Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2000-05-04
2002-03-19
Wolfe, Willis R. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C073S114220, C123S486000
Reexamination Certificate
active
06360161
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to fuel injection systems for internal combustion engines, and more particularly to, a method and apparatus for installing fuel injector coefficient data, that is specific to a particular fuel injector, in an engine controller when replacing a fuel injector.
In typical prior art fuel injected engines, it is generally considered desirable that each injector deliver approximately the same quantity of fuel in approximately the same timed relationship to the engine for proper operation. It is well known that problems arise when the performance, or more particularly the timing, and the quantity of fuel delivered by the injectors diverge beyond acceptable limits. For example, injector performance deviation or variability will cause different torques to be generated between cylinders due to unequal fuel amounts being injected, or from the relative timing of such fuel injection. Further, knowledge that such variations occur, requires engine system designers to account for this variability by designing an engine system to provide an output equal to the maximum theoretical output less an amount due to the worse case fuel injector variability rather than design a system for peak or maximum cylinder pressures or output.
Various attempts have been made for solving these problems associated with fuel injectors. One straight forward approach is to simply adhere to rigid manufacturing and test procedures to assure each injector meets a rigid desired design specification. Unfortunately, the increased manufacturing and assembly costs and the low yield of acceptable units makes this approach undesirable.
Sophisticated electronic equipment and control have made it possible to better control the problem of timing and delivery variations of similar fuel injectors. One such control involves compensating for individual injector variations and includes an electronic control module having a memory for storing compensation signals for each injector. The compensation signals used are derived from observed performance parameter values taken at a number of operating conditions and further include a plurality of sensors for detecting at least one and preferably a number of operating parameters. One or more operating parameter signals are then generated which are then provided to the memory. The electronic control module adjusts the base fuel delivery signal for each injector as a function of the compensation data signal for that injector. Unfortunately, some of the more complex and advanced fuel injectors now being manufactured do not follow readily predictable fuel-flow characteristics with increased pulse-width inputs, as was the case with earlier style injectors. Consequently, unless individual compensation signals are determined for an extremely large number of operating points resulting from different pulse widths, such systems would not operate satisfactorily with those advanced fuel injectors. Also, the amount of memory to store a sufficiently large number of compensation signals covering the full range of fuel injector operation would be excessively large, and the cost involved in the necessary testing to determine such a large number of compensation signals would be unacceptable.
The advanced fuel injector are very complicated and difficult to manufacture and therefore it is very difficult to have consistent operating characteristics between injectors even though they are intended to be substantially identical. Further, although varying pulse width of a control signal is used to vary the amount of fuel an injector provides to a cylinder (hereinafter referred to as fuel flow or flow rate), a performance curve of these complicated fuel injectors (fuel flow vs. pulse width) cannot be accurately defined by a second-order polynomial as can some older types of fuel injectors. Instead, the advanced fuel injectors must be defined by a third-order polynomial. Consequently, determining the pulse width for a desired RPM by extrapolating between sample data points does not provide satisfactory performance. By calculating the pulse width for each fuel injector individually for each desired RPM setting, substantially increased effectiveness of these advanced complicated fuel injectors can be achieved.
To determine the proper pulse width for a desired RPM for each fuel injector used in the engine, the coefficients for a third-order polynomial, which most closely define a performance curve of each fuel injector, are stored in a read/write memory associated with a specific cylinder in the engine. In addition, the basic form of a third-order polynomial is also stored and available for use by a microprocessor in the ECU (electronic control unit). The microprocessor retrieves the coefficients for each fuel injector and then uses the coefficients for the specific fuel injector to solve the basic third-order polynomial to determine the appropriate pulse width for a given throttle position or desired RPM thereby causing the correct amount of fuel to be injected into the cylinder to achieve the desired RPM.
Before the coefficients of a third-order polynomial representing the performance curve of a specific fuel injector can be stored in the read/write memory so as to be retrievable by the engine ECU, they must be determined. It is also important that a failed fuel injector can be replaced by a new injector which will also operate effectively with any cylinder.
Accordingly, each fuel injector is tested on a test flow bench by applying a signal pulse having a selected minimum width and then measuring the fuel flow rate. The pulse width is then increased a known amount and the resulting fuel flow rate again is measured. The process is repeated a number of times, such as 8 to 10 times, to obtain a series of data points which relate pulse width to a fuel flow rate.
These data points are then used to determine a third-order polynomial such as ax
3
+bx
2
+cx+d=0, which can also be used to define a performance curve representative of the fuel flow output of the fuel injector for any pulse width. The pulse width can then be correlated to the desired RPM. The degree of fit (R
2
) of said data points to the performance curve defined by the third-order polynomial is also determined within selected limits such that those fuel injectors which fall outside of the selected degree of fit are discarded. The coefficients of at least a portion of those fuel injectors which fall within the selected degree of fit are used to determine a nominal performance curve. Selected upper and lower limits are then set with respect to the nominal curve at each of the pulse-width values used to test the multiplicity of fuel injectors and then the fuel injectors are compared with the nominal curve to determine if the performance curve of each individual fuel injector stays within or exceeds the upper and lower limits of the nominal curve. Those that stay within the upper and lower limits are then used for assembly and replacement parts.
It will be appreciated by those skilled in the art that the third-order polynomial coefficients for each curve representing a fuel injector may be determined by various techniques including manual calculations. A regressive analyzer can also be particularly useful. Such a regressive analyzer can provide the degree of fit according to a least squares method wherein R
2
=1 is considered a perfect fit. A degree of fit for R
2
>0.998 has been found to provide a suitable threshold for attaining or discarding fuel injectors as discussed above.
When an engine is initially manufactured, the coefficient data can be determined empirically by any such method. Coefficient data for each of the particular fuel injectors to be installed in the engine is written into read/write memory for use by the ECU microprocessor. To subsequently replace a failed fuel injector, it is then necessary to replace the third-order polynomial coefficient data to the read/write memory over the coefficient data of the failed fuel injector, so that during future
Francis Dell C.
Koerner Scott A.
Taylor Patrick R.
Tetzlaff Patrick C.
Bombardier Motor Corporation of America
Cook & Franke SC
Wolfe Willis R.
Ziolkowski Timothy J.
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