System and method for preventing misfire during engine startup

A system according to the principles of the present disclosure includes a stop-start module and a throttle control module. The stop-start module stops an engine when a driver depresses a brake pedal while an ignition system is on and the engine is idling. The throttle control module selectively opens a throttle valve when fuel injection in the engine is stopped while the ignition system is on based on engine speed and a manifold pressure within an intake manifold. The stop-start module starts the engine when the driver releases the brake pedal.

FIELD

The present disclosure relates to internal combustion engines, and more specifically, to systems and methods for preventing misfire during engine startup.

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. When an engine misfires, an air/fuel mixture provided to a cylinder may not combust at all or may combust only partially.

Misfire prevention systems have been developed to prevent engine misfire. Traditional misfire prevention systems, however, do not prevent engine misfire as effectively as desired.

SUMMARY

A system according to the principles of the present disclosure includes a stop-start module and a throttle control module. The stop-start module stops an engine when a driver depresses a brake pedal while an ignition system is on and the engine is idling. The throttle control module selectively opens a throttle valve when fuel injection in the engine is stopped while the ignition system is on based on engine speed and a manifold pressure within an intake manifold. The stop-start module starts the engine when the driver releases the brake pedal.

DETAILED DESCRIPTION

An engine control system may automatically shut down an engine when the engine is idling to reduce fuel consumption and emissions. The engine control system may automatically shut down the engine when a driver depresses a brake pedal and vehicle speed is zero. The engine control system may automatically restart the engine when the driver releases the brake pedal after the engine is automatically shut down.

During engine shutdown, a rotation direction of a crankshaft in the engine may be reversed before the crankshaft stops. In turn, a piston coupled to the crankshaft may stop near top dead center (TDC) before movement of the piston is reversed. This reversal of piston movement during engine shutdown may be referred to as rock back. As the piston rocks back, the piston may draw exhaust gas into the cylinder in which the piston is disposed. Exhaust gas may also be drawn into an intake manifold of the engine due to a pressure difference between the intake manifold and the cylinders. When the engine is restarted, exhaust gas may flow from the intake manifold to the cylinder, and exhaust gas present within the cylinder may cause the cylinder to misfire.

An engine control system and method according to the principles of the present disclosure prevents engine misfire when an engine is restarted by opening a throttle when the engine is shutting down. The throttle may be opened when the engine speed is less than a predetermined speed and the pressure within an intake manifold is less than a predetermined pressure. The throttle may be closed when the manifold pressure is greater than or equal to the predetermined pressure. Opening a throttle when an engine is shutting down increases the pressure within an intake manifold of the engine. In turn, exhaust gas is not drawn into the intake manifold, and less exhaust gas is present in the cylinder to cause the cylinder to misfire when the engine is restarted.

An engine control system and method according to the principles of the present disclosure prevents engine misfire by advancing spark timing when the engine is restarted. The spark timing may be advanced by an amount that is proportional to the position of the piston in the cylinder relative to TDC before movement of the piston is reversed while the engine is shutting down. Advancing the spark timing in proportion to the piston position before movement of the piston is reversed ensures that exhaust gas present in the cylinder is combusted, and thereby prevents the cylinder from misfiring.

Referring toFIG. 1, an engine system100includes an engine102that combusts an air/fuel mixture to produce drive torque for a vehicle based on driver input from a 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.

Air is drawn into the engine102through an intake system108. For example only, the intake system108may include an intake manifold110and a throttle valve112. For example only, 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. While the engine102may include multiple cylinders, for illustration purposes a single representative cylinder118is shown. For example only, the engine102may include 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. The ECM114may instruct a cylinder actuator module120to selectively deactivate some of the cylinders, which may improve fuel economy under certain engine operating conditions.

The engine102may operate using a four-stroke cycle. The four strokes, described below, are named the intake stroke, the compression stroke, the combustion stroke, and the 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 fuel injection to achieve a desired air/fuel ratio. Fuel may be injected into the intake manifold110at a central location or at multiple locations, such as near the intake valve122of each of the cylinders. In various implementations (not shown), fuel may be injected directly into the cylinders or into mixing chambers associated with the cylinders. The fuel actuator module124may halt injection of fuel to 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, which 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. The combustion stroke may be defined as the time between the piston reaching TDC and the time at which the piston returns to 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 cylinder actuator module120may deactivate the cylinder118by disabling opening of the intake valve122and/or the exhaust valve130. In various other implementations, the intake valve122and/or the exhaust valve130may be controlled by devices other than camshafts, such as electromagnetic actuators.

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 ECM114may start the engine102and stop the engine102based on input received from an ignition system160. The ignition system160may include a key or a button. The ECM114may start the engine102when a driver turns the key from an off position to an on position or when the driver presses the button. The ECM114may stop the engine102when a driver turns the key from the on position to the off position or when the driver presses the button while the engine102is running.

A driver may depress a brake pedal162to decelerate and/or stop the vehicle. The engine system100may measure the position of the brake pedal162using a brake pedal position (BPP) sensor164. The ECM114may determine when the brake pedal162is depressed or released based on input received from the BPP sensor164and/or based on input received from a brake line pressure sensor (not shown).

The engine system100may measure the speed of the vehicle using a vehicle speed sensor (VSS)178. The engine system100may measure the position of the crankshaft 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.

The ECM114may communicate with a transmission control module194to coordinate shifting gears in a transmission (not shown). For example, the ECM114may reduce engine torque during a gear shift. The ECM114may communicate with a hybrid control module196to coordinate operation of the engine102and an electric motor198.

The electric motor198may also function as a generator, and may be used to produce electrical energy for use by vehicle electrical systems and/or for storage in a battery. In various implementations, various functions of the ECM114, the transmission control module194, and the hybrid control module196may be integrated into one or more modules.

The ECM114may determine engine speed based on input received from the CKP sensor180. The CKP sensor180may include a Hall effect sensor, optical sensor, an inductor sensor, and/or another suitable type of sensor that is positioned adjacent to a disk having N teeth (e.g., 58 teeth). The disk may rotate with the crankshaft while the sensor remains stationary. The sensor may detect when the teeth pass by the sensor. The ECM114may determine the engine speed based on an amount of crankshaft rotation between tooth detections and a period between the tooth detections.

The CKP sensor180may include a bidirectional crankshaft sensor that detects the direction in which the teeth are traveling as the teeth pass by the sensor. Thus, the CKP sensor180can detect crankshaft position and the direction of crankshaft rotation. The ECM114may determine when the direction of crankshaft rotation is reversed based on input received from the CKP sensor180.

The ECM114may automatically shut down the engine102when the engine102is idling to reduce fuel consumption and emissions. The ECM114may shut down the engine102when the vehicle speed is less than or equal to a predetermined speed (e.g., zero) and the driver depresses the brake pedal162. The ECM114may automatically restart the engine102when the driver releases the brake pedal162.

The ECM114may prevent the engine102from misfiring during startup by opening the throttle valve112for a brief period (e.g., between 15 and 200 milliseconds) while the engine102is shutting down. The ECM114may open the throttle valve112when the engine speed is less than a predetermined speed and the manifold pressure (i.e., the pressure within the intake manifold110) is less than a predetermined pressure. The ECM114may close the throttle valve112when the manifold pressure is greater than or equal to the predetermined pressure.

The ECM114may prevent the engine102from misfiring during startup by advancing spark timing when the engine102is started. The spark timing may be advanced by an amount that is proportional to the position of the piston within the cylinder118relative to TDC before rock back (i.e., before movement of the piston is reversed while the engine102is shutting down). The ECM114may determine the piston position based on input received from the CKP sensor180.

If the engine102includes multiple cylinders, the ECM114may independently advance spark timing for one or more of the cylinders when the engine102is started. The ECM114may advance the spark timing for the cylinders by an amount that is proportional to the position of the pistons within the cylinders relative to TDC before rock back. The ECM114may determine the piston positions based on input received from the CKP sensor180.

Referring toFIG. 2, the ECM114may include a speed determination module202, a stop-start module204, a throttle control module206, a fuel control module208, a spark control module210, and a position determination module212. The speed determination module202determines engine speed. The speed determination module202may determine engine speed based on input received from the CKP sensor180. The speed determination module202may determine engine speed based on an amount of crankshaft rotation between tooth detections and the corresponding period. The speed determination module202outputs the engine speed.

The stop-start module204automatically stops and restarts the engine102when the engine102is idling. The stop-start module204may automatically stop the engine102when the vehicle speed is less than or equal to a predetermined speed (e.g., zero) and the driver depresses the brake pedal162. The stop-start module204may automatically restart the engine102when the driver releases the brake pedal162. The stop-start module204may receive the vehicle speed from the VSS sensor178. The stop-start module204may determine when the driver depresses or releases the accelerator pedal based on input received from the BPP sensor164.

The stop-start module204may ensure that additional conditions are satisfied before automatically stopping the engine102. For example, the stop-start module204may ensure that the engine coolant temperature is greater than a first temperature, a transmission oil temperature is greater than a second temperature, and ambient air temperature is within a temperature range. The first temperature, the second temperature, and the temperature range may be predetermined.

The stop-start module204may receive the engine coolant temperature from the ECT sensor182. The stop-start module204may estimate the ambient air temperature based on the intake air temperature. The start-stop module204may receive the intake air temperature from the IAT sensor192. The stop-start module204may receive the transmission oil temperature from the transmission control module194and/or a transmission oil temperature sensor (not shown).

The stop-start module204may automatically stop and restart the engine102by sending signals to the throttle control module206, the fuel control module208, and/or the spark control module210. The throttle control module206may stop or start the engine102by instructing the throttle actuator module116to close or open the throttle valve112. The fuel control module208may stop or start the engine102by instructing the fuel actuator module124to stop or start providing fuel to the cylinder118. The spark control module210may stop or start the engine102by instructing the spark actuator module126to stop or start providing spark to the cylinder118.

The position determination module212determines the position of the piston within the cylinder118. The position determination module212may determine the position of the piston relative to TDC based on input received from the CKP sensor180. If the engine102includes multiple cylinders, the position determination module212may determine the positions of the pistons within the cylinders relative to TDC based on input received from the CKP sensor180. The position determination module212may determine the piston position(s) based on a predetermined relationship between the crankshaft position and the piston position(s). The position determination module212outputs the piston position(s).

The throttle control module206may prevent the engine102from misfiring during startup by instructing the throttle actuator module116to open the throttle valve112while the engine102is shutting down. The throttle control module206may send instructions to open the throttle valve112at a first time when the engine speed is less than a first speed and the manifold pressure is less than a first pressure. Opening the throttle valve112before the first time may cause the engine102to vibrate. Opening the throttle valve112after the first time may not prevent the engine102from misfiring. The throttle control module206may receive the manifold pressure from the MAP sensor184. The throttle control module206may send instructions to close the throttle valve112when the manifold pressure is greater than or equal to the first pressure.

The spark control module210may prevent the engine102from misfiring during startup by instructing the spark actuator module126to advance spark timing when the engine102is started. The spark control module210may send instructions to advance spark timing by an amount that is proportional to the piston position(s) relative to TDC before rock back (i.e., before movement of the piston(s) is reversed while the engine102is shutting down). The spark control module210may receive the piston position(s) from the position determination module212.

The spark control module210may independently advance spark timing for one or more cylinders in the engine102when the engine102is started. When the engine102is restarted after an automatic stop, a misfire may occur during the second firing event (i.e., the second event in a firing order of the engine102) as the engine102is restarted. Thus, the spark control module210may advance the spark timing of the cylinder in which the second firing event occurs as the engine102is restarted.

Referring toFIG. 3, a method for preventing engine misfire during engine startup begins at302. At304, the method determines whether an automatic stop is enabled. An automatic stop may be enabled when a vehicle speed is less than or equal to a predetermined speed (e.g., zero) and a driver depresses a brake pedal. If an automatic stop is enabled, the method continues at306.

At306, the method determines whether an engine speed is greater than a first speed. The first speed may be a predetermined speed (e.g., 400 revolutions per minute). If the engine speed is greater than the first speed, the method continues at308. At308, the method determines whether a manifold pressure (i.e., a pressure within an intake manifold) is greater than or equal to a first pressure. The first pressure may be a predetermined pressure (e.g., 10 kilopascals less than ambient pressure).

If the manifold pressure is less than the first pressure, the method continues at310. At310, the method opens a throttle valve. If the manifold pressure is greater than or equal to the first pressure, the method continues at312. At312, the method closes the throttle valve. At314, the method determines the position of one or more pistons in an engine before rock back (i.e., before movement of the piston(s) is reversed while the engine is stopping).

At316, the method determines whether an automatic start is enabled. An automatic start may be enabled when a driver releases the brake pedal after an automatic stop. If an automatic start is enabled, the method continues at318. At318, the method advances spark timing for one or more cylinders in the engine based on the piston position(s) before rock back. The method may advance spark timing by an amount that is proportional to a difference between the piston position and TDC.

A system and method for preventing engine misfire according to the principles of the present disclosure may apply to vehicles equipped with a stop-start system and vehicles that are not equipped with a stop-start system. A system and method may prevent engine misfire during engine startup by minimizing the amount of valve overlap during engine shutdown to prevent exhaust gas from flowing into an intake manifold. Valve overlap may be minimized by adjusting a camshaft resting position. However, minimizing valve overlap during engine shutdown may increase cold start emissions.

A system and method may prevent engine misfire during engine startup by purging the contents of cylinders in an engine before providing spark to the cylinders. However, this may increase the amount of time required to start the engine. The size of a starter motor that starts the engine may be increased to reduce the amount of time required to start the engine. However, this may increase the cost of the starter motor.