System and method for preventing fouling of spark plugs in a variable displacement engine

Abstract

The present disclosure provides "systems and methods for preventing spark plug fouling in a variable displacement engine". Methods and systems are provided for reducing fouling of spark plugs in cylinders of a variable displacement engine configured to propel a vehicle. In one example, a method includes: in response to deactivation of one or more cylinders of the engine, providing a spark to the one or more cylinders at predefined positions respectively on one or more pistons coupled to the one or more cylinders, wherein the predefined positions include the one or more pistons being within a bottom dead center position threshold. In this way, spark plug fouling can be reduced or eliminated during cylinder deactivation conditions.

Description

Technical Field

[0001] The present description generally relates to methods and systems for controlling a vehicle engine to reduce spark plug fouling in a vehicle capable of selectively deactivating one or more engine cylinders. Background Art

[0002] An engine may be configured to operate with a variable number of active or deactivated cylinders while optionally maintaining the overall exhaust mixture air-fuel ratio around stoichiometry to increase fuel economy. Such an engine is referred to as a variable displacement engine (VDE). In some examples, a portion of the engine cylinders may be deactivated during selected conditions, where the selected conditions may be defined by parameters such as a speed / load window and various other operating conditions including vehicle speed. The VDE control system may deactivate selected cylinders by controlling a plurality of cylinder valve deactivators that affect the operation of the intake and exhaust valves of the cylinders or by controlling a plurality of selectively deactivatable fuel injectors that affect cylinder fueling. By reducing the displacement in low torque demand situations, the engine is operated at a higher manifold pressure, thereby reducing engine friction due to pumping and resulting in reduced fuel consumption.

[0003] There are several examples of how engine cylinders are typically deactivated in a four-stroke engine, which includes an intake stroke, a compression stroke, a combustion (power) stroke, and an exhaust stroke. In a first example, during the intake stroke, an air-fuel charge is drawn into the cylinder, the air-fuel charge is compressed, a spark is provided to cause combustion, but the combustion gases are not exhausted and instead the exhaust valve is kept closed. This traps the high-pressure charge in the cylinder. The advantage of this method is lower oil migration / consumption because the high pressure in the deactivated cylinder prevents oil from migrating into the cylinder. However, such a method has different disadvantages: there is a significant torque disturbance during deactivation and there is a pumping loss during the first event after deactivation (the pumping loss is smaller if the deactivation is for a short period, but is larger if there are frequent deactivations and restarts).

[0004] Another example of cylinder deactivation includes the same steps as in the first example above, but instead of trapping high-pressure charge, the cylinder is emptied, and instead of re-inhaling intake charge after the exhaust stroke, a vacuum is trapped in the cylinder by closing the exhaust valve (while keeping the intake valve closed). Such an example has the advantage over the first example that the significant torque disturbances during deactivation are reduced, and due to the lower pumping work, the fuel efficiency is increased during frequent deactivation and startup. However, a different disadvantage of such a method is that the fuel consumption may increase due to trapping a vacuum in the cylinder. The increased fuel consumption may lead to at least two undesirable problems. The first problem may include fouled spark plugs. The second problem may include the fact that crankcase vapors and / or oil migrating from the crankcase to the cylinder may result in a combustible mixture, which may lead to a combustion event in the cylinder. Deactivating the spark during cylinder deactivation may prevent an accidental combustion of the crankcase vapor / oil migration; however, the fouling and oil migration may still cause spark plug deterioration (spark plug fouling).

[0005] U.S. Patent No. 9,261,067 B2 teaches a method for reducing spark plug fouling in deactivated cylinders, the method including supplying a spark at a specifically determined moment when deactivating the cylinder. However, the inventors have recognized problems with such a method. For example, the supply of the spark is not specified in relation to the engine cycle state or the position of the piston coupled to the cylinder. Thus, supplying a spark according to US 9,261,067 B2 when deactivating the cylinder may result in an unwanted combustion event. SUMMARY OF THE INVENTION

[0006] Accordingly, the inventors herein have developed systems and methods for at least partially addressing the problems mentioned above. In one example, a method includes reducing spark plug fouling in a cylinder of an engine configured to propel a vehicle by providing a spark to the cylinder after deactivating the cylinder, wherein the spark is provided when a piston coupled to the cylinder is within a bottom dead center threshold. By providing the spark when the piston is within the threshold of bottom dead center, unwanted combustion events can be reduced or eliminated, and at the same time, spark plug fouling can be additionally reduced or eliminated.

[0007] As an example, the engine may include a variable displacement engine, and wherein in response to deactivating the cylinder by trapping a negative pressure relative to atmospheric pressure in the cylinder during deactivation, the spark is provided to the cylinder after the cylinder has been deactivated. In this example, trapping the negative pressure during deactivation may include discharging a combustible mixture of air and fuel into the engine's exhaust system and then sealing the cylinder to isolate the atmosphere.

[0008] In an example where multiple cylinders are selected for deactivation, such a method as described above may include providing spark to the multiple cylinders at predefined positions of multiple pistons coupled to the multiple cylinders in response to deactivation of the multiple cylinders.

[0009] In some examples of such methods, the spark ignition energy of the spark provided to the cylinders after deactivation of the cylinders is variable. For example, the spark ignition energy may be increased after a predetermined number of spark events when the cylinders are deactivated. Additionally, in some examples, the spark frequency of the spark provided to the cylinders may be variable depending on vehicle operating conditions.

[0010] The above advantages and other advantages and features of the present description will be readily apparent from the following detailed description and considered alone or in conjunction with the accompanying drawings.

[0011] It should be understood that the above summary is provided to introduce in a simplified form a series of concepts that are further described in the detailed description. This does not mean identifying the key or essential features of the claimed subject matter, the scope of the claimed subject matter being uniquely defined by the claims that follow the detailed description. Additionally, the claimed subject matter is not limited to implementations that solve any of the above or other disadvantages described in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 An exemplary variable displacement engine system is schematically shown.

[0013] Figure 2 A partial engine view is shown.

[0014] Figure 3A An exemplary method for selecting a cylinder deactivation strategy and an exemplary method for performing cylinder deactivation by trapping vacuum in cylinders selected for deactivation are shown.

[0015] Figure 3B Shown is the connection Figure 3A to an exemplary method and includes performing cylinder deactivation by trapping high-pressure charge in cylinders selected for deactivation.

[0016] Figure 4 Shown is according to Figure 3A an exemplary diagram for deactivating engine cylinders of a method.

[0017] Figure 5 Shown is according to Figure 3A another exemplary diagram for deactivating engine cylinders of a method.

[0018] Figure 6 Shown is according to Figure 3AAnother exemplary diagram for deactivating an engine cylinder of the method.

[0019] Figure 7 Shows for deactivating an engine cylinder selectively according to the indicated oil quality and according to Figure 3A and Figure 3B An exemplary diagram of the method.

[0020] Figure 8A Shows an exemplary method for selecting a cylinder deactivation strategy, an exemplary method for performing cylinder deactivation by trapping vacuum in the cylinders selected to be deactivated, and an exemplary method for mitigating torque disturbances caused by unexpected combustion events.

[0021] Figure 8B Shows an exemplary method for receiving Figure 8A and includes performing cylinder deactivation by trapping positive pressure in the cylinders selected to be deactivated, and mitigating torque disturbances caused by unexpected combustion events.

[0022] Figure 9 Depicts an exemplary diagram for restarting a deactivated cylinder in response to an indication of unexpected combustion in the deactivated cylinder.

[0023] Figure 10 Depicts an exemplary timeline for reducing or avoiding torque disturbances caused by unexpected combustion in deactivated cylinders, and an exemplary timeline for reassigning cylinders to be started / deactivated after the unexpected combustion event. Detailed Description

[0024] The following description relates to systems and methods for reducing spark plug fouling in a vehicle having a variable displacement engine (VDE) (e.g., the engine depicted at Figure 1 ). Such engines may be capable of selectively deactivating one or more engine cylinders (e.g., at Figure 2The engine cylinders depicted herein). Two methods can be utilized to deactivate engine cylinders in response to conditions that satisfy a cylinder deactivation event or a VDE event. In one example, high-pressure charge can be trapped in the cylinder selected to be deactivated. Trapping the high-pressure charge can reduce oil migration to the cylinder when the cylinder is deactivated, thereby preventing spark plug fouling. However, such methods can result in undesirable torque disturbances during deactivation. Additionally, such methods can result in pumping losses, which can be significant in cases where cylinders are frequently deactivated and restarted. In another example, a vacuum can be trapped in the cylinder selected to be deactivated. Trapping the vacuum can reduce or avoid torque disturbances that would otherwise be present during deactivation (as opposed to trapping high-pressure charge in the selected cylinder). However, due to trapping the vacuum, there can be an increase in oil migration to the selected cylinder. Such increased oil migration can result in spark plug fouling in some instances. To prevent such spark plug fouling, spark can be provided to the deactivated cylinder having the trapped vacuum, where the spark is provided when the piston coupled to the cylinder is near bottom dead center (BDC) (e.g., within a threshold percentage of degrees relative to BDC). Thus, Figure 3A Describe a method in which it can be determined whether to perform cylinder deactivation by trapping a vacuum or trapping high-pressure charge. For example, such determination can vary with the indicated oil quality. Figure 3A Further describe controlling the spark during cylinder deactivation in the case of deactivating the cylinder by trapping a vacuum in the cylinder. Alternatively, if Figure 3A it is indicated that it is preferred to perform cylinder deactivation by trapping high-pressure charge, then Figure 3B describe such a method. Figure 4 Describe a figure in which spark is provided to the cylinder near BDC at each instance (e.g., twice per engine cycle) when the piston coupled to the cylinder is near BDC. Alternatively, Figure 5 describe a figure in which spark is provided to the cylinder near BDC at every other instance (e.g., once per engine cycle) when the piston is near BDC. Additionally, Figure 5 describe an example in which the spark energy is increased during each subsequent spark event after two spark events when the piston is near BDC, where the two spark events include a base spark ignition energy. Figure 6 Show another figure in which spark is provided to the deactivated cylinder at each instance when the piston coupled to the deactivated cylinder is near BDC, where a base spark ignition energy is provided during a predetermined number of engine cycles or spark events, and where after the predetermined number of engine cycles (or spark events) have elapsed, the spark ignition energy is subsequently increased for the remainder of the time the cylinder is deactivated. Figure 7Depict another figure where a cylinder is deactivated by first trapping a vacuum in the cylinder and where a spark is provided near BDC when deactivating the cylinder, and subsequently at a later time during the same drive cycle, the cylinder is deactivated by trapping a high-pressure charge in the cylinder. For example, determining whether to deactivate the cylinder by trapping a vacuum or a high-pressure charge can be based on the quality of the engine oil.

[0025] By providing a spark near BDC to the deactivated cylinder, accidental combustion events in the deactivated cylinder can be reduced. However, it is recognized herein that in some examples and in some situations, such accidental combustion events may still occur. Thus, turning Figure 8A to an example method for reducing or avoiding torque disturbances caused by accidental combustion in a cylinder when trapping a negative pressure relative to atmospheric pressure in the cylinder to deactivate the cylinder. Figure 8B Depict a similar method under conditions where a positive pressure relative to atmospheric pressure is trapped in the cylinder. Figure 9 Depict an example figure for restarting a deactivated cylinder in response to such accidental combustion events. Figure 10 Depict an example timeline for reducing torque disturbances caused by accidental combustion events, and an example timeline for reassigning deactivated cylinders to be restarted and simultaneously reassigning activated cylinders to be deactivated in response to accidental combustion events when the engine is operating in a variable displacement engine mode (VDE mode).

[0026] Figure 1 Show an example variable displacement engine (VDE) 10 having a first row 15a and a second row 15b. In the depicted example, the engine 10 is a V6 engine where each of the first and second rows has three cylinders. However, in alternative embodiments, the engine may have a different number of engine cylinders, such as 4, 8, 10, 12, etc. The engine 10 has an intake manifold 16 with a throttle 20, and an exhaust manifold 18 coupled to an emissions control system 30. The emissions control system 30 includes one or more catalysts and one or more air-fuel ratio sensors, such as the catalysts and air-fuel ratio sensors described with respect to Figure 2 As a non-limiting example, the engine 10 can be included as part of a propulsion system for a passenger vehicle.

[0027] During selected conditions, such as when the full torque capacity of the engine is not needed, one or more cylinders (e.g., one of the first cylinder bank or the second cylinder bank) can be selected for deactivation (also referred to herein as the VDE operating mode). Specifically, one or more cylinders can be deactivated by cutting off the corresponding fuel injectors while commanding the intake and exhaust valves to close. When the fuel injectors of the deactivated cylinders are closed, the remaining enabled cylinders continue to perform combustion with the fuel injectors active and operating. To meet the torque requirements, the engine may generate the same amount of torque on those cylinders where the injectors remain enabled. This may require a higher manifold pressure, resulting in reduced pumping losses and increased engine efficiency. Also, the lower effective surface area exposed to combustion (only from the enabled cylinders) reduces engine heat loss, thereby improving the engine's thermal efficiency. In an alternative example, the engine system 10 can have cylinders where the intake and / or exhaust valves can be selectively deactivated, and deactivating the cylinders includes deactivating the intake and / or exhaust valves.

[0028] The deactivated cylinders can be grouped in a row-specific manner. For example, in Figure 1 , the first group of cylinders can include three cylinders of the first row 15a, while the second group of cylinders can include three cylinders of the second row 15b. In an alternative example, instead of deactivating one or more cylinders from each row together, two cylinders from each row of a V6 engine can be selectively deactivated together. In another example, only one cylinder can be deactivated.

[0029] The engine 10 can operate on a variety of substances that can be delivered via the fuel system 8. The engine 10 can be at least partially controlled by a control system including the controller 12. The controller 12 can receive various signals from sensors 4 coupled to the engine 10 and send control signals to various actuators 22 coupled to the engine and / or the vehicle.

[0030] The fuel system 8 can be further coupled to a fuel vapor recovery system (not shown) that includes one or more charcoal canisters for storing refueling fuel and day fuel vapor. During selected conditions, one or more valves of the fuel vapor recovery system can be adjusted to purge the stored fuel vapor into the engine intake manifold, thereby improving fuel economy and reducing exhaust emissions. In one example, the purge vapor can be directed near the intake valve of a specific cylinder. For example, during the VDE operating mode, the purge vapor can be directed only to the cylinders that are firing. This can be achieved in an engine configured with different intake manifolds for different groups of cylinders. Alternatively, one or more vapor management valves can be controlled to determine which cylinders receive the purge vapor.

[0031] The controller 12 can receive indications of cylinder knock or pre-ignition from one or more knock sensors 82 distributed along the engine block. When multiple knock sensors are included, the multiple knock sensors can be distributed symmetrically or asymmetrically along the engine block. Thus, one or more knock sensors 82 can be accelerometers or ionization sensors. Regarding Figure 2 Other details describing the engine 10 and exemplary cylinders.

[0032] Figure 2 Depict an exemplary embodiment of a combustion chamber or cylinder of an internal combustion engine 10. The engine 10 can receive control parameters from a control system including the controller 12 and inputs from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. A cylinder (also referred to herein as a "combustion chamber') 14 of the engine 10 can include a combustion chamber wall 136 and a piston 138 positioned therein. The piston 138 can be coupled to a crankshaft 140 such that the reciprocating motion of the piston is converted into rotational motion of the crankshaft. The crankshaft 140 can be coupled to at least one drive wheel of a passenger vehicle via a driveline. Additionally, a starter motor can be coupled to the crankshaft 140 via a flywheel (for example) to effect a starting operation of the engine 10.

[0033] The cylinder 14 can receive intake air via a series of intake passages 142, 144, and 146. The intake passage 146 can communicate with other cylinders of the engine 10 in addition to the cylinder 14. In some embodiments, one or more of the intake passages can include a boosting device, such as a turbocharger or a supercharger. By way of example, Figure 2 An engine 10 configured with a turbocharger is shown, the turbocharger including a compressor 174 disposed between the intake passages 142 and 144, and an exhaust turbine 176 disposed along an exhaust passage 148. The compressor 174 can be powered at least in part by the exhaust turbine 176 via a shaft 180, wherein the boosting device is configured as a turbocharger. However, in other examples, such as in the case where the engine 10 is equipped with a supercharger, the exhaust turbine 176 can optionally be omitted, wherein the compressor 174 can be powered by a mechanical input from a motor or the engine. A throttle valve 20 including a throttle plate 164 can be provided along the intake passage to change the flow rate and / or pressure of the intake air supplied to the engine cylinders. By way of example, the throttle valve 20 can be disposed downstream of the compressor 174, as Figure 2 shown, or alternatively, the throttle valve can be provided upstream of the compressor 174.

[0034] The exhaust passage 148 can receive exhaust gases from cylinders of the engine 10 other than the cylinder 14. The exhaust gas sensor 128 is shown as being coupled upstream of the emission control device 178 to the exhaust passage 148. The sensor 128 can be selected from various suitable sensors for providing an indication of the air / fuel ratio of the exhaust gases, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or CO sensor. The emission control device 178 can be a three-way catalyst (TWC), a NOx trap, various other emission control devices, or a combination thereof.

[0035] The exhaust gas temperature can be estimated by one or more temperature sensors (not shown) positioned in the exhaust passage 148. Alternatively, the exhaust gas temperature can be inferred based on engine operating conditions such as, for example, speed, load, air / fuel ratio (AFR), spark advance, etc. Additionally, the exhaust gas temperature can be calculated by one or more of the exhaust gas sensors 128. It will be appreciated that the exhaust gas temperature can alternatively be estimated by any combination of the temperature estimation methods listed herein.

[0036] Each cylinder of the engine 10 can include one or more intake valves and one or more exhaust valves. By way of example, the cylinder 14 is shown as including at least one intake poppet valve 150 and at least one exhaust poppet valve 156 located in the upper region of the cylinder 14. In some embodiments, each cylinder of the engine 10, including the cylinder 14, can include at least two intake poppet valves and at least two exhaust poppet valves located in the upper region of the cylinder.

[0037] The intake valve 150 can be controlled by the controller 12 via cam actuation by way of a cam actuation system 151. The cam actuation system 151 can include a first camshaft sensor 188. Similarly, the exhaust valve 156 can be controlled by the controller 12 via a cam actuation system 153. The cam actuation system 153 can include a second camshaft sensor 189. In some examples, one or more of the first camshaft sensor 188 and the second camshaft sensor 189 can be utilized to determine piston position, such as whether the piston is at top dead center or bottom dead center or somewhere between top dead center and bottom dead center. In some examples, such determination can be provided in combination with data received from the crankshaft position sensor 120 via the controller. It will be understood that in Figure 2The camshaft is not shown, but engine 10 may include a camshaft. The cam actuation systems 151 and 153 may each include one or more cams and may utilize one or more of a cam profile switching (CPS) system, a variable cam timing (VCT) system, a variable valve timing (VVT) system, and / or a variable valve lift (VVL) system. The controller 12 may operate the systems to change valve operation. The positions of the intake valve 150 and the exhaust valve 156 may be determined by valve position sensors 155 and 157, respectively. In alternative embodiments, the intake valve and / or the exhaust valve may be controlled by electric valve actuation. For example, cylinder 14 may alternatively include an intake valve controlled by electric valve actuation and an exhaust valve controlled by cam actuation including a CPS system and / or a VCT system, or may additionally include an exhaust valve controlled by electric valve actuation. In other embodiments, the intake valve and the exhaust valve may be controlled by a common valve actuator or actuation system or a variable valve timing actuator or actuation system.

[0038] Cylinder 14 may have a compression ratio that is the ratio of the volumes when the piston 138 is at bottom center to top center. Conventionally, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. For example, this may occur when using a higher octane fuel or a fuel with a higher latent heat of vaporization. If direct injection is used, the compression ratio may also be increased due to the effect of direct injection on engine knock.

[0039] In some embodiments, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. The ignition system 190 may provide an ignition spark to the combustion chamber 14 via the spark plug 192 in response to a spark advance signal SA from the controller 12 in a selected operating mode.

[0040] In some embodiments, each cylinder of engine 10 may be configured with one or more fuel injectors for supplying fuel thereto. As a non-limiting example, cylinder 14 is shown including one fuel injector 166. The fuel injector 166 is shown directly coupled to cylinder 14 to directly inject fuel into the cylinder in proportion to the pulse width of a signal FPW received from the controller 12 via an electronic driver 168. In this manner, the fuel injector 166 provides what is considered a fuel injector for directly injecting fuel (also referred to hereinafter as "DI") into the combustion cylinder 14. While Figure 1Injector 166 is shown as a side injector, but the injector can also be located at the top of the piston, for example, near the location of spark plug 192. When operating the engine with an alcohol-based fuel, such a location can improve mixing and combustion due to the lower volatility of some alcohol-based fuels. Alternatively, the injector can be positioned at and near the intake valve head to improve mixing. Fuel can be delivered to fuel injector 166 from a high-pressure fuel system 8 including a fuel tank, a fuel pump, and a fuel rail. Alternatively, fuel can be delivered at a lower pressure by a single-stage fuel pump, in which case the timing of direct fuel injection may be more limited during the compression stroke than in the case of using a high-pressure fuel system. Additionally, although not shown, the fuel tank can have a pressure transducer that provides a signal to controller 12. It will be appreciated that in alternative embodiments, injector 166 can be an intake port injector that provides fuel into the intake port upstream of cylinder 14.

[0041] It will also be appreciated that although the depicted embodiments illustrate operating the engine by injecting fuel via a single direct injector; in alternative embodiments, the engine can be operated by using two or more injectors (e.g., a direct injector and an intake port injector, two direct injectors, or two intake port injectors) and varying the relative injection amounts from each injector.

[0042] Fuel can be delivered to the cylinder by an injector during a single cycle of the cylinder. Additionally, the distribution and / or relative amount of fuel delivered from the injector can vary with the operating conditions. Further, for a single combustion event, multiple injections of the delivered fuel can be performed during each cycle. The multiple injections can be performed during the compression stroke, the intake stroke, or any suitable combination thereof. Moreover, fuel can be injected during the cycle to adjust the air-fuel ratio (AFR) of combustion. For example, fuel can be injected to provide a stoichiometric AFR. An AFR sensor can be included to provide an estimate of the in-cylinder AFR. In one example, the AFR sensor can be an exhaust sensor, such as EGO sensor 128. By measuring the amount of residual oxygen in the exhaust, the sensor can determine the AFR. Thus, the AFR can be provided as a lambda (λ) value, i.e., as the ratio of the actual AFR to the stoichiometry of a given mixture. Thus, λ of 1.0 indicates a stoichiometric mixture, a mixture rich in stoichiometry can have a λ value less than 1.0, and a mixture lean in stoichiometry can have a λ value greater than 1.

[0043] As described above, Figure 2 Only one cylinder of a multi-cylinder engine is shown. Thus, each cylinder can similarly include its own set of intake valves / exhaust valves, fuel injectors, spark plugs, etc.

[0044] The fuel tank in the fuel system 8 can hold fuels having different fuel qualities, such as different fuel compositions. These differences can include different alcohol contents, different octane ratings, different heats of vaporization, different fuel mixtures, and / or combinations thereof, etc.

[0045] The engine 10 can also include knock sensors 82 coupled to each cylinder 14 to identify abnormal cylinder combustion events. In an alternative embodiment, one or more knock sensors 82 can be coupled to selected locations on the engine block. The knock sensor can be an accelerometer on the cylinder block or an ionization sensor configured in the spark plug of each cylinder. The output of the knock sensor can be combined with the output of a crankshaft acceleration sensor to indicate an abnormal combustion event in the cylinder. In one example, based on the output of the knock sensor 82 in one or more defined windows (e.g., a crank angle time window), abnormal combustion due to one or more of knock and pre-ignition can be detected and distinguished. For example, pre-ignition can be indicated in response to a knock sensor signal generated in an earlier window (e.g., before the cylinder spark event), while knock can be indicated in response to a knock sensor signal generated in a later window (e.g., after the cylinder spark event). Additionally, pre-ignition can be indicated in response to a larger (e.g., above a first threshold) and / or less frequent knock sensor output signal, while knock can be indicated in response to a smaller (e.g., above a second threshold, the second threshold being lower than the first threshold) and / or more frequent knock sensor output signal.

[0046] Additionally, the applied mitigation actions can be adjusted based on whether the abnormal combustion is due to knock or pre-ignition. For example, spark retard and EGR can be used to address knock, while cylinder enrichment, cylinder lean-out, engine load limitation, and / or delivery-cooled external EGR can be used to address pre-ignition.

[0047] One or more of the fuel injectors 166, intake valves 150, and exhaust valves 156 can be selectively deactivated. As Figure 1As discussed herein, during conditions when the full torque capacity of the engine is not required, such as during low load conditions, cylinder 14 can be selectively deactivated by disabling cylinder fuel injection and / or the operation of the intake and exhaust valves of the cylinder. Thus, the remaining cylinders that are not deactivated can continue to operate and the engine can continue to rotate. As discussed above, one method of deactivating a cylinder can include trapping high pressure charge in the cylinder, which can prevent oil migration into the cylinder, but this can result in significant torque disturbances during deactivation and pumping losses during the first event after deactivation. Another method of cylinder deactivation can include trapping a vacuum in the cylinder. Such methods can reduce torque disturbances during deactivation and can increase fuel efficiency due to lower pumping work when frequently deactivating and starting one or more cylinders. The disadvantage of trapping a vacuum in the deactivated cylinder is that fuel consumption may increase, which can result in fouled spark plugs. Additionally, the vacuum conditions can cause oil and / or crankcase vapors to migrate into the deactivated cylinder, which can result in unintended combustion events. To address such problems of fouled spark plugs, increased fuel consumption, and / or unwanted / unintended combustion events, the inventors herein have developed methods to solve such problems. Such methods are described in detail below at Figures 3A to 3B As will be described in detail below. Briefly, the methods described herein can enable trapping a vacuum in the deactivated cylinder, which in turn can reduce torque disturbances during deactivation. The methods can include continuing to provide spark to the deactivated engine cylinder, but wherein the spark is provided when the piston (e.g., 138) coupled to the deactivated cylinder is at or near bottom dead center (BDC) (e.g., within a predetermined number of degrees). By providing the spark near BDC, the methods described herein can reduce or eliminate unwanted combustion events and can reduce or eliminate fouling of the spark plugs. More specifically, by continuously providing spark, residual oil fouling of the spark plugs can be prevented. Additionally, by providing the spark at BDC, unwanted combustion events can be reduced or eliminated due to the larger cylinder volume at BDC.

[0048] Thus, as discussed herein, BDC can refer to the position of the piston (e.g., 138) closest to the crankshaft (e.g., 140), and top dead center (TDC) can refer to the position of the piston farthest from the crankshaft. For example, it can be understood that BDC and TDC are 180° apart. By thus defining BDC relative to TDC, a predetermined number of degrees relative to BDC can be readily determined via a controller (e.g., 12) based on one or more of camshaft position and / or crankshaft position.

[0049] The controller 12 is shown as a microcomputer that includes a microprocessor unit 106, input / output ports 108, an electronic storage medium, shown in this particular example as a read-only memory chip 110, for executable programs and calibration values, a random access memory 112, a keep-alive memory 114, and a data bus. In addition to the signals previously discussed, the controller 12 can receive various signals from sensors coupled to the engine 10, including a measurement of intake mass air flow (MAF) from a mass air flow sensor 122; engine coolant temperature (ECT) from a temperature sensor 116 coupled to the coolant jacket 118; engine oil temperature from a temperature sensor 187; oil quality from an oil quality sensor 186; a surface ignition sense signal (PIP) from a Hall effect sensor 120 (or other type) coupled to the crankshaft 140 (also referred to herein as a crankshaft position sensor); throttle position (TP) from a throttle position sensor; an absolute manifold pressure signal (MAP) from a sensor 124; cylinder AFR from an EGO sensor 128; and abnormal combustion from a knock sensor 82 and a crankshaft acceleration sensor. An engine speed signal RPM can be generated by the controller 12 from the signal PIP. The manifold pressure signal MAP from the manifold pressure sensor can be used to provide an indication of the vacuum or pressure in the intake manifold.

[0050] In some examples, the engine 10 can include an oil level indicator or an oil quality sensor 186. The oil quality sensor 186 can include one or more sensors that can measure the electrical conductivity of the oil, mechanical properties of the oil, soot concentration in the oil, the presence and / or amount of water in the oil, etc. For example, measuring the electrical conductivity can include the ease with which current passes through the oil to enable determination of the abundance of contaminants in the oil (e.g., the lower the resistance, the more contaminants). Measurement of mechanical properties can include a piezoelectric sensor that can enable determination of the thickness of the oil.

[0051] In some examples, the oil quality sensor 186 can be utilized to determine what method to employ to deactivate one or more engine cylinders (e.g., trap high-pressure charge or trap negative pressure relative to the atmosphere), as will be discussed in more detail below.

[0052] In some examples, the engine 10 can further include an in-cylinder pressure sensor 185. The in-cylinder pressure sensor can be configured to send data related to the pressure in the cylinder to the controller.

[0053] The storage medium read-only memory 110 can be programmed with computer-readable data that represents instructions executable by the processor 106 for performing the methods described below and other variations that are contemplated but not specifically listed. Refer to Figures 3A to 3BShows an exemplary routine.

[0054] In some examples, the engine 10 may be included in a hybrid vehicle having multiple torque sources available for one or more vehicle wheels 197. In other examples, the engine 10 may be included in a conventional vehicle having only an engine. In the example shown, the vehicle includes an engine 10 and an electric machine 194. The electric machine 194 may be a motor or a motor / generator. The crankshafts 140 of the engine 10 and the electric machine 194 are connected to the vehicle wheels 197 via a transmission 196 when engaging one or more clutches. In the depicted example, a first clutch 193 is provided between the crankshaft 140 and the electric machine 194, and a second clutch 198 is provided between the electric machine 194 and the transmission 196. The controller 12 may send signals to the actuators (not shown) of each clutch (e.g., 193, 198) to engage or disengage the clutch so as to connect or disconnect the crankshaft 140 from the electric machine 194 and the components connected to the electric machine, and / or to connect or disconnect the electric machine 194 from the transmission 196 and the components connected to the transmission. The transmission 196 may be a gearbox, a planetary gear system, or another type of transmission. The powertrain may be configured in various ways, including configured as a parallel, series, or series-parallel hybrid vehicle.

[0055] The electric machine 194 receives electrical power from the traction battery 195 to provide torque to the vehicle wheels 197. The electric machine 194 may also operate as a generator, for example, during a braking operation, to provide electrical power to charge the battery 195.

[0056] Thus, a system for a vehicle may include a variable displacement engine that includes a set of cylinders and where each cylinder is coupled to a fuel injector and a spark plug, and where each cylinder includes a piston. The system may further include a controller that stores instructions in a non-transitory memory, the instructions which when executed cause the controller to determine, in response to conditions being met for deactivating one or more cylinders from the set of cylinders, whether to deactivate the one or more cylinders by trapping a vacuum in the one or more cylinders or by trapping a high-pressure charge in the one or more cylinders. In response to trapping the vacuum in the one or more cylinders, the controller may provide a spark when one or more pistons in the one or more cylinders are within a bottom dead center threshold, but may not supply fuel to the one or more cylinders when deactivating the one or more cylinders. Alternatively, in response to trapping the high-pressure charge in the one or more cylinders, the controller may stop supplying spark and fuel to the one or more cylinders.

[0057] Such a system may also include a crankshaft coupled to a variable displacement engine, a crankshaft position sensor, a camshaft coupled to the variable displacement engine, and a camshaft position sensor. The controller may store additional instructions for operating to indicate, via one or more of the crankshaft sensor and / or the camshaft sensor, whether one or more pistons of the cylinder or cylinders are respectively within the bottom dead center threshold, where the bottom dead center threshold includes a predetermined number of degrees relative to the bottom dead center position when deactivating the cylinder or cylinders by trapping the vacuum, and where in response to the one or more pistons being within the bottom dead center position threshold, providing a spark via the spark plug.

[0058] Such a system may also include an oil quality sensor. In this example, the controller may store additional instructions for operating to determine to deactivate the cylinder or cylinders by trapping the vacuum in response to an indication that the oil quality is greater than an oil quality threshold, and to deactivate the cylinder or cylinders by trapping the high-pressure charge in response to an indication that the oil quality is below the oil quality threshold.

[0059] Another example of a system for a vehicle may include a variable displacement engine that includes a set of cylinders and where each cylinder is coupled to a fuel injector and a spark plug, and where each cylinder includes a piston, a crankshaft mechanically coupled to the variable displacement engine, and a crankshaft position sensor. Such a system may also include a controller that stores instructions in a non-transitory memory that, when executed, cause the controller to deactivate a first subset of cylinders including one or more cylinders from the set of cylinders in response to a predetermined condition being met, where deactivating the first subset of cylinders includes at least sealing the first subset of cylinders and stopping fuel injection to the first subset of cylinders. The controller may store additional instructions for operating to maintain a second subset of cylinders including one or more cylinders from the set of cylinders in an activated state to combust air and fuel and to monitor the acceleration of the crankshaft when the first subset of cylinders is deactivated. In response to the acceleration of the crankshaft being greater than a crankshaft acceleration threshold, the controller may store additional instructions for operating to retard the spark provided to the activated cylinders included in the second subset of cylinders, the activated cylinders including cylinders arranged to combust air and fuel immediately after the acceleration of the crankshaft that is greater than the crankshaft acceleration threshold. The controller may store additional instructions for operating to assign, immediately after retarding the spark provided to the activated cylinders, restarting the first subset of cylinders to combust air and fuel and deactivating the second subset of cylinders.

[0060] In this system, the acceleration of the crankshaft that is greater than the crankshaft acceleration threshold is due to an unexpected combustion in a deactivated cylinder included in the first cylinder subset. In this example, the controller may store additional instructions for the following operation: discharging the residual combustion gas in the deactivated cylinder caused by the unexpected combustion before restarting the first cylinder subset including the deactivated cylinder.

[0061] In another example of such a system, the controller may store additional instructions for the following operation: providing spark to the first cylinder subset when deactivating the first subset, and providing spark to the second cylinder subset when deactivating the second subset, wherein providing spark includes providing spark when a piston coupled to a cylinder included in the first subset and / or the second subset is in a predetermined position relative to the crankshaft.

[0062] Another example of such a system may further include an oil quality sensor. In this example, the controller may store additional instructions for the following operation: deactivating the first cylinder subset and / or the second cylinder subset by trapping a negative pressure relative to atmospheric pressure in the first cylinder subset and / or the second cylinder subset in response to an indication that the oil quality for cooling, lubricating, and / or cleaning the variable displacement engine is greater than an oil quality threshold, and deactivating the first cylinder subset and / or the second cylinder subset by trapping a positive pressure relative to atmospheric pressure in the first cylinder subset and / or the second cylinder subset in response to an indication that the oil quality is below the oil quality threshold.

[0063] Now turning to Figure 3A , a flowchart of an advanced exemplary method 300 for reducing unexpected / undesired combustion events and preventing spark plug fouling in response to the deactivation of one or more engine cylinders is shown. Method 300 will be described with reference to the system described in Figures 1 to 2 , but it should be understood that method 300 may be applied to other systems without departing from the scope of the present disclosure. Method 300 may be executed by a controller (e.g., controller 12) and may be stored as executable instructions in a non-transitory memory. Instructions for implementing method 300 and the remainder of the methods included herein may be executed by the controller based on instructions stored on the controller's memory and in combination with signals received from sensors of the vehicle system, such as the sensors described above with reference to Figures 1 to 2 . According to the method depicted below, the controller may employ engine system actuators such as spark plugs (e.g., 192), fuel injectors (e.g., 166), etc.

[0064] Method 300 begins at 302 and may include estimating and / or measuring engine operating conditions. These may include (for example) engine speed, desired torque (e.g., from a pedal position sensor), manifold pressure (MAP), manifold air flow (MAF), BP, engine temperature, catalyst temperature, intake air temperature, spark timing, air temperature, knock limit, etc.

[0065] Proceeding to 304, method 300 may include determining an engine operating mode (e.g., VDE or non-VDE) based on the estimated operating conditions. For example, if the torque demand is low, the controller may determine that one or more cylinders can be deactivated while the remaining active cylinders meet the torque demand. In contrast, if the torque demand is high, the controller may determine that all cylinders need to remain active.

[0066] Proceeding to 306, method 300 may include verifying whether VDE mode conditions (e.g., cylinder deactivation conditions) are met. In one example, the cylinder deactivation conditions may be verified when the torque demand is less than a threshold. If the cylinder deactivation conditions are verified, the VDE mode is selected. If the cylinder deactivation conditions are not verified, then at 310, the routine includes maintaining all cylinders active and combusting.

[0067] If the cylinder deactivation conditions and the VDE operating mode are verified, then method 300 may proceed to 312. At 312, method 300 may include determining the quality of the oil included in the engine for lubricating, cleaning, and cooling various engine components. In one example, the oil is engine oil or motor oil. Determining the quality of the oil at 312 may include determining whether the quality of the oil is above or below an oil quality threshold, where an oil quality above the threshold indicates a higher (e.g., better) quality of oil, and where an oil quality below the threshold indicates a lower (e.g., poorer) quality of oil. Higher or better quality oil may include oil that lubricates, cleans the engine, and / or extracts heat from the engine more effectively, while lower quality or poorer quality oil may include oil that lubricates, cleans the engine, and / or extracts heat from the engine less effectively. In one example, an oil quality above the threshold may include oil that can prevent fouling of the spark plugs in the case of continuously providing spark to the deactivated cylinders during a VDE event. In other words, as long as spark is provided when the cylinders are deactivated (near BDC), the migration of oil into the deactivated engine cylinders (where a vacuum is trapped in the cylinders) may not contaminate the spark plugs. Alternatively, an oil quality below the threshold may include an oil quality where, in the case of oil migration occurring when the cylinders are deactivated, the spark plugs may still become fouled even if spark is provided during the deactivation.

[0068] In some examples, the oil quality threshold may be adjusted based on vehicle operating conditions such as vehicle speed, engine speed, engine load, engine temperature, oil temperature, etc. For example, based on various vehicle operating conditions, it may be indicated how likely it is for a deactivated cylinder that traps vacuum in the cylinder after deactivation to experience oil migration. For example, lower engine speed, lower vehicle speed, lower engine load, etc. may result in less oil migration to a deactivated cylinder with trapped vacuum compared to higher engine speed, higher vehicle speed, higher engine load, etc. Thus, the oil quality threshold may be adjusted based on how likely it is for one or more deactivated cylinders to experience oil migration, where such susceptibility is based on the vehicle operating parameters mentioned above. As an example, consider a situation where the oil quality is low but the vehicle operating conditions make it unlikely for the oil to migrate to the deactivated cylinder (with trapped vacuum). Such conditions may include lower engine speed, lower engine load, etc. In this example, the threshold may be adjusted to lower the threshold. In another example, the threshold may be increased in response to vehicle operating conditions that make it more likely for the oil to migrate to the deactivated cylinder (with trapped vacuum).

[0069] Thus, at 312, if it is indicated that the oil quality is below the threshold, then method 300 may proceed Figure 3B , where deactivation of one or more engine cylinders may be performed such that high-energy charge is trapped in the cylinder, which may reduce the likelihood of spark plug fouling by reducing / preventing oil migration to the cylinder. However, a drawback of such methods may be torque disturbances during deactivation. Thus, when possible, it may be desirable to deactivate the cylinder by trapping vacuum rather than high-pressure charge. In any case, methods for trapping high-pressure charge during deactivation will be discussed in detail below at Figure 3B .

[0070] Alternatively, at 312, in response to an indication that the oil quality is greater than the oil quality threshold, method 300 may proceed to 314. At 314, method 300 may include selecting one or more engine cylinders for deactivation based on the estimated engine operating conditions. In some examples, a group of cylinders or a bank of cylinders may be deactivated. The selection may be based on (e.g.) which cylinder or cylinders were deactivated during a previous VDE operating mode. For example, if the first cylinder or first group of cylinders on the first engine bank were deactivated during a previous cylinder deactivation condition, then the controller may select the second cylinder or second group of cylinders on the second engine bank for deactivation during the current VDE operating mode. As another example, the selection may be based on the regeneration status of the first exhaust catalyst (or emission control device) coupled to the first bank relative to the regeneration status of the second exhaust catalyst (or emission control device) coupled to the second bank.

[0071] After that selection, still at 314, the controller can selectively deactivate one or more engine cylinders. As used herein, the deactivation can include selectively deactivating the fuel injectors of the selected one or more engine cylinders (e.g., shutting them off). More specifically, as discussed above, the deactivation of one or more engine cylinders as discussed herein can include the controller commanding the deactivation of the selected one or more cylinders just after an exhaust stroke has been performed. In other words, the exhaust valves can be commanded to close via the controller (e.g., 12) just after the pistons corresponding to the one or more selected cylinders to be deactivated have pushed the combustion gases out of the exhaust valves into the exhaust system. Additionally, the intake valves corresponding to the one or more selected cylinders can be commanded / maintained closed via the controller. In this way, high-pressure charge is not trapped in the cylinders (see Figure 3B ), but rather a vacuum (negative pressure relative to atmospheric pressure) can be trapped in the one or more selected cylinders. As discussed, trapping a vacuum in the one or more selected cylinders can reduce or eliminate torque disturbances during deactivation, but can result in increased fuel consumption, spark plug fouling, and / or unwanted combustion events in the absence of mitigating actions.

[0072] Accordingly, moving to 316, method 300 can include commanding a spark to be provided to one or more deactivated engine cylinders near BDC. In one example, "near" BDC can include within 5 degrees or less of BDC. In another example, "near" BDC can include within 10 degrees or less of BDC. In another example, "near" BDC can include within 20 degrees or less of BDC. In other words, a spark can be provided to each of the one or more deactivated engine cylinders at a predetermined threshold (e.g., a predetermined number of degrees) of BDC.

[0073] To determine whether the pistons of the deactivated engine cylinders are near BDC (e.g., within the BDC threshold), a crankshaft position sensor (e.g., 120) and / or one or more camshaft sensors (e.g., 188, 189) can be utilized.

[0074] In one example, a spark can be provided near BDC (e.g., within the BDC threshold) at each instance corresponding to the piston of the deactivated cylinder being near BDC. More specifically, each engine cycle (intake stroke, compression stroke, power stroke, and exhaust stroke) can include two instances corresponding to the piston of the deactivated cylinder being near BDC. Thus, in one example, a spark can be provided whenever the piston is near BDC.

[0075] In an example where spark is provided at each instance where the piston is within the BDC threshold, the ignition energy of the spark can be controlled via a controller. For example, since spark is provided at each instance when the piston is near BDC, the ignition energy can be kept relatively low. In other words, the frequency of providing spark (e.g., at each BDC instance) can prevent any oil that may migrate into the deactivated cylinder from contaminating the spark plug without the need to increase the ignition energy.

[0076] As discussed herein, increasing the ignition energy of the spark delivered to the cylinder can include increasing the ignition coil dwell timing. For example, the ignition coil dwell timing can be increased by maintaining the voltage applied to the ignition coil of the spark plug at a substantially constant value for a duration longer than a typical ignition coil dwell time. The longer dwell time may increase the primary current to which the coil is charged and thus increase its stored inductive energy. As an example, a typical ignition coil dwell time can include 2.5 milliseconds, and increasing the dwell time can include increasing the ignition coil dwell time to 2.8 milliseconds, which may thus increase the peak primary current from 8 amperes to 10 amperes.

[0077] Increasing the ignition energy may additionally or alternatively include increasing the number of firings of the ignition coil during each spark event. Herein, a higher firing frequency is used to increase the number of sparks output by the ignition coil in each spark event for a determined number of BDC events after cylinder deactivation. In one example, the firing frequency can be increased from one firing per spark event to five firings per spark event.

[0078] As discussed herein, the ignition energy that is not “increased” can be referred to as “base” ignition energy. The base ignition energy can include an ignition coil dwell time of 2.5 milliseconds, and / or a firing frequency of one firing per spark event. Thus, the incremented or increased ignition energy can include an increased ignition energy compared to the base ignition energy.

[0079] In another example, spark can be provided at each timing of the BDC except for the first timing of the BDC after deactivation. More specifically, whenever spark is provided, electrical energy can be utilized, which can reduce the state of charge (SOC) of the on-vehicle power supply (e.g., battery 195). Thus, in a hybrid vehicle, it may be necessary to use electrical energy as efficiently as possible. Therefore, in one example, instead of providing spark at the first timing of the BDC after deactivation, spark can be provided at each subsequent timing of the BDC. In this example, the spark provided can include a base ignition energy. In other words, since spark is provided at each timing of the BDC after the first timing after deactivation, the ignition energy can be kept low. By providing the base ignition energy at each timing of the BDC, any oil contamination of the spark plug that may migrate to the deactivated cylinder can be prevented without increasing the ignition energy.

[0080] In another example, spark is provided at every other timing of the BDC after deactivation. In other words, spark can be provided once per engine cycle. In this example, instead of providing spark at the first BDC timing after deactivation, spark can be provided at the second BDC timing and at every other BDC timing thereafter. In one example, the ignition energy can be kept at the base ignition energy during a predetermined number of spark events (e.g., every other BDC timing), but the ignition energy can then be increased. In one example, the predetermined number of spark events during which the ignition energy is kept low can include two spark events, three spark events, 5 to 10 spark events, 10 to 20 spark events, etc. In one example, the predetermined number of spark events can include a number of spark events during which not a large amount of oil is yet expected to migrate into the cylinder, such that providing spark at the base ignition energy is sufficient to prevent fouling of the spark plug. However, after the predetermined number of spark events has elapsed, the ignition energy can be increased because the more time spent in the deactivated state with a vacuum trapped in the deactivated cylinder, the more likely it is that a large amount of oil will migrate into the deactivated cylinder. Thus, in this example, the ignition energy can be increased during the remaining duration of the deactivation.

[0081] In another example, the spark provided near BDC after deactivating one or more engine cylinders can vary with vehicle speed. For example, the frequency of spark events near BDC can be increased proportionally with an increase in vehicle speed and decreased proportionally with a decrease in vehicle speed. Consider an example where the vehicle is traveling at a higher speed (e.g., 40 mph or higher). After deactivating one or more engine cylinders, the faster engine speed can make the engine more prone to oil migration compared to when the cylinders are deactivated at a lower speed (e.g., less than 40 mph). Such examples are intended to be illustrative and are in no way intended to be restrictive. In other words, there can be a threshold vehicle speed (e.g., 40 mph) where if one or more cylinders are deactivated and the vehicle speed is above the threshold speed, then the frequency of spark events may increase compared to the frequency of spark events when the vehicle speed is below the threshold speed. In one example, if the vehicle speed is above the threshold speed at deactivation, then a spark is provided near BDC at each BDC timing after deactivation. Alternatively, if the vehicle speed is below the threshold speed at deactivation, then a spark is provided near BDC at every other BDC timing after deactivation.

[0082] In some examples, the frequency of the spark provided near BDC and / or the ignition energy of the provided spark can vary with the pressure within the cylinder at deactivation. For example, when the pressure in the deactivated cylinder becomes more negative relative to atmospheric pressure, oil migration may be more likely, so the frequency of the provided spark can be increased and / or the ignition energy can be increased. In one example, the pressure in the deactivated cylinder can be monitored via an in-cylinder pressure sensor (e.g., 185). As an example, at deactivation, the pressure in the cylinder can be monitored and a spark can be provided in response to the pressure in the cylinder reaching a predetermined negative pressure or vacuum relative to atmospheric pressure. For example, a spark at a base ignition energy can be provided initially. However, when deactivating the cylinder, in response to the pressure reaching a second negative pressure threshold that is more negative than a first threshold, the spark frequency and / or ignition energy can be increased, thereby reducing oil migration to the deactivated cylinder. In some examples, rather than relying on an in-cylinder pressure sensor, other methods can be used to infer the in-cylinder pressure. Examples can include the time spent in the deactivated state, etc.

[0083] In another example where the spark provided near BDC varies with vehicle speed, the spark provided can include an ignition energy that increases above a base ignition energy when the vehicle speed is above a threshold, and a reduced (e.g., base) ignition energy when the vehicle speed is below the threshold. For example, if the vehicle speed is above the threshold, the spark provided can include an increased ignition energy, where any spark does not include the base ignition energy. In this example, the spark can be provided at each BDC timing or every other BDC timing. In an example where the vehicle speed is below the threshold, then the spark provided can include the base ignition energy. In this example, the base ignition energy can be provided at each BDC timing or every other BDC timing after deactivation. Additionally, the base ignition energy can be provided during a predetermined number of spark events, similar to the case discussed above, and then the base ignition energy can be increased after the predetermined number of spark events has elapsed.

[0084] It will be appreciated, and the above examples are intended to be illustrative, and there may be situations where the frequency of spark events near BDC for a deactivated engine cylinder can be adjusted. For example, the following situations are within the scope of the present disclosure: for example, delaying the provision of a spark near BDC after deactivation by a predetermined number of BDC timings (e.g., 1, 2, 3, 4, 5, greater than 5 but less than 10, greater than 10 but less than 20, greater than 20 but less than 30, etc.), and then starting to provide a spark near BDC. In this example, when starting to provide the spark, the spark can be provided every other BDC timing, every third BDC timing, every fourth BDC timing, etc. In this example, the ignition energy can include the base ignition energy or can include an increased ignition energy. In one example, the base ignition energy can be performed for each spark event during a predetermined number of spark events, and after the predetermined number of spark events has elapsed, subsequent spark events can then include increased ignition energy spark events.

[0085] In another example, the spark frequency and / or ignition energy provided under each spark event can vary with oil temperature. For example, at a higher oil temperature, it can be expected that oil migration occurs more readily into a deactivated engine cylinder (with the trapped vacuum) than at a lower oil temperature. Thus, in response to an indicated oil temperature greater than a threshold, where the threshold includes an oil temperature at which it is expected that more oil will migrate into the deactivated cylinder than when the engine oil temperature is below the threshold, the spark frequency and / or ignition energy provided under each spark event can be increased compared to a condition where the engine oil temperature is below the threshold. As discussed above, the frequency and / or ignition energy provided can additionally be adjusted based on vehicle operating conditions (e.g., vehicle speed).

[0086] The engine can continue to be operated in a VDE mode with one or more engine cylinders deactivated until a restart condition is met at step 318 of method 300. In one example, the restart condition can be met when the engine torque demand increases above a threshold. In another example, the restart condition can be considered met when the engine has been operated in the VDE mode for a specified duration. Thus, at 318, a non-VDE condition can be confirmed. If the non-VDE condition is not confirmed, then the engine can continue to be operated in the VDE mode at 320, where one or more selected deactivated cylinders are sealed (e.g., intake and exhaust valves closed), fuel injection to the deactivated cylinders is stopped, and spark is provided to one or more deactivated cylinders near BDC timing.

[0087] After confirming the non-VDE condition, at 318, the deactivated cylinders can be restarted. Specifically, the deactivated fuel injectors can be restarted, and spark can be provided to the deactivated engine cylinders. Restarting the deactivated engine cylinders can include commanding spark to be provided to the restarting cylinders near TDC (e.g., exactly before TDC or within a threshold number of degrees of TDC).

[0088] In this way, spark plug fouling can be prevented in situations where deactivation of one or more engine cylinders includes trapping vacuum in one or more engine cylinders. Such methods can be desirable compared to methods where high-pressure charge is trapped in the cylinders because when vacuum is trapped in the cylinders, torque disturbances can be reduced or eliminated in response to deactivation and / or restart. However, as discussed above, there can be conditions where the oil quality is such that trapping high-pressure charge in the deactivated cylinders can be desirable in order to reduce / prevent oil migration into the cylinders, thereby preventing / reducing the chance of spark plug fouling, and thus reducing fuel consumption, etc.

[0089] Thus, returning to step 312 of method 300, if it is indicated that the oil quality is below a threshold, then method 300 can proceed to Figure 3B .

[0090] Figure 3B Depicting method 350, which can include a sub-method of method 300 depicted at Figure 3A . Method 350 begins at 355 and can include determining which cylinder(s) will be deactivated. The selection of which cylinder(s) will be deactivated can be performed as previously discussed at step 314 of method 300, and thus will not be restated here for the sake of brevity.

[0091] In response to determining which cylinder(s) are to be deactivated, method 350 may proceed to 360. At 360, method 350 may include deactivating a cylinder by trapping high-pressure charge in the selected cylinder(s) to be deactivated. More specifically, to trap high-pressure charge in a cylinder, the following method may be utilized. For a particular cylinder, the cylinder may intake air during the intake stroke and may be provided with fuel injection and spark during the compression stroke (or in some examples may be provided with fuel injection during the intake stroke) to combust air and fuel. However, instead of exhausting the combusted gases, high-pressure charge may be trapped within the cylinder by the controller commanding / maintaining the intake and exhaust valves corresponding to the particular cylinder selected to be deactivated to be closed. By preventing the combusted gases from being transported to the exhaust system, high-pressure charge (e.g., combusted air and fuel) may be trapped in the cylinder. Although trapping high-pressure charge has been discussed, it can be understood that in some examples, air may be inhaled into the cylinder arranged to be deactivated and then the cylinder may be sealed without combustion (no fuel injection or spark), thus trapping a positive pressure relative to atmospheric pressure in the particular cylinder. In some examples, trapping positive pressure instead of high-pressure charge may include (for example) an indication that the oil quality is below a threshold but greater than a second oil quality threshold. Although such actions are within the scope of the present disclosure, the description with respect to Figure 3B focuses on trapping high-pressure charge.

[0092] It can be understood that in the case of trapping high-pressure charge in a cylinder, no spark may be provided when deactivating the cylinder and fuel injection to the cylinder may be cut off.

[0093] In response to trapping high-pressure charge in the cylinder, method 350 may proceed to 365. Steps 365 to 375 are substantially equivalent to steps 318 to 322 of method 300 and will not be restated for the sake of brevity. Briefly, the cylinder may remain deactivated with the trapped high-pressure charge until a non-VDE condition is met, at which time the cylinder may be restarted to combust air and fuel. However, in some examples, even in the case of trapping high-pressure charge in the cylinder (or positive pressure caused by inhaled air but without combustion before sealing the cylinder), after a period of time, the cylinder may also be prone to accidental combustion. Therefore, in some examples, the pressure in the deactivated cylinder may be monitored (e.g., via in-cylinder pressure sensor 185), and if the pressure drops below a threshold, a spark may be provided near BDC to reduce or avoid any potential spark plug fouling. If an in-cylinder pressure sensor is not included in the vehicle or the in-cylinder pressure sensor does not operate as desired, then in some examples, a spark may be provided near BDC to the cylinder deactivated by trapping high-pressure charge or positive pressure after a predetermined number of engine cycles or after a predetermined duration has elapsed, etc.

[0094] Now turning to Figure 4 , an exemplary FIG. 400 is shown for providing spark and fuel injection to an engine cylinder. In exemplary FIG. 400, a single engine cylinder is shown for clarity. Additionally, FIG. 400 illustrates deactivation of the engine cylinder. More specifically, FIG. 400 includes four engine cycles (engine cycles 1 - 4), and illustrates the strokes (exhaust, intake, compression, and power) for each engine cycle. The engine positions for each engine cycle are illustrated, showing where top dead center (TDC) and bottom dead center (BDC) are relative to each engine cycle. FIG. 400 includes a graph 405 indicating valve timing. Line 406 illustrates exhaust valve timing, where line 407 illustrates intake valve timing. FIG. 400 also includes a graph 410 indicating piston position relative to the four engine cycles. FIG. 400 also includes a graph 415 indicating spark ignition energy relative to the four engine cycles. The spark ignition energy can be increased (+) or decreased (-). FIG. 400 also includes a graph 420 indicating whether fuel injection to the engine cylinder is on or off relative to the four engine cycles.

[0095] Referring to engine cycle 1, the exhaust valve first opens and closes during the exhaust stroke (line 406), and then the intake valve opens and closes during the intake stroke (line 407). Spark and fuel injection are provided to the engine cylinder during the compression stroke. In this exemplary FIG. 400, it can be understood that the spark ignition energy includes a base spark ignition energy.

[0096] Engine cycle 2 depicts the same process as engine cycle 1. In other words, engine cycles 1 and 2 illustrate conditions where the cylinder is not deactivated, so the intake and exhaust valves open and close, and fuel injection and spark are provided to the engine. In other words, engine cycles 1 and 2 depict engine cycles where the conditions for operating the engine in VDE mode are not met.

[0097] Engine cycle 3 illustrates that the exhaust valve opens and then closes. It can be understood that under engine cycle 3, the conditions for operating the engine in VDE mode are met. For clarity, the engine cylinder depicted at FIG. 400 includes a cylinder that is selected to be deactivated (although there may be other cylinders that are alternatively selected, depending on the vehicle operating conditions). Thus, after the exhaust stroke, which includes the exhaust valve opening and then closing, the intake valve is commanded to close / maintain the intake valve closed via the controller, and fuel injection is stopped (e.g., fuel injection is turned off). By closing the exhaust valve after expelling the exhaust from the cylinder (and maintaining the intake valve closed, without fuel injection), a vacuum can be formed in the deactivated cylinder. Such a vacuum may cause oil to migrate into the cylinder, as discussed above. Thus, to prevent fouling of the spark plug when deactivating the cylinder, as discussed above, a spark can be provided at BDC, and this will be further discussed below.

[0098] At engine cycle 3, the piston is at BDC just after the intake stroke following deactivation. However, in this exemplary FIG. 400, a spark is not provided at the first BDC timing. Instead, a spark is provided at the second BDC timing (just after the power stroke in engine cycle 3). As discussed above, providing a spark at BDC can include providing a spark "near" BDC, which can include providing a spark within a predetermined threshold (predetermined crank angle) of BDC. Referring to engine cycle 4, a spark is provided at each BDC timing after the second BDC timing. In the exemplary FIG. 400, it can be understood that the ignition energy provided under each spark event includes a base ignition energy.

[0099] In other words, the exemplary FIG. 400 depicts the following scenario: the spark is delayed (delayed by one BDC timing after deactivation), but a spark is provided at each BDC timing after the first BDC timing. Since a spark is provided at each BDC timing after the first BDC timing, the spark ignition energy includes a base ignition energy because due to the frequency of spark provision (e.g., at each BDC timing after the first BDC timing), it can be expected that spark plug fouling can be avoided.

[0100] The exemplary FIG. 400 only illustrates four engine cycles, but it can be understood that the deactivation of the engine cylinder illustrated at Figure 4 can be performed during any number of engine cycles. Thus, it can be understood that after engine cycle 4, a spark can continue to be provided at each BDC timing, where the spark provided includes a base ignition energy. In response to meeting the conditions for restarting the deactivated cylinder, it can be understood that the fuel injector can be restarted to provide fuel fill to the cylinder, and a spark can be provided near TDC (e.g., just before TDC or within a threshold of TDC).

[0101] Now turning to Figure 5 , an exemplary FIG. 500 is shown for providing spark to a deactivated engine cylinder. Similar to what was discussed above for Figure 4 , for clarity Figure 5 , a single engine cylinder is illustrated. FIG. 500 includes four engine cycles (engine cycles 1-4), and illustrates the strokes (exhaust, intake, compression, and power) for each engine cycle. The engine positions for each engine cycle are illustrated, showing where TDC and BDC are relative to each engine cycle. FIG. 500 includes a graph 505 indicating valve timing. Line 506 illustrates exhaust valve timing. FIG. 500 also includes a graph 510 indicating piston position relative to the four engine cycles. FIG. 500 also includes a graph 515 indicating spark ignition energy relative to the four engine cycles. FIG. 500 also includes a graph 520 indicating fuel injection to the engine cylinder as being either on or off relative to the four engine cycles. Exemplary FIG. 500 depicts the situation where the indicated VDE condition is met, and the cylinder selected to be deactivated includes the cylinder illustrated at FIG. 500. Thus, the cylinder is deactivated at engine cycle 1, as will be discussed in more detail below.

[0102] Referring to engine cycle 1, it can be understood that the VDE condition is met, and thus the exhaust valve first opens and closes during the exhaust stroke (line 506). When the cylinder is selected to be deactivated, the intake valve is maintained closed at engine cycle 1. As discussed above, by opening and then closing the exhaust valve to deactivate the cylinder, a vacuum can be trapped in the cylinder, which, without mitigation actions, may promote oil migration into the cylinder. Thus, to prevent the spark plug corresponding to the deactivated cylinder from being contaminated due to oil migration, a spark can be provided near BDC. In this exemplary FIG. 500, it can be understood that it illustrates the situation where a spark is provided at every other BDC instance, and the first two BDC instances include providing a spark at a base ignition energy, while the subsequent BDC instances include providing a spark at an increased ignition energy (compared to the base ignition energy).

[0103] Accordingly, referring to engine cycle 1, after deactivation of the cylinder, with fuel delivery to the engine cylinder cut off (graph 520), spark is not provided at the first BDC timing, but rather at the second BDC timing. Similarly, referring to engine cycles 2, 3, and 4, spark is provided once per engine cycle. By providing spark near BDC, it is understood that due to the larger cylinder volume when the piston is near BDC, misfire is expected. In other words, even if a combustion event occurs when the piston is near BDC, torque may not be generated. By providing spark once per engine cycle rather than at each BDC timing, spark plug fouling can be reduced or prevented and battery power consumption can be reduced compared to providing spark at each BDC timing. Thus, in one example, such a method of providing spark at every other BDC timing can vary with the SOC of the battery. For example, if the battery charge is below a threshold, it may be desirable to provide spark in a manner that provides spark at every other BDC timing or once per engine cycle.

[0104] After the first two spark events (engine cycle 1 and engine cycle 2) at base ignition energy, it is illustrated that subsequent spark events (engine cycle 3 and engine cycle 4) include increased ignition energy compared to the base ignition energy. In other words, since spark is provided only once per engine cycle, as the deactivation time (and the number of engine cycles) increases, the opportunity for oil migration (and thus spark plug fouling) increases. Thus, after a predetermined number of spark events at base ignition energy (two in this exemplary graph 500), the spark energy can be increased to ensure that spark plug fouling does not occur. It is understood that providing increased ignition energy can include using more energy stored in the battery, and thus the amount of increased ignition energy can vary with the battery SOC. By way of example, the ignition energy of each spark event (post-base ignition energy spark event) can be controlled via a controller to maintain a desired battery SOC during subsequent applications. In other words, the ignition energy can be controlled to maintain a threshold battery SOC. The threshold SOC can include a battery SOC that does not adversely affect subsequent applications that use battery power.

[0105] Exemplary graph 500 illustrates only four engine cycles, but it is understood that deactivation of the engine cylinder as illustrated can be performed during any number of engine cycles. Figure 5 Thus, it is understood that after engine cycle 4, spark can continue to be provided at every other BDC timing, where the spark provided includes increased ignition energy. In response to conditions being met for restarting the deactivated cylinder, it is understood that the fuel injector can be restarted to provide fuel injection to the cylinder, and spark can be provided near TDC (e.g., exactly before TDC or within a threshold of TDC).

[0106] Now turning to Figure 6 , another exemplary FIG. 600 is shown for providing spark to a deactivated engine cylinder. Similar to what was discussed above at Figure 4 and Figure 5 , for clarity, a single engine cylinder is illustrated. FIG. 600 includes a number of engine cycles, including engine cycle 1, engine cycle 2, engine cycle "n" (which may occur a duration after engine cycle 2), and engine cycle "n+1" which may occur immediately after engine cycle "n". For each engine cycle shown, the strokes (exhaust, intake, compression, and power) are illustrated. The engine positions for each engine cycle are illustrated, showing where TDC and BDC are relative to each engine cycle. FIG. 600 includes a graph 605 indicating valve timing. Line 606 illustrates exhaust valve timing. FIG. 600 also includes a graph 610 indicating piston position relative to the engine cycle. FIG. 600 also includes a graph 615 indicating spark ignition energy relative to the engine cycle. FIG. 600 also includes a graph 620 indicating whether fuel injection to the engine cylinder is on or off relative to the engine cycle. Exemplary FIG. 600 depicts the situation where the VDE condition is met and the cylinder selected to be deactivated includes the cylinder illustrated at FIG. 600. Thus, the cylinder is deactivated at engine cycle 1, as will be discussed in more detail below.

[0107] Referring to engine cycle 1, it can be understood that the VDE condition is met, and thus the exhaust valve first opens and closes during the exhaust stroke (line 606). When the cylinder is selected to be deactivated, the intake valve is maintained closed at engine cycle 1. As discussed above, by opening and then closing the exhaust valve to deactivate the cylinder, a vacuum can be trapped in the cylinder, which, without mitigation action, may promote oil migration into the cylinder. Thus, in order to prevent the spark plug corresponding to the deactivated cylinder from being contaminated due to oil migration, a spark can be provided near BDC (e.g., within a BDC threshold). In this exemplary FIG. 600, it can be understood that it illustrates the situation where a spark is provided at each BDC timing, and the spark provided includes a base ignition energy for a predetermined number of engine cycles (or in some examples, a predetermined duration), and then transitions to an increased ignition energy after the predetermined number of engine cycles or predetermined duration has elapsed.

[0108] Accordingly, referring to engine cycle 1, after deactivation of the cylinder, with fuel delivery to the engine cylinder cut off (graph 620), spark is provided at the first BDC timing and at each subsequent BDC timing (see engine cycles 2, n, and n+1). In other words, two sparks are provided in each engine cycle. Initially, the sparks provided include the base ignition energy indicated at engine cycles 1 and 2. Sparks including the base ignition energy are provided during a predetermined number of engine cycles. The predetermined number of engine cycles may include a number of engine cycles during which it is expected that the base ignition energy will be sufficient to prevent fouling of the spark plug. In some examples, the predetermined number of engine cycles may vary with engine load, vehicle speed, engine speed, oil temperature, etc. In other words, the number of predetermined engine cycles during which the base ignition energy is provided may be variable depending on vehicle operating conditions.

[0109] After the predetermined number of engine cycles during which the base ignition energy is provided has elapsed, the ignition energy may be increased during any subsequent engine cycle. Similar to the engine cycles in which the base ignition energy is provided at each BDC timing, after the ignition energy is increased, the increased ignition energy may be provided at each subsequent BDC timing. Alternatively, in some examples, after the ignition energy is increased, spark may be provided only at every other BDC timing. As depicted at graph 600, engine cycle n corresponds to the first engine cycle in which the spark ignition energy has been increased, and engine cycle n+1 corresponds to the second engine cycle after the spark ignition energy has been increased.

[0110] As discussed above, by providing spark at BDC, it can be appreciated that due to the larger cylinder volume when the piston is at BDC, misfire is expected. Additionally, even if a combustion event occurs at BDC, since the piston is at BDC, torque may not be generated. By providing two sparks in each engine cycle, spark plug fouling can be reduced or prevented. In some examples, such a method of providing spark at each BDC timing may vary with the SOC of the battery. For example, if the battery charge is above a threshold, it may be desirable to provide spark in a manner such that spark is provided at each BDC timing or two sparks are provided in each engine cycle. The threshold battery charge may include a charge level at which providing spark at each BDC timing will not deplete the battery to a level that may adversely affect any subsequent vehicle operating conditions that may utilize power from the battery.

[0111] Now turning to Figure 7, showing another exemplary Figure 700. Specifically, Figure 700 illustrates the following scenario: for a particular drive cycle with two VDE events, one of the VDE events is performed by trapping vacuum in one or more cylinders selected to be deactivated, while the other VDE event is performed by trapping high-pressure charge in the one or more cylinders selected to be deactivated. Similar to what was discussed above at Figures 4 to 6 for clarity, a single engine cylinder is depicted at Figure 7 . Figure 700 includes a number of engine cycles depicted as E, I, C, and P, corresponding to the exhaust stroke, intake stroke, compression stroke, and power stroke, respectively. Additionally, similar to Figures 4 to 6 , Figure 700 illustrates the engine position, showing where TDC (T) and BDC (B) are relative to each engine cycle. Figure 700 includes a graph 705 indicating valve timing. For the exemplary Figure 700, it can be understood that the valves shown as opening and closing during the exhaust stroke (E) correspond to the exhaust valves of the cylinder, and the valves shown as opening and closing during the intake stroke (I) correspond to the intake valves of the cylinder. Figure 700 also includes a graph 710 indicating the piston position relative to the engine cycle. Figure 700 also includes a graph 715 indicating the spark ignition energy relative to the engine cycle. Figure 700 also includes a graph 720 indicating whether fuel injection to the engine cylinder is on or off relative to the engine cycle. Figure 700 also includes a graph 725 indicating the quality of the oil (e.g., engine oil or motor oil) used for lubricating, cleaning the engine, and / or removing heat from the engine. Line 726 represents the threshold oil quality, above which the VDE event can include deactivating the cylinder to trap vacuum, and if the oil quality is below the threshold oil quality, then in response to the VDE event, the cylinder can trap high-pressure charge.

[0112] It can be understood that Figure 700 depicts a single drive cycle, which is divided into five segments, and the five segments will be elaborated below.

[0113] Section 1 describes a portion of the drive cycle where the VDE conditions are met and the oil quality is higher than the threshold oil quality. Additionally, it can be understood that the cylinder illustrated at 700 includes a cylinder that is selectively deactivated. Thus, when the oil quality is higher than the threshold, the exhaust valve opens and then closes to deactivate the cylinder. In other words, it can be understood that the exhaust valve opens to convey the burned gases out of the cylinder, and then the exhaust valve closes, thus trapping a vacuum in the cylinder. As discussed above, trapping a vacuum in the cylinder may cause oil to migrate into the cylinder, which may cause fouling of the spark plug. Therefore, to mitigate such issues, as illustrated at 700, a spark is provided at every other BDC timing when deactivating the cylinder. In the exemplary illustration at 700, it can be understood that the spark provided includes a base spark ignition energy. By continuously providing a spark near BDC when fuel injection to the deactivated cylinder is cut off, and in the case of trapping a vacuum in the sealed cylinder (intake and exhaust valves closed), fouling of the spark plug can be prevented or reduced during Section 1 of the drive cycle.

[0114] At the end of Section 1, although not specifically stated, it can be understood that the conditions for restarting the engine cylinder are met. As discussed above, such conditions may include torque demands that cannot be met when the cylinder (or cylinders) is deactivated. Thus, Section 2 depicts a portion of the drive cycle where the exhaust and intake valves resume operation and fuel injection and spark are provided. Importantly, a spark is provided just before TDC when restarting the cylinder, which is in contrast to providing a spark near BDC when deactivating the cylinder.

[0115] The operation of the engine proceeds for a certain duration, as illustrated in Section 3, where the cylinder combusts air and fuel. Although not explicitly stated, it can be understood that other cylinders of the engine may be deactivated during Section 3, but for the cylinder shown, it can be understood that the cylinder continuously combusts air and fuel throughout the duration of Section 3.

[0116] Section 4 describes a portion of the drive cycle where the engine cylinder combusts air and fuel. At the end of Section 4, it can be understood that the conditions for deactivating the illustrated cylinder are met. However, the oil quality has deteriorated below the oil quality threshold (graph 725). Thus, a vacuum is not trapped in the cylinder, and it may be necessary to trap a high-pressure charge to prevent oil from migrating into the deactivated cylinder. Therefore, it can be understood that at the start of Section 5, the cylinder is deactivated, which includes the cylinder taking in intake air, fuel injection and spark being provided to the cylinder, but the exhaust valve is not opened after the last combustion event before deactivation (and the intake valve remains closed). After deactivating the cylinder with the trapped high-pressure charge, no spark is provided to the cylinder and fuel injection is cut off. In this way, when the oil quality is below the threshold oil quality, oil migration into the deactivated cylinder during a VDE event can be prevented.

[0117] Although not explicitly stated, it is understood that after section 5, the engine can be restarted to complete the drive cycle and the like.

[0118] Thus, the method depicted at Figures 3A to 3B can implement a method that includes, in a first operating condition of a vehicle propelled by a variable displacement engine, the first operating condition including an indication that the oil mass for cooling, lubricating, and / or cleaning the variable displacement engine is greater than an oil mass threshold, operating the vehicle in a first mode, including selectively deactivating the cylinders by trapping a vacuum in the cylinders of the variable displacement engine. Such methods can also include, in a second operating condition of the vehicle, the second operating condition including an indication that the oil mass of the oil is below the oil mass threshold, operating the vehicle in a second mode, including selectively deactivating the cylinders by trapping high-pressure charge in the cylinders. In such methods, operating the vehicle in the first mode further includes: after deactivating the cylinders, providing a spark event to the cylinders when the piston coupled to the cylinders is within a bottom dead center threshold, where the bottom dead center includes the position of the piston in the case where the piston is closest to the crankshaft of the variable displacement engine.

[0119] In one example of such methods, providing the spark event can vary with in-cylinder pressure. Additionally, in some examples, the spark event can be provided once per engine cycle or twice per engine cycle, where an engine cycle includes an exhaust stroke, an intake stroke, a compression stroke, and a power stroke, and where each spark event includes one or more firings of the ignition coil of the spark plug configured to provide the spark event. Additionally, the ignition energy of the spark event can be variable depending on the vehicle operating conditions.

[0120] In another example of such methods, deactivating the cylinders in the second mode by trapping high-pressure charge in the cylinders can also include burning a mixture of air and fuel in the cylinders with the cylinders sealed to isolate the atmosphere, and then maintaining the cylinder seal with the burned air and fuel trapped in the cylinders.

[0121] Furthermore, in such methods, the first mode and the second mode can include stopping the fuel injection provided to the cylinders, and where the second mode can further include stopping the spark provided to the cylinders.

[0122] Regarding Figures 3A to 3B the method and corresponding to Figures 4 to 7The figures depict exemplary scenarios for preventing spark plug fouling when deactivating one or more cylinders of an engine. Such methods rely on providing a spark near BDC for the deactivated cylinders, as discussed in detail above, in order to reduce or avoid accidental combustion events when the cylinders are deactivated. However, it is recognized herein that there can be situations where accidental combustion events can still occur even with the condition of providing a spark near BDC, and in the case of such events, mitigating actions can be taken to reduce the unwanted consequences of such accidental combustion events. Thus, Figures 8A to 8B depicts another embodiment or example of the method depicted in Figures 3A to 3B wherein, when one or more cylinders are deactivated, an accidental combustion event of the engine is monitored, and in response to an indication of an accidental combustion event, a mitigating action is taken.

[0123] Thus, turning to Figure 8A , which depicts a flowchart of an advanced exemplary method 800 for reducing spark plug fouling during operation of an engine in a VDE mode, wherein the mechanism for deactivating the cylinders of the engine varies with the oil quality, and wherein mitigating actions are taken in response to an indication of accidental combustion during operation of the engine in a VDE mode. Method 800 will be described with reference to the system described in Figures 1 to 2 , but it should be understood that method 800 can be applied to other systems without departing from the scope of the present disclosure. Method 800 can be executed by a controller (e.g., controller 12) and can be stored as executable instructions in a non-transitory memory. Instructions for implementing method 800 and the remainder of the methods included herein can be executed by the controller based on instructions stored on the memory of the controller and in combination with signals received from sensors of the vehicle system, such as the sensors described above with reference to Figures 1 to 2 . According to the method depicted below, the controller can employ engine system actuators, such as spark plugs (e.g., 192), fuel injectors (e.g., 166), etc.

[0124] It can be understood that there are a number of steps of method 800 that are the same as or substantially the same as the steps of method 300 discussed above. Thus, for the sake of brevity, such steps will be described briefly at Figure 8A .

[0125] Method 800 begins at 802 and can include estimating and / or measuring engine operating conditions. These can include (e.g.) engine speed, desired torque (e.g., from a pedal position sensor), manifold pressure (MAP), manifold air flow (MAF), BP, engine temperature, catalyst temperature, intake temperature, spark timing, air temperature, knock limit, etc.

[0126] Proceeding to 804, method 800 may include determining an engine operating mode (e.g., VDE or non - VDE) based on the estimated operating conditions (see step 304 of method 300).

[0127] Proceeding to 806, method 800 may include verifying whether VDE conditions are met. In one example, the cylinder deactivation condition may be verified when the torque demand is less than a threshold. If the cylinder deactivation condition is verified, then the VDE mode is selected. If the cylinder deactivation condition is not verified, then at 810, the routine includes maintaining all cylinders active and combusting.

[0128] If the cylinder deactivation condition and the VDE operating mode are verified, then method 800 may proceed to 812. At 812, method 800 may include determining the quality of the oil included in the engine for lubricating, cleaning, and cooling various engine components. As discussed above at step 312 of method 300, determining the quality of the oil at 312 may include determining whether the quality of the oil is above or below an oil quality threshold, where an oil quality above the threshold indicates a higher (e.g., better) quality of oil, and where an oil quality below the threshold indicates a lower (e.g., poorer) quality of oil. Higher or better - quality oil may include oil that lubricates, cleans the engine, and / or extracts heat from the engine more effectively, while lower - quality or poorer - quality oil may include oil that lubricates, cleans the engine, and / or extracts heat from the engine less effectively. What defines the oil quality threshold and the circumstances for adjusting such oil quality thresholds have been discussed in detail above at 312, and thus will not be restated here for the sake of brevity.

[0129] At 812, if it is indicated that the oil quality is below the threshold, then method 800 may proceed Figure 8B , where deactivation of one or more engine cylinders may be performed such that pressure (positive pressure relative to atmospheric pressure) is trapped in the cylinders, which may reduce the likelihood of spark plug fouling by reducing / preventing oil migration to the cylinders. As discussed, a drawback of such methods may be the torque disturbance present during deactivation. Thus, when possible, it may be desirable to deactivate the cylinders by trapping a vacuum rather than pressure.

[0130] Alternatively, at 812, in response to an indication that the oil quality is greater than an oil quality threshold, method 800 may proceed to 814. At 814, method 800 may include selecting one or more engine cylinders for deactivation based on the estimated engine operating conditions. In some examples, a group of cylinders or a bank of cylinders may be deactivated. The selection may be based on, for example, which cylinder or cylinders were deactivated during a previous VDE operating mode. For example, if the first cylinder or the first group of cylinders on the first engine bank were deactivated during a previous cylinder deactivation condition, the controller may select the second cylinder or the second group of cylinders on the second engine bank for deactivation during the current VDE operating mode. As another example, the selection may be based on the regeneration state of the first exhaust catalyst (or emission control device) coupled to the first bank relative to the regeneration state of the second exhaust catalyst (or emission control device) coupled to the second bank.

[0131] In another example, to be described below, determining which cylinder(s) to deactivate at 814 may vary depending on whether it is indicated that a cylinder will be prone to an unexpected combustion event when deactivated by trapping vacuum in the particular cylinder. For example, if a particular cylinder has previously been indicated to cause an unexpected combustion event when deactivated, deactivation of such a cylinder may be prevented, while those other cylinders that have not been indicated to be prone to an unexpected combustion event may include cylinders that can be deactivated.

[0132] After the selection, still at 814, the controller may selectively deactivate the one or more engine cylinders by trapping vacuum in the one or more cylinders, as discussed above. In this way, instead of trapping a positive or high pressure charge relative to atmospheric pressure in the cylinders (see Figure 3B ), a vacuum (negative pressure relative to atmospheric pressure) may be trapped in the one or more selected cylinders. As discussed, trapping a vacuum in the one or more selected cylinders may reduce or eliminate torque disturbances during deactivation, but may result in increased fuel consumption, spark plug fouling, and / or unwanted combustion events if appropriate mitigation actions are not taken.

[0133] Accordingly, proceeding to 816, method 800 may include commanding a spark to be provided to one or more deactivated engine cylinders near BDC. As discussed above, in one example, "near" BDC may include within 5 degrees or less, within 10 degrees or less, or within 20 degrees or less of BDC.

[0134] To determine whether the piston of a deactivated engine cylinder is near BDC (e.g., within a BDC threshold), a crankshaft position sensor (e.g., 120) and / or one or more camshaft sensors (e.g., 188, 189) may be utilized.

[0135] In the above Figure 3A At step 316 of method 300 discussed above, the frequency of providing sparks near BDC is discussed extensively, as well as how the ignition energy for each spark event can be adjusted. Accordingly, such information will not be provided here for the sake of brevity, but it is understood that the description above regarding step 316 of method 300 applies equally to step 816 of method 800.

[0136] As discussed, providing sparks near BDC can prevent unwanted fouling of spark plugs corresponding to deactivated cylinders, and furthermore, by providing sparks near BDC, accidental combustion events can be reduced. However, there may be situations in which accidental combustion events still occur. Accordingly, in response to such events, mitigating actions can be taken, and the details of such mitigating actions are provided in the continuing discussion of the Figure 8A method.

[0137] Accordingly, moving to 818, method 800 can include monitoring crankshaft acceleration. The crankshaft acceleration can be monitored (e.g.) at least in part via a crankshaft position sensor (e.g., 120). In the case of monitoring crankshaft acceleration at 818, method 800 can proceed to 820. At 820, method 800 can include indicating whether an accidental combustion event has been detected. More specifically, an accidental combustion event can indicate whether the crankshaft acceleration exceeds a predetermined crankshaft acceleration threshold. For example, the crankshaft acceleration threshold can vary with vehicle speed, engine speed, engine load, or other operating conditions that may affect crankshaft acceleration. As an example, the expected crankshaft acceleration can be indicated via a look-up table stored at the controller, the look-up table varying with one or more of vehicle speed, engine speed, engine load, etc. Subsequently, another look-up table can include information regarding what crankshaft acceleration threshold to utilize based on the expected crankshaft acceleration. In some examples, the crankshaft acceleration threshold can be an acceleration that is a fixed amount greater than the expected crankshaft acceleration.

[0138] At 820, if the crankshaft acceleration is not greater than the crankshaft acceleration threshold, or in other words, no unexpected combustion is indicated, then method 800 can proceed to 822. At 822, method 800 can include indicating whether the non-VDE mode condition is met, or in other words, whether the restart condition is met. As discussed above, the restart condition can be met when the engine torque demand increases above a threshold. In another example, the restart condition can be considered met when the engine has been operating in VDE mode for a specified duration. Thus, at 822, the non-VDE condition can be confirmed. If the non-VDE condition is not confirmed, then the engine can continue to be operated in VDE mode, where one or more selected deactivated cylinders are sealed (e.g., intake and exhaust valves closed), fuel injection to the deactivated cylinders is stopped, and spark is provided to one or more deactivated cylinders near BDC timing.

[0139] Alternatively, at 822, after confirming the non-VDE condition, at 830, the deactivated cylinders can be restarted. Specifically, the deactivated fuel injectors can be restarted, and spark can be provided to the deactivated engine cylinders. Restarting the deactivated engine cylinders can include commanding spark to be provided to the restarting cylinders near TDC (e.g., exactly before TDC or within a threshold number of degrees of TDC).

[0140] In response to restarting the engine cylinders at 830, method 800 can proceed to 832. At 832, method 800 can include updating vehicle operating parameters. By way of example, updating the vehicle operating parameters at 832 can include storing information collected during the time the engine was operated in VDE mode at the controller. More specifically, such information can include whether an unexpected combustion event was detected. In an example where no unexpected combustion event was detected, such information can be stored at the controller to indicate that no particular engine cylinder is prone to or likely to experience an unexpected combustion event at this time. Thus, updating the vehicle operating parameters at 832 can include not designating any particular engine cylinder as being prone to or likely to experience an unexpected combustion event when deactivated under the captured vacuum. However, updating the vehicle operating parameters at 832 can include storing information about which engine cylinders were deactivated such that during a subsequent time when a request to operate the engine in VDE mode is indicated, the remaining cylinders can be deactivated while the most recently deactivated cylinder can be kept started. Method 800 can then end.

[0141] Returning to 820, in response to an indication of an unexpected combustion, method 800 may proceed to 824. At 824, method 800 may include determining the next cylinder to be fired, where the next cylinder to be fired includes the next cylinder expected or arranged to be fired after an unexpected combustion event. In one example, such an indication may be based on the firing order of the cylinders that are activated.

[0142] In the case where the next cylinder to be fired has been determined at 824, method 800 may proceed to 826. At 826, method 800 may include retarding the spark for the determined next cylinder to be fired. For example, retarding the spark at 826 may vary with the crankshaft acceleration indicated at 820. More specifically, based on the crankshaft acceleration indicated at 820, the amount of increased torque provided by the engine due to the unexpected combustion may be determined. To compensate for this increased torque such that the torque output of the engine equals the average requested torque output, the spark for the next cylinder to be fired may be retarded by the determined amount. In this way, torque disturbances that typically occur due to unexpected combustion events may be reduced or completely avoided.

[0143] After mitigating the torque disturbances that may otherwise occur in the case where the spark for the cylinder arranged to be fired after an unexpected combustion event is not retarded, method 800 may proceed to 828. At 828, method 800 may include setting the deactivated cylinders to be the cylinders to be fired upon ignition, while the activated cylinders may be deactivated. In other words, the fired and non-fired (deactivated) cylinders may be set to another set of fired and non-fired cylinders. It can be understood that setting the deactivated cylinders to be the cylinders to be fired when deactivating the currently activated cylinders may include maintaining the total torque output the same as before switching the cylinder states.

[0144] At 828, the restart of the cylinder indicated to have an unexpected combustion may be performed as follows. First, before inhaling the air / fuel charge and providing spark to a particular cylinder, the exhaust valve may be opened to purge the residual combustion gases resulting from the unexpected combustion in the cylinder having the unexpected combustion.

[0145] Once mitigation actions have been taken to avoid torque disturbances due to accidental combustion and residual combustion gases that caused the accidental combustion have been cleared from the cylinder, method 800 can continue to monitor crankshaft acceleration to indicate whether any more accidental combustion events are detected. In the case of indicating another accidental combustion event, although not explicitly stated, it can be understood that steps 824 - 828 can be performed again, but where at step 828, the deactivated cylinder that was previously indicated as the source of accidental combustion can be not selected for restart during the switch of the cylinder to be deactivated to a restarting cylinder, and vice versa. In other words, any cylinder indicated as prone or likely to have accidental combustion can be designated as a cylinder that can not be selected for deactivation.

[0146] In the absence of another accidental combustion event, method 800 can proceed to 822, where it can be indicated whether non - VDE mode conditions are met. If not, then method 800 can return to 816, where a spark can be provided near BDC for the deactivated cylinder, and where crankshaft acceleration can continue to be monitored to indicate any accidental combustion events.

[0147] Returning to 822, in response to indicating that non - VDE mode conditions are met, method 800 can proceed to 830. As discussed, at 830, method 800 can include restarting the deactivated engine cylinders. More specifically, fuel injection and spark to the deactivated cylinders can be restored. It can be understood that when restarting the deactivated cylinders, even though such cylinders may not have experienced an accidental combustion event, crankcase vapors and / or oil may have migrated into the cylinders. Thus, for restarting the cylinders, in some examples, before drawing in an air / fuel charge and providing a spark to restart the cylinder, the contents of such cylinder can first be discharged to the exhaust system by opening the exhaust valve coupled to such cylinder.

[0148] Proceeding to 832, method 800 can include updating vehicle operating parameters. More specifically, updating the vehicle operating parameters at 832 can include storing information at the controller about which specific cylinders are prone to accidental combustion events, such that at a subsequent time when VDE mode conditions are met, such cylinders are not deactivated. In other words, the controller can designate engine cylinders that have been indicated as prone to accidental combustion as non - deactivatable until the vehicle has been serviced by a technician and issues related to accidental combustion have been mitigated. Thus, in some examples, a malfunction indicator lamp (MIL) can be illuminated at the vehicle dashboard to indicate which cylinder(s) caused the accidental combustion, such that such unwanted effects can be mitigated. Method 800 can then end.

[0149] Returning to 812, in the case where the indicated oil quality is below the oil quality threshold, method 800 can proceed to Figure 8B , as discussed. Thus, turning to Figure 8B , which depicts an exemplary method 850 for trapping a positive pressure relative to atmospheric pressure in a particular engine cylinder that is set to be deactivated to deactivate the cylinder. Additionally, if conditions are indicated that satisfy the criteria for performing a spark plug cleaning routine, then such methods can include performing such a routine when deactivating a cylinder. Method 850 is derived from method 800 and method 850 will be described with reference to the system described in Figures 1 to 2 , but it should be understood that method 850 can be applied to other systems without departing from the scope of the present disclosure. Method 850 can be executed by a controller, such as controller 12, and can be stored as executable instructions in a non-transitory memory. Instructions for implementing method 850 and the remainder of the methods included herein can be executed by the controller based on instructions stored on the controller's memory and in conjunction with signals received from sensors of the vehicle system, such as the sensors described above with reference to Figures 1 to 2 . According to the methods depicted below, the controller can employ engine system actuators, such as spark plugs (e.g., 192), fuel injectors (e.g., 166), etc.

[0150] Method 850 begins at 855 and can include determining which cylinder(s) will be deactivated. As described above in Figure 3AAs discussed in detail at step 314 of, in some examples, a set of cylinders or a bank of cylinders can be deactivated, where such a selection can be based on which cylinder or cylinders were deactivated during a previous VDE operating mode. In other examples, the selection can additionally or alternatively be based on the regeneration state of a first exhaust catalyst (or emissions control device) coupled to the first bank relative to the regeneration state of a second exhaust catalyst (or emissions control device) coupled to the second bank. Additionally, in other examples, the selection can additionally or alternatively be based on whether a particular cylinder of the engine is indicated to be prone to or exhibit unintended combustion when deactivated. More specifically, in one example, a cylinder indicated to be prone to unintended combustion when deactivated can be designated as a non-deactivatable cylinder. Such examples can include cylinders indicated to be prone to unintended combustion under conditions where a cylinder is deactivated via trapped vacuum or trapped positive pressure. In other examples, if a particular cylinder is indicated to be prone to unintended combustion when deactivated via trapped vacuum, then such one or more cylinders can still be deactivated via trapped positive pressure. In other words, conditions that result in unintended combustion when one or more cylinders are deactivated under trapped vacuum may not inherently result in unintended combustion when cylinders are deactivated in a different manner (trapped positive pressure relative to vacuum), and thus, in some examples, one or more cylinders that exhibit unintended combustion when deactivated via trapped vacuum can be deactivated via trapped positive pressure. However, in other examples, as discussed, if one or more cylinders are indicated to result in unintended combustion when deactivated, then such one or more cylinders can subsequently be designated as non-deactivatable regardless of how the deactivation is performed (e.g., trapped vacuum or trapped positive pressure).

[0151] Upon determining at 855 to deactivate a cylinder, method 850 can proceed to 860. At 860, method 850 can include deactivating a selected cylinder to trap positive pressure in the cylinder. It can be appreciated that there are two ways to trap positive pressure in a cylinder selected to be deactivated. In one example, air can be charged into the cylinder via an open intake valve without providing fuel injection and spark, and air charge can be trapped in the cylinder by closing the intake valve without correspondingly opening the exhaust valve. In some examples, such a method can be utilized if the oil quality is less than an oil quality threshold but greater than a second oil quality threshold. A second example of how positive pressure can be trapped in a cylinder can include inhaling an air / fuel charge and providing spark, but not exhausting the burned air and fuel, thereby trapping a high-pressure charge. Such examples have been discussed above with respect to Figure 3B in detail.

[0152] Accordingly, as discussed, at 860, method 850 may include trapping a positive pressure relative to atmospheric pressure in one or more cylinders selected to be deactivated. Moving to 865, method 850 may include indicating whether conditions for spark plug cleaning are met. It will be appreciated that in this example, spark plug cleaning may include providing a spark to the deactivated cylinder(s) such that spark plug fouling may be reduced or avoided. When positive pressure is trapped in the cylinder, the likelihood of such spark plug fouling may be reduced due to the reduced likelihood of crankcase vapors and oil migrating to the deactivated cylinder(s) as compared to when one or more cylinders are deactivated by trapping a vacuum. However, over time, the positive pressure in the deactivated cylinder(s) may bleed off, the cylinder(s) may cool, and thus, oil and crankcase vapors may be more likely to migrate. Accordingly, the conditions for spark plug cleaning being met may include that a threshold duration has elapsed since the cylinder(s) were deactivated. The conditions for spark plug cleaning being met may additionally or alternatively include an indication that a threshold number of engine cycles have occurred since the cylinder(s) were deactivated.

[0153] At 865, if it is not indicated that the conditions for performing spark plug cleaning are met, then method 850 may proceed to 868, where it may be indicated whether non-VDE mode conditions are met. As discussed above, non-VDE mode conditions (e.g., restart conditions) may be met when engine torque demand increases above a threshold. In another example, the restart condition may be considered met when the engine has operated in VDE mode for a specified duration. Accordingly, at 868, the non-VDE conditions may be confirmed. If the non-VDE conditions are not confirmed, then the engine may continue to be operated in VDE mode, where one or more selected cylinders are deactivated (e.g., intake and exhaust valves closed and fuel injection to the deactivated cylinder(s) stopped).

[0154] Alternatively, at 868, after the non-VDE conditions are confirmed, at 870, the deactivated cylinder(s) may be restarted. Specifically, the deactivated fuel injector(s) may be restarted and a spark may be provided to the deactivated engine cylinder(s). Restarting the deactivated engine cylinder(s) may include commanding a spark to be provided to the restarting cylinder(s) near TDC (e.g., exactly before TDC or within a threshold number of degrees of TDC).

[0155] In response to restarting an engine cylinder at 870, method 850 can proceed to 872. At 872, method 850 can include updating vehicle operating parameters. By way of example, updating vehicle operating parameters at 872 can include storing information collected during the time the engine is operating in VDE mode at a controller. More specifically, such information can include which cylinders were deactivated, the duration of cylinder deactivation, and conditions for spark plug cleaning not being met. Such information can be stored at the controller and can be used for subsequent cylinder deactivation events.

[0156] Returning to 865, in response to the conditions for spark plug cleaning being met, method 850 can proceed to 876. At 876, method 850 can include providing a spark near BDC for each cylinder that has been selectively deactivated, as discussed above at step 816 of method 800. The remaining steps (878 - 886) of method 850 have been described above with respect to steps 818 - 828 of method 800 and will thus only be described briefly here. In the case of providing a spark near BDC at 876, method 800 can include monitoring crankshaft acceleration at 878. Proceeding to 880, in response to a crankshaft acceleration greater than the predetermined crankshaft acceleration threshold discussed above, or in other words, in response to an unexpected combustion event, method 850 can proceed to 882. At 882, method 850 can include determining the next cylinder to be fired based on the ignition order of the cylinders being started, and at 884, method 850 can include retarding the spark for the determined next cylinder to be fired such that the average torque from the unexpected combustion event and the combustion event with reduced torque (due to the retarded spark on the next cylinder to be fired) equals the average requested torque output of the engine. By retarding the spark for the determined next cylinder to be fired, torque disturbances that would otherwise exist due to unexpected combustion can be reduced or avoided.

[0157] Proceeding to 886, method 800 can include restarting the deactivated cylinders and reassigning the cylinders to be deactivated. In this exemplary method 850, it can be understood that deactivating a cylinder can include trapping positive pressure in a selected cylinder when the oil quality is below an oil quality threshold, as opposed to trapping a vacuum in the cylinder. In the process of restarting a deactivated cylinder that was the source of an unexpected combustion event, it can be understood that residual combustion gases from the unexpected combustion event can first be exhausted to the exhaust system before drawing in an air / fuel charge and initiating combustion by providing a spark.

[0158] In addition, it can be understood that during the process of reassigning the cylinders to be deactivated and the cylinders to be started, any cylinder previously indicated as prone to accidental combustion can be designated as non - deactivatable. In other words, during the cylinder reassignment of step 886 of method 850, such cylinders can be kept running. However, as discussed, in other examples, such actions can depend on whether such cylinders were previously indicated as prone to accidental combustion when being deactivated by trapping vacuum in the cylinder or when being deactivated by trapping positive pressure in the cylinder. In some examples where it has been previously implied that a cylinder is prone to accidental combustion but such indication occurs when the cylinder is deactivated to trap vacuum, then such a cylinder can be prevented from being deactivated to trap vacuum, but can still be deactivated to trap positive pressure. However, in this example, any cylinder previously indicated as prone to accidental combustion when being deactivated to trap positive pressure can be prevented from subsequently being deactivated by trapping vacuum or positive pressure. In any case, in response to mitigating torque disturbances caused by accidental combustion and further in response to reassigning the deactivated / restarted engine cylinders, method 850 can continue to monitor the crankshaft acceleration for accidental combustion events.

[0159] Under the condition that no other accidental combustion event is indicated, method 850 can proceed to 868 and can include indicating whether the non - VDE mode condition is met, as discussed above. If not, then method 850 can continue to operate the engine in the VDE operating mode. Alternatively, in response to meeting the non - VDE condition, method 850 can proceed to 870 and can include restarting the deactivated cylinders by supplying fuel and spark to the cylinders.

[0160] Proceeding to 872, method 850 can include updating vehicle operating parameters. Updating the vehicle operating parameters at 872 can include storing at the controller which cylinder(s) had an accidental combustion event during operation of the engine in the VDE mode. Such information can be used for subsequent cylinder deactivation events. In some examples, updating the vehicle operating parameters at 872 can include setting the MIL at the instrument panel to alert the vehicle operator of a request to service the vehicle. In addition, updating the vehicle operating parameters at 872 can include designating one or more cylinders as non - deactivatable due to an accidental combustion event. More specifically, because an accidental combustion was detected even when trapping positive pressure in the cylinder, it is highly likely that accidental combustion may also occur subsequently when trapping vacuum in the cylinder during deactivation or when trapping positive pressure again during deactivation. Thus, while in some examples cylinders that exhibit accidental combustion under the condition of deactivating the cylinder by trapping vacuum can still be deactivated by trapping positive pressure, in cases where accidental combustion is detected under the condition of trapping positive pressure during deactivation, such cylinders can be designated as non - deactivatable, as discussed.

[0161] Although the above description of the Figures 8A to 8B method includes methods for reducing torque disturbances caused by unexpected combustion in an engine cylinder, where in some examples, spark is provided near BDC for deactivated cylinders, it is understood that such methods may not be limited to the condition where spark is provided near BDC for deactivated cylinders. In some examples, such methods may be utilized under the condition that spark is provided at other predetermined locations that do not necessarily include being near BDC (e.g., within a threshold number of degrees of BDC). In other words, without departing from the scope of the present disclosure, such methods for reducing torque disturbances after unexpected combustion and for reassigning activated / deactivated cylinders after unexpected combustion are not limited to the case of providing spark to deactivated cylinders near BDC.

[0162] In addition, it is recognized herein that, without departing from the scope of the present disclosure, determining whether to trap negative or positive pressure in cylinders arranged to be deactivated may be independent of oil quality in some examples. In other words, methods for reducing or avoiding torque disturbances caused by unexpected combustion in deactivated cylinders may be applicable to deactivated cylinders that have been deactivated independently of oil quality (by trapping positive or negative pressure during deactivation). Further, in some examples, methods for reducing or avoiding spark plug fouling may be performed regardless of oil quality without departing from the scope of the present disclosure.

[0163] Thus, Figures 8A to 8B the method can implement a method that includes: deactivating a subset of cylinders of a variable displacement engine while other cylinders of the engine combust air and fuel; reducing or avoiding torque disturbances caused by unexpected combustion events in the deactivated cylinders by reducing the torque output of the engine; and restarting the deactivated cylinders that had unexpected combustion events, and during subsequent cylinder deactivation events, not deactivating the cylinders that had unexpected combustion events. In this way, under conditions where unexpected combustion events occur when operating an engine with deactivated cylinders, torque disturbances associated with the unexpected combustion events can be reduced or avoided, which can improve engine efficiency and can improve customer satisfaction.

[0164] In one example of the method, the unexpected combustion event includes an acceleration of a crankshaft coupled to the engine that is greater than a threshold crankshaft acceleration. Additionally, in some examples, the method may include discharging residual combustion gases from the deactivated cylinders that had unexpected combustion events before restarting the deactivated cylinders that had unexpected combustion events.

[0165] In another example of the method, reducing the torque output of the engine can include reducing the torque contribution of the fired cylinders arranged to combust air and fuel immediately after an unexpected combustion event. In this example, reducing the torque contribution of the fired cylinders can further include retarding the spark provided to the fired cylinders for combusting air and fuel, where the amount by which the spark is retarded varies with the torque provided to the engine via the unexpected combustion event.

[0166] Additionally, in an example of the method, the method can further include deactivating a subset of the cylinders of the engine by trapping a negative pressure relative to atmospheric pressure or a positive pressure relative to atmospheric pressure in the subset of cylinders of the engine. As an example, trapping the negative pressure can be in response to an indication that the oil quality of the oil used for cooling, lubricating, and / or cleaning the engine is greater than an oil quality threshold, and where trapping the positive pressure can be in response to an indication that the oil quality of the oil is below the oil quality threshold. Additionally, such methods can include providing a spark at a predetermined position of one or more pistons coupled to the subset of deactivated cylinders, where providing the spark can further vary with the pressure in the subset of deactivated cylinders, and where providing the spark can be used to prevent fouling of one or more spark plugs configured to provide the spark to the subset of deactivated cylinders. In one example, the predetermined position of the one or more pistons can include a position within a threshold number of degrees relative to the bottom dead center position.

[0167] Finally, in an example of the method, the engine can include a variable displacement engine. In this example, restarting the deactivated cylinders can further include restarting a subset of the deactivated cylinders that includes the deactivated cylinders that had an unexpected combustion event, and deactivating the other cylinders of the engine that operate to combust fuel.

[0168] Another example of the method can include: monitoring the acceleration of a crankshaft coupled to the engine while deactivating a first set of cylinders of the engine and firing a second set of cylinders to combust air and fuel. In response to the acceleration of the crankshaft being greater than a crankshaft acceleration threshold, the method can include retarding the spark provided via the fired cylinders included in the second set of cylinders, the fired cylinders including cylinders arranged to combust air and fuel immediately after the acceleration of the crankshaft is greater than the crankshaft acceleration threshold. The method can further include restarting the deactivated cylinders that are the cause of the acceleration of the crankshaft being greater than the crankshaft acceleration threshold, and deactivating the cylinders from the second set of cylinders.

[0169] In such methods, delaying the spark may include delaying the spark by an amount determined to vary with the amount of acceleration of the crankshaft. Additionally, in such methods, delaying the spark may compensate for an increase in engine torque caused by an acceleration of the crankshaft greater than a crankshaft acceleration threshold, which may in turn reduce or avoid torque disturbances otherwise associated with the increase in engine torque.

[0170] Such methods may further include restarting all of the first group of deactivated cylinders immediately after delaying the spark provided by the fired cylinders included in the second group, and deactivating all of the second group of fired cylinders.

[0171] Additionally, in such methods, immediately before restarting the deactivated cylinders, residual combustion gases from the deactivated cylinders that are the cause of an acceleration of the crankshaft greater than the crankshaft acceleration threshold are first expelled from the deactivated cylinders.

[0172] Additionally, in such methods, deactivating the first group of cylinders may include stopping fuel injection and sealing the first group of cylinders, and may further include providing a spark to the first group of deactivated cylinders at a predetermined position of one or more pistons coupled to the first group of deactivated cylinders, where providing the spark may vary at least with the pressure in the first group of deactivated cylinders.

[0173] Now turning to Figure 9 , exemplary FIG. 900 is shown. Specifically, FIG. 900 depicts a drive cycle in which particular cylinders are deactivated by trapping a vacuum in the cylinders, and in which spark plug cleaning is performed by providing a spark at BDC while the cylinders are deactivated. Additionally, FIG. 900 depicts an unexpected combustion event while the cylinders are deactivated, and thus FIG. 900 further depicts expelling residual combustion gases from the combustion event and subsequently restarting the cylinders after the unexpected combustion event. Similar to what was discussed above at Figures 4 to 7 , for clarity, a single engine cylinder is depicted at Figure 9 . FIG. 900 includes a number of engine cycles, which include four strokes depicted as E, I, C, and P, corresponding to the exhaust stroke, intake stroke, compression stroke, and power stroke, respectively. Additionally, similar to Figures 4 to 7, Figure 900 illustrates the engine position and shows where TDC (T) and BDC (B) are relative to each engine cycle. Figure 900 includes a graph 905 indicating valve timing. For the exemplary Figure 900, it can be understood that the valves shown as opening and closing during the exhaust stroke (E) correspond to the exhaust valve 906 of the cylinder, and the valves shown as opening and closing during the intake stroke (I) correspond to the intake valve 907 of the cylinder. Figure 900 also includes a graph 910 indicating the piston position relative to the engine cycle. Figure 900 also includes a graph 915 indicating the spark ignition energy relative to the engine cycle. Figure 900 also includes a graph 920 indicating whether the fuel injection to the engine cylinder is on or off relative to the engine cycle. Figure 900 also includes a graph 925 indicating whether an unexpected combustion event is indicated relative to the engine cycle.

[0174] It can be understood that Figure 900 depicts a portion of a single drive cycle, divides the portion of the single drive cycle into three segments, and the three segments will be described below.

[0175] Segment 1 illustrates a portion of the drive cycle in which the VDE condition is met, and although not explicitly stated, it can be understood that the oil quality is higher than the threshold oil quality. Additionally, it can be understood that the cylinder illustrated in Figure 900 includes a cylinder selected to be deactivated. Thus, in the case where the oil quality is higher than the threshold, the exhaust valve opens and then closes to deactivate the cylinder. In other words, it can be understood that the exhaust valve opens to convey the burned gases out of the cylinder, and then the exhaust valve closes, thus trapping a vacuum in the cylinder. As discussed above, trapping a vacuum in the cylinder may cause oil to migrate into the cylinder, which may cause fouling of the spark plug. Therefore, to mitigate such problems, as illustrated in Figure 900, a spark is provided at every other BDC timing when deactivating the cylinder. In the exemplary Figure 900, it can be understood that the spark provided includes the base spark ignition energy. By continuously providing a spark near BDC when fueling to the deactivated cylinder is cut off and in the case where a vacuum is trapped in the sealed cylinder (intake and exhaust valves closed), fouling of the spark plug can be prevented or reduced during segment 1 of the drive cycle.

[0176] However, during segment 2 of the portion of the drive cycle represented by Figure 900, an unexpected combustion event is detected (graph 925). As discussed above, an unexpected combustion can be indicated by a crankshaft acceleration greater than a predetermined crankshaft acceleration threshold when the engine is operating in the VDE mode. Thus, as described above regarding Figure 8AAs described by method 800 depicted herein, a cylinder is restarted during segment 3 of the portion of the drive cycle depicted by FIG. 900. More specifically, in response to an indication of an unexpected combustion, the cylinder is restarted during segment 3 by first opening the exhaust valve, which can expel residual combustion gases from the cylinder. Once the residual combustion gases from the unexpected combustion event have been expelled, air intake and fuel filling are restarted. Additionally, a spark is provided near TDC rather than BDC of the compression stroke. Thus, for the remainder of segment 3, the previously deactivated cylinder is started to combust air and fuel. Additionally, while fuel injection to the restarted cylinder is described as occurring during the compression stroke, fuel injection can be provided during the intake stroke.

[0177] In this manner, a deactivated cylinder that experiences an unexpected combustion when a spark is provided near BDC can be restarted in a way that ensures that residual combustion gases from the unexpected combustion event do not remain in the cylinder after restart, thus increasing the likelihood of achieving the desired combustion efficiency after restart.

[0178] Thus, FIG. 900 specifically depicts how a particular deactivated cylinder can be restarted in response to an indication of an unexpected combustion. For clarity, only a single engine cylinder is depicted at FIG. 900. However, as discussed above with respect to Figure 8A If mitigation actions are not taken, an unexpected combustion during cylinder deactivation can result in torque disturbances, as discussed. Such mitigation actions can include delaying the spark on the next cylinder that is scheduled to fire after an unexpected combustion event, as discussed. Thus, Figure 10 Exemplary timeline 1000 is depicted, which depicts how mitigation actions can be taken in response to an unexpected combustion to reduce or avoid torque disturbances that would otherwise be present when operating the engine in VDE mode.

[0179] Thus, turning to Figure 10, the exemplary timeline 1000 includes a graph 1005 depicting the valve timing of the first cylinder (C1) of the engine over time. The graph 1005 illustrates several strokes of the engine, including the exhaust (E) stroke, the intake (I) stroke, the compression (C) stroke, and the power (P) stroke. The opening / closing of the exhaust valve that occurs during the exhaust stroke is depicted by line 1006, while the opening / closing of the intake valve that occurs during the intake stroke is depicted by line 1007. The timeline 1000 also includes a graph 1010 that indicates the piston position of the piston coupled to C1 over time. The piston can be at top dead center (TDC), bottom dead center (BDC), or somewhere in between. The timeline 1000 also includes a graph 1015 that indicates the spark energy provided over time via a spark plug coupled to C1. The timeline 1000 also includes a graph 1020 that indicates the fuel injection provided to C1 over time. The timeline 1000 also includes a graph 1025 that indicates over time whether an unexpected combustion of C1 is indicated. As discussed, an unexpected combustion can be indicated by monitoring the crankshaft acceleration when the engine is operating in VDE mode. In response to a crankshaft acceleration greater than a predetermined crankshaft acceleration threshold, an unexpected combustion event can be indicated.

[0180] The timeline 1000 also includes a graph 1030 that indicates the valve timing of the second cylinder (C2) of the engine over time. Similar to graph 1005, graph 1030 illustrates several strokes of the engine, including the exhaust (E) stroke, the intake (I) stroke, the compression (C) stroke, and the power (P) stroke. The opening / closing of the exhaust valve is depicted by line 1032, while the opening / closing of the intake valve is depicted by line 1031. The timeline 1000 also includes a graph 1035 that indicates the piston position of the piston coupled to C2 over time. The piston can be at TDC, BDC, or somewhere in between. The timeline 1000 also includes a graph 1040 that indicates the spark energy provided over time via a spark plug coupled to C2. As will be discussed below, a mitigation action in response to an unexpected combustion when the engine is operating in VDE mode can include delaying the spark for C2, and thus, for clarity, the non-delayed spark position is indicated via a dashed-line graph 1045. The timeline 1000 also includes a graph 1050 that indicates the fuel injection provided to C2 over time.

[0181] It will be appreciated that C1 and C2 are arbitrary designations, and specifically, as will be discussed below, C1 includes cylinders that are deactivated but experience an unexpected combustion while deactivated. C2 includes the next cylinder to be ignited, or the cylinder that is arranged to ignite immediately after an unexpected combustion event has occurred in C1. Other cylinders of the engine may be deactivated and other cylinders may still be started, as discussed above. In other words, for clarity, only C1 and C2 are shown.

[0182] At time t0, it will be appreciated that C1 has been deactivated (graph 1005), where a vacuum is trapped in the cylinder. Thus, between times t0 and t1, the exhaust valve (line 1006) and the intake valve (line 1007) are maintained closed, thus maintaining the seal of C1. In the case where C1 is deactivated to trap a vacuum, in this exemplary timeline 1000, a spark is provided near BDC at every other BDC opportunity.

[0183] Furthermore, at time t0, C2 is started, or in other words, C2 is in operation to combust air and fuel. Thus, the exhaust valve (line 1032) is opened during the exhaust stroke between times t0 and t1, and the intake valve (line 1031) is opened during the intake stroke between times t0 and t1. Furthermore, fuel (graph 1050) and a spark (graph 1040) are provided to C2 between times t0 and t1. In this exemplary timeline 1000, fuel is provided during the intake stroke. However, in other examples, fuel may be provided during the compression stroke without departing from the scope of the present disclosure.

[0184] At time t1, an unexpected combustion corresponding to the unexpected combustion at C1 is detected. In the case of the unexpected combustion indicated at C1, the next cylinder to be ignited (C2) is determined via the controller. To mitigate the potential torque perturbation caused by the unexpected combustion event (torque perturbation caused by a crankshaft acceleration greater than the desired crankshaft acceleration), the spark to C2 is delayed at time t2 immediately after the unexpected combustion event at time t1. For illustrative purposes, the non-delayed spark timing is illustrated by graph 1045. By delaying the spark for the next cylinder to be ignited C2 after the unexpected combustion event at C1 (corresponding to a torque-reducing combustion event), the average torque from the unexpected combustion event and the torque-reducing combustion event can be equal to the average requested torque output of the engine. In this way, torque perturbations that might otherwise be caused by the unexpected combustion can be reduced or avoided.

[0185] Mitigation actions in response to an unexpected combustion event may also include restarting a deactivated cylinder that was the cause of the unexpected combustion event and deactivating another cylinder. As discussed above, in some examples, such actions may include restarting a deactivated cylinder that was the cause of the unexpected combustion event and restarting any other deactivated cylinders (not the cause of the unexpected combustion). Such actions may also include deactivating more than one activated cylinder. In other words, a set of deactivated cylinders may be restarted and another set of activated cylinders may be deactivated. In this exemplary timeline 1000, for clarity, only two cylinders are shown.

[0186] Accordingly, restarting a deactivated cylinder may include: at time t3, after taking mitigation actions to reduce or avoid torque disturbances, opening the exhaust valve corresponding to C1 to expel residual combustion gases from C1. In response to expelling the residual combustion gases from C1, at time t4, the intake valve corresponding to C1 is opened to draw air into C1. At time t5, fuel is provided to C1, and at time t6, a spark is provided to C1 when the piston coupled to C1 is near TDC. Between times t6 and t7, C1 remains activated to combust air and fuel.

[0187] Returning to time t4, after delaying the spark for C2 to mitigate torque disturbances caused by the unexpected combustion at C1, C2 is arranged to be deactivated. In this exemplary timeline, deactivation corresponds to trapping a vacuum in the cylinder. Accordingly, at time t4, the exhaust valve is opened and then closed (line 1032), and subsequently, the intake valve is not opened. After deactivating C2, between times t4 and t7, a spark is provided to the deactivated C2 near every other BDC opportunity to prevent fouling of the spark plug of C2. Additionally, although not explicitly stated, it can be understood that no unexpected combustion events are detected at the deactivated C2 during the duration of timeline 1000. Additionally, it can be understood that timeline 1000 depicts a scenario showing only a portion of a drive cycle and thus does not illustrate restarting C2 in response to an indication of a non-VDE condition. However, it can be understood that after an indication of non-VDE mode conditions is satisfied, C2 (and any other deactivated cylinders) may be restarted as discussed above.

[0188] In this manner, engine cylinders can be deactivated while preventing spark plug fouling without the undesired torque disturbances that would otherwise exist with high-pressure charge trapping in the cylinders selected for deactivation, as opposed to trapping a vacuum. Preventing or reducing spark plug fouling can increase engine life, increase fuel economy, and increase customer satisfaction.

[0189] The technical effect is realized that by continuing to provide a spark near BDC when one or more cylinders are deactivated, spark plug fouling can be prevented under the conditions when a vacuum is trapped in the cylinder after deactivation. Another technical effect is realized that preventing spark plug fouling by providing a spark can depend on vehicle operating conditions, such as vehicle speed, engine speed, engine load, battery SOC, etc., such that the frequency of spark events near BDC can vary according to the operating conditions. Another technical effect is realized that there can be situations where it is preferable or desirable to trap high-pressure charge rather than a vacuum in the cylinders selected for deactivation, where such situations can include conditions where the oil quality deteriorates below an oil quality threshold.

[0190] The systems described herein and those referenced herein Figures 1 to 2 and those referenced herein Figures 3A to 3BThe described method can implement one or more systems and one or more methods. In one example, a method includes reducing fouling of a spark plug in a cylinder by providing a spark to the cylinder after deactivating the cylinder of an engine configured to propel a vehicle, wherein the spark is provided when a piston coupled to the cylinder is within a bottom dead center threshold. In a first example of the method, the method further includes, wherein the bottom dead center includes the position of the piston in a case where the piston is closest to the crankshaft of the engine. A second example of the method optionally includes the first example and further includes, wherein the bottom dead center threshold includes the piston being within a predetermined number of degrees relative to the bottom dead center, and wherein the predetermined number of degrees includes within five degrees or less of the bottom dead center, within ten degrees or less of the bottom dead center, or within twenty degrees or less of the bottom dead center. A third example of the method optionally includes any one or more or each of the first example and the second example and further includes, wherein the engine includes a variable displacement engine. A fourth example of the method optionally includes any one or more or each of the first example to the third example and further includes, wherein the spark is provided to the cylinder after deactivating the cylinder in response to trapping a negative pressure relative to atmospheric pressure in the cylinder during deactivation. A fifth example of the method optionally includes any one or more or each of the first example to the fourth example and further includes, wherein trapping the negative pressure during deactivation includes discharging a combustion mixture of air and fuel into an exhaust system of the engine and then sealing the cylinder to isolate the atmosphere. A sixth example of the method optionally includes any one or more or each of the first example to the fifth example and further includes, wherein deactivating the cylinder includes stopping fuel supply to the cylinder. A seventh example of the method includes any one or more or each of the first example to the sixth example and further includes, wherein under conditions of selecting a plurality of cylinders for deactivation, a spark is provided to the plurality of cylinders at predefined positions of a plurality of pistons coupled to the plurality of cylinders in response to deactivation of the plurality of cylinders. An eighth example of the method optionally includes any one or more or each of the first example to the seventh example and further includes, wherein a spark ignition energy including the spark provided to the cylinder after deactivating the cylinder is variable. A ninth example of the method optionally includes any one or more or each of the first example to the eighth example and further includes, increasing the spark ignition energy after a predetermined number of spark events when the cylinder is deactivated. A tenth example of the method optionally includes any one or more or each of the first example to the ninth example and further includes, wherein a spark frequency of the spark provided to the cylinder can vary according to vehicle operating conditions.

[0191] Another example of the method includes: in a first operating condition of a vehicle propelled by a variable displacement engine, the first operating condition including an indication that an oil quality for cooling, lubricating, and / or cleaning the oil of the variable displacement engine is greater than an oil quality threshold, operating the vehicle in a first mode, including selectively deactivating cylinders by trapping a vacuum in the cylinders of the variable displacement engine; in a second operating condition of the vehicle, the second operating condition including an indication that the oil quality of the oil is below the oil quality threshold, operating the vehicle in a second mode, including selectively deactivating the cylinders by trapping high-pressure charge in the cylinders; and wherein operating the vehicle in the first mode further includes: after deactivating the cylinders, providing a spark event to the cylinders when a piston coupled to the cylinders is within a bottom dead center threshold, where the bottom dead center includes the position of the piston in the case where the piston is closest to the crankshaft of the variable displacement engine. In a first example of the method, the method further includes, wherein providing the spark event varies with in-cylinder pressure. A second example of the method optionally includes the first example and further includes, wherein the spark event is provided once per engine cycle or twice per engine cycle, where the engine cycle includes an exhaust stroke, an intake stroke, a compression stroke, and a power stroke. A third example of the method optionally includes any one or more or each of the first example to the second example and further includes, wherein the ignition energy of the spark event can vary according to vehicle operating conditions. A fourth example of the method optionally includes any one or more or each of the first example to the third example and further wherein deactivating the cylinders in the second mode by trapping high-pressure charge in the cylinders further includes burning a mixture of air and fuel in the cylinders with the cylinders sealed to isolate the atmosphere, and then maintaining the cylinder seal with the burned air and fuel trapped in the cylinders. A fifth example of the method optionally includes any one or more or each of the first example to the fourth example and further includes wherein the first mode and the second mode include stopping fuel injection to the cylinders, and wherein the second mode further includes stopping providing a spark to the cylinders.

[0192] A system for a vehicle, the system for the vehicle including a variable displacement engine, the variable displacement engine including a bank of cylinders and wherein each cylinder is coupled to a fuel injector and a spark plug, and wherein each cylinder includes a piston; and a controller that stores instructions in a non-transitory memory, the instructions when executed causing the controller to: determine whether to deactivate the cylinder or cylinders from the bank of cylinders by trapping vacuum in the cylinder or cylinders or by trapping high-pressure charge in the cylinder or cylinders in response to a condition being met for deactivating the cylinder or cylinders; and in response to trapping the vacuum in the cylinder or cylinders, provide spark when one or more of the pistons in the cylinder or cylinders is within a bottom dead center threshold, but not provide fuel to the cylinder or cylinders when the cylinder or cylinders are deactivated, and in response to trapping the high-pressure charge in the cylinder or cylinders, stop providing spark and fuel to the cylinder or cylinders. A first example of the system further includes a crankshaft coupled to the variable displacement engine; a crankshaft position sensor; a camshaft coupled to the variable displacement engine; a camshaft position sensor; and wherein the controller stores additional instructions for: indicating whether one or more of the pistons of the cylinder or cylinders are respectively within the bottom dead center threshold via one or more of the crankshaft sensor and / or the camshaft sensor, wherein the bottom dead center threshold includes a predetermined number of degrees relative to the bottom dead center position when deactivating the cylinder or cylinders by trapping the vacuum, and wherein in response to the one or more pistons being within the bottom dead center position threshold, provide spark via the spark plug. A second example of the system optionally includes the first example and further includes an oil quality sensor; and wherein the controller stores additional instructions for: determining to deactivate the cylinder or cylinders by trapping the vacuum in response to an indication that the oil quality is greater than an oil quality threshold, and deactivating the cylinder or cylinders by trapping the high-pressure charge in response to an indication that the oil quality is below the oil quality threshold.

[0193] Note that the exemplary control and estimation routines included herein can be used for a variety of engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in a non-transitory memory and can be executed by a control system including a combination of a controller with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. Accordingly, the various acts, operations, and / or functions illustrated can be performed in the sequence illustrated, in parallel, or in some cases omitted. Similarly, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the acts, operations, and / or functions illustrated can be repeatedly performed depending on the particular strategy used. Further, the acts, operations, and / or functions described can clearly represent code to be programmed into the non-transitory memory of a computer-readable storage medium for an engine control system, where the described acts are implemented by executing the instructions in a system including a combination of various engine hardware components and an electronic controller.

[0194] It will be appreciated that the configurations and routines disclosed herein are exemplary in nature and these specific embodiments should not be viewed in a limiting sense, as numerous variations are possible. For example, the above techniques can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, 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.

[0195] The appended claims particularly point out certain combinations and sub-combinations 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 incorporating one or more such elements, neither requiring nor precluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or properties are claimed by amending the claims or presenting new claims in this application or a related application. Such claims, whether broader, narrower, equal, or different in scope from the original claims, are also regarded as included within the subject matter of the present disclosure.

[0196] According to the present invention, a method includes reducing fouling of a spark plug in a cylinder by providing a spark to the cylinder after deactivating the cylinder of an engine configured to propel a vehicle, where the spark is provided when a piston coupled to the cylinder is within a bottom dead center threshold.

[0197] According to an embodiment, the present invention is further characterized in that the bottom dead center includes the position of the piston when the piston is closest to the crankshaft of the engine.

[0198] According to an embodiment, the present invention is further characterized in that the bottom dead center threshold includes the piston being within a predetermined number of degrees relative to the bottom dead center, and wherein the predetermined number of degrees includes within five degrees or less of the bottom dead center, within ten degrees or less of the bottom dead center, or within twenty degrees or less of the bottom dead center.

[0199] According to an embodiment, the present invention is further characterized in that the engine includes a variable displacement engine.

[0200] According to an embodiment, the present invention is further characterized in that in response to deactivating the cylinder by trapping a negative pressure relative to atmospheric pressure in the cylinder during deactivation, the spark is provided to the cylinder after the cylinder has been deactivated.

[0201] According to an embodiment, the present invention is further characterized in that trapping the negative pressure during deactivation includes discharging a combustion mixture of air and fuel into the exhaust system of the engine and then sealing the cylinder to isolate the atmosphere.

[0202] According to an embodiment, the present invention is further characterized in that deactivating the cylinder includes stopping fuel supply to the cylinder.

[0203] According to an embodiment, the present invention is further characterized in that under conditions of selecting a plurality of cylinders for deactivation, the spark is provided to the plurality of cylinders at predefined positions of a plurality of pistons coupled to the plurality of cylinders in response to the deactivation of the plurality of cylinders.

[0204] According to an embodiment, the present invention is further characterized in that the spark ignition energy of the spark provided to the cylinder after deactivation of the cylinder is variable.

[0205] According to an embodiment, the present invention is further characterized in that the spark ignition energy is increased after a predetermined number of spark events when the cylinder is deactivated.

[0206] According to an embodiment, the present invention is further characterized in that the spark frequency of the spark provided to the cylinder can vary according to vehicle operating conditions.

[0207] According to the present invention, a method includes: in a first operating condition of a vehicle propelled by a variable displacement engine, the first operating condition including an indication that an oil quality for cooling, lubricating, and / or cleaning the oil of the variable displacement engine is greater than an oil quality threshold, operating the vehicle in a first mode, including selectively deactivating cylinders by trapping vacuum in cylinders of the variable displacement engine; in a second operating condition of the vehicle, the second operating condition including an indication that the oil quality of the oil is lower than the oil quality threshold, operating the vehicle in a second mode, including selectively deactivating cylinders by trapping high-pressure charge in the cylinders; and wherein operating the vehicle in the first mode further includes: after deactivating the cylinders, providing a spark event to the cylinders when a piston coupled to the cylinders is within a bottom dead center threshold, wherein the bottom dead center includes the position of the piston in a case where the piston is closest to a crankshaft of the variable displacement engine.

[0208] According to an embodiment, the present invention is further characterized in that providing the spark event varies with the in-cylinder pressure.

[0209] According to an embodiment, the present invention is further characterized in that the spark event is provided once per engine cycle or twice per engine cycle, wherein an engine cycle includes an exhaust stroke, an intake stroke, a compression stroke, and a power stroke, and wherein each spark event includes one or more firings of an ignition coil of a spark plug configured to provide the spark event.

[0210] According to an embodiment, the present invention is further characterized in that an ignition energy of the spark event can vary according to a vehicle operating condition.

[0211] According to an embodiment, the present invention is further characterized in that deactivating the cylinders in the second mode by trapping high-pressure charge in the cylinders further includes burning a mixture of air and fuel in the cylinders in a case where the cylinders are sealed to isolate the atmosphere, and then maintaining the cylinders sealed in a case where the burned air and fuel are trapped in the cylinders.

[0212] According to an embodiment, the present invention is further characterized in that the first mode and the second mode include stopping fuel injection to the cylinders, and wherein the second mode further includes stopping providing spark to the cylinders.

[0213] According to the present invention, there is provided a system for a vehicle, the system for the vehicle having: a variable displacement engine including a set of cylinders, each cylinder of which is coupled to a fuel injector and a spark plug, and each cylinder including a piston; and a controller that stores instructions in a non-transitory memory, the instructions, when executed, cause the controller to: determine whether to deactivate the cylinder or cylinders from the set of cylinders by trapping vacuum in the cylinder or cylinders or by trapping high-pressure charge in the cylinder or cylinders in response to a condition being met for deactivating the cylinder or cylinders; and in response to trapping the vacuum in the cylinder or cylinders, provide a spark when one or more pistons in the cylinder or cylinders are within a bottom dead center threshold, but not supply fuel to the cylinder or cylinders when the cylinder or cylinders are deactivated, and in response to trapping the high-pressure charge in the cylinder or cylinders, stop providing spark and fuel to the cylinder or cylinders.

[0214] According to an embodiment, the invention is further characterized by a crankshaft coupled to the variable displacement engine; a crankshaft position sensor; a camshaft coupled to the variable displacement engine; a camshaft position sensor; and wherein the controller stores additional instructions for: indicating via one or more of the crankshaft sensor and / or the camshaft sensor whether one or more pistons of the cylinder or cylinders are respectively within the bottom dead center threshold, wherein the bottom dead center threshold includes a predetermined number of degrees relative to the bottom dead center position when deactivating the cylinder or cylinders by trapping the vacuum, and wherein in response to the one or more pistons being within the bottom dead center position threshold, provide a spark via the spark plug.

[0215] According to an embodiment, the invention is further characterized by an oil quality sensor; and the controller stores additional instructions for: determining to deactivate the cylinder or cylinders by trapping the vacuum in response to an indication that the oil quality is greater than an oil quality threshold, and deactivating the cylinder or cylinders by trapping the high-pressure charge in response to an indication that the oil quality is below the oil quality threshold.

Claims

1. A method for a vehicle, the method comprising: Reducing fouling of a spark plug in a cylinder by providing a spark to the cylinder after deactivating a cylinder of an engine configured to propel the vehicle, wherein the spark is provided when a piston coupled to the cylinder is within a bottom dead center threshold, and wherein the bottom dead center threshold includes the piston being within a predetermined number of degrees relative to bottom dead center.

2. The method of claim 1, wherein bottom dead center includes the position of the piston in a case where the piston is closest to a crankshaft of the engine.

3. The method of claim 1, wherein the predetermined number of degrees includes within five degrees or less of bottom dead center.

4. The method of claim 1, wherein the predetermined number of degrees includes within ten degrees or less of bottom dead center.

5. The method of claim 1, wherein the predetermined number of degrees includes within twenty degrees or less of bottom dead center.

6. The method of claim 1, wherein the engine includes a variable displacement engine.

7. The method of claim 1, wherein the spark is provided to the cylinder after deactivating the cylinder in response to trapping a negative pressure relative to atmospheric pressure in the cylinder upon deactivation.

8. The method of claim 7, wherein trapping the negative pressure upon deactivation includes exhausting a combustion mixture of air and fuel into an exhaust system of the engine and then sealing the cylinder to isolate the atmosphere.

9. The method of claim 1, wherein deactivating the cylinder includes stopping fuel supply to the cylinder.

10. The method of claim 1, wherein in selecting conditions for deactivating a plurality of cylinders, a spark is provided to the plurality of cylinders at predefined positions of a plurality of pistons coupled to the plurality of cylinders in response to deactivation of the plurality of cylinders.

11. The method of claim 1, wherein a spark ignition energy of the spark provided to the cylinder after deactivation of the cylinder is variable.

12. The method of claim 11, the method further comprising increasing the spark ignition energy after a predetermined number of spark events upon deactivating the cylinder.

13. The method of claim 1, wherein a spark frequency of the spark provided to the cylinder can vary according to vehicle operating conditions.

14. A system for a vehicle, the system for a vehicle comprising: A variable displacement engine, the variable displacement engine including a set of cylinders and wherein each cylinder is coupled to a fuel injector and a spark plug having an ignition coil, and wherein each cylinder includes a piston; and A controller, the controller storing instructions in a non-transitory memory, the instructions when executed causing the controller to: Determine whether to deactivate one or more cylinders from the set of cylinders by trapping a vacuum in the one or more cylinders or by trapping a high-pressure charge in the one or more cylinders in response to a condition for deactivating the one or more cylinders being met; and In response to trapping the vacuum in the one or more cylinders, spark is provided when one or more pistons in the one or more cylinders are within a bottom dead center threshold, but fuel is not provided to the one or more cylinders when the one or more cylinders are deactivated, and in response to trapping the high-pressure charge in the one or more cylinders, both spark and fuel are stopped from being provided to the one or more cylinders, wherein the bottom dead center threshold includes the piston being within a predetermined number of degrees relative to bottom dead center.

15. The system of claim 14, the system further comprising: a crankshaft coupled to the variable displacement engine; a crankshaft position sensor; a camshaft coupled to the variable displacement engine; a camshaft position sensor; and wherein the controller stores additional instructions for: indicating via one or more of the crankshaft position sensor and / or the camshaft position sensor whether one or more pistons of the one or more cylinders are respectively within the bottom dead center threshold, and wherein in response to the one or more pistons being within the bottom dead center position threshold, spark is provided via the spark plug.

16. The system of claim 14, the system further comprising: an oil quality sensor; and wherein the controller stores additional instructions for: determining to deactivate the one or more cylinders by trapping the vacuum in response to an indication that the oil quality is greater than an oil quality threshold, and deactivating the one or more cylinders by trapping the high-pressure charge in response to an indication that the oil quality is below the oil quality threshold.

17. The system of claim 14, wherein the controller stores additional instructions for: providing spark once per engine cycle or providing spark twice per engine cycle, wherein the engine cycle includes an exhaust stroke, an intake stroke, a compression stroke, and a power stroke; and wherein providing spark includes one or more firings of the ignition coil of the spark plug.

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