Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Patent
1999-03-15
2000-07-04
Wolfe, Willis R.
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
73119A, F02M 6500, G01M 1900
Patent
active
060851422
DESCRIPTION:
BRIEF SUMMARY
The present invention relates in general to a calibration method for a fuel-injection system provided with a plurality of injectors for an internal-combustion engine, implemented by means of an electronic control unit dedicated to the management of the engine. More specifically, the present invention relates to a method according to the preamble of claim 1, which eliminates problems due to the production tolerances of the injectors.
The present invention has been developed in particular for petrol-engine injectors but its use may possibly also be extended to engines of other types, for example, to Diesel engines.
It is known that practically all petrol internal-combustion engines for motor-vehicles are now provided with electronic injection systems and catalytic devices for reducing the pollutants present in the exhaust gases in order to conform to current legal norms relating to exhaust-gas emissions and, at the same time, to ensure optimal performance. Engines of this type thus have injection systems comprising one or more injectors for admitting fuel to the intake ducts of the engine.
In order to achieve the desired objectives with regard to exhaust-gas emissions and engine performance it is of primary importance to be able to control precisely the amount of fuel injected into each cylinder of the engine. For this reason, so-called multi-point injection systems with timed sequential injection are becoming ever more widespread. In practice, these are injection systems comprising one injector for each cylinder of the engine, the electronic control unit controlling each injector individually.
However, a technical problem arises owing to the characteristics of the injectors currently available on the market. In fact, it is known that the injectors produced have a considerable flow-rate tolerance. Flow-rate means the amount of fuel passing through the injector per unit of time at a given fuel pressure.
Since all of the injectors of an internal-combustion engine are supplied with fuel at the same pressure (which is also substantially constant), the amount of fuel injected by each injector per unit of time depends on the flow-rate characteristic of the individual injector.
This flow-rate characteristic of each individual injector may vary by plus or minus 20% from the nominal flow-rate provided for in the design specification of an injector of a given type, owing to the method by which the injectors are produced.
Thus, although the electronic control unit controls precisely the open time of each individual injector, the amount of fuel injected by each individual injector cannot be controlled precisely because of the differences in the flow-rate characteristics which may be encountered amongst injectors fitted in the same injection system.
This has necessitated the introduction of control and checking procedures in order to produce injectors having lower flow-rate tolerances. The production of injectors having a flow-rate tolerance of plus or minus 4% has thus been achieved, but at the price of a large increase in production costs.
However, even a tolerance of plus or minus 4% is quite high for use in modern electronic-injection systems.
The trend towards increasingly strict norms relating to exhaust-gas emissions and a requirement for the integrity of the system for reducing them to be maintained for up to 100,000 miles (about 160,000 km), give rise to a need to identify techniques more suitable for achieving these objectives.
For this purpose, for example, the American norm CARB (California Air Resources Board)--OBD II (On Board Diagnostics) which is shortly also to be applied in Europe requires, amongst other things, detection of misfires in the vehicle during its normal use.
The identification of this anomaly must be indicated by the switching-on of an indicator light which is disposed on the vehicle dashboard and which, once switched on, can be switched off only by the intervention of a technical service centre authorized for the maintenance of the vehicle. This measure protects the catalyst or catalytic c
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Di Leo Luigi
Palazzetti Mario
Ponti Cesare
C.R.F. S.C.P.A.
Wolfe Willis R.
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