GB2215868A

GB2215868A - Process for operating an electronically controlled fuel-infection system for internal combustion engines

Info

Publication number: GB2215868A
Application number: GB8902668A
Authority: GB
Inventors: Manfred Henning; Han-Jurgen Muller
Original assignee: Pierburg GmbH
Current assignee: Pierburg GmbH
Priority date: 1988-02-10
Filing date: 1989-02-07
Publication date: 1989-09-27
Also published as: IT8947580A0; FR2626936A1; GB8902668D0; DE3803952A1; IT1229548B

Description

6 8 2 2 PROCESS FOR OPERATING AN ELECTRONICALLY CONTROLLED FUEL-INJECTION

SYSTEM FOR INTERNAL COMBUSTION ENGINES The invention relates to a process for operating an electronically controlled fuel-injection system for internal combustion engines of the kind which have electromagnetically actuated fuel-injection valves injecting pulses of fuel into the engine in synchronisation with the rotation of the crankshaft, the durations of the pulses depending on the existing operating variables of the engine, each fuel-injection valve injecting fuel for its own individual cylinder, the dosage of fuel injected in each pulse being individually measured for the cylinder, the injections taking place sequentially into the intake passage upstream of the inlet valve of each cylinder so that the injected fuel is stored here, temporarily, before the inlet valve opens.

It is known to process the engine-operating variables such as mass-rateof-flow of intake air, engine speed, throttle-valve angle, intake-passage pressure, engineoperating temperature, a signal from an exhaust-gas sensor and the like in a computer, for determining the intended duration of each fuel-injection pulse. A process of this kind is described in the German Patent Specification DE-PS3108601. For detecting a requirement for acceleration, changes in airflow are measured and, if the rate of change exceeds a threshold value, indicating a requirement for acceleration, the duration of the injection pulse is extended, or an extra pulse is injected, to increase the supply of fuel for the engine, the extra supply of fuel being determined, under the existing engine-operating conditions, by the greatest mass of air which can be aspirated by each cylinder in each suction stroke of the piston.

But a disadvantage of the known process is that the extra supply of fuel thus determined produces an excessively rich mixture, i.e. above stoichimetric richness, which can produce peaks in the exhaust gas composition. Furthermore, the known process does not make it possible to adjust the injection pulses to agree constantly with the continuously changing aspirated airflow for each cylinder through each 720' cycle of crankshaft angle of rotation, which is a characteristic of 4-stroke engines.

2 The intention in the present invention is therefore to provide a process by which the quantity of fuel stored, temporarily, in the intake passage of each cylinder, upstream of the inlet valve, is adjusted constantly to agree with the continuously changing engine-operating conditions, irrespective of whether they are produced by gradual transitions or by abrupt acceleration.

The problem is solved by the characteristics claimed in the main claim.

What is obtained is that during each 720' crankshaft angle of rotation cycle the supply of fuel to the engine is regulated constantly, on the basis of corrections occurring at a specified frequency, to agree with the existing engine-operating conditions.

The invention will now be described in greater detail with reference to the time-circles shown in the drawing, but whose proportions are purely diagrammatic and do not represent real time-intervals. In the drawing, the outer circle 1 represents the time taken by the crankshaft to complete 720' of crankshaft-angle-of rotation (720' CAOR), i.e. to complete the working cycle of any one of the cylinders in a 4-stroke engine. At the top of the diagram TDC represents the instant when the piston arrives at top-dead-centre, just before the beginning of its suction stroke. The symbol IVO represents the instant when the inlet valve of the cylinder opens and the symbol IVC represents the instant when it closes. The time-interval between the IVO and IVC therefore represents the period during which the inlet valve of this particular cylinder remains open, under the existing engine-operating conditions.

Referring now to the inner circle 2, the time-interval tl represents the timing and duration of the fuel-injection pulse for this cylinder, i.e. the injection of fuel into its intake passage, upstream of the inlet valve, calculated by the electronic computer from the existing engineoperating conditions such as intake airflow, engine speed, throttle-valve angle, intake-passage pressure and the like. Below that in the diagram the time-interval t2 represents a lengthening of the calculated time- interval tl made possible by the fact that the injection pulse had not yet started when its calculated length was extended, or had not yet terminated.

3 Still further down in the diagram the time-interval C represents the timing and duration of a subsequent, separate injection pulse added after the first-calculated pulse has already terminated. Finally, the timeinterval t4 represents the timing and duration of a still further separate injection pulse which can be added, if desired, to increase mixture richness for acceleration when the rate of change in the airflow exceeds a threshold value, the duration of the t4 pulse depending on engine-operating conditions.

From the diagram it will be seen that the injection pulse can be extended at any time during the period between the first closing of the inlet valve at the instant IVC up till the next closing after 720' of crankshaft rotation has taken place. If the injection pulse, including any extension of the pulse, is not yet completed when the inlet valve closes the second time, for example because the calculation of fuel requirement has taken too long, the second closing of the inlet valve necessarily terminates the intake of fuel by the cylinder in this operating cycle, the intake of fuel remaining, in this case, incomplete. The injection of fuel for the next operating cycle is then calculated afresh from the existing operating conditions.

The first-calculated injection pulse duration tl is extended by the extra period C only if the extension exceeds a specified threshold increase of, for example, 10%. A further pulse of fuel, such as t4, is injected only in response to a still greater pulse extension of, for example, 20%, the resulting mixture enrichment being determined by the existing engineoperating conditions.

Finally the invention also extends to an internal combustion engine having a fuel injection system governed by the process defined above.

4

Claims

CLAIMS i 1. A process for operating an electronically controlled

fuel-injection system for 1 internal combustion engines of the kind which have electromagnetically actuated fuel-injection valves by means of which pulses of fuel are injected into the engine in synchronisation with the rotation of the crankshaft, the durations of the pulses depending on the existing operating variables of the engine, each fuel-injection valve injecting fuel for its own individual cylinder, the dosage of fuel injected in each pulse being individually measured for the cylinder, the injections taking place sequentially into the intake passage upstream of the inlet valve of each cylinder so that the injected fuel is stored here, temporarily, before the inlet valve opens, characterised in that, individually for each cylinder: i - after the duration (tl) of the injection pulse for the cylinder has been calculated a first time by the computer - during the interval of time between a first closing of the inlet valve and its next closing - the computer repeatedly re-calculates the pulse duration - at a specified ftequency of calculation - from the existing engine-operating variables, and in that - when the re-calculated duration of the injection pulse exceeds the duration first calculated by a time-interval (t2, t3) which exceeds a specified threshold value - a pulse of fuel whose duration has been increased by this amount is injected into the intake passage of the cylinder.
2. Process as claimed in Claim 1, characterised in that the pulse duration (tl) first calculated, is extended by Q2) only if the injection valve has not yet begun, or not yet completed, the injection of first- calculated duration.
3. Process as claimed in Claim 1, characterised in that if the injection of first-calculated duration has already been completed, then the extension of pulse duration is applied to the fuel-injection valve as a separate injection pulse (G).
4. Process as claimed in one of the above claims, characterised in that the calculated extension of injection-pulse duration terminates, at the latest, with the closing of the inlet valve, no extension taking place after that.
5. Process as claimed in one of the above claims, characterised in that of the newly calculated injection pulses only those are applied which extend the first-calculated injection duration by more than 10%.
6. Process as claimed in one of the above claims, characterised in that if a second specified threshold is exceeded, in the extension of injection-pulse duration, a further injection pulse (t4) is applied, for acceleration-enrichment of the mixture, whose duration depends on the existing engine-operating variables.
7. A process as defined in claim 1 and substantially as hereinbefore described with reference to the accompanying drawing.
8. An internal combustion engine having a fuel injection system governed by the process defined in any one or more of the preceding'Clairns.

Published 1989 at7he Patent Otftoe, State House, 86171 High HolbornLondonWCIR 4TP. Further copies maybe obtainedtrom The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR6 3RD. Printed by Multiplex techniques lid, St Mary Cray, Xent, Con. 1/87