Fuel pressure sensor performance diagnostic systems and methods based on hydrodynamics of injecton

An engine control system comprises a model pressure determination module and a sensor diagnostic module. The model pressure determination module determines a modeled fuel rail pressure based on an injection duration of a fuel injector and a desired fuel mass injected by the fuel injector. The sensor diagnostic module generates a status of a fuel rail pressure sensor based on a comparison of the modeled fuel rail pressure and a sensed fuel rail pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. 12/433,254 filed on Apr. 30, 2009. The disclosure of the above application is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates to diagnosis of a fuel pressure sensor and more particularly to diagnosis of a fuel pressure sensor based on hydrodynamics of fuel injection.

BACKGROUND

A fuel rail pressure sensor generates a pressure signal based on fuel pressure inside a fuel rail of an engine. The pressure sensor may output signals within a sensor range. For example, when the pressure sensor is de-energized (unplugged), the output may be a lower limit, and when the pressure sensor is short-circuited to a power source, the output may be the upper limit. The lower limit and the upper limit may define the sensor range.

The fuel pressure in the engine operates within an operating range corresponding to operating conditions of the engine. The pressure sensor is selected so that the operating range is between the lower limit and the upper limit of the sensor. The pressure sensor may sense the full operating range of the engine without reaching the lower limit or the upper limit of the sensor range. Fuel control may use the fuel pressure to determine fueling to the engine. A malfunctioning fuel pressure sensor may affect fuel control.

SUMMARY

An engine control system comprises a model pressure determination module and a sensor diagnostic module. The model pressure determination module determines a modeled fuel rail pressure based on an injection duration of a fuel injector and a desired fuel mass injected by the fuel injector. The sensor diagnostic module generates a status of a fuel rail pressure sensor based on a comparison of the modeled fuel rail pressure and a sensed fuel rail pressure.

In other features, the comparison includes determining a difference between the modeled fuel rail pressure and the sensed fuel rail pressure, and the status includes a failure status when the difference is greater than a predetermined threshold.

In still other features, the desired fuel mass is based on a mass airflow into an engine. A fuel injection duration module determines the fuel injection duration based on a base fueling duration and a fuel correction value. A base fueling module determines the base fueling duration based on the sensed fuel rail pressure and the desired fuel mass. A base fueling module retrieves the base fueling duration from a lookup table based on at least one of fuel mass flow rate, fuel rail pressure, a reference rail pressure and a reference fuel flow rate. The fuel correction value is based on an oxygen signal generated by an oxygen sensor disposed in an exhaust system.

DETAILED DESCRIPTION

The fuel pressure sensor performance diagnostic systems and methods of the present disclosure detect a malfunction of the fuel pressure sensor based on a comparison of the sensed fuel rail pressure (FRP) and a modeled FRP (FRPmod). FRPmodmay be based on a desired fuel mass to be injected into an engine and a fuel injection duration. The diagnostic systems and methods evaluate the fuel injector as a control volume having an upstream end located where the injector attaches to the fuel rail and a downstream end located at an opening of the fuel injector inside the cylinder. The diagnostic systems and methods apply principles of hydrodynamics to determine FRPmodat the upstream end of the fuel injector.

Referring now toFIG. 1, an exemplary implementation of an internal combustion engine system100is shown. Air enters an engine102through an air inlet104and travels to an intake manifold106. A mass airflow sensor108, disposed in the inlet104, generates a mass airflow (MAF) signal based on the air entering the engine102and sends the MAF signal to an engine control module (ECM)110.

An intake throttle valve (ITV)112may be disposed in the inlet104to control the air entering the engine102. The ECM110may control the ITV112by a throttle signal that may be based on an input from a driver or other input conditions. The ITV112may open and close to increase and decrease the mass airflow. Throttle position sensors114generate throttle position (TP) signals based on the ITV position and send the TP signals to the ECM110. The intake manifold106distributes the air to cylinders116.

Fuel injectors118may be attached to a fuel rail120to inject fuel into the cylinders116. The amount of fuel injected creates an air/fuel mixture having an air/fuel ratio. The air/fuel ratio may be a mass ratio of an air charge in the cylinders116and the fuel mass injected. The air/fuel mixture may be a stoichiometric air/fuel ratio of approximately 14.7/1. The air charge may be determined based on the mass airflow from the MAF sensor108. A desired fuel mass may be based on the mass airflow.

The fuel injector118is in fluid communication with the fuel rail120and includes an injector opening. The injector opening may include an effective cross-sectional area (Ae) through which fuel may be injected into the cylinder116. The fuel injector118may flow a reference flow rate (dmf/dt)refof fuel through the opening at a reference fuel rail pressure (Pref). For example only, the fuel injector118may flow 24 lb/hr of fuel at 40 psi.

The ECM110may open and close the injector118based on an injection duration. The injection duration may be the time during which the injector is open and fuel may flow through the injector118. For example only, the injector118may open when the injection duration is greater than zero and remain open for the injection duration.

A fuel pressure sensor121senses a fuel rail pressure (FRP) of the fuel rail120and sends an FRP signal based on the pressure to the ECM110. The ECM110may determine the injection duration based on the FRP and the fuel desired mass. For example only, the ECM110may open the injector118for the injection duration to deliver the desired fuel mass.

Pistons (not shown) within the cylinders116compress the air/fuel mixture. In a spark-ignition gasoline engine, a spark plug122may ignite the air/fuel mixture. The ECM110may generate a spark signal to control the ignition by the spark plug122. In a diesel or compression-ignition engine, the air/fuel mixture may be ignited by compression in the cylinders116. The principles of the present disclosure may be applied to both gasoline and diesel engines.

Upon ignition, the air/fuel mixture combusts and causes an increase in pressure inside the cylinders116. The pressure causes the pistons to rotate a crankshaft (not shown) in the engine102and produce a drive torque. An engine speed sensor124detects rotational movement of the crankshaft and sends an engine speed (RPM) signal to the ECM110based on a number of crankshaft revolutions per minute.

The combustion of the air/fuel mixture also causes exhaust gas to form in the cylinders116. The pistons force the exhaust gas to exit the cylinders116through an exhaust system including an exhaust manifold126and an exhaust pipe128. The exhaust gas may contain an amount of oxygen remaining from the combustion of the air/fuel mixture.

An oxygen sensor130may be located in the exhaust system. The oxygen sensor generates an oxygen signal based on the amount of oxygen in the exhaust gas and sends the oxygen signal to the ECM110. The amount of oxygen may correspond to the air/fuel mixture combusted in the cylinders116. For example, when the air/fuel mixture is greater than the stoichiometric ratio (a lean mixture), the exhaust gas may contain more oxygen than when the air/fuel mixture is less than the stoichiometric ratio (a rich mixture). The ECM110may use the amount of oxygen in the exhaust to adjust the injection duration.

Continuing with the engine system ofFIG. 1, a low-pressure pump (LPP)132may supply fuel from a fuel tank134to a fuel line136. The LPP132may be powered by an electric motor that is controlled by an LPP duty cycle signal generated by the ECM110. For example, as the LPP duty cycle increases, the motor speed may increase, causing the LPP132to supply more fuel to the fuel line136. The LPP130may provide fuel to the fuel line136at a first pressure. The first pressure may be a low fuel pressure that is less than the fuel pressure in the fuel rail120.

A high-pressure pump (HPP)138supplies fuel from the fuel line136to the fuel rail120. The HPP138may be a centrifugal pump connected to the crankshaft of the engine102by a shaft140. The HPP138may be connected to the crankshaft by a belt and pulley system (not shown). As the crankshaft rotates, the HPP138rotates and supplies fuel to the fuel rail120at a pump flow rate (Qpmp).

Qpmpmay be based on engine speed. Qpmpmay be based on characteristics of the HPP138. For example, the characteristics may include a pump flow capacity and/or a pump frequency. The pump flow capacity may be a fuel volume supplied by the HPP138. The pump frequency may be a number of times the HPP138supplies the fuel volume per rotation of the HPP138.

An HPP valve142may be located near an inlet of the HPP138. The HPP valve142may control the fuel entering the HPP138from the fuel line136. The valve142may be opened and closed by an electric motor that is controlled by an HPP duty cycle signal generated by the ECM110. For example, as the HPP duty cycle increases, a voltage supplied to the motor may increase, causing the valve142to open.

When the valve142is open, fuel may flow into the HPP138. Increasing the opening may increase the fuel flowing into the HPP138. Qpmpmay also be based on the HPP duty cycle. The HPP duty cycle may be based on the engine speed or mass airflow. The HPP138supplies pressurized fuel to the fuel rail120at a second pressure that is greater than the first pressure. The fuel rail120distributes the fuel to the fuel injectors118.

Referring now toFIG. 2, an exemplary implementation of the engine control module110is shown. A fueling determination module202may determine the desired fuel mass based on the MAF signal. The desired fuel mass is the mass of fuel that mixes with the air mass in the cylinder116to create the desired air/fuel ratio. The desired fuel mass may be determined based on the air entering the cylinder116and a stoichiometric air/fuel ratio.

A base fueling module204may determine a base fueling duration or base pulse width (BPW) for the fuel injector118. The BPW may be based on the desired fuel mass and the sensed FRP. For example only, the BPW may be a lookup table based on fuel mass and fuel pressure. For a given desired fuel mass and fuel pressure, a BPW may be specified.

A fuel injection duration module206generates the injection duration or final pulse width signal based on the BPW and a fuel correction value. For example, the fuel correction may be based on the oxygen signal from the oxygen sensor130. The fuel correction may correct the injection duration when the pressure sensor121is malfunctioning.

For example only, a malfunctioning pressure sensor121may indicate a higher FRP value than actually exists in the fuel rail120. The higher, incorrect FRP value may then be used to determine the BPW from the lookup table. The BPW may be less than a BPW using the correct FRP value. The injection duration, therefore, may also be less than what is needed to deliver the desired fuel mass.

The decreased injection duration may cause less fuel to be injected into the cylinder116than the desired fuel mass because the injector118is open for a shorter duration. The oxygen sensor130may detect an increased oxygen amount in the exhaust gas due to the decrease in fuel injected. Fuel injection duration module206may adjust the injection duration based on the oxygen amount to compensate for the incorrect FRP value.

A model pressure determination module208determines a modeled fuel rail pressure (FRPmod) based on the desired fuel mass and the injection duration. The model pressure determination module208may evaluate the fuel injector118as a control volume. The control volume may have an upstream end located where the injector118attaches to the fuel rail120and a downstream end located at the opening of the fuel injector118.

A fuel mass flow rate (dmf/dt) at the injector opening may be determined based on the desired fuel mass and the injection duration. The pressure at the injector opening may be much less than the rail pressure. The model pressure determination module208may assume the pressure at the injector opening to be zero. The model pressure determination module208may assume a mass flow rate at the upstream end to be zero. The model pressure determination module208may determine FRPmodbased on the desired fuel mass, the injection duration, and the reference pressure and the reference flow rate of the injector118.

A sensor diagnostic module210compares FRPmodto the sensed FRP. When the absolute value of the difference between FRPmodand the sensed FRP is greater than a predetermined pressure threshold, the sensor diagnostic module210outputs a fault status of the fuel pressure sensor121. The sensor diagnostic module210may indicate the status to the base fueling module204. When a fault status is generated, the base fueling module204may determine the BPW using FRPmodand the desired fuel mass rather than using the sensed FRP.

Regarding the model pressure determination module208, FRPmodmay be determined based on hydrodynamics principles. Mathematically speaking, for an incompressible liquid in a control volume such as fuel in the fuel injector118, the fuel injector118may be modeled according to Bernoulli's equation:

vrail22+Prailρ=vinj22+Pinjρ(1)
where vrailis a velocity of a point in the fuel where the injector118communicates with the fuel rail120, and Prailis the fuel rail pressure. Furthermore, vinjis a velocity of a point in the fuel at the injector opening and Pinjis a pressure at the injector opening. A density of the fuel (ρ) may be measurable in grams per meter cubed.

By assuming the fuel rail120has an infinite volume of fuel relative to a volume of fuel injected, vrailmay be assumed to be zero. Prailmay be assumed to be much higher than Pinjwhen the fuel injector118is open. Therefore, Pinjmay be assumed zero. Thus, vinjcan be stated in terms of the fuel rail pressure and the fuel density ρ:

vinj=2⁢Prailρ(2)
For the cross-sectional area Aeand a drag coefficient Cdof the injector opening, a fuel mass flow rate

ⅆmfⅆt
through the injector opening may be stated as:

ⅆmfⅆt=Cd×Ae×2⁢ρ⁢⁢Prail(3)
The reference injector flow rate

(ⅆmfⅆt)ref
mentioned above may similarly be stated as:

(ⅆmfⅆt)ref=Cd×Ae×2⁢ρ⁢⁢Pref(4)
Equations (3) and (4) may be combined to simplify leaving:

Furthermore, the BPW may be mathematically stated in terms of the desired fuel mass (mf) to be injected and the fuel mass flow rate

B⁢⁢P⁢⁢W=mfPrailPref⁢(ⅆmfⅆt)ref(7)
Because the BPW may depend on the sensed FRP, a malfunctioning pressure sensor121may cause an error in the BPW calculation.

The injection duration or final pulse width (PW) may be corrected for a malfunctioning pressure sensor121. From equation (7), the injection duration or final pulse width (PW) may be substituted for the base pulse width (BPW) and the modeled fuel rail pressure (FRPmod) may be substituted for the fuel rail pressure:

Referring now toFIG. 3, a flowchart300depicts exemplary steps of an engine control system according to the principles of the present disclosure. Control begins in step302where control determines the mass airflow based on the MAF signal from the MAF sensor108. In step304, control determines the desired fuel mass based on the mass airflow. In step306, control determines the fuel correction value based on the oxygen signal from the oxygen sensor130. In step308, control determines the fuel rail pressure (FRP) based on the FRP signal from the pressure sensor121.

Control determines the base pulse width (BPW) based on the desired fuel mass and the sensed FRP in step310. In step312, control determines the injection duration based on the BPW and the fuel correction value. In step314, control determines the model fuel rail pressure (FRPmod) based on the desired fuel mass and the injection duration using principles of hydrodynamics.

In step316, control may determine a difference between FRPmodand the sensed FRP. In step318, control determines whether the difference is greater than a predetermined threshold. The difference may include an absolute value of the difference between FRPmodand the sensed FRP. Control may also determine more than one threshold.

For example only, control may determine a first threshold for when the sensed FRP is greater than FRPmodand a second threshold for when the sensed FRP is less than FRPmod. When the difference between FRPmodand the sensed FRP is greater than the predetermined threshold, control may indicate a failure of the pressure sensor121in step320. Control may indicate that the BPW should be based on FRPmodrather than the sensed FRP. Otherwise, control may return to step302.