Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1992-02-28
1993-09-21
Miller, Carl S.
Internal-combustion engines
Charge forming device
Fuel injection system
123501, F02M 5100
Patent
active
052459721
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for carrying out sequential injection processes when predetermined injection angles are reached.
BACKGROUND OF THE INVENTION
Sequential injection methods, which are referred to below as SEFI methods (SEFI=Sequential Fuel Injection), are performed on internal combustion engines in which one injection valve is allocated to one cylinder or to one group of cylinders. A computer sets the values for the beginning and end of the activation of a respective injection valve depending on the particular operating condition of the internal combustion engine. A variant employed in practice consists in setting the injection start angle and calculating the end of injection from an injection duration. Another variant adopts the method of setting the injection end angle and calculating the injection start angle from a respective injection end angle and an associated injection duration.
A problem in both variants is the fact that it is not possible to exactly achieve the calculated angles for the start of injection and the end of injection. This is because in known SEFI methods for a 4 cylinder engine, a so-called segment signal is only emitted every 180.degree. of crankshaft angle. If an injection angle, whether a start angle or an end angle, is set at, for example, 552.degree. crankshaft angle, three segment marks are counted out after the beginning of the current work cycle, a crankshaft angle of 540.degree. thereby is reached. The missing 12.degree. are determined by counting out time pulses.
The number of time pulses which occurs within an angular range of 12.degree. crankshaft angle depends on the speed of the internal combustion engine. If there is a relatively rapid change in speed during the period of time between the calculation of the number of time pulses to be counted out and the instant at which the counting out of the pulses is actually started, the injection angle which is actually desired is missed by a considerable amount. Rapid speed changes within this period of time occur particularly in the starting period and in other cases in which the internal combustion engine initially has only a low speed, which is then increased a great extent.
The object on which the present invention is based is to provide a SEFI method which permits more exact achievement of predetermined injection angles than was hitherto possible.
SUMMARY OF THE INVENTION
In the method according to the invention, crankshaft-angle increment signals are generated and these are counted in relation to a reference signal. As soon as the count value of the increment signals reaches a set injection-angle increment value, the injection process assigned to this increment value is carried out; that is to say, a valve begins or ends the injection of fuel.
By virtue of the fact that no time measurement of any kind is now used to determine whether a predetermined injection angle has been reached, the method cannot be influenced by speed fluctuations with regard to the determination of the set angles.
If, for each injection process, the associated injection start angle is set, this angle can be achieved with the accuracy of the increment pitch, e.g., an accuracy of 6.degree. crankshaft angle, regardless of how large the speed fluctuations that are experienced. However, the angular position of the end of injection is then not exactly fixed since it is of primary importance that a predetermined injection duration should be complied with. With the method according to the invention, however, it is possible to limit the end of injection to a maximum crank angle, e.g. to the angle at which the inlet valve for the cylinder for which injection is being performed at that precise moment it closes. In conventional segment SEFI methods, this was not possible, since it was impossible to determine accurately the instant of the closing of this valve in the case of speed changes.
It is advantageous in practice if the end of injection occurs at a certain angle before the angle for opening the inlet valve. Fro
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patent: 5068794 (1991-11-01), Hosaka
patent: 5090390 (1992-02-01), Feldinger
patent: 5095874 (1992-03-01), Schnaibel
Denz Helmut
Grieser Klemens
Miller Carl S.
Robert & Bosch GmbH
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