Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-08-30
2001-04-24
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
Reexamination Certificate
active
06220225
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the formation of a fuel-metering signal during and after the start of an internal combustion engine having intake manifold injection.
BACKGROUND OF THE INVENTION
Start and post-start corrections in the formation of a fuel-metering signal are known, for example, from U.S. Pat. No. 4,089,317 and are controlled downwardly, that is, the corrections are successively switched off.
The necessity of the start and post-start corrections results from the fuel storage characteristic of the intake manifold. More specifically, injected fuel partially condenses to form a wall film of fuel which adheres to the wall of the intake manifold. Low temperatures and high induction pressures favor the condensation and high temperatures and low intake manifold pressures favor the vaporization of the fuel from the wall film.
The condensation effects a reduction of the fuel quantity inducted into the combustion chamber of the engine. The vaporization increases this quantity. For a cold engine after a start, the influence of the condensation is, as a rule, preponderant which, for example, can be compensated by an increase in the fuel-injection pulsewidth. Basic investigations as to the fuel storage characteristic of wall films are presented, for example, in the article published in SAE Paper 810494.
In addition, a transition compensation UK is used in modern engine controls. This compensation is intended to compensate for the influence of wall film effects on the mixture composition in the combustion chamber during transition between different operating states. Thus, when the throttle flap is opened, an increase of the wall film mass occurs and, when closing the throttle flap, a reduction of the wall film mass occurs.
The fuel metering is correspondingly additionally increased via the injection valves when opening the throttle flap and is greatly reduced when closing the throttle flap in order to compensate for the effect of the fuel flow from the wall film.
This transition compensation is matched to the operationally-warm engine. It has been shown that, in known engine controls, unwanted large incorrect mixture adaptations occur in the time range of the first seconds after a start.
Thus, also significant overenrichment of the air/fuel mixture has been observed under the influence of an increase of the fuel-metering signals as a consequence of the start/post-start corrections under specific conditions.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a further improvement of the fuel-metering signal formation during and after a start of the engine.
The electronic control apparatus of the invention is for forming a fuel-metering signal for an internal combustion engine wherein increased fuel metering occurs during and after a start of the engine. The electronic control apparatus includes: means for forming an index for the pressure in the intake manifold of the engine; means for forming the gradient of the index; and, means for reducing the increased metering of fuel in dependence upon the gradient.
The invention is based on the realization that the clear overenrichments are caused by an intense reduction of the wall film which, in turn, is determined by the gradient of the intake manifold pressure and supplementally by temperature influences.
Before the start of the engine, an ambient pressure of approximately 1,000 mbar is present in the combustion chambers at sea level. Typically, a pressure of approximately 300 mbar develops in the intake manifold in the stable idle of the engine.
This pressure drop permits fuel from the wall film, which is present, to vaporize. The rate of vaporization increases with an increasing pressure gradient and increasing wall film temperature and intake air temperature.
According to the invention, a correction is superposed on the start/post-start enrichment in the first seconds of the operation of the engine. This correction effects a multiplicative leaning and is dependent upon pressure gradient and temperature.
The teaching of the invention thereby considers the excessive reduction of wall film, which can occur after the start of an engine which is not quite cold and the large pressure gradients which occur. In this way, an intense overenrichment of the air/fuel mixture is advantageously countered for the hot start. This reduces, inter alia, the emission of uncombusted hydrocarbons and tends to reduce consumption.
Also advantageous is the continuous controlling down of the leaning correction after a start in order to prevent jumps in the torque as a consequence of an otherwise possible jump-like enrichment via the deactivation of the function.
REFERENCES:
patent: 4089317 (1978-05-01), Drews et al.
patent: 4143621 (1979-03-01), Long
patent: 5215062 (1993-06-01), Asano et al.
patent: 5497752 (1996-03-01), Sagisaka et al.
patent: 5690074 (1997-11-01), Ogawa
patent: 0843086 (1998-05-01), None
patent: 2290392 (1995-12-01), None
patent: 8-49584 (1996-02-01), None
Mencher Bernhard
Mueller Gunter
Dolinar Andrew M.
Ottesen Walter
Robert & Bosch GmbH
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