System and method for operating engine cylinders

Abstract

Engine control method comprising: Activating and deactivating a cylinder of an engine via a controller in response to a firing fraction of the engine cylinders and a residual value, wherein the residual value is based on the firing fraction of the engine cylinders.

Description

REGIONThe present invention relates to a system and method for selectively activating and deactivating cylinders of an engine to conserve fuel while meeting torque demand. The system and methods vary which cylinders of an engine fire from one engine cycle to the next engine cycle.BACKGROUND AND SUMMARYAn engine may include a plurality of cylinders to provide a higher level of torque. During high torque demand conditions, intake manifold pressure may be high so that engine pumping losses may be reduced. However, in closed and partially open throttle conditions, engine efficiency may be reduced due to higher pumping losses and lower thermal efficiency. One way to reduce engine pumping losses while maintaining engine torque at higher load conditions is selectively enabling and disabling engine cylinders. Engine cylinders may be deactivated by maintaining intake and exhaust valves closed via an engine cycle without injecting fuel into the deactivated cylinders. Cylinders may be deactivated and reactivated in groups, but a large number of cylinder groups and firing patterns stored in memory of the controller may be necessary if cylinder activation and deactivation is simply based on switching predetermined groups and patterns of engine cylinders on and off. Therefore, it may be desirable to provide a way to select cylinders for activation and deactivation without relying on predetermined cylinder groups or patterns.DE 11 2014 001 434 T5 describes the management of engine ignition patterns and pattern transitions during the cylinder deactivation operation. In this case, the cylinders of an engine are activated or deactivated in accordance with a required ignition component, wherein different ignition sequences are possible for each ignition component.The inventors herein have recognized the above-mentioned problems and have developed an engine control method comprising: activating and deactivating a cylinder of an engine via a controller in response to an ignition fraction of the engine cylinders and a residue, the residue based on the ignition fraction of the engine cylinders.By enabling and disabling the cylinders of an engine in response to a firing fraction of the engine cylinders and a residue based on the firing fraction of the cylinders, it may be possible to provide the technical result of changing which cylinders of a cylinder are disabled and not firing without having to store a large number of cylinder firing groups or patterns. In particular, an engine firing fraction may be a basis for calculations having a remainder that varies between an upper threshold and a lower threshold. The residue is updated for each newest cylinder event (e.g., a cylinder stroke or other event associated with the cylinder) and an engine cylinder is activated or not activated based on a value provided by summing the firing fraction of the engine cylinders and the residue. As the remainder reciprocates between the upper threshold and the lower threshold, engine cylinders are activated or not activated. The engine cylinders are activated and combust air and fuel at a ratio of the firing fraction of the engine cylinders.The present description may provide several advantages. In particular, the approach may simplify cylinder deactivation by reducing the complexity of skip-activation cylinder control algorithms. Further, the approach provides smooth transitions between operating an engine with different firing fractions of engine cylinders. Moreover, the approach may reduce control reservoir utilization by reducing engine cylinder groupings or patterns that form a basis for enabling or disabling engine cylinders.BRIEF DESCRIPTION OF THE DRAWINGSThe advantages described herein are more fully understood by reading an example of an embodiment referred to herein as a detailed description when taken alone or with reference to the drawings, wherein: FIG. 1 is a schematic diagram of a motor; FIG. 2A is a schematic diagram of an eight cylinder engine having two cylinder banks; FIG. 2B is a schematic diagram of a four cylinder engine having a single cylinder bank; FIG. 3A is a diagram of a first example operating sequence; FIG. 3B is a diagram of a second example operating sequence; and FIGS. 4 and 5 are flowcharts of an example method of operating an engine.DETAILED DESCRIPTIONThe present description relates to determining which cylinders of an engine are active during an engine cycle and are firing or deactivated and not firing. The motor may be a motor as shown in FIGS. 1-2B. The engine may be operated via a controller according to the sequences shown in FIGS. 3A and 3B. A method of operating the engine of FIGS. 1-2B to provide the sequences of FIGS. 3A and 3B is shown in FIGS. 4 and 5.Referring to FIG. 1, an internal combustion engine 10 including a plurality of cylinders, one cylinder of which is shown in FIG. 1, is controlled by an electronic engine controller 12. Engine 10 includes combustion chamber 30 and cylinder walls 32 with piston 36 positioned therein and connected to crankshaft 40.Combustion chamber 30 is shown communicating with intake manifold 44 and exhaust manifold 48 via respective intake valve 52 and exhaust valve 54. Each intake valve and exhaust valve may be operated by an intake valve variable actuation unit 51 and an exhaust valve variable actuation unit 53, which may be actuated mechanically, electrically, hydraulically, or by a combination thereof. The intake valve operating unit 51 and an exhaust valve operating unit may open the intake valve 52 and the exhaust valve 54 synchronously or asynchronously with the crankshaft 40. The position of the intake valve 52 may be determined by an intake valve position sensor 55. The position of the exhaust valve 54 may be determined by an exhaust valve position sensor 57.A fuel injector 66 is shown positioned to inject fuel directly into the cylinder 30, which is known to those skilled in the art as direct injection. Alternatively, fuel may be injected into an intake passage, known to those skilled in the art as port injection. Fuel injector 66 supplies liquid fuel proportional to the pulse width of the signal from controller 12, and fuel is supplied from a fuel system 175 to fuel injector 66. Moreover, intake manifold 44 is shown communicating with an optional electronic throttle 62 (e.g., a throttle valve) that adjusts a position of a throttle plate 64 to control air flow from an air filter 43 and air inlet 42 to intake manifold 44. Throttle 62 regulates air flow from air filter 43 in engine air inlet 42 to intake manifold 44. In some examples, throttle 62 and throttle 64 may be positioned between intake valve 52 and intake manifold 44 such that throttle 62 is an intake manifold throttle.A distributorless ignition system 88 provides spark to the combustion chamber 30 via a spark plug 92 in response to the controller 12. A universal exhaust gas oxygen (UEGO) sensor 126 is shown coupled to exhaust manifold 48 and upstream of a catalyst 70. Alternatively, a two-state exhaust oxygen sensor may be substituted for the UEGO sensor 126.The catalyst 70 may include multiple catalyst bricks, in one example. In another example, multiple emission control devices, each with multiple stones, may be used. The catalyst 70 may be a three-way catalyst in one example.Controller 12 is shown in FIG. 1 as a conventional microcomputer including: microprocessor unit 102, input / output ports 104, read-only memory 106 (e.g., non-transitory memory), random access memory 108, keep alive memory 110, and a conventional data bus. Controller 12 is shown receiving various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including: engine cooling fluid temperature (ECT) from a temperature sensor 112 coupled to a cooling sleeve 114; a position sensor 134 coupled to an accelerator pedal 130 for sensing force applied by a human driver 132; a measurement of engine manifold pressure (MAP) from a pressure sensor 122 coupled to intake manifold 44; an engine position sensor from a Hall effect sensor 118 sensing a position of crankshaft 40; a measurement of engine inducted mass air from sensor 120; a position of the brake pedal from brake pedal position sensor 154 when human driver 132 actuates brake pedal 150; and a measurement of throttle position from a barometric pressure sensor 58 may also be sampled for processing by controller 12 (sensor not shown). In a preferred aspect of the present description, during each revolution of the crankshaft, the engine position sensor 118 generates a predetermined number of equi-spaced pulses from which the engine speed (U / min) may be determined.In some examples, the engine may be coupled to an electric motor / battery system in a hybrid vehicle. Further, in some examples, other engine configurations may be employed, for example, a diesel engine.During operation, each cylinder within engine 10 typically undergoes a four stroke cycle: the cycle includes the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, generally, the exhaust valve 54 closes and the intake valve 52 opens. Air is introduced into the combustion chamber 30 via the intake manifold 44, and the piston 36 moves to the bottom of the cylinder to increase the volume within the combustion chamber 30. The position at which the piston 36 is near the bottom of the cylinder and at the end of its stroke (e.g., when the combustion chamber 30 is at its largest volume) is typically referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, the intake valve 52 and the exhaust valve 54 are closed. The piston 36 moves toward the cylinder head to compress the air within the combustion chamber 30. The point at which the piston 36 is at the end of its stroke and closest to the cylinder head (e.g., when the combustion chamber 30 is at its smallest volume) is typically referred to by those skilled in the art as top dead center (TDC). In a process referred to as injection hereinafter, fuel is introduced into the combustion chamber. In a process referred to herein as ignition, the injected fuel is ignited by known igniting means such as the spark plug 92, resulting in combustion. During the power stroke, the expanding gases push the piston 36 back to BDC. The crankshaft 40 converts the piston motion into a rotational torque of the radial shaft. Finally, during the exhaust stroke, the exhaust valve 54 opens to release the combusted air-fuel mixture to the exhaust manifold 48, and the piston returns to TDC. It should be noted that the above is shown as an example only and that the timing of opening and closing the intake valve and the exhaust valve may vary to provide positive or negative valve overlap, late intake valve closing, or various other examples, for example.Referring now to FIG. 2A, an example multi-cylinder engine including two cylinder banks is shown. The engine includes cylinders and associated components as shown in FIG. 1. The engine 10 includes eight cylinders 210. Each of the eight cylinders is numbered and the numbers of the cylinders are included within the cylinders. Fuel injections 66 selectively deliver fuel to each of the cylinders that are activated (e.g., combusting fuel during an engine stroke). Cylinders 1- 8 may be selectively deactivated to improve engine fuel economy when less than full engine torque capacity is requested. For example, during an engine cycle (e.g., two revolutions for a four stroke engine), cylinders 2, 3, 5, and 8 (e.g., a pattern of deactivated cylinders) may be deactivated. During another engine cycle, cylinders 1, 4, 6, and 7 may be deactivated. Further, other patterns of cylinders may be selectively deactivated based on vehicle operating conditions. Each cylinder includes intake valve variable actuators 51 and exhaust valve variable actuators 53. an engine cylinder may be deactivated by maintaining its intake valve variable actuators 51 and exhaust valve variable actuators closed on and off valves of the cylinder during a cycle of operation of the cylinder. An engine cylinder may be activated by having its intake valve variable actuators 51 and exhaust valve variable actuators 53 open and close the intake and exhaust valves of the cylinder during a cycle of operation of the cylinder. The engine 10 includes a first cylinder bank 204 including four cylinders 1, 2, 3, and 4. The engine 10 also includes a second cylinder bank 202 including four cylinders 5, 6, 7, and 8. The cylinders of each bank may be active or deactivated during an engine cycle.Referring now to FIG. 2B, an example multi-cylinder engine including a cylinder bank is shown. The engine includes cylinders and associated components as shown in FIG. 1. The engine 10 includes four cylinders 210. Each of the four cylinders is numbered and the numbers of the cylinders are included within the cylinders. Fuel injections 66 selectively deliver fuel to each of the cylinders that are activated (e.g., combusting fuel during an engine duty cycle, with intake and exhaust valves opening and closing during an active cylinder duty cycle). Cylinders 1- 4 may be selectively deactivated (e.g., not combusting fuel during an engine duty cycle with the intake and exhaust valves maintained closed throughout an engine duty cycle) to improve engine fuel efficiency when less than full engine torque capacity is requested. For example, during an engine cycle (e.g., two revolutions for a four stroke engine), cylinders 2 and 3 (e.g., a pattern of deactivated cylinders) may be deactivated. During another engine cycle, cylinders 1 and 4 may be deactivated. Further, other patterns of cylinders may be selectively deactivated based on vehicle operating conditions.The engine 10 includes a single cylinder bank 250 including four cylinders 1-4. The cylinders of the single bank may be active or deactivated during an engine cycle. Each cylinder includes intake valve variable actuators 51 and exhaust valve variable actuators 53. an engine cylinder may be deactivated by maintaining its intake valve variable actuators 51 and exhaust valve variable actuators closed on and off valves of the cylinder during a cycle of operation of the cylinder. An engine cylinder may be activated by having its intake valve variable actuators 51 and exhaust valve variable actuators 53 open and close the intake and exhaust valves of the cylinder during a cycle of operation of the cylinder.Therefore, the system of FIGS. 1-2B provides for an engine system, comprising: an engine including one or more cylinder deactivation mechanisms; a controller including executable instructions stored in non-transitory memory to activate and ignite a cylinder or deactivate and not ignite the cylinder in response to a value based on an ignition fraction of the engine cylinders and a residue, the residue being a value based on the ignition fraction of the engine cylinders and a previous residue, the previous residue being initialized with a predetermined value. The engine system includes the firing fraction of the engine cylinders being an actual total number of cylinder firing events divided by an actual total number of cylinder compression strokes over a predetermined actual total number of cylinder compression strokes. The engine system includes the residue that is a remaining value after adding the previous residue to the firing fraction of the engine cylinders; and wherein the residue is further decreased by a value of 1 each time a cylinder ignites.In some examples, the system further comprises additional instructions to adjust the previous remainder responsive to the firing fraction of the engine cylinders changing and the firing fraction of the engine cylinders providing a stationary cylinder firing pattern with a reference cylinder; and additional instructions to not adjust the previous remainder responsive to the firing fraction of the engine cylinders changing and the firing fraction of the engine cylinders not providing a stationary cylinder firing pattern with the reference cylinder. The engine system includes deactivating the engine cylinder by maintaining intake and exhaust valves of the cylinder closed over a cycle of operation of the cylinder. The engine system includes deactivating the engine cylinder by ceasing fuel flow to the engine cylinder.Referring now to FIG. 3A, plots of an engine operating sequence are shown. The three diagrams are aligned in time and take place simultaneously. The sequence may be provided by the system of FIGS. 1 and 2A having the method of FIGS. 4 and 5 stored as executable instructions in non-transitory memory. The sequence of FIG. 3A is based on an eight cylinder engine with an order of ignition or combustion of 1, 3, 7, 2, 6, 5, 4, 8, the firing fraction of the engine cylinders for this sequence is 0.333.The first plot at the top of FIG. 3A is a plot of a decision on cylinder activation (e.g., firing where intake and exhaust valves open and close during a cylinder duty cycle) or deactivation (e.g., no firing where intake and exhaust valves are maintained closed during a cylinder duty cycle) for engine cylinders versus engine event number. An engine event may be an occurrence of a stroke of a cylinder (e.g., intake, compression, power stroke, exhaust), an opening or closing timing of an intake or exhaust valve, an ignition timing of an air-fuel mixture in the cylinder, a position of a piston in the cylinder with respect to crankshaft position, or another event associated with the engine. The engine event number corresponds to a particular cylinder. Engine event number one may correspond to, for example, a compression stroke of cylinder number one. Engine event number two may correspond to a compression stroke of cylinder number three.The decision to activate or deactivate a cylinder and open and close the cylinder's intake and exhaust valves may be made a predetermined number of cylinder events (e.g., a cylinder event, or alternatively a cylinder duty cycle or eight cylinder events for an eight cylinder engine) before the cylinder is to be activated or deactivated to allow time to begin the process of opening and closing intake and exhaust valves of the cylinder to be evaluated. For example, for an eight cylinder engine with an firing order of 1, 3, 7, 2, 6, 5, 4, 8, the decision to enable or disable cylinder number seven may be made during an intake or compression stroke of cylinder number seven an engine cycle before cylinder number seven is disabled. Alternatively, the decision to activate or deactivate a cylinder may be made a predetermined number of engine events or cylinder events before the selected cylinder is activated or deactivated. The cylinder which is in its compression stroke at the time corresponding to the event number is activated when the ignition decision value indicated by the circle is one. The cylinder which is in its compression stroke at the time corresponding to the event number is not activated when the ignition decision value indicated by the circle is zero. The vertical axis represents the firing decision and the horizontal axis represents the cylinder event number or actual total number of cylinder events.The second plot at the top of FIG. 3A is a plot of a value of a remainder versus cylinder event number or the actual total number of cylinder events. The remainder value and how it is obtained will be described in more detail in the description of Figs. 4 and 5. The vertical axis represents the value of the remainder. The horizontal axis represents the cylinder event number or actual total number of cylinder events.The third diagram at the top of FIG. 3A is a diagram of cylinder numbers corresponding to the firing decisions shown in the first diagram at the top of FIG. 3. The vertical axis represents the cylinder number for the present cylinder being evaluated. The horizontal axis represents the cylinder event number or actual total number of cylinder events. The solid circles represent an active cylinder with combustion during the cylinder's cycle of operation. The unfilled circles represent deactivated cylinders without combustion during the cylinder's duty cycle.In this example, the first engine event corresponds to cylinder number three, as indicated at 310. Cylinder number three ignites, as indicated by the filled circle at 310, and the firing decision at 312, which is one. The residual value corresponding to the first engine event is 0 as indicated at 314. The second engine event corresponds to cylinder number seven, as indicated at 320. Cylinder number seven does not fire, as indicated by the open circle at 320 and the firing decision at 322 being zero. The residual value corresponding to the second engine event is 0.333 (i.e., 1 divided by 3) as indicated at 324. The third engine event is cylinder number two, as indicated at 332. Cylinder number two is also deactivated and does not fire, as indicated by the empty circle at 332 and the firing decision of zero at 336. The remainder for this event is 0.667 (i.e., 2 divided by 3) as shown in 334.Firing decisions for the remaining cylinders follow a similar convention.It may be observed that the cylinders of the engine are activated and fire three times for all nine compression cycles so that the engine follows the desired firing fraction of engine cylinders of 0.333. The residual is incremented for each engine event, and if the resulting residual is less than 1, the corresponding cylinder is deactivated. Each time the residue exceeds a value of one, the corresponding cylinder is activated and fired and the residue is reduced by a value equal to 1. The firing fraction of engine cylinders of 0.333 is a non-steady state pattern because the cylinders that are activated change from engine cycle to engine cycle. Further, there is no selection for a reference cylinder because the activated cylinders change from engine cycle to engine cycle. All engine cylinders may fire over one or more engine cycles in a non-steady state pattern.Referring now to FIG. 3B, plots of an engine operating sequence are shown. The three diagrams are aligned in time and take place simultaneously. The sequence may be provided by the system of FIGS. 1 and 2A having the method of FIGS. 4 and 5 stored as executable instructions in non-transitory memory. The sequence of FIG. 3B is based on an eight cylinder engine with an order of ignition or combustion of 1, 3, 7, 2, 6, 5, 4, 8, the firing fraction of the engine cylinders for this sequence is 0.5.The first plot at the top of FIG. 3B is a plot of a cylinder activation or deactivation decision for engine cylinders versus engine event number. The vertical axis represents the firing decision and the horizontal axis represents the engine event number or actual total number of engine events.The second plot at the top of FIG. 3B is a plot of a value of a remainder versus the engine event number or the actual total number of cylinder events. The remainder value and how it is obtained will be described in more detail in the description of Figs. 4 and 5. The vertical axis represents the value of the remainder. The horizontal axis represents the engine event number or actual total number of cylinder events.The third diagram at the top of FIG. 3B is a diagram of cylinder numbers corresponding to the firing decisions shown in the first diagram at the top of FIG. 3. The vertical axis represents the cylinder number for the engine event being evaluated. The horizontal axis represents the cylinder event number or actual total number of cylinder events. The solid circles represent an active cylinder with combustion during the cylinder's cycle of operation. The unfilled circles represent deactivated cylinders without combustion during the cylinder's duty cycle.In this example, the first engine event corresponds to cylinder number one, as indicated at 352. Cylinder number one ignites, as indicated by the filled circle at 352 and the firing decision at 354 is one. The residual value corresponding to the first engine event is 0 as indicated at 356. The second engine event corresponds to cylinder number three, as indicated at 360. Cylinder number three is deactivated and not firing, as indicated by the unfilled circle at 360 and the firing decision at 362 being 0. The residual value corresponding to the second engine event is 0.5, as indicated at 364. Firing decisions for the remaining cylinders follow a similar convention.It may be observed that the cylinders of the engine are activated and fire five times for all ten compression cycles so that the engine follows the desired firing fraction of engine cylinders of 0.5. Each time the residue exceeds one, the cylinder is activated and fired at this time and the residue is decremented by 1. Therefore, the residual value stored in the working memory varies between zero and one. The firing fraction of engine cylinders of 0.5 is a steady state pattern because the cylinders that are activated do not change from engine cycle to engine cycle. For example, cylinders 1, 6, 7 and 4 are always firing while cylinders 2, 3, 5 and 8 are never firing during the sequence. For a stationary pattern, any of the igniting cylinders may be selected as the reference cylinder. The sequence may be initialized on the basis that the reference cylinder is first fired. In this example, cylinder number one may be the reference cylinders.Referring now to FIGS. 4 and 5, a flowchart is shown illustrating cylinder activation and deactivation for engine cylinders that may change operating state in each cylinder cycle. The method of FIGS. 4 and 5 may be incorporated into and cooperate with the system of FIGS. 1-2B. Further, at least portions of the method of FIGS. 4 and 5 may be incorporated as executable instructions stored in non-transitory memory, while other portions of the method may be performed via a controller that converts operating states of devices and actuators in the physical world. Method 400 includes operations based on cylinder events, as indicated below. Event-based operations may be initiated by hardware interrupts generated by an engine position sensor or a signal based on input from an engine position sensor.At 402, method 400 judges if an engine stop is requested. An engine stop may be requested via a driver pressing a key or turning a key. Further, an engine stop may be requested via a controller in response to various vehicle operating conditions. If method 400 judges that there is a request for an engine stop, method 400 continues to end. Otherwise, method 400 proceeds to 404.At 404, method 400 judges if a new engine event is present. A new engine event may occur as the engine rotates and the engine cylinders progress through their strokes (e.g., intake, compression, power stroke, and exhaust). An engine event occurs for each engine cylinder during an engine cycle (e.g., two revolutions). Therefore, for an eight cylinder engine, there are eight engine events every two engine revolutions. An engine event may be when a cylinder begins or ceases at a particular stroke (e.g., intake, compression, expansion stroke, or exhaust), a time of valve opening or closing for the cylinder, a position of a piston in the cylinder relative to the crankshaft position, a timing to initiate ignition or combustion in the cylinder, or another event associated with the cylinder. If method 400 judges that a cylinder event has occurred, method 400 proceeds to 406. Otherwise, method 400 returns to 402.At 406, the method determines vehicle operating conditions. Vehicle operating conditions may include, but are not limited to, requested engine torque, engine speed, and vehicle speed. The requested engine torque may be based on an accelerator pedal position and vehicle speed. The position of the accelerator pedal and the vehicle speed may form a basis for indexing a table or function in the controller's memory, for example. The table or function outputs a requested engine torque from empirically determined values stored in the table. Method 400 continues with 408.At 408, method 400 determines a desired firing fraction of engine cylinders. The desired firing fraction of the engine cylinders is an actual total number of cylinder firing events divided by an actual total number of cylinder compression strokes over a predetermined actual total number of cylinder compression strokes. In one example, the desired firing fraction of the engine cylinders is determined from the requested engine torque. In particular, permitted engine cylinder firing fraction values may be stored in a table or function that may be indexed by desired engine torque and engine speed. Engine cylinder firing fraction values that may provide the requested engine torque may be part of a group of available engine cylinder firing fraction values. Thereafter, based on other vehicle operating conditions, desired firing fractions of the engine cylinders may be eliminated from the group of available firing fraction values of the engine cylinders. For example, some engine cylinder firing fractions may be removed from the group if the cylinder firing fractions provide higher engine vibration levels. Thereafter, the firing fraction of the engine cylinders that provides the least number of active engine cylinders during a cycle may be selected from the group of available firing fraction values of the engine cylinders to provide the desired firing fraction of the engine cylinders. In this way, a single desired firing fraction of the engine cylinders may be selected from a group of a large number of firing fractions of the engine cylinders. Method 400 proceeds to 410 after the desired firing fraction of the engine cylinders is determined.At 410, method 400 judges if the desired firing fraction of engine cylinders has changed since a last engine event. If the answer is yes, method 400 proceeds to 412. Otherwise, the answer is no and method 400 proceeds to 450. For example, if at a last previous engine event, the firing fraction of the engine cylinders was 0.333 and a firing fraction of the engine cylinders for the current engine event is 0.5, the answer is yes and method 400 proceeds to 412. Otherwise, the answer is no and method 400 proceeds to 450.At 450, method 400 determines a cylinder activation and firing decision according to the method of FIG. 5. method 400 returns to 402 after the cylinder activation and firing decision is made.At 412, method 400 judges if the desired firing fraction of engine cylinders is a steady state pattern with a reference cylinder. In one example, each firing fraction of the engine cylinders stored in the table or function at 408 includes accompanying attributes indicating whether the firing fraction of the engine cylinders is a steady state pattern with a reference cylinder. The attribute may be a value of one, for example, if the firing fraction of the engine cylinders is a stationary pattern with a reference cylinder. The attribute may be a value of zero if the firing fraction of the engine cylinders is not a steady state pattern with a reference cylinder. Method 400 judges whether the desired firing fraction of engine cylinders is a steady state pattern based on the values of the attributes. If method 400 judges that the firing fraction of engine cylinders is a steady state pattern, the answer is yes and method 400 proceeds to 444. Otherwise, the answer is no and method 400 proceeds to 414.At 414, method 400 determines a number of engine events where firing is to be skipped (e.g., engine compression strokes where the cylinders are deactivated). More specifically, method 400 determines an integer number of engine events to skip (e.g., no engine cylinder activation or ignition) prior to activating and igniting a cylinder based on the following equation: where E1is an integer number of engine events to skip, floor is a function that rounds down to the next integer (e.g., floor (arg) is -2 when arg is -1.7), max is a function that returns a maximum value from a group of values (e.g., max (-1.0) returns a value of zero), and previous remainder is a value of a past most recent remainder of the last most recent engine event. If the cylinder corresponding to the current engine event is cylinder number one of cylinders with an firing order of 1, 3, 7, 2, 6, 5, 4, 8, then the previous remainder corresponds to the remainder associated with cylinder number eight for the last engine event. Method 400 continues to 416.At 416, method 400 judges if the value of E1is greater than or equal to zero. If yes, the answer is yes and method 400 proceeds to 420. Otherwise, the answer is no and method 400 proceeds to 430.At 420, method 400 judges to activate and ignite the cylinder based on the cylinder associated with the current engine event. For example, if the current engine event is a compression stroke for cylinder number one of an engine having an firing order of 1, 3, 7, 2, 6, 5, 4, 8, then cylinder number three may be activated and fired because cylinder number three is a predetermined number of engine events away from cylinder number one in the engine firing order (e.g., an engine event removed). Alternatively, cylinder number one may be activated and fired during a next cylinder cycle. Method 400 continues with 422.At 422, method 400 changes the value of the remainder to zero. Therefore, the remainder takes a new value to become a new remainder for the current engine event. The new remainder becomes the previous remainder for the next engine event. Method 400 returns to 402.At 430, method 400 judges not to activate and not ignite the cylinder based on the cylinder associated with the current engine event. For example, if the current engine event is a compression stroke for cylinder number one of an engine having an firing order of 1, 3, 7, 2, 6, 5, 4, 8, then cylinder number three may not be activated and not fired because cylinder number three is a predetermined number of engine events away from cylinder number one in the engine firing order (e.g., an engine event removed). Alternatively, cylinder number one may not be activated and fired during a next cylinder cycle. Method 400 continues with 432.At 432, method 400 determines a residue value based on the following equation: where new residue is the value for the new residue, max is a function that returns a maximum value from a group of values, desired ZA is the desired firing fraction of engine cylinders of 408, and E1 is the integer number of engine events to skip over. The current value of the residue takes a new value to become a new residue for the current engine event. The new remainder becomes the previous remainder for the next engine event. The new remainder and the remainder are real numbers. Method 400 returns to 402.At 440, method 400 determines the actual total number of engine events after the reference cylinder. For example, if the current engine event for cylinder number 6 is an engine with an ignition order of 1, 3, 7, 2, 6, 5, 4, 8 and the reference cylinder is cylinder number 3, the actual total number of engine events after cylinder number 3 is three. The actual total number of engine events after the reference cylinder may be stored as a variable E 2. Method 400 continues with 442.At 442, method 400 determines a basis for determining a previous residual value. The basis for determining the previous residue may be a variable X1and may be determined via the following equation: where X1is the basis variable for determining a previous residue value, modis a function that divides a first argument by a second argument and returns an integer residue (e.g., mod(arg1, arg2)), E2is the actual total number of engine events after the reference cylinder, and Nzylis the number of engine cylinders. Method 400 continues with 444.At 444, method 400 determines a value for a previous remainder based in part on the actual total number of cylinder events after the reference cylinder of 440. The previous residue is determined by the equation: where previous residue is a value of a most recent past residue from the most recent engine event, mod is a function that divides a first argument by a second argument and returns an integer residue (e.g., mod(arg1, arg2)), XI is a variable as described at 442, and Nzyl is a number of cylinders of the engine. Method 400 continues to 414 after the previous remainder is determined.Referring now to FIG. 5, method 500 retrieves the desired firing fraction of the engine cylinders determined at 408 from controller memory and continues to 504.At 504, method 500 adds a value of the previous remainder from the last engine event to the desired firing fraction of the engine cylinders. Method 500 continues with 506.At 506, method 500 judges if the result of adding the previous remainder to the desired firing fraction of the engine cylinders is greater than or equal to a value of one. If yes, the answer is yes and method 500 continues to 520. Otherwise, the answer is no and method 500 continues to 510.At 520, method 500 updates a cylinder firing schedule to activate and ignite the cylinder corresponding to the engine event prior to the next engine cycle or during the next engine cycle. For example, if the cylinder corresponding to the current engine event is cylinder number one and the engine firing order is 1, 3, 7, 2, 6, 5, 4, 8, then cylinder number one is activated and fired during the next cylinder cycle. Alternatively, a cylinder may be activated that is a predetermined number of firing events away from the current cylinder. For example, if the cylinder corresponding to the current engine event is cylinder number one and the engine firing order is 1, 3, 7, 2, 6, 5, 4, 8, then cylinder number two may be activated and fired during the current cylinder duty cycle. Method 500 continues to 522.At 522, method 500 determines a value for the new remainder. Method 500 determines a residual value based on the following equation: where new residual is the value of the new residual, desired ZA is the desired firing fraction of the engine cylinders from 408, and previous residual is a value of a most recent past residual from the most recent engine event. Method 500 returns to 450 of FIG. 4.At 510, method 500 deactivates the cylinder and does not fire it for the current / next engine event in the engine firing order. For example, if the cylinder corresponding to the current engine event is cylinder number one and the engine firing order is 1, 3, 7, 2, 6, 5, 4, 8, then cylinder number one is not activated and fired during the next cylinder cycle. Alternatively, a cylinder may be activated that is a predetermined number of firing events away from the current cylinder. For example, if the cylinder corresponding to the current engine event is cylinder number one and the engine firing order is 1, 3, 7, 2, 6, 5, 4, 8, then cylinder number two may not be activated and fired during the current cylinder duty cycle. Method 500 continues to 512.At 512, method 500 determines a value for the new remainder. Method 500 determines a residual value based on the following equation: where new_resist is the value of the new residue, desired ZA is the desired firing fraction of the engine cylinders from 408, and previous residue is a value of a most recent past residue from the most recent engine event. Method 500 returns to 450 of FIG. 4.Therefore, the methods of FIGS. 4 and 5 provide for an engine control method, comprising: enabling and disabling a cylinder of an engine via a controller in response to an ignition fraction of the engine cylinders and a residue, the residue based on the ignition fraction of the engine cylinders. The method includes deactivating the engine cylinder by maintaining intake and exhaust valves of the cylinder closed over a cycle of operation of the cylinder. The method includes deactivating the engine cylinder by ceasing fuel flow to the engine cylinder. The method further comprises adjusting the residual value in response to a cylinder event, wherein the cylinder event is an event associated with operation of the cylinder. The method includes the event associated with operation of the cylinder, which is a position of a piston in the cylinder or a stroke of the cylinder. The method includes the firing fraction of the engine cylinders being an actual total number of cylinder firing events divided by an actual total number of cylinder compression strokes over a predetermined actual total number of cylinder compression strokes. The method includes the remainder being a remaining value after adding the previous remainder to the firing fraction of the engine cylinders; and wherein the previous remainder is initialized with a predetermined value.The methods of FIGS. 4 and 5 also provide for an engine control method, comprising: providing, via a controller, an firing fraction of the engine cylinders based on a desired engine torque; adjusting a previous residue value in response to the firing fraction of the engine cylinders changing and the firing fraction of the engine cylinders providing a stationary cylinder firing pattern with a reference cylinder, wherein the previous residue value is not adjusted in response to the firing fraction of the engine cylinders changing and the firing fraction of the engine cylinders does not provide a stationary cylinder firing pattern with the reference cylinder; and firing or not firing, via the controller, an engine cylinder in response to the previous residue.In some examples, the method includes igniting the engine cylinder by providing spark to the engine cylinder, and further comprises: activating the engine cylinder by opening and closing intake and exhaust valves of the engine cylinder during an engine cylinder's duty cycle, where the engine cylinder is ignited. The method further comprises deactivating the engine cylinder by maintaining intake and exhaust valves of the engine cylinder closed during an engine cylinder duty cycle, wherein the engine cylinder is not ignited. The method includes firing the engine cylinder when the rounded value is greater than zero and not firing the engine cylinder when the rounded value is less than zero. The method further includes not adjusting the previous remainder in response to the firing fraction of the engine cylinders not changing. The method includes adjusting the previous remainder, including adjusting the previous remainder for the reference cylinder.It should be appreciated that the example control and estimation routines included herein may be employed with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be executed by the control system including the controller in combination with the various sensors, actuators, and other engine system parts. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, the various illustrated acts, acts, and / or functions may be performed in the sequence depicted, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the characteristics and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the acts, acts, and / or functions depicted may be repeatedly performed depending on the particular strategy being deployed. Further, at least a portion of the described acts, acts, and / or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the control system. The control actions may also convert the operating state of one or more sensors or actuators in the physical world when the described actions are performed by executing the instructions in a system including the various engine system parts in combination with one or more controllers.This concludes the description. Reading these by those skilled in the art would prevent many changes and modifications without departing from the spirit and scope of the description. For example, I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could take advantage of the present description.

Claims

An engine control method, comprising: enabling and disabling, via a controller, a cylinder of an engine in response to a firing fraction of the engine cylinders and a residue, the residue based on the firing fraction of the engine cylinders.The method of claim 1, wherein the cylinder is deactivated by maintaining intake and exhaust valves of the cylinder closed over a cycle of operation of the cylinder.The method of claim 1, wherein the cylinder is deactivated by ceasing fuel flow to the cylinder.The method of claim 1, further comprising adjusting the residual value in response to a cylinder event, wherein the cylinder event is an event associated with operation of the cylinder.The method of claim 4, wherein the event associated with operation of the cylinder is a position of a piston in the cylinder or a stroke of the cylinder.The method of claim 1, wherein the firing fraction of the engine cylinders is an actual total number of cylinder firing events divided by an actual total number of cylinder compression strokes over a predetermined actual total number of cylinder compression strokes.The method of claim 1, wherein the residual value is a remaining value after adding the previous residual value to the firing fraction of the engine cylinders, and wherein the previous residual value is initialized with a predetermined value.An engine system, comprising: an engine including one or more cylinder deactivation mechanisms; a controller including executable instructions stored in non-transitory memory to activate and ignite a cylinder or deactivate and not ignite the cylinder in response to a value based on an ignition fraction of the engine cylinders and a residue, the residue being a value based on the ignition fraction of the engine cylinders and a previous residue, the previous residue being initialized with a predetermined value.The engine system of claim 8, wherein the firing fraction of the engine cylinders is an actual total number of cylinder firing events divided by an actual total number of cylinder compression strokes over a predetermined actual total number of cylinder compression strokes.The engine system of claim 8, wherein the residual is a residual value after adding the previous residual to the firing fraction of the engine cylinders.The engine system of claim 10, further comprising: additional instructions to adjust the previous remainder in response to the firing fraction of the engine cylinders changing and the firing fraction of the engine cylinders providing a stationary cylinder firing pattern with a reference cylinder; and additional instructions to not adjust the previous remainder in response to the firing fraction of the engine cylinders changing and the firing fraction of the engine cylinders not providing a stationary cylinder firing pattern with the reference cylinder.The engine system of claim 8, wherein the cylinder is deactivated by maintaining intake and exhaust valves of the cylinder closed over a cycle of operation of the cylinder.The engine system of claim 8, wherein the cylinder is deactivated by ceasing fuel flow to the cylinder.

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