Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
1999-09-22
2001-05-08
Dombroske, George (Department: 2855)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C073S116070, C073S117020, C123S463000, C701S111000
Reexamination Certificate
active
06230095
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the diagnosis and prediction of power imbalance conditions between cylinders of an internal combustion engine. Specifically, this invention provides a system and method for detecting the existence of such a power imbalance and for providing a prognosis as to the nature of the imbalance. The prognosis can be used to provide a warning to the vehicle operator or as a tool for engine service recommendations.
BACKGROUND OF THE INVENTION
Most industrial and automotive internal combustion engines include a pair of cylinder banks, each including a plurality of cylinders. For example, a V-8 engine includes two banks of four cylinders each. With the advent of electronic controls, the operating conditions of each of the cylinders is controlled by an on-board engine control computer or an electronic controller. The typical electronic controller provides signals to electrically actuated fuel control systems, firing timing systems and air intake systems. In diesel engines, the electronic controller performs the critical task of controlling the timing of operation of the fuel injectors to ensure optimum combustion performance. The electronic controller also acts as a speed governor, accepting input from the accelerator pedal and sensing engine load conditions to establish an engine speed.
Power imbalance between engine cylinders can have obviously deleterious effects on overall engine performance. Moreover, cylinder power imbalance can cause an engine to “run dirty” so that the engine emissions exceed federal and local environmental regulations. The causes of cylinder power imbalance are many, but can be broadly categorized as reductions in combustion quality. This reduction can arise in a diesel engine from a drop in injector nozzle opening pressure, a stuck plunger, clogged injectors, unsealed valves, valve gap discrepancies, and the like. Other causes can arise in the fuel pump or can be attributed to a “dead” cylinder.
Many approaches have been implemented to identify when a cylinder power imbalance exists, or when a particular cylinder performance is below acceptable operating limits. However, these prior approaches only operate as a sort of “go—no go” gauge and are generally only useful to determine that a cylinder is a problem. Thus far, none of these prior systems can diagnose the source of the engine power problem. Moreover, no prior system has the capability to provide a prognosis of future engine performance so that the vehicle operator can avoid break-downs on the road due to deteriorating engine performance.
Consequently, there remains a need in the arena of engine performance evaluation for a system that can not only diagnose, but also predict engine performance problems. This need is best fulfilled by an on-board system that performs its appointed evaluation automatically when the engine is at idle conditions.
SUMMARY OF THE INVENTION
The present invention provides a system and method for not only diagnosing but also predicting causes of engine performance degradation. The invention is particularly suited to evaluating changes in cylinder power balance conditions over time, engine hours or mileage. In one feature of the invention, a firing time differential value is calculated for each cylinder based upon the firing time of the cylinder relative to the firing time of the prior cylinder. In one embodiment, these cylinder differential values are compared to a predetermined limit value derived from empirical data for an optimally performing engine. If any differential firing time value for a cylinder exceeds the limit value, a warning signal is generated indicating that a problem exists with the engine, such as cylinder power imbalance.
In a further aspect of the invention, this diagnostic aspect is carried a step further by features that evaluate the firing time differential data over time to form a prognosis as to the cause and severity of the degradation in engine performance. In one embodiment a one dimensional analysis is conducted in which a trend value is derived from all of the firing time differentials obtained at a specific engine hour or mileage. This trend value is then compared to trend values from prior test sequences at earlier engine hours or mileage.
In one feature, if the trend value for the current test sequence exceeds a trend boundary, a warning signal is generated indicating a degradation in engine performance. Under this circumstance, the rate and magnitude of the change in trend value can be calculated and evaluated as an indication of the source and severity of the problem. In one embodiment, the magnitude of the trend parameter change over time can provide an indication that the engine performance deterioration is due to a different cause from prior test sequences. An evaluation of the rate of change of the trend value can provide an indication of the rate of degradation of engine performance. With either parameter, the vehicle operator or engine technician is provided with a real time assessment of the prognosis for engine performance. If the rate and magnitude values exceed certain thresholds, alarms can be provided to prompt immediate engine servicing.
In another aspect of the invention, a two dimensional analysis is contemplated. In this analysis, the cylinder firing time differentials are first obtained for a number of tests as a baseline point for a new engine operated at low idle. A matrix of firing time differentials is developed for all of the cylinders and all of the number of tests. In accordance with this embodiment, a variance matrix is created from the baseline firing time differential matrix, and a singular value decomposition applied to the resulting matrix. This decomposition yields two principal eigenvalues corresponding to the engine cylinder contributing the greatest amount to the cylinder imbalance at the baseline point in the engine life. Two vectors are extracted from the eigenvalue transformation matrix corresponding to the two principal eigenvalues, which vectors are stored in the memory of engine control computer for later use to obtain trend variables during subsequent test sequences.
Subsequent test sequences can be conducted at engine idle at future engine operation hours or mileages, such as every 150 hours or 1000 miles. In each subsequent test sequence, a vector of new differential firing times is obtained over all of the engine cylinders. This vector is mathematically projected into the subspace defied by the two decomposition vectors to obtain the trend variables associated with the test sequence at the particular engine hour/mileage.
In a feature of the invention, these trend variables are converted to polar coordinates. The magnitude or radius of the polar coordinates provides an indication of the severity of the cylinder degradation. The polar angle is indicative of the source of the power imbalance. In addition, changes in the polar angle can indicate a different cause for the engine performance degradation from prior engine hours or mileage.
It is one object of the present invention to provide a system and method that is capable of diagnosing sources of degradation in engine performance. A further object is realized by features of the invention that allow a prognosis for future engine performance to be obtained.
Another object is to provide a system and method that can provide a real time evaluation and indication of the source and severity of conditions causing a degradation in cylinder power, for example. Other objects and special benefits provided by the present invention can be discerned from the following written description and accompanying figures.
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patent: 5605132 (19
Baker & Daniels
Cummins Engine Company, Inc.
Dombroske George
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