Measuring and testing – With fluid pressure – Motor part or auxiliary
Reexamination Certificate
2001-11-14
2003-05-20
Larkin, Daniel S. (Department: 2856)
Measuring and testing
With fluid pressure
Motor part or auxiliary
C073S114220
Reexamination Certificate
active
06564616
ABSTRACT:
The present invention relates to a method of diagnosing leakage in an internal combustion engine common-rail injection system.
BACKGROUND OF THE INVENTION
As is known, of the various problems that can occur in a common-rail injection system, the worst and most dangerous are one or more of the injectors jamming in the open position, and fuel leakage in the high-pressure fuel supply circuit, which results in fuel discharge in the form of a very fine spray.
On the one hand, high-pressure fuel leakage may cause a fire if the fuel spray should strike particularly hot engine surfaces; and, on the other, a jammed-open injector results in continuous fuel supply to the cylinders, in turn resulting not only in excessive fuel consumption but also in abnormal combustion characterized by pressure peaks and a considerable temperature increase in the cylinders.
Such defects can only be tolerated so long without causing serious damage to the engine, e.g. to the connecting rod, piston, or injector nozzles, and may immediately impair performance and safety of the vehicle.
To safeguard against such hazards, diagnostic units were proposed to detect fuel leakage in the injection system and to act on the injection system to cut off fuel supply to the injectors and so stop the engine immediately.
More specifically, such units operated by comparing the fuel pressure in the common rail or total fuel consumption of the engine with respective threshold values, and determined the presence or not of any hazardous situations accordingly.
Common-rail injection systems, however, are also subject to fuel leakage in the low-pressure fuel supply circuit—caused, for example, by fine cracks in the low-pressure conduits—or to faulty low-pressure fuel supply circuit components preventing correct fuel supply to the high-pressure fuel supply circuit.
Such leakage and defects, however, are not as serious as a jammed-open injector or high-pressure fuel spray, by not immediately impairing engine performance or the safety of the vehicle, which, in such cases, in fact, can safely be driven at least to the nearest repair shop.
Known diagnostic units of the above type, however, were unable to distinguish between fuel leakage in the high-pressure fuel supply circuit and fuel leakage or faults in the low-pressure fuel supply circuit, so that, even in the case of minor, nonhazardous faults in the low-pressure fuel supply circuit, known diagnostic units immediately disabled the vehicle, thus causing considerable inconvenience to the driver, out of all proportion to the immediate danger involved.
One of the many solutions proposed to at least partly eliminate the above drawback is described in the Applicant's European Patent Application EP-0786593, which proposes a fuel catch structure for determining fuel leakage from the high-pressure fuel supply conduits connecting the injectors to the common rail.
More specifically, the fuel catch structure comprises a number of sleeves made of elastomeric material, surrounding the injector supply conduits, and for catching any fuel leaking from the conduits; a catch header connected to and for collecting from the sleeves any fuel leaking from the injector supply conduits; a fluid sensor located at the bottom of the catch header to generate a leak signal indicating the presence of fuel in the catch header; and an alarm circuit connected to the fluid sensor to generate an alarm signal in the presence of fuel in the catch header.
Though advantageous in many respects, the above solution has several drawbacks preventing its advantages from being fully exploited.
More specifically, fuel leakage from the high-pressure supply conduits is determined using additional dedicated components not normally provided on the vehicle—such as the sleeves, catch header, fluid sensor, and alarm circuit—and which, besides costing money to manufacture or purchase and assemble, also call for regular servicing.
Moreover, the catch structure described above was only capable of determining one type of fault in the high-pressure fuel supply circuit—namely, fuel leakage from the high-pressure supply conduits—so that any other faults in the high-pressure fuel supply circuit, such as a jammed-open injector, remained undiagnosed.
Another solution proposed to at least partly eliminate the above drawbacks is described in the Applicant's European Patent Application EP-0785349, which proposes a diagnostic unit designed to determine the type of fault in the high-pressure fuel supply circuit, and in particular to distinguish between a jammed-open injector and a generic fault in the high-pressure fuel supply circuit.
More specifically, the diagnostic unit employs an accelerometer signal related to engine vibration intensity and generated by an accelerometer sensor on the engine block; and a position signal indicating the angular position of the drive shaft (engine angle). More specifically, the diagnostic unit compares the amplitude of the accelerometer signal with a first reference value; compares with a second reference value the engine angle value at which the amplitude of the accelerometer signal exceeds the first reference value; and determines a jammed-open injector condition according to the outcome of the two comparisons.
Though advantageous in many respects, the above solution has one drawback preventing its advantages from being fully exploited.
More specifically, the type of fault in the high-pressure fuel supply circuit is determined using an additional dedicated component not normally provided on the vehicle, i.e. the accelerometer sensor, which, besides costing money to manufacture or purchase and assemble, also calls for regular servicing.
To eliminate the above drawback, the Applicant's European Patent Application EP-0785358 proposes a diagnostic unit designed to determine the type of fault in the fuel supply circuit as a whole, and in particular to distinguish between a jammed-open injector and a generic fault in the fuel supply circuit, without requiring the use of an additional accelerometer sensor not normally provided on the vehicle.
More specifically, the diagnostic unit first determines the presence of faults in the fuel supply circuit by comparing the fuel pressure in the common rail or the total fuel consumption of the engine with respective threshold values; and, in the event any faults are determined, distinguishes between a jammed-open injector and a generic fault in the fuel supply circuit on the basis of the engine torque, which is determined using a position and speed signal indicating the speed and angular position of the drive shaft and generated by a drive shaft speed and angular position detecting device already provided on the vehicle and substantially comprising a sound wheel fitted to the drive shaft, and an electromagnetic sensor associated with the sound wheel.
More specifically, if any faults are detected in the fuel supply circuit, the diagnostic unit reduces—in particular, cuts off—fuel injection into each engine cylinder; calculates, on the basis of said position and speed signal, the contribution of each cylinder to the value of the useful torque generated by the engine; compares each contribution with a respective reference value; and determines a jammed-open injector condition when at least one contribution is above the respective reference value, and a fault condition in the fuel supply circuit when all the contributions are below the respective reference values.
That is, if the diagnosed fuel leakage is caused by a fault in the fuel supply circuit, the reduction in the amount of fuel injected into the cylinders produces a corresponding reduction in the useful torque contribution of each cylinder; which reduction can easily be calculated as a function of the reduced injection time of each injector. Conversely, if the diagnosed fuel leakage is caused by a jammed-open injector, the reduction in the amount of fuel injected produces a smaller reduction in useful torque contributions than in the previous case, owing to the jammed-open injector feeding fuel continuously to
Antonioli Pierpaolo
Davide Cristiana
Reale Mario
C R F Societa Consortile per Azioni
Larkin Daniel S.
Pennie & Edmonds LLP
Politzer Jay L
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