System and method for controlling spark timing when cylinders of an engine are deactivated to reduce noise and vibration

A system according to the principles of the present disclosure includes a cylinder activation module and a spark timing module. The cylinder activation module selectively deactivates and reactivates a cylinder of an engine based on a driver torque request. When the cylinder is deactivated, the spark timing module selectively increases an amount by which spark timing of at least one active cylinder of the engine is retarded based on noise and vibration generated by the engine when the cylinder is deactivated.

FIELD

The present disclosure relates to systems and methods for controlling spark timing when cylinders of the engine are deactivated to reduce noise and vibration.

BACKGROUND

Internal combustion engines combust an air and fuel mixture within cylinders to drive pistons, which produces drive torque. Air flow into the engine is regulated via a throttle. More specifically, the throttle adjusts throttle area, which increases or decreases air flow into the engine. As the throttle area increases, the air flow into the engine increases. A fuel control system adjusts the rate that fuel is injected to provide a desired air/fuel mixture to the cylinders and/or to achieve a desired torque output. Increasing the amount of air and fuel provided to the cylinders increases the torque output of the engine.

In spark-ignition engines, spark initiates combustion of an air/fuel mixture provided to the cylinders. In compression-ignition engines, compression in the cylinders combusts the air/fuel mixture provided to the cylinders. Spark timing and air flow may be the primary mechanisms for adjusting the torque output of spark-ignition engines, while fuel flow may be the primary mechanism for adjusting the torque output of compression-ignition engines.

Under some circumstances, one or more cylinders of an engine may be deactivated to decrease fuel consumption. For example, one or more cylinders may be deactivated when the engine can produce a requested amount of torque while the one or more cylinders are deactivated. Deactivation of a cylinder may include disabling opening intake and exhaust valves of the cylinder and disabling fueling of the cylinder.

SUMMARY

A system according to the principles of the present disclosure includes a cylinder activation module and a spark timing module. The cylinder activation module selectively deactivates and reactivates a cylinder of an engine based on a driver torque request. When the cylinder is deactivated, the spark timing module selectively increases an amount by which spark timing of at least one active cylinder of the engine is retarded based on noise and vibration generated by the engine when the cylinder is deactivated.

DETAILED DESCRIPTION

Engine vibration is transmitted to a driver through powertrain mounts, a vehicle body, and driver interface components such as a driver seat, a steering wheel, and pedals. Engine vibration, and vehicle body vibration resulting from engine vibration, generates noise that is sensed by the driver. When one or more cylinders of an engine are deactivated, torque pulses of cylinders that remain active may approach a resonant frequency of the vehicle structure from the powertrain mounts to the driver interface components. Thus, the driver may perceive an increase in vehicle noise and vibration.

A system and method according to the principles of the present disclosure adjusts the spark timing of one or more cylinders to reduce vehicle noise and vibration when one or more cylinders of an engine are deactivated. The spark timing of the one or more cylinders is adjusted to create a phase shift that offsets a base frequency of the other cylinders in the engine. As a result, the magnitude of vibrations perceived by the driver may be reduced, or alternatively may be masked through a white noise effect.

In one example, spark timing is retarded in less than all of the active cylinders. In another example, spark timing is retarded in all of the active cylinders and one or more additional cylinders are activated to offset a torque reduction caused by retarding the spark timing. The additional cylinders may only be temporarily activated as needed to offset the torque reduction.

Referring now toFIG. 1, an engine system100includes an engine102that combusts an air/fuel mixture to produce drive torque for a vehicle. The amount of drive torque produced by the engine102is based on driver input from a driver input module104. Air is drawn into the engine102through an intake system108. The intake system108includes an intake manifold110and a throttle valve112. The throttle valve112may include a butterfly valve having a rotatable blade. An engine control module (ECM)114controls a throttle actuator module116, which regulates opening of the throttle valve112to control the amount of air drawn into the intake manifold110.

Air from the intake manifold110is drawn into cylinders of the engine102. For illustration purposes, a single representative cylinder118is shown. However, the engine102may include multiple cylinders. For example, the engine102may include 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. The ECM114may deactivate one or more of the cylinders, which may improve fuel economy under certain engine operating conditions.

The engine102may operate using a four-stroke cycle. The four strokes include an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. During each revolution of a crankshaft (not shown), two of the four strokes occur within the cylinder118. Therefore, two crankshaft revolutions are necessary for the cylinder118to experience all four of the strokes.

During the intake stroke, air from the intake manifold110is drawn into the cylinder118through an intake valve122. The ECM114controls a fuel actuator module124, which regulates a fuel injector125to control the amount of fuel provided to the cylinder to achieve a desired air/fuel ratio. The fuel injector125may inject fuel directly into the cylinder118or into a mixing chamber associated with the cylinder118. The fuel actuator module124may halt fuel injection into cylinders that are deactivated.

The injected fuel mixes with air and creates an air/fuel mixture in the cylinder118. During the compression stroke, a piston (not shown) within the cylinder118compresses the air/fuel mixture. The engine102may be a compression-ignition engine, in which case compression in the cylinder118ignites the air/fuel mixture. Alternatively, the engine102may be a spark-ignition engine, in which case a spark actuator module126energizes a spark plug128in the cylinder118based on a signal from the ECM114. The spark ignites the air/fuel mixture. The timing of the spark may be specified relative to the time when the piston is at its topmost position, referred to as top dead center (TDC).

The spark actuator module126may be controlled by a timing signal specifying how far before or after TDC to generate the spark. Because piston position is directly related to crankshaft rotation, operation of the spark actuator module126may be synchronized with crankshaft angle. In various implementations, the spark actuator module126may halt provision of spark to deactivated cylinders.

Generating the spark may be referred to as a firing event. The spark actuator module126may have the ability to vary the timing of the spark for each firing event. The spark actuator module126may even be capable of varying the spark timing for a next firing event when the spark timing signal is changed between a last firing event and the next firing event. In various implementations, the engine102may include multiple cylinders and the spark actuator module126may vary the spark timing relative to TDC by the same amount for all cylinders in the engine102.

During the combustion stroke, the combustion of the air/fuel mixture drives the piston down, thereby driving the crankshaft. As the combustion of the air/fuel mixture drives the piston down, the piston moves from TDC to its bottommost position, referred to as bottom dead center (BDC).

During the exhaust stroke, the piston begins moving up from BDC and expels the byproducts of combustion through an exhaust valve130. The byproducts of combustion are exhausted from the vehicle via an exhaust system134.

The intake valve122may be controlled by an intake camshaft140, while the exhaust valve130may be controlled by an exhaust camshaft142. In various implementations, multiple intake camshafts (including the intake camshaft140) may control multiple intake valves (including the intake valve122) for the cylinder118and/or may control the intake valves (including the intake valve122) of multiple banks of cylinders (including the cylinder118). Similarly, multiple exhaust camshafts (including the exhaust camshaft142) may control multiple exhaust valves for the cylinder118and/or may control exhaust valves (including the exhaust valve130) for multiple banks of cylinders (including the cylinder118).

The time at which the intake valve122is opened may be varied with respect to piston TDC by an intake cam phaser148. The time at which the exhaust valve130is opened may be varied with respect to piston TDC by an exhaust cam phaser150. A phaser actuator module158may control the intake cam phaser148and the exhaust cam phaser150based on signals from the ECM114. When implemented, variable valve lift (not shown) may also be controlled by the phaser actuator module158.

The position of the crankshaft may be measured using a crankshaft position (CKP) sensor180. The temperature of the engine coolant may be measured using an engine coolant temperature (ECT) sensor182. The ECT sensor182may be located within the engine102or at other locations where the coolant is circulated, such as a radiator (not shown).

The pressure within the intake manifold110may be measured using a manifold absolute pressure (MAP) sensor184. In various implementations, engine vacuum, which is the difference between ambient air pressure and the pressure within the intake manifold110, may be measured. The mass flow rate of air flowing into the intake manifold110may be measured using a mass air flow (MAF) sensor186. In various implementations, the MAF sensor186may be located in a housing that also includes the throttle valve112.

The throttle actuator module116may monitor the position of the throttle valve112using one or more throttle position sensors (TPS)190. The ambient temperature of air being drawn into the engine102may be measured using an intake air temperature (IAT) sensor192. The ECM114may use signals from the sensors to make control decisions for the engine system100.

When the ECM114deactivates one or more cylinders of the engine102, the ECM114adjusts (e.g., retards) the spark timing of the active cylinders to reduce vehicle noise and vibration. The ECM114adjusts the spark timing of the active cylinders to create a phase shift that offsets a base frequency of the other cylinders in the engine102. As a result, the magnitude of vibrations perceived by the driver may be reduced, or alternatively may be masked through a white noise effect.

Referring now toFIG. 2, an example implementation of the ECM114includes a driver torque module202, a crankshaft speed module204, and a cylinder activation module206. The driver torque module202determines a driver torque request based on the driver input from the driver input module104. The driver input may be based on a position of an accelerator pedal. The driver input may also be based on cruise control, which may be an adaptive cruise control system that varies vehicle speed to maintain a predetermined following distance. The driver torque module202may store one or more mappings of accelerator pedal position to desired torque, and may determine the driver torque request based on a selected one of the mappings. The driver torque module202outputs the driver torque request.

The crankshaft speed module204determines the speed of the crankshaft. The crankshaft speed module204may determine the crankshaft speed based on input received from the CKP sensor180. The crankshaft speed module204may determine the crankshaft speed based on an amount of crankshaft rotation between tooth detections and the corresponding period. The crankshaft speed module204outputs the crankshaft speed.

The cylinder activation module206determines a quantity of cylinders of the engine102to deactivate or reactivate based on the driver torque request. The cylinder activation module206may command deactivation of a quantity of cylinders when the engine102can satisfy the driver torque request while the cylinders are deactivated. The cylinder activation module206may command reactivation of a quantity of cylinders when the engine102cannot satisfy the driver torque request while the cylinders are deactivated. The cylinder activation module206outputs the quantity of cylinders to be deactivated or reactivated.

A firing sequence module208determines a firing sequence of the cylinders in the engine102. The firing sequence module208may assess and/or adjust the firing sequence after each engine cycle. Alternatively, the firing sequence module208may assess and/or adjust the firing sequence before each firing event in the engine102. The engine102completes an engine cycle as spark is generated in each cylinder in the firing sequence. Thus, an engine cycle may correspond to 720 degrees of crankshaft rotation. The firing sequence module208outputs the firing sequence.

The firing sequence module208may change the firing sequence from one engine cycle to the next engine cycle to change the quantity of active cylinders without changing the order in which cylinders are firing. For example, for an 8-cylinder engine having a firing order of 1-8-7-2-6-5-4-3, a firing sequence of 1-8-7-2-5-3 may be specified for one engine cycle, and a firing sequence of 1-7-2-5-3 may be specified for the next engine cycle. This decreases the quantity of active cylinders from 6 to 5.

Alternatively, the firing sequence module208may change the firing sequence from one engine cycle to the next engine cycle to change which cylinders are firing, and thereby change which cylinders are active, without changing the quantity of active cylinders. For example, when three cylinders of the 8-cylinder engine described above are deactivated, a firing sequence of 1-7-2-5-3 may be specified for one engine cycle, and a firing sequence of 8-2-6-4-3 may be specified for the next engine cycle. This deactivates cylinders1,7, and5and reactivates cylinders8,6, and4. Adjusting the quantity of active cylinders and/or adjusting which cylinders are active reduces the magnitude of engine vibrations, or alternatively masks the engine vibrations through a white noise effect.

A spark timing module210determines the spark timing of the active cylinders in the engine102. The spark timing module210may specify the spark timing in terms of a number of degrees of crankshaft rotation before a piston in a cylinder reaches TDC. The spark timing module210may vary the spark timing relative to TDC by the same amount for all of the active cylinders. Alternatively, the spark timing module210may vary the spark timing relative to TDC by a different amount for one or more of the active cylinders. The spark timing module210may assess and/or adjust the spark timing of the active cylinders after each engine cycle. Alternatively, the spark timing module210may assess and/or adjust the spark timing before each firing event in the engine102.

Initially, the spark timing module210may retard the spark timing of each active cylinder by a predetermined amount (e.g., 1 or 2 degrees) relative to a spark timing that yields a maximum brake torque and thereby maximizes fuel economy. Retarding the spark timing by the predetermined amount reduces emissions such as carbon monoxide. The spark timing module210may then retard the spark timing of one or more of the active cylinders by an additional amount to create a phase shift that cancels a base frequency resulting from the spark timing of the other active cylinders. For example, the spark timing module210may retard the spark timing of every third cylinder in the firing sequence relative to the other active cylinders by an amount that is between 1 and 10 degrees.

Alternatively, the spark timing module210may retard the spark timing of all of the active cylinders by an additional amount, and the cylinder activation module206may activate one or more additional cylinders to compensate for the resulting torque reduction. The cylinder activation module206may only temporarily activate the additional cylinders to minimize a reduction in fuel economy caused by activating additional cylinders. For example, the cylinder activation module206may alternate the number of active cylinders between 5 cylinders during one engine cycle and 6 cylinders during another engine cycle, resulting in an effective cylinder count of 5.5.

A noise and vibration (N&V) prediction module212predicts the magnitude and/or frequency of noise and vibration generated by the engine102based on the firing sequence and the spark timing. The N&V prediction module212may predict the noise and vibration based on a predetermined relationship between the firing sequence, the spark timing, and the noise and vibration. The predetermined relationship may be developed through laboratory testing and may be embodied in an equation and/or a lookup table. The N&V prediction module212outputs the predicted noise and vibration.

In various implementations, the predetermined relationship may be embodied as a transfer function of the relationship between an input frequency at powertrain mounts and an output frequency at a driver interface component such as a driver seat, a steering wheel, or a pedal. The transfer function may be developed by inputting a known frequency at the powertrain mounts using, for example a shaker table, and measuring the output frequency at the driver interface component using, for example, an accelerometer. Thus, the transfer function may model the frequency response of the structure between the powertrain mounts and the driver interface component.

The firing sequence module208and the spark timing module210adjust the firing sequence and the spark timing, respectively, based on the predicted noise and vibration. The firing sequence module208and the spark timing module210may optimize the firing sequence and the spark timing, respectively, to maximize fuel economy while ensuring that the predicted noise and vibration satisfies predetermined criteria. The firing sequence module208and the spark timing module210output the firing sequence and the spark timing, as optimized, to a spark control module214.

The spark control module214instructs the spark actuator module126to generate spark in cylinders of the engine102according to the firing sequence and the spark timing. The spark control module214may output a signal indicating which of the cylinders is next in the firing sequence. The spark control module214may also output a signal indicating the spark timing for the next cylinder in the firing sequence.

The ECM114may execute several iterations of determining a firing sequence, determining spark timing, and predicting noise and vibration based on the firing sequence and the spark timing before sending instructions to the spark actuator module126. The firing sequence module208and the spark timing module210may be incorporated in the N&V prediction module212, in which case the N&V prediction module212may output the firing sequence and the spark timing to the spark control module214.

Referring now toFIG. 3, an example implementation of the N&V prediction module212is shown. The N&V prediction module212may adjust the spark timing of one or more cylinders to oppose torque excitation in a specific frequency range that may excite a driveline without opposing transient torque requests or steady state torque requests. The N&V prediction module212accomplishes this by applying a band-pass filter to discrete time samples of feedforward data (e.g., torque requests) and feedback data (e.g., crankshaft speed) and determining a spark torque request based on the filtered data. The band-pass filter removes input frequencies corresponding to the steady-state torque requests (e.g., frequencies less than 2 hertz) and input frequencies corresponding to the transient torque requests (e.g., frequencies greater than 50 hertz). Transient torque requests may be generated at wide-open throttle. Steady-state torque requests may be generated while cruising and/or traveling up or down a slight grade.

The example implementation of the N&V prediction module212includes a first band-pass filter302, a second band-pass filter304, a multiplier306, an operator308, and a mapping310of an input torque to an output torque. The first band-pass filter302receives discrete-time samples of the driver torque request from the driver torque module202. The first band-pass filter302may receive discrete-time samples of other types of torque requests such as a transmission torque request generated, for example, to facilitate a transmission shift.

The second band-pass filter304receives discrete-time samples of the crankshaft speed from the crankshaft speed module204. Additionally or alternatively, the second band-pass filter304may receive discrete-time samples of other feedback data such as transmission output shaft speed and/or accelerometer measurement data. The accelerometer measurement data may be received from an accelerometer located at a powertrain mount and/or an accelerometer located at a driver interface component such as a driver seat, a steering wheel, or a pedal.

The band-pass filters302,304filter the discrete-time samples at a predetermined frequency range (e.g., between 2 hertz and 50 hertz) to remove content outside of the predetermined frequency range. The filtered feedback data samples output by the second band-pass filter304are multiplied by the multiplier306to convert the feedback data samples into torque values. The torque values are then subtracted from the filtered torque request samples output by the first band-pass filter302to yield a torque difference that is provided to the mapping310.

The mapping310determines a spark torque request based on the torque difference and a predetermined relationship between the spark torque request and the torque difference. The predetermined relationship may be embodied in an equation and/or a lookup table. The mapping310outputs the spark torque request to the spark control module214, which determines spark timing based on the spark torque request. In various implementations, the mapping310may determine spark timing based on the torque difference and a predetermined relationship between the spark timing and the torque difference, and may output the spark timing to the spark control module214.

Referring now toFIG. 4, a method for controlling spark timing when cylinders of an engine are deactivated begins at402. At404, the method determines whether one or more cylinders of the engine are deactivated. The method may deactivate one or more cylinders when the engine can satisfy a driver torque request while the cylinders are deactivated. The method may determine the driver torque request based on driver input such as an accelerator pedal position or a cruise control setting. If one or more cylinders of the engine are deactivated, the method continues at406.

At406, the method determines a firing sequence based on the number of cylinders that are deactivated. The method may adjust the firing sequence before each engine cycle or before each firing event. The method may change the firing sequence from one engine cycle to the next engine cycle to change the number of active cylinders without changing the order which cylinders are firing. Additionally or alternatively, the method may change the firing sequence from one engine cycle to the next engine cycle to change which cylinders are firing and thereby change which cylinders are active.

At408, the method determines spark timing for each cylinder in the firing sequence. To reduce emissions while maximizing fuel economy, the method may initially retard the spark timing of each cylinder by a predetermined amount (e.g., 1 or 2 degrees) relative to a spark timing that yields maximum brake torque. The method may then retard the spark timing of one or more of the cylinders, but not all of the cylinders, by an additional amount to create a phase shift that cancels a base frequency resulting from the spark timing of the other cylinders in the engine. For example, the method may retard the spark timing of every third cylinder in the firing sequence relative to the other active cylinders by an amount that is between 1 and 10 degrees.

At410, the method predicts the magnitude and/or frequency of noise and vibration generated by the engine based on the firing sequence and the spark timing. The method may predict the noise and vibration based on a predetermined relationship between the firing sequence, the spark timing, and the noise and vibration. The predetermined relationship may be embodied in an equation and/or a lookup table.

At412, the method determines whether the noise and vibration predicted for retarding the spark timing of less than all of the cylinders by the additional amount satisfies predetermined criteria. If the noise and vibration satisfies predetermined criteria, the method continues at414and retards the spark timing of less than all of the cylinders by the additional amount. Otherwise, the method continues at416.

At416, the method determines whether the noise and vibration has been analyzed for all of the firing sequence and spark timing combinations that involve retarding spark timing by the additional amount in less than all of the active cylinders. If the noise and vibration has been analyzed for all of the firing sequence and spark timing combinations involving retarding spark timing by the additional amount in less than all of the active cylinders, the method continues at418. Otherwise, the method continues at406.

At418, the method retards the spark timing of all of the active cylinders by the additional amount. The method may also activate one or more additional cylinders of the engine as needed to offset a torque reduction caused by retarding the spark timing. The method may only temporarily activate the additional cylinders to minimize a reduction in fuel economy caused by activating additional cylinders. For example, between engine cycles, the method may alternate the number of active cylinders between two integers (e.g., between 5 active cylinders and 6 active cylinders).

Referring now toFIG. 5, cylinder torque pulses502are plotted with respect to an x-axis504that represents time and a y-axis506that represents torque. The cylinder torque pulses502may be calculated based on cylinder pressure measurements. To generate the cylinder torque pulses502, spark timing relative to TDC may be varied by the same amount (e.g., 25 degrees before TDC) for all active cylinders in an engine having one or more cylinders that are deactivated. As a result, the peak values of the cylinder torque pulses502are approximately equal.

Referring now toFIG. 6, a frequency response602corresponding to the cylinder torque pulses502is plotted with respect to an x-axis604and a y-axis606. The x-axis604represents frequency in hertz (Hz). The y-axis606represents the magnitude of the frequency response602. The frequency response602is proportional to a ratio of an input frequency at powertrain mounts to an output frequency at a driver interface component such as a driver seat, a steering wheel, or a pedal. The input frequency may be known based on, for example, a control setting of a shaker table. Alternatively, the input frequency may be determined based on the cylinder pressure measurements. The output frequency may be measured using, for example, accelerometers mounted to the driver interface components.

As shown inFIG. 6, the magnitude of the frequency response602reaches a relatively high resonant frequency at approximately 15 Hz and is otherwise relatively low within the frequency range between 0.1 Hz and 40 Hz. Thus, varying the spark timing by the same amount for all active cylinders may yield a relatively high resonant frequency, which may cause noise and vibration that is perceived by a driver.

Referring now toFIG. 7, cylinder torque pulses702,704are plotted with respect to an x-axis706that represents time and a y-axis708that represents torque. The cylinder torque pulses702,704may be calculated based on cylinder pressure measurements. Spark timing relative to TDC may be varied by a first amount (e.g., 25 degrees before TDC) to generate the cylinder torque pulses704. Spark timing may be retarded by a second amount (e.g., 1 to 10 degrees) relative to the first amount to generate the cylinder torque pulses702. As a result, the peak values of the cylinder torque pulses702are less than the peak values of the cylinder torque pulses704.

Referring now toFIG. 8, a frequency response802corresponding to the cylinder torque pulses702,704is plotted with respect to an x-axis804and a y-axis806. The x-axis804represents frequency in Hz. The y-axis806represents the magnitude of the frequency response802. The frequency response802is proportional to a ratio of an input frequency at powertrain mounts to an output frequency at a driver interface component such as a driver seat, a steering wheel, or a pedal. The input frequency may be known based on, for example, a control setting of a shaker table vibrating the powertrain mounts. Alternatively, the input frequency may be determined based on the cylinder pressure measurements. The output frequency may be measured using, for example, accelerometers mounted to the driver interface components.

As shown inFIG. 8, the magnitude of the frequency response802is more evenly distributed in the frequency range between 0.1 and 40 Hz and reaches a relatively low peak value at approximately 10 Hz. Thus, retarding the spark timing for some active cylinders, but not all active cylinders, may yield a relatively low resonant frequency and may not cause noise and vibration that is perceived by a driver.

The apparatuses and methods described herein may be partially or fully implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on at least one non-transitory tangible computer readable medium. The computer programs may also include and/or rely on stored data. Non-limiting examples of the non-transitory tangible computer readable medium include nonvolatile memory, volatile memory, magnetic storage, and optical storage.