warning light or by using another appropriate driver notification mechanism.

[0049] As is understandable to the expert, the torque output of a cylinder can be calculated in various ways, and there are a variety of parameters that generally specify the expected torque of a cylinder. Therefore, the reference check(s) need not necessarily involve a direct torque calculation. Instead, the reference check can be performed for any parameter generally representative of the engine torque, and the reference value can be compared with the corresponding value used by the Skip Fire control unit 10 when determining the various engine settings.

[0050] For example, as is well known in engineering, the mass airflow (MAC) of a cylinder is often used in cylinder torque calculations and can occasionally be used as a proxy for the expected cylinder torque output. Thus, parameters such as the MAC, which indicate engine power, can be determined by the diagnostic module during reference verification and compared with the values ​​of the corresponding parameters used by the Skip Fire control unit 10, or converted into values ​​used by the Skip Fire control unit and compared with those. For example, if the Skip Fire control unit uses parameters such as...Using engine torque fraction (ETF) or cylinder torque fraction (CTF) as described above, the values ​​calculated by the diagnostic unit 165 as a reference check can be converted into ETF or CTF and compared with the corresponding values ​​used by the Skip Fire control 10 or vice versa.

[0051] One specific reference verification approach involves calculating the net mean effective pressure (NMEP) of each fired combustion chamber. The NMEP can be determined in various ways. For example, a polynomial equation can often be formulated to calculate the NMEP within an expected cylinder operating range. An example formula for determining the NMEP of an average fired combustion chamber is given below: NMEP=−1.0694−0.0046082a−0.11426b+0.0090753b2+14.6983c−1.4779c2+0.059602ac−0.00070015a2c+0.15207ac2−00012281d+(3.1081*10−8)d2−0.00049374cd where a = ignition timing advance (0-60° BTDC), b = air / fuel ratio (AFR), c = MAC (g / cylinder / cycle), and d = engine speed (rpm). To use Eq. 1 to determine NMEP, the four variables to be used must be determined. The ignition timing advance (variable "a" in Eq. 1) can be obtained from the powertrain setting determination unit 30. The engine speed (variable "d" in Eq. 1) can be determined from a crankshaft speed sensor. The MAC (variable "c" in Eq. 1) can be determined using a cam phase detected by a cam phase sensor, an intake manifold pressure detected by an intake manifold pressure sensor, an air temperature detected by a temperature sensor, and an engine speed detected by a crankshaft rotation sensor. The air / fuel ratio (variable “b” in Eq. 1) can be measured directly using a sensor positioned downstream of the engine in an exhaust system.If all variables are known, Eq. 1 can be used to determine the NMEP for the average fired power cycle for a given combustion chamber. Using the known firing rate, the engine operating torque can be determined based on the torques (NMEP) produced by each combustion chamber. It is understood that the NMEP formula given above is merely an example and that the type of polynomial used and the actual values ​​of the constants used will vary for any given engine design. As discussed above, this calculation can alternatively be performed cylinder by cylinder, and the results for the fired cylinders can be summed to determine the net engine torque.

[0052] Another approach to verifying the relationship between MAC and motors would be to calculate MAC based on a polynomial in a similar manner. For example, a motor-specific formula for MAC could look like this: MAC=−0.50137+7.1986e−05*a+0.090317*b−0.0035901*b2+0.073815*c−0.003444*c2−0.00490 97*a*c+2.3724e−06*a2*c−2.8312e−05*a*c2+2.2408e−05*d−5.1431e−09*d2+2.7313e−06*c*d; where: a = ignition timing advance (0-60 BTDC), b = air / fuel ratio (AFR), c = NMEP (bar) and d = rpm. In this example, the average expected value for NMEP can be used in the MAC calculation.

[0053] Next, a specific reference verification approach is described. In this embodiment, the diagnostic module 165 determines an engine reference torque using a torque model, the torque model involving estimates of torque at the working chamber level. This means that the diagnostic module 165 determines an estimated torque level produced by a single (fired) working chamber for the purpose of evaluating the accuracy of the engine torque calculated in step 210. The effect of negative torque from an unfired, skipped cylinder can also be included in the engine reference torque calculation. (It is assumed that conventional engine systems do not estimate torque at the working chamber level for this purpose.) The working chamber torque can be any value equal to, proportional to, or representing the working chamber torque.For example, in some of the examples described here, the net mean effective pressure (NMEP) for a working chamber is calculated, although any other suitable value could be used, e.g., indicated mean effective pressure (IMEP), cylinder torque fraction (CTF), etc.

[0054] To determine the combustion chamber torque, the diagnostic module determines 165 different operating parameters, such as ignition timing advance, air / fuel ratio, air mass charge, and engine speed (e.g., the variables mentioned above). These variables are generally calculated using a different method than that used to determine the engine operating torque, in order to provide an independent estimate of the engine torque.

[0055] For example, the air mass charge can be determined in various ways. Any known air mass charge calculation method can be used; for example, methods that incorporate input from an air flow meter can be used instead of a velocity density-based approach. Alternatively, the approach described in pending U.S. patent application No. 13 / 794,157, which is incorporated herein by reference in its entirety, can be used. Instead of measuring the air-fuel ratio as described above, a fuel charge can be calculated based on an injector behavior curve. Using a MAC value calculated by any known method, an air / fuel ratio can be determined.

[0056] It is understood that the MAC (Maximum Active Combustion Value) can vary considerably between successive ignitions, especially in engines with a smaller number of combustion chambers, i.e., three- and four-cylinder engines. Consider the case of a four-cylinder engine operating with a 3 / 4 firing ratio. In this case, the first ignition after the skipped firing opportunity has a relatively high MAC, the second ignition a moderate MAC, and the third and final ignition a lower MAC. The intake manifold then refills during the skipped firing opportunity, and the cycle repeats.

[0057] The diagnostic module 165 calculates the engine reference torque using a torque model, which involves estimating the torque at a single combustion chamber level. As previously described, the torque output of a combustion chamber varies with its ignition history. Thus, the values ​​of the variables used in Eq. 1 can be adjusted from combustion chamber to combustion chamber in a known manner to provide a more accurate engine reference torque. Alternatively, operating parameters (e.g., ignition timing advance, MAC, etc.) can be assumed in the calculation, which are the average of the various known parameters for several combustion chambers, and then adjustments are made for each combustion chamber. The torque model can use Eq. 1 or a different torque model based on a different equation and possibly different variables.Alternatively, a reference table can be used to determine the motor reference torque.

[0058] After estimating the working chamber torque, the diagnostic module 165 determines a motor reference torque. In this particular example, the diagnostic module 165 determines a net motor reference torque. This means that the diagnostic module determines the total torque produced by the motor (some of which may be lost in the form of friction or pumping losses).

[0059] To determine the net engine reference torque, the working chamber reference torque is scaled in various embodiments to determine the torque at the engine level instead of at the working chamber level. In various embodiments, the scaling is based on an ignition fraction used to operate the engine's working chambers (e.g., the ignition fraction 119 of Fig. 1).

[0060] The diagnostic module 165 then determines a reference engine braking torque. This torque represents the engine's torque output and thus takes into account factors such as friction and pumping losses. In various implementations, the reference engine braking torque is the net engine reference torque minus the torque lost due to friction and pumping losses.

[0061] Friction can be estimated in various ways. In some embodiments, for example, the friction estimate is based on the ignition fraction. This is because the ignition fraction / frequency can influence the extent of pumping losses and friction in a skip-fire engine control system. For example, if more combustion chambers are fired, there can be more friction and pumping losses due to the repeated opening and closing of the intake and exhaust valves. If more combustion chambers are skipped, there can be lower pumping losses because the valves are not opened and closed as often. In other words, the friction estimate and / or the calculation of the reference braking torque based on the net reference torque can vary depending on the ignition fraction.

[0062] There are many other possible causes of friction and pumping losses. For example, combustion chambers can be vented in various ways. In some designs, a low-pressure spring is incorporated within the combustion chamber. This means that after exhaust gases are vented from the combustion chamber in a previous operating cycle, neither the intake nor the exhaust valves are opened during a subsequent operating cycle, creating a low-pressure / vacuum environment in the combustion chamber. In still other designs, a high-pressure spring is incorporated within the vented combustion chamber, preventing the escape of air and / or exhaust gases. These other designs can have different effects on friction or pumping losses. In various designs, these effects are taken into account when calculating the engine reference braking torque and estimating friction / pumping losses.

[0063] Any suitable data structure, formula, algorithm, or control system can be used to determine the engine reference braking torque. In some embodiments, a lookup table can be used. For example, the diagnostic module 165 can access a lookup table that uses the ignition timing as an index and specifies friction and / or engine reference braking torque for a given ignition timing. The lookup table can contain indices for other operating parameters, such as engine speed, etc.

[0064] After the diagnostic module estimates friction / pump losses and / or determines the engine reference braking torque, the diagnostic module 165 compares the engine reference (braking) torque with the engine operating torque determined in step 205. The diagnostic module 165 then performs diagnostic routines based on this comparison. For example, if the difference between the engine reference braking torque and the operating torque exceeds a predetermined threshold, the diagnostic module 165 may determine that there is a problem with the method used to calculate the engine operating torque. Various diagnostic / corrective actions may then be taken; for example, the diagnostic module 165 may send a signal that triggers the display of a warning message indicating that an engine problem should be diagnosed and addressed.

[0065] The operations described in the method can be performed very quickly. In some embodiments, for example, the operations described in the method are performed from ignition opportunity to ignition opportunity (or from duty cycle to duty cycle). In other embodiments, the method 200 is performed less frequently (e.g., from engine cycle to engine cycle or at another time interval suitable for diagnostic purposes, such as every 500 ms).

[0066] The invention has been described primarily in connection with a control system for a four-stroke reciprocating engine suitable for use in motor vehicles. However, it is understood that the described skip-fire approaches are well suited for use in a wide variety of internal combustion engines. These include engines for virtually any type of vehicle—among them passenger cars, trucks, boats, construction equipment, aircraft, motorcycles, scooters, etc.—and virtually any other application involving combustion chamber ignition and employing an internal combustion engine.The various approaches described work with engines operating under a wide variety of thermodynamic cycles – including virtually every type of two-stroke piston engine, diesel engine, gasoline engine, dual-cycle engine, Miller cycle engine, Atkinson cycle engine, Wankel engine and other types of rotary engines, mixed-cycle engines (such as dual gasoline and diesel engines), radial engines, etc. It is further assumed that the described approaches will work well with newly developed internal combustion engines, regardless of whether they operate using currently known or later developed thermodynamic cycles.

[0067] In some preferred embodiments, the ignition timing module uses sigma-delta conversion. Although sigma-delta converters are considered well-suited for use in this application, it is understood that the converters can employ a variety of modulation schemes. For example, pulse width modulation, pulse height modulation, CDMA-oriented modulation, or other modulation schemes can be used to provide the control pulse signal. Some of the described embodiments utilize first-order converters. However, other embodiments may employ higher-order converters or a collection of predetermined firing sequences.

[0068] In general, skip-fire engine control involves the selective omission of ignition in certain cylinders during selected firing opportunities. Thus, a particular cylinder can be fired during one engine cycle, then skipped during the next, and then selectively skipped or fired during the following cycle. This allows for even finer control of the effective engine displacement. For example, firing every third cylinder in a four-cylinder engine results in an effective displacement that is one-third of the total engine displacement, a proportional displacement that cannot be achieved by simply deactivating a set of cylinders.In theory, almost any effective displacement can be achieved using skip fire control, although in practice most implementations restrict operation to a set of available ignition fractions, sequences, or patterns.

[0069] It is understood that the powertrain control designs considered in the present application do not relate to those in Fig. The special arrangements shown in Figure 1 are limited. One or more of the illustrated modules may be integrated with one another. Alternatively, the features of a particular module may instead be divided among multiple modules. The control may also include additional features, modules, or steps based on other patent applications, including U.S. Patent Nos. 7,954,474; 7,886,715; 7,849,835; 7,577,511; 8,099,224; 8,131,445; 8,131,447; 9,200,587; 13 / 963,686; 13 / 953,615; 13 / 886,107; 9,239,037; 13 / 963,819; 13 / 961,701; 9,120,478; 13 / 843,567; 13 / 794,157; ​​13 / 842,234; 8,616,181; 9,086,020; 8,701,628; 14 / 207,109; and 8,880,258 and preliminary US patent applications Nos. 14 / 638,908 and 9,175,613, which are incorporated herein by reference in their entirety. Any features, modules, and steps described in the above patents may be added to the Controller 100.In various alternative implementations, these functional blocks can be achieved algorithmically using a microprocessor, the ECU or other computing device, using analog or digital components, using programmable logic, using combinations of the foregoing and / or in any other suitable manner.

[0070] The engine control unit and modules that are in Fig. 1. These functions and operations can be represented as computer code and stored in a non-volatile, computer-readable storage medium (e.g., the electronic control unit of a vehicle). When executed by one or more processors, the computer code causes the control unit / engine to perform one of the functions and operations (e.g., the operations of procedure 200 of Fig. 2), which are described herein. The motor control and modules may include any hardware or software suitable for performing the operations described herein.

[0071] The invention has been described primarily in connection with a skip-fire control arrangement in which cylinders are deactivated during skipped power cycles by deactivating both the inlet and outlet valves to prevent air from being pumped through the cylinders during skipped power cycles. However, it is understood that in some skip-fire valve actuation schemes, consideration is given to deactivating only the outlet valves or only the inlet valves to effectively deactivate the cylinders and prevent air from being pumped through them. Some of the described approaches work equally well in such applications.Furthermore, although it is generally preferred to deactivate the cylinders and thereby prevent air from flowing through them during skipped duty cycles, there are some specific situations where it may be desirable to allow air to flow through a cylinder during a selected skipped duty cycle. For example, this may be desirable when engine braking is required and / or due to specific diagnostic or operational requirements related to exhaust systems. The described valve control approaches work equally well in such applications.

[0072] The invention is very well suited for use in conjunction with dynamic skip-fire operation, in which an accumulator or other mechanism tracks the portion of an ignition that was requested but not provided, or that was provided but not requested, so that ignition decisions can be made from ignition opportunity to ignition opportunity. However, the described methods are equally suitable for use in virtually any skip-fire application (operating modes in which, during operation in a particular operating mode, individual cylinders are sometimes fired and sometimes skipped), including skip-fire operation using fixed ignition patterns or firing sequences, as may be the case when using rolling cylinder deactivation and / or various other skip-fire methods.Similar methods can also be used in the control of a variable stroke motor, where the extent of the strokes in each work cycle is changed to effectively vary the displacement of an engine.

[0073] In some applications referred to as multi-altitude skip fire, individual firing cycles during skip fire operation can be intentionally run at different cylinder delivery altitudes—that is, by intentionally using different air charge and corresponding fuel delivery altitudes. In multi-altitude skip fire, the different firing altitudes are distributed across at least some effective firing portions during operation. For example, U.S. Patent No. 9,399,964, hereby referenced, describes some such approaches. The concept of individual cylinder control used in dynamic skip fire can also be applied to dynamic multi-altitude engine operation, in which all cylinders are fired (that is, no cylinders are skipped), but individual firing cycles are intentionally distributed across different cylinder delivery altitudes.Dynamic skip fire, dynamic multi-altitude skip fire, and dynamic multi-charge-altitude engine operation can be collectively considered different types of dynamic altitude modulation (DAM) engine operation, in which the delivery of each duty cycle (e.g., skip / fire, high / low, skip / high / low, etc.) during engine operation is dynamically determined, typically on a duty-cycle (ignition opportunity to ignition opportunity) basis for a single cylinder. It is understood that dynamic altitude modulation engine operation differs from conventional variable displacement operation, in which, once the engine enters a reduced-displacement operating state, a defined set of cylinders operates in generally the same manner until the engine transitions to a different operating state.The described torque monitoring device and monitoring approaches can be used to verify the accuracy of the calculated engine operating torque regardless of the type of engine control with ignition altitude modulation used, including skip fire operation, multi-altitude skip fire operation, dynamic multi-altitude operation, etc.

[0074] In multi-altitude skip-fire operation, dynamic multi-charge-altitude operation, etc., where two or more fired charge altitudes are used, effective firing rates can be employed in the various calculations based on firing rate. In this context, the term "effective firing rate" can refer to either (i) an actual firing rate, which is a percentage (or proportion) of the firing opportunities where ignition actually occurs (those that are not skipped) relative to the total number of firing opportunities, or (ii) a percentage (or proportion) of the cylinders that would need to be fired at a reference firing rate to provide the set, requested, target, or delivered engine power. Such a reference firing rate can be a fixed value, a relative value, or a situation-dependent value.The latter use of the term "effective ignition fraction" is particularly useful when referring to multi-altitude skip fire and multi-charge altitude engine operation, where fired work cycles are intentionally operated at different cylinder output altitudes.

[0075] Although only a few embodiments of the invention have been described in detail, it is understood that the invention can be implemented in many other forms without deviating from the concept or scope of protection of the invention. For example, the drawings and embodiments occasionally describe special arrangements, working steps, and control mechanisms. It is understood that these mechanisms and steps can be modified to meet the requirements of various applications. For example, some or all of the operations and features of the diagnostic module are not required, and instead, some or all of these operations can be transferred, where appropriate, to other modules, such as the ignition timing calculation device and / or the ignition timing determination unit. Furthermore, it is understood that, although the in Fig.The methods described in Equation 2 do not imply a specific sequence, but this sequence is not required. In some embodiments, one or more of the described operations may be rearranged, replaced, modified, or omitted. Various engine torque measurement methods have been used, such as NMEP, IMEP, BMEP, etc. It is understood that the methods described here are equally applicable regardless of the exact nomenclature used to represent engine torque. Likewise, Equation 1 should be interpreted merely as an illustration, and other types of formulas using different variables or lookup tables may be used to determine a parameter that specifies engine torque. Thus, the present embodiments are to be considered exemplary and not limiting, and the invention is not to be restricted to the details provided herein.

Claims

[1] Method for performing diagnostic procedures on a skip fire engine control system, wherein the skip fire engine control system comprises an engine with multiple working chambers, the method comprising: Calculating an engine operating torque; Operating an engine with skip fire to provide engine operating torque; Calculating a motor reference torque using a torque model, wherein the torque model includes the individual estimation of the torque for each working chamber; comparing the engine reference torque with the engine operating torque to assess the accuracy of the calculation of the engine operating torque; Identifying a potential error if a discrepancy between the calculated engine reference torque and the calculated engine operating torque exceeds a threshold; and Implementing a measure in response to the identification of the potential error, where the engine reference torque is calculated at least in part based on a skip fire ignition component used to operate the engine. [2] Method according to claim 1, wherein the calculation of the engine reference torque takes into account differences in one or more operating parameters for different working chambers caused by different ignition histories of at least some of the working chambers. [3] Method according to claim 1 or 2, wherein: at least two chambers of labor have different chamber settings; Each of the working chamber settings is a setting for air mass charge, air / fuel ratio, or ignition timing advance; and The torque model takes into account the different working chamber settings. [4] Method according to any of the preceding claims, wherein the torque model is based on a calculation of the indicated mean effective pressure (IMEP) or the net mean effective pressure (NMEP) of a working chamber. [5] Method according to any of the preceding claims, wherein the torque model is based on a friction estimate and wherein the friction estimate varies depending on a skip fire ignition fraction used to operate the engine. [6] A method according to any of the preceding claims, further comprising: Estimating a working chamber reference torque; and Scaling the working chamber reference torque based on an ignition fraction to determine the engine reference torque. [7] A method according to any of the preceding claims, further comprising: Scaling the working chamber reference torque based on the ignition fraction to determine a net engine reference torque; Estimating friction based on the ignition fraction; and Determining a motor reference braking torque based on the net motor reference torque and the estimated friction. [8] Method according to one of the preceding claims, wherein the calculation of the engine reference torque and the comparison of the engine reference torque with the engine operating torque is carried out from ignition opportunity to ignition opportunity. [9] Engine control, which includes: a torque estimation module designed to calculate an engine operating torque; an ignition control unit designed to operate an engine with skip fire to provide engine operating torque; and a diagnostic module that is designed to do the following: Calculating a motor reference torque using a torque model, wherein the torque model includes individually estimating the torque for each working chamber; Comparing the engine reference torque with the engine operating torque to assess the accuracy of the engine operating torque calculation; Identifying a potential error if a discrepancy between the calculated engine reference torque and the calculated engine operating torque exceeds a threshold; and Initiating the implementation of a measure in response to the identification of the potential error, where the engine reference torque is calculated at least in part based on a skip fire ignition component. [10] Motor control according to claim 9, wherein the calculation of the motor reference torque takes into account differences in operating parameters for different working chambers caused by different ignition histories of the different working chambers. [11] Motor control according to claim 9 or 10, wherein: at least two of the chambers of labor have different chamber of labor attitudes; Each of the working chamber settings is a setting for air mass charge, air / fuel ratio, or ignition timing advance; and The torque model takes into account the different working chamber settings. [12] Engine control unit according to any one of claims 9 to 11, wherein the diagnostic module is further configured as follows: Estimating a working chamber reference torque; and Scaling the working chamber reference torque based on an ignition fraction to determine the engine reference torque. [13] Engine control unit according to any one of claims 9 to 12, wherein the diagnostic module is further configured as follows: Scaling the working chamber reference torque based on the ignition fraction to determine a net engine reference torque; Estimating friction based on the ignition fraction; and Determining a motor reference braking torque based on the net motor reference torque and the estimated friction. [14] Non-volatile computer-readable storage medium comprising executable computer code stored in a tangible manner, wherein the computer-readable storage medium comprises: executable computer code that can be used to calculate an engine operating torque; executable computer code that can be used to operate a skip-fire motor to provide the motor operating torque; executable computer code that can be used to calculate a motor reference torque using a torque model, wherein the torque model includes the individual estimation of the torque for each working chamber; executable computer code that can be used to compare the engine reference torque with the engine operating torque and to assess the accuracy of the calculation of the engine operating torque; Executable computer code that can be used to identify a potential error when a discrepancy between the calculated engine reference torque and the calculated engine operating torque exceeds a threshold; and Executable computer code that can be used to direct the execution of an action in response to the identification of a possible error, where the engine reference torque is calculated at least in part based on a skip fire ignition component. [15] Computer-readable storage medium according to claim 14, wherein the calculation of the engine reference torque takes into account differences in operating parameters for different working chambers caused by different ignition histories of at least some of the working chambers. [16] Computer-readable storage medium according to claim 14 or 15, wherein: at least two of the chambers of labor have different chamber of labor attitudes; Each of the working chamber settings is a setting for air mass charge, air / fuel ratio, or ignition timing advance; and The torque model takes into account the different working chamber settings. [17] Method according to any one of claims 1 to 8, wherein the controlled ignition component is taken into account when calculating the engine reference torque. [18] Method according to one of claims 1-8 or 17, wherein the torque model used in calculating the engine reference torque individually estimates the torque associated with each ignition opportunity of each working chamber. [19] Method according to any one of claims 1 to 8 or 17 to 18, wherein the action taken in response to the identification of the possible fault comprises generating a warning for a driver of a vehicle comprising the engine. [20] Method according to any one of claims 1 to 8 or 17 to 19, wherein the action taken in response to the identification of the possible fault comprises recording an identification of the fault in a diagnostic system. [21] Method according to any one of claims 1 to 8 or 17 to 20, further comprising determining that there is a problem with the engine, an engine setting or an engine control, at least in part based on the identification of the possible fault. [22] Method according to any one of claims 1 to 8 or 17 to 21, wherein the action taken in response to the identification of the possible fault is a diagnostic or remedial action. [23] Engine control according to any one of claims 9 to 13, wherein the action taken in response to the identification of the possible fault is a diagnostic or corrective action. [24] Engine control according to one of claims 9 to 13 or 23, wherein the torque model used in calculating the engine reference torque individually estimates the torque associated with each ignition opportunity of each working chamber. [25] Engine control according to one of claims 9 to 13 or 23 to 24, wherein the directed action taken in response to the identification of the possible fault comprises generating a warning for a driver of a vehicle comprising the engine. [26] Engine control according to one of claims 9 to 13 or 23 to 25, wherein the action taken in response to the identification of the possible fault comprises recording an identification of the fault in a diagnostic system. [27] Non-volatile computer-readable storage medium according to any one of claims 14 to 16, wherein the guided action is a diagnostic or remedial action. [28] Non-volatile computer-readable storage medium according to any one of claims 14 to 16 or 27, wherein the torque model used in calculating the engine reference torque individually estimates the torque associated with each ignition opportunity of each working chamber. [29] Non-volatile computer-readable storage medium according to any one of claims 14 to 16 or 27 to 28, wherein the directed action comprises generating a warning for a driver of a vehicle comprising the engine. [30] Non-volatile computer-readable storage medium according to one of claims 14 to 16 or 27 to 29, wherein the guided action comprises recording an identification of the fault in a diagnostic system.

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