On-board detection of pressure regulator malfunction

#The present invention is directed to a diagnostic system for an internal combustion engine to detect a defective fuel line pressure regulator. More specifically, the invention is directed to an on-board diagnostic system for detecting a malfunctioning fuel line pressure regulator during engine operation.

#It is becoming increasingly desirable to provide on-board diagnostic means for certain components of internal combustion engines, especially components which impact on critical engine performance criteria. This is particularly true in the motor vehicle industry, where high precision in the control of fuel supply to the engine has become essential to various present and planned engine management features designed to meet emissions, performance, drivability, and maintenance objectives. It is now well known how to adjust the fuel flow to the cylinders of an engine to maintain desired fuel/air mixture ratio for meeting engine emission requirements by electronically controlling the actuation timing and duration of the engine's fuel injectors. Electronic fuel injector control may be incorporated into known electronic engine control (EEC) modules performing a variety of engine control functions. In accordance with such known systems, the timing of injector actuation is controlled by the timing of the corresponding actuation signal sent by the control module. The duration of injector actuation, during which fuel is passed through the injector from a fuel rail or like fuel supply means, is controlled by the duration of the actuation signal from the control module, that is, by the pulse width of the signal.

#Reliably controlling fuel supply to an engine by controlling fuel injector actuation signal timing and duration (i.e., pulse width) assumes the absence of various possible fuel system problems, such as unstable pressure in the fuel supply line. Thus, especially in support of maintaining the efficacy of electronic engine management devices adapted to control air/fuel ratio by controlling the actuation of fuel injectors, it would be desirable to provide an on-board diagnostic system to periodically test for pressure regulator malfunction during engine operation. It is a primary object of the present invention to provide such on-board diagnostic system. Additional objects and features of various embodiments of the invention will be apparent from the following disclosure.

#Certain preferred embodiments are described below with reference to the appended drawing, in which FIG. 1 is a schematic illustration of an internal combustion engine fuel system comprising an on-board diagnostic system for detecting fuel pressure regulator malfunction during engine operation in accordance with a first embodiment of the invention.

#The present invention addresses the aforesaid diagnostic need by providing an on-board diagnostic system for detecting fuel line pressure regulator malfunction. Such malfunction can occur through normal engine use. While the present invention is applicable generally to any internal combustion engine burning liquid fuel supplied to fuel injectors via a fuel rail, it is especially advantageous for multi-cylinder motor vehicle engines. Accordingly, without intending to limit the scope of the invention, the discussion below will focus primarily on four stroke multi-cylinder motor vehicle engines. In that regard, reference in this discussion to an engine cycle or to a complete engine cycle (of a four stroke engine) is intended to mean two full revolutions of the engine. In a four stroke engine, each cylinder fires once during two full revolutions. Thus, in one complete engine cycle each cylinder fires once.

#A properly running engine having a diagnostic system as herein disclosed will have a characteristic fuel line pressure wave pattern for a given segment of an engine cycle, at a given point along the fuel line, under given engine operating conditions. Typically, pressure regulator malfunction results in fuel line pressure irregularity. The aforesaid signal processing means analyzes the pressure signals from the aforesaid pressure sensor over a selected test interval of certain duration or spanning one or more complete engine cycles, to obtain a characteristic value, preferably corresponding to average fuel pressure over the test interval period, to be compared to a corresponding stored value. Specifically, the signal processing means compares the test interval value to a stored value corresponding to proper pressure regulator functioning. The stored values may be stored, for example, in ROM memory of an EEC module. Upon detecting a difference between the two values, the signal processing means generates an output signal. Optionally, it may also generate a different output signal if no malfunction is detected.

#In certain preferred versions or embodiments, the signal processing means comprises a wave form analyzer, most preferably a Fast Fourier Transform analyzer. Such signal processing means, which are commercially available and known to those skilled in the art, may be used to analyze a certain preselected frequency range of the pressure signals, preferably a frequency range of about 50 to 1000 Hz, more preferably 50 to 200 Hz. Fast Fourier Transform analysis of pressure signals within such frequency range over a test interval, as described above, preferably yields a value of certain magnitude corresponding to amplitude for one or more frequencies or frequency sub-ranges (both frequencies and frequency sub-ranges being referred to herein simply as frequencies). Within the constraints of available signal processing speed and capacity, greater diagnostic accuracy and reliability will be obtained by diagnosis based on determination of a larger number of samples of pressure signal value over the test interval. The signal processing means then compares the magnitude value to its corresponding stored value. The aforesaid output signal is generated by the signal processing means when the difference between at least one magnitude value and its corresponding stored value exceeds a preselected amount. Any such difference would indicate a pressure irregularity in the fuel supply line which the pressure regulator is unable to correct or suppress. In preferred embodiments, the magnitude value corresponds to average actual fuel line pressure and the stored value corresponds to proper average fuel line pressure. The difference between the two values indicates the amount by which average fuel line pressure differs from the proper average pressure. Thus, a difference greater than zero or other preselected amount can be set as the threshold above which the output signal is generated.