EP0398903B1 - Method for acceleration enrichment in fuel injection systems - Google Patents

Abstract

Following detection of an acceleration enrichment condition in a fuel injection system of the type having a hot-wire air quantity sensor, a plurality of initial enrichment injections (RTIBA) replace the normal injections (ti) based on engine load, these initial injections being applied for the next X 180° or 360° crankshaft rotations and being of a length which is independent of engine load (TL) but being dependent upon engine variables (such as engine speed n, hot-wire voltage ULHM and change in hot-wire voltage ΔULHM) which are available at the instant of detection of the acceleration enrichment requirement. Following completion of the X 180° or 360° crankshaft rotations, or if the normally calculated injection period (ti) based on engine load has become greater than the length of the initial injections (RTIBA), then the normally calculated value (ti) is again adopted. The length of the initial injection or injections (RTIBA), dependent upon the engine temperature as well as on the 'load substitute variables' of the speed n, hot-wire voltage ULHM, change in hot wire voltage ΔULHM, are determined from stored look-up tables.

Description

State of the Art
• The present invention relates to fuel injection systems having acceleration enrichment (BA), of the kind described in the precharacterising clause of claim 1.
• During acceleration conditions, it is conventional practice for the lengths of the injection pulses applied to the injection valves to be increased by an acceleration enrichment factor (FBA) in accordance with the expression: $${\text{ti = t}}_{\text{L}}{\text{.FBA. πF}}_{\text{korr}}\text{+ ts}$$

  

     where t_L is a basic injection value proportional to $$\frac{{\text{air flow quantity (Q}}_{\text{L}}\text{)}}{\text{engine speed (n)}}$$

  

  
     FBA is the acceleration enrichment factor
     π F_korr is a combination of other correcting factors, well known in the art, and
     ts is a battery voltage correction factor.
• In conventional injection systems, it is often possible to respond to rapid dynamic transition conditions by outputting a correspondingly increased injection time (ti) only after a relatively long delay. This can be true even when a value for the acceleration enrichment factor (FBA) is actually available at the instant an acceleration enrichment requirement is detected and is taken into account in the next injection pulse. The reason for this is that, as a result of time delays in detecting the engine speed and the hot wire signal, as well as a result of program running times, the required acceleration enrichment factor is applied to a value of t_L (basic load) which is too small, so that the excess quantity required at that instant is therefore not produced.
• One known system, constructed in accordance with the precharacterising clause of claim 1, and having ignition pulses every 180° of crankshaft rotation, attempts to overcome this problem by providing a single ignition-synchronous intermediate injection (RTIBA) between the last normal injection without acceleration enrichment (FBA) and the first enriched injection ti = t_L.FBA + ts. This known example is illustrated in Figure 1 of the accompanying drawings. The value of this intermediate injection (RTIBA) is dependent on the prevailing value of the engine temperature (ν_Mot) so that. $${\text{RTIBA = f (ν}}_{\text{Mot}}\text{)}$$

  
• In the event that the engine has ignition pulses at 360° crank angles, then the acceleration enrichment factor (FBA) in this known system is increased once by a preselectable constant y, such that: $$\text{FBAUE = FBA. y}$$

  
• In either case, after the single intermediate injection has taken place, the normal enrichment factor in accordance with equation (1) applies.
• In another known system, a single intermediate injection is output in asynchronism with ignition immediately upon detection of an acceleration enrichment requirement. Should the detection of an acceleration enrichnent requirement occur within the course of an existing injection period (ti), then that period is extended by RTIBA = f ( ν _Mot).
• A problem with the latter arrangements is that the program running time of the asynchronous main program controlling the fuel injection system varies considerably. It can therefore happen that the "FBAUE" is connected to a relatively high actual value of t_L and can thus lead in this case to a value for ti which is too high. The length of an "increased" injection pulse ti is thus dependent on detection and program running times. On the other hand it is conceivable that cases could arise in which the "normally" calculated output ti remains too small because of extremely long program running times. The length of the first injection pulses (ti) following acceleration enrichment detection can thus be more dependent on the widely varying dynamics of the program than on the desired prescribed values of the practical application.
• It is also known (U.S. 4 126 107) to provide, upon detection of an acceleration enrichment condition, one or more additional injection pulses (RTIBA) of fixed length, independently of the primary injection pulses (ti). A disadvantage of this arrangement is that the additional injection pulses are of fixed length and do not take account of prevailing operating conditions.
• A further known system (U.S. 3 673 989) provides, upon detection of an acceleration enrichment condition, a plurality of extra fixed length pulses in between normally calculated injection periods, the number of these pulses depending upon the demanded level of engine acceleration. Such a system has the disadvantage that it does not take into account the prevailing engine load and/or engine speed.
• In a further known system, illustrated in Fig.3 of the accompanying drawings, a plurality of intermediate injections RTIBA are output in between and in addition to normally calculated injection periods ti (= t_L.FBA + ts) until the rotational speed of the engine has exceeded a threshold, which can be freely selected per datum. During this time, the intermediate injections RTIBA achieve an excess quantity of injected fuel. However, both the excess quantity as well as the break-off criterion, after fulfilment of which only normally calculated T_L Periods are output, are formed by relatively rough methods in this known technique, which do not adapt the fuel enrichment sufficiently accurately to the acceleration demanded.
• It is an object of the present invention to provide an acceleration enrichment arrangement which improves on the known arrangements and which is particularly suitable for use with injection systems of the type equipped with hot-wire air quantity detectors where the reaction times between hot-wire voltage (air requirement) and the calculation of the associated load t_L, as well as the calculated t_L and the output of ti using this value of t_L, are considerable, sometimes perhaps of the order of 120 ms so that, in the event of rapid transition operations, this can lead to driving errors, or depending on the dimensioning of the acceleration enrichment data, to poor exhaust gas emission conditions.
Advantages of the Invention
• The above object is achieved by adopting the features set forth in the characterising part of claim 1. This has the advantage that the first X acceleration enrichment injections are clearly defined, being dependent not on load (T_L) which takes some time to calculate, but rather on "load substitute variables" (such as engine speed n, hot wire voltage ULHM and change of hot wire voltage ΔULHM) which are available much more rapidly. X is a freely programmable datum. The initial injections do of course also depend, as in previous cases, on the engine temperature ν_mot.
Drawings
• The invention is described further, by way of example only, with reference to the accompanying drawings, in which:-
• Fig 1 is a graphical representation of the operation of one known arrangement for achieving acceleration enrichment (BA);
• Fig.2 is a graphical representation of the operation of an embodiment in accordance with the present invention; and
• Fig.3 is a graphical representation of the operation of a second known arrangement.
• In systems in accordance with the present invention, the reaction times which a computer requires to detect an actual basic duration of injection (= load) t_L are eliminated in that, once an acceleration requirement has been detected, initial injection pulses RTIBA are output in synchronism with the ignition pulses

  

  . The lengths of these initial pulses RTIBA are independent of engine load T_L but are arranged to be dependent upon "load substitute variables" such as the prevailing hot-wire voltage (ULHM), change in hot-wire voltage (ΔULHM) and engine speed (n). Thus, the load replacement variable RTIBA = f (ν_Mot, n, ULHM, ΔUHM). It will be noted that the latter variables are available at the instant of acceleration enrichment detection. The length of the initial injection pulses is obtained in the simplest way in that the values of tables, which are dependent on ν_mot, n, ULHM, ΔULHM and are filed in the data region of the system, are traced (in part without interpolation) and linked to one another. In this way, long calculations of the load are avoided.
• The maximum number of initial injection pulses RTIBA determined in this way is freely selectable. The length of the initial injections RTIBA, which are dependent on the motor temperature ν_mot, as well as on the "load substitute variables" of the speed n, ULHM, ΔULHM, can be determined very quickly by accessing the table. Thus, such initial injections can be provided for the next X 180° crankshaft rotations or X 360° crankshaft rotations (X being freely selectable). Subsequently, following completion of X crankshaft revolutions (180° or 360°), the "normally calculated" injection period ti is output again every 360° (crankshaft angle) in the normal manner in accordance with equation (l), i.e.: $${\text{ti}}_{\text{norm}}{\text{= t}}_{\text{L}}{\text{.FBA. πF}}_{\text{korr}}\text{+ ts}$$

  

  where πF_korr is a mathematical expression for the product of all other correction factors.
• However, should the "normally calculated" value of ti become larger than the "initial injections RTIBA" (load replacement variables), then tin_orm is immediately adapted, even if the preselected number of initial injections has not been reached. The dynamics of the control system is then once again able to cope with the external dynamic requirements.
• Thus, the first X acceleration enrichment output values are clearly defined and applicable virtually immediately. They are not dependent on load t_L, but on "load substitute variables", which are available more rapidly.
• Referring to Fig.2 of the drawings, in the illustrated case, three initial injections RTIBA occur before the normally calculated value of ti becomes greater than the initial pulses RTIBA, i.e. $${\text{ti > RTIBA = f (ν}}_{\text{Mot}}\text{, n, ULHM, ΔULHM)}$$

  
• The fourth injection pulse is then a "normally calculated" enrichment pulse in accordance with equation (1).
• In practice the following initial injections (RTIBA) have been found appropriate:

  

Claims (2)

1. A method of acceleration enrichment in an internal combustion engine fuel injection system of the type having a plurality of injection valves for the injection of fuel into the inlet manifold of the engine and which are adapted to be opened for variable periods (ti) every 360° of crankshaft rotation in dependence upon engine load conditions, a hot-wire air quantity sensor for use in calculating prevailing engine load conditions, and means for providing fuel enrichment (BA) by extra operation of the injection valves when a predetermined acceleration condition of the engine is detected,
characterised in that,
following detection of an acceleration enrichment requirement, X > 1 normal injections (ti) are replaced by initial injections (RTIBA), whose length is -except for the first initial injection - independent of the instantaneous engine load (tL), but depend upon engine variables detected at the time of detection of the acceleration enrichment requirement, the initial injections ending either when the predetermined number X has been reached or when the length of the normal injections (ti) becomes greater than the length of the inital injections.

2. A method of acceleration enrichment as claimed in claim 1, wherein the length of the initial injection or injections (RTIBA), dependent on the engine temperature as well as on the "load substitute variables" of the speed n, hot wire voltage ULHM, change in hot wire voltage ΔULHM, are determined from stored look-up tables.

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