Patent Application
20080120015
The present invention relates to detection systems, and more particularly to liquid fuel detection systems.
Internal combustion engines combust an air/fuel (A/F) mixture within cylinders to drive pistons and to provide drive torque. Air is delivered to the cylinders and an intake manifold via a throttle. A fuel injection system supplies fuel from a fuel tank to provide fuel from a desired A/F mixture to the cylinders. To prevent release of fuel vapor, vehicles also typically include an evaporative emissions system, which includes a canister that absorbs fuel vapor from a fuel tank, a canister vent valve and a purge valve. The canister vent valve allows air to flow into the canister. The purge valve supplies a combination of air and vaporized fuel from the canister to the intake system.
Closed-loop control systems adjust inputs of a system based on feedback from outputs of the system. By monitoring the amount of oxygen in the exhaust, closed-loop fuel control systems manage fuel delivery to an engine. Based on the output of oxygen sensors, the engine control module adjusts the fuel delivery to match the ideal A/F ratio (14.7 to 1). By monitoring the engine speed variation at idle, closed-loop speed control systems manage engine intake airflows and spark advance.
Under some circumstances, liquid fuel rather than fuel vapor can be present in the canister. Controlling the fuel system when liquid fuel is present in the canister can be a difficult task. Liquid fuel in the canister can produce high engine emissions, undesirable idle surge, steady throttle surge, or engine stall. If this problem occurs, a vehicle may also fail evaporative emissions requirements.
Accordingly, a liquid fuel detection system for a fuel vapor system of a vehicle providing fuel vapor to an engine operating in closed loop includes an oxygen sensor that generates an oxygen signal based on an oxygen level in engine exhaust. An engine speed sensor generates a speed signal based on a speed of the engine. And a control module receives the oxygen signal and the speed signal, determines a fuel control factor based on the oxygen signal, determines a long term modifier based on long term changes of the fuel control factor, and detects the presence of liquid fuel in the fuel vapor system based on the fuel control factor, the speed signal, and the long term modifier.
In another feature, the control module detects the presence of liquid fuel when the fuel control modifier drops below a minimum for a selectable period of time.
In another feature, the control module detects the presence of liquid fuel in the fuel vapor system when the speed signal and the fuel control factor indicate engine instability.
In other features, the control module detects the presence of liquid fuel in the fuel vapor system when engine idle conditions are met. Engine idle conditions are met if throttle position is less than a minimum throttle position value and vehicle speed is less than a minimum vehicle speed value.
In still other features, the control module sets a liquid fuel notification code when the presence of liquid fuel is detected a selectable number of times and the control module sends an off-board communication signal when the presence of liquid fuel is detected a selectable number of times.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.
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The engine system 12 includes an engine 18, a fuel injection system 20, an intake manifold 22, and an exhaust manifold 24. Air is drawn into the intake manifold 22 through a throttle 26. The throttle 26 regulates mass air flow into the intake manifold 22. Air within the intake manifold 22 is distributed into cylinders 28. The air is mixed with fuel and the air/fuel mixture is combusted within cylinders 28 of the engine 18. Although two cylinders 28 are illustrated, it can be appreciated that the engine 18 can include more or fewer cylinders 28 including, but not limited to 1, 3, 4, 5, 6, 8, 10 and 12 cylinders. The fuel injection system 20 includes liquid injectors that inject liquid into the cylinders 28.
Exhaust flows through the exhaust manifold 24 and is treated in a catalytic converter 30. First and second exhaust oxygen sensors 32 and 34 (e.g., wide-range A/F ratio sensors) communicate exhaust A/F ratio signals to the control module 16. A mass air flow (MAF) sensor 36 is located within an air inlet and communicates to the control module 16 a MAF signal based on the mass of air flowing into the engine system 12. An engine speed sensor 38 senses the speed of the engine and communicates an engine speed signal to the control module 16. A throttle position sensor 40 senses the position of the throttle 26 and communicates a throttle position signal to the control module 16.
The control module 16 controls the fuel and air provided to the engine based on oxygen sensor signals and throttle valve position. This form of fuel control is also referred to as closed loop fuel control. Closed loop fuel control is used to maintain the air/fuel mixture at or close to an ideal stoichiometric air/fuel ratio by commanding a desired fuel delivery to match the airflow. Stoichiometry is defined as an ideal air/fuel ratio, which is 14.7 to 1 for gasoline. The engine control may command different airflow to compensate the engine speed changes during engine idle operation.
The engine system 12 operates in a lean condition (i.e. reduced fuel) when the A/F ratio is higher than a stoichiometric A/F ratio. The engine system 12 operates in a rich condition when the A/F ratio is less than the stoichiometric A/F ratio. A fuel control factor helps determine whether the A/F ratio is within an ideal range, i.e., greater than a minimum value and less than a maximum value. An exemplary fuel control factor includes a short term integrator (STI) that provides a rapid indication of fuel enrichment based on input from the oxygen sensor signals. For example, if the signals indicate an air/fuel ratio greater than a specified reference, STI is increased a step and if the signals indicate an air/fuel ratio less than the specified reference, STI is decreased a step. A fuel control modifier monitors changes in the fuel control factor over a long term. An exemplary fuel control modifier includes a long term modifier (LTM). LTM monitors STI and uses integration to produce its output.
The fuel system 14 includes a fuel tank 42 that contains liquid fuel and fuel vapor. A fuel inlet 44 extends from the fuel tank 42 to enable fuel filling. A fuel cap 46 closes the fuel inlet 44 and may include a bleed hole (not shown). A modular reservoir assembly (MRA) 48 is disposed within the fuel tank 42 and includes a fuel pump 50. The MRA 48 includes a liquid fuel line 52 and a fuel vapor line 54.
The fuel pump 50 pumps liquid fuel through the liquid fuel line 52 to the fuel injection system 20 of the engine 18. A fuel vapor system includes the fuel vapor line 54 and a canister 56. Fuel vapor flows through the fuel vapor line 54 into the canister 56. A fuel vapor line 58 connects a purge valve 60 to the canister 56. The control module 16 modulates the purge valve 60 to selectively enable fuel vapor flow to the intake system of the engine 18. The control module 16 modulates a canister vent valve 62 to selectively enable air flow from atmosphere into the canister 56.
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Once control detects liquid fuel in the fuel vapor system, control may set a notification code at 160 and a notification signal is sent at 170. The signal can be in the form of a diagnostic code that can be retrieved by a service tool connected to the vehicle, in the form of a signal that illuminates an indicator light viewable by an operator and/or in the form of a diagnostic code that is broadcast to a remote service technician. Alternatively (flow not shown), control may wait until fuel has been detected in the vapor system a consecutive number of times or a selected number of times within a specified time period before setting a notification signal or sending the notification signal.
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Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.
