EP0390667B1 - Electronically controlled internal-combustion engine fuel injection supply device - Google Patents

Description

The invention relates to fuel supply devices for an internal combustion engine, of the type which include electrically controlled injectors delivering fuel under pressure into the engine intake manifold and an electronic control circuit connected to sensors for operating parameters of the engine, in particular of the speed of the latter, supplying the injector with periodic signals of variable duty cycle as a function of said parameters.

The invention applies to all so-called indirect injection devices, that is to say delivering fuel into the intake manifold to the engine (and not directly into the combustion chambers). The injection is multipoint, that is to say by several injectors controlled either all simultaneously, or in groups, or even individually, which each open into a branch of the pipe upstream of a corresponding intake valve.

As a general rule, indirect injection devices function as synchronous during periods when the engine is running at steady speed. A given injector is actuated when the motor shaft passes in a determined orientation. In the case of multi-point injection, by injectors controlled individually or in groups, the various injectors (or the various groups) are generally controlled with a relative phase shift, to limit variations in the fuel supply pressure.

The electronic circuits controlling the injection devices must be provided to ensure satisfactory operation during transient phases of operation. For example, it has already been proposed to replace synchronous injection with asynchronous injection to supply the engine with the additional fuel it needs to accelerate (US-A-4,573,443). It has also been proposed to switch from synchronous operation to asynchronous operation when the engine operating parameters lead to injector control pulses deemed too low in the case of a synchronous injection (US-A-4,200,063) .

Also known (US-A-3,628,510) is an injection system having an analog control circuit, without digital memory. During engine start-up, the circuit adds control pulses to normal pulses, to increase the flow rate supplied to the engine.

The invention aims to solve a different problem, that of starting the engine and, possibly, of the initially cold engine warming up, which requires increasing the quantity of fuel supplied to the engine. Various solutions have already been proposed. In particular, an additional cold starting injector was used which sprays fuel under pressure very finely into the manifold: this solution requires an additional injector and a large fraction of the atomized fuel wets the walls of the intake manifold, which is unfavorable. , especially when the temperature is very low and the fuel remains in the state of adherent droplets. A more advantageous solution consists, during the launch phase, of injecting fuel at low pressure continuously into the manifold (FR-A-2 332 431). But even when the fuel jet is sent directly to the tail of the intake valves to cause it to burst, the spraying may remain insufficient.

The invention aims to provide a device of the above defined type which better meets the requirements of practice than those known to date, in particular in that it facilitates starting the engine, while the engine is running at low speed driven by the starter, which would result in synchronous operation at a low and irregular frequency.

For this, the invention starts from the observation that, when an electromagnetic control injector is closed, a particularly intense spraying of the fuel jet passing through the injector occurs. This observation has already been made in the document BOSCH, "Technische Unterrichtung" Motronic, 1. edition, 1983, p. 20-24, which describes a device according to the preamble of claim 1, as well as in EP-A-0 231 887, in which synchronous injection pulse trains are used, the pulse train duration of which is a decreasing function of the engine temperature, while the duration of each pulse is an increasing function of that same temperature. Consequently, the invention proposes a device according to the characterizing part of claim 1.

Thanks to this arrangement, the number of injector closings per unit of time is greatly increased. In practice, it will be sought to arrive at a number of opening and closing cycles as high as possible insofar as this number remains compatible with a sufficient flow rate of the injector and with the minimum duration of the cycle. In practice, we will generally be led to adopt a cycle time (opening time plus closing time) not exceeding 60 ms.

Thanks to the increased frequency of the cycles, the spraying is improved and a satisfactory engine launch can be obtained with a lesser amount of fuel, which, among other consequences, significantly reduces pollution.

As a general rule, it will be necessary to limit the duration of the asynchronous injection operation defined above, in particular to avoid "drowning" the engine. The maximum duration of the asynchronous operation described above is advantageously a function decreasing engine temperature. The cycle time and the opening duty cycle of the injectors are controlled as a function of the initial temperature of the coolant. The values to be given to the duty cycle, to the duration of the injection cycle, and to the maximum duration of the asynchronous injection are stored in the form of tables stored in read only memory.

• la Figure 1 est un schéma de principe montrant un dispositif d'injection multipoint auquel est applicable l'invention ;
• la Figure 2 est un diagramme montrant les phases successives d'une séquence de démarrage représentative, lors de la mise en oeuvre d'un dispositif selon l'invention ;
• la Figure 3 est un diagramme faisant apparaître les instants successifs d'injection, au cours de la phase pendant laquelle l'injection est asynchrone ; et
• la Figure 4 est un organigramme de principe du procédé.

The invention will be better understood on reading the following description of a particular embodiment, given by way of non-limiting example. The description refers to the accompanying drawings, in which:

• Figure 1 is a block diagram showing a multipoint injection device to which the invention is applicable;
• Figure 2 is a diagram showing the successive phases of a representative start-up sequence, when implementing a device according to the invention;
• Figure 3 is a diagram showing the successive instants of injection, during the phase during which the injection is asynchronous; and
• Figure 4 is a flow diagram of the process.

The multipoint injection device shown in Figure 1 has a known general constitution. It comprises an air supply circuit on which is interposed a throttle member 10 controlled by the conductor and provided with an opening sensor 12 providing an electrical output signal representative of the opening angle of the throttling organ. Usually the throttle is mounted in a block called "throttle body" 14 which can contain two organs controlled simultaneously. The air path comprises, downstream of the body 14, a tube 15 with several branches each opening upstream of the intake valve 16 of a combustion chamber of the engine.

In the illustrated embodiment, an additional air duct 18 provided with an electrically controlled valve 20 makes it possible, during certain phases of operation, and in particular at start-up, while the member 10 is closed, to bring into the air tubing which bypasses the throttle body 14.

• une sonde de température d'air 22 fournissant un signal électrique représentatif de la température de l'air arrivant au corps de papillon ;
• un capteur 24 de pression d'air dans la tubulure 15, fournissant un signal qui, combiné à celui du capteur d'ouverture 12 ou à celui donnant la vitesse du moteur, permet de calculer le débit d'air admis au moteur.

The device shown also comprises:

• an air temperature sensor 22 providing an electrical signal representative of the temperature of the air arriving at the throttle body;
• an air pressure sensor 24 in the pipe 15, providing a signal which, combined with that of the opening sensor 12 or that giving the engine speed, makes it possible to calculate the air flow admitted to the engine.

The sensors 12 and 24 can be replaced by a direct flow measurement element.

A fuel supply circuit includes an electric pump 26 controlled by a relay 28 actuated when the ignition contact 50 is closed. The pump 26 feeds, via a filter 30 and a ramp 32, the injectors 34 of which only one is shown and which are arranged immediately upstream of the corresponding intake valves 16. The fuel pressure sent to the injectors is maintained, by a pressure regulator 36 provided with a return pipe to the tank 38, to a value which can be fixed or a function of the pressure prevailing in the tubing, measured by the sensor 24.

• une sonde de température de liquide de refroidissement 40,
• un capteur de position et de vitesse du moteur, constitué par un capteur 42 fournissant une impulsion électrique à chaque passage d'une dent de la couronne 44, présentant une brêche permettant de repérer une position angulaire déterminée de la couronne,
• éventuellement, une sonde (non représentée) de mesure de la teneur en oxygène dans le collecteur d'échappement, lorsque le dispositif est prévu pour assurer une régulation bouclée.

The device shown in Figure 1 also includes additional operating parameter sensors, consisting of:

• a coolant temperature sensor 40,
• a position and speed sensor of the motor, constituted by a sensor 42 supplying an electrical impulse with each passage of a tooth of the crown 44, having a gap making it possible to locate a determined angular position of the crown,
• optionally, a probe (not shown) for measuring the oxygen content in the exhaust manifold, when the device is designed to ensure looped regulation.

• la température ϑl du liquide de refroidissement du moteur, fournie par la sonde 40,
• la température d'air ϑa, fournie par la sonde 22,
• l'angle α d'ouverture du papillon, fourni par le capteur 12,
• la vitesse du moteur, sous forme d'une série d'impulsions à fréquence variable, fournies par le capteur 42,
• la pression absolue dans la tubulure, fournie par le capteur 24.

The injectors are controlled by an electronic circuit 46 supplied by the storage battery 48 as soon as the ignition contact 50 is closed. This electronic circuit supplies the injectors 34 with electrical control signals in the form of rectangular pulses, of variable duty cycle. In the embodiment shown, it receives input signals representative of:

• the temperature ϑl of the engine coolant, supplied by the probe 40,
• the air temperature ϑa, supplied by the probe 22,
• the opening angle α of the butterfly, supplied by the sensor 12,
• the speed of the motor, in the form of a series of variable frequency pulses, supplied by the sensor 42,
• the absolute pressure in the tubing, supplied by the sensor 24.

We will not describe here the operation of the engine in steady state, because it can be conventional. During this operating phase, the electronic circuit 46 provides each injector 34 with a opening pulse synchronized with the control of the corresponding intake valve 16 and of duration as a function of the operating parameters, and in particular of the air flow rate controlled by the throttle member 10. The law of variation of the duration of each control pulse is fixed by a program stored in circuit 46, in a read only memory.

According to one embodiment of the invention, the device 46 contains a cold start program, also stored in a read only memory which causes operation in three successive phases, the last two of which can be omitted in the event of engine launching. still at its normal operating temperature.

• lorsque la vitesse de rotation N du moteur atteint une valeur prédéterminée N₀ indiquant que le moteur est autonome (généralement entre 200 et 400 t/mn), ou
• au bout d'un intervalle de temps déterminé, choisi de façon à éviter de noyer le moteur en cas de lancement avorté, cette durée est fonction de la température du liquide de refroidissement,
  la durée la plus courte étant prise en considération.

Phase I begins as soon as the engine is driven by the starter (the start time being indicated by the signals from sensor 42 or the starter supply) and stops:

• when the speed of rotation N of the motor reaches a predetermined value N₀ indicating that the motor is autonomous (generally between 200 and 400 rpm), or
• at the end of a determined time interval, chosen so as to avoid flooding the engine in the event of an aborted launch, this duration is a function of the temperature of the coolant,
  the shortest duration being taken into account.

The program memorized in circuit 46, shown diagrammatically in FIG. 4, must prohibit returning to phase I when one has left it to pass to phase II or III, unless complete re-initialization, implying an engine stop.

• ayant une durée sélectionnée parmi quelques valeurs seulement, et choisie uniquement en fonction de la température initiale ϑl, et
• dont la période de récurrence est égale à n fois une période de base d'environ 8 ms, n ne pouvant également prendre que quelques valeurs.

A solution allowing both to adapt the injection times to the initial state of the engine and to keep a simple constitution of the circuit 46, consists in providing the circuit 46 so that it provides, in phase I, rectangular signals

• having a duration selected from only a few values, and chosen only as a function of the initial temperature ϑl, and
• whose recurrence period is equal to n times a base period of approximately 8 ms, n also being able to take only a few values.

The opening duty cycle will be chosen all the greater as ϑl is lower and we will be led to adopt a longer recurrence period for the lower values of ϑl.

For example, the values in the table below can be adopted (the injection duration, the recurrence period and the maximum duration chosen being those corresponding, in the table, to the value of ϑl closest to the measured temperature). ϑl (° C) Duration of injection Recurrence period Maximum duration t₀ of phase I -30 (and below) 32 ms 48 ms 4.0 s -20 32 ms 48 ms 2.6s -10 24 ms 48 ms 2.0s 0 16 ms 48 ms 1.5 s 10 8 ms 32 ms 1.1 s 20 6 ms 32 ms 0.7 s 30 5.75 ms 32 ms 0.6 s 40 5.75 ms 32 ms 0.6 s 50 5.0 ms 32 ms 0.5 60 4 ms 32 ms 0.5 s 70 3 ms 32 ms 0.5 s 80 (and above) 2 ms 32 ms 0.5 s

To dewater the engine in the event of a starting fault due to an excess of fuel, the circuit 46 can be provided to substitute, for the asynchronous injection, a synchronous injection of normal operation if the throttling member 10 is brought to its full opening position, detected by sensor 12.

FIG. 3 shows, by way of example, a possible distribution over time of the injections, at a constant recurrence frequency (second line), with respect to the signals (first line) supplied by the sensor 42 and whose frequency is variable from makes the engine rotate irregularly during launch. The instants of ignition (third line from the top) remain synchronized with the rotation of the motor shaft.

Start-up phase II begins when the engine reaches a speed indicating that it is operating autonomously or after a fixed period of time. It lasts for a determined number of engine operating cycles or, which comes to the same thing, until the engine has passed through its top dead center M successive times.

During this phase II, the injection is synchronous but the duration of each injection is equal to the duration of injection resulting from the calculation carried out by the circuit 46 for the steady state at engine temperature (generally lower than the temperature normal regime), with a multiplicative or additive correction.

The method of determining the "base time", that is to say the duration of each synchronized injection as a function of ϑl during heating, will be described below.

The number M of cycles can be chosen in particular as a function of the characteristics of each type of engine: a duration of between 0 cycles (some motors suitable for operation without phase II) and 255 cycles will generally give good results. During this phase II, the multiplicative or additive correction will be maintained at a constant value. The multiplier coefficient will generally be between 1 and 3.

Phase III begins when phase II expires. During this phase, the circuit 46 decreases according to a linear law or approaching a linear law, the multiplicative or additive correction, depending on the number of engine cycles. One solution which often gives good results consists in decrementing the correction by 1 / 256th of its original value at each cycle, until canceled.

Phase III ends when the multiplicative correction becomes equal to 1 or the additive correction becomes equal to 0.

From this instant, the circuit 46 resumes operation of the conventional type, implying an enrichment with respect to the stoichiometric fuel / air ratio which is a decreasing function of the temperature.

Beyond phase III, the engine must still receive, in order to function properly at idle, a flow rate of air-fuel mixture greater than the flow rate required for idling at normal operating temperature. In addition, this mixture must be enriched in relation to the stoichiometric content. Numerous laws for selecting the flow rate and the enrichment corresponding to particular engines are already known.

In practice, the increase in the quantity of mixture supplied to the engine will be obtained by opening the valve 20 placed in bypass on the butterfly block, the electronic control circuit automatically adapting the flow of fuel injected to the flow of air, with a enrichment fixed for example by a table map giving, for each engine temperature, a specific fuel / air ratio.

Claims (10)

1. A fuel supply device operating by indirect multipoint injection for an internal combustion engine, comprising one injector (34) per engine cylinder and an electronic control circuit (46) connected to sensors (12, 22, 24, 40, 42) responsive to operating parameters of the engine, particularly the engine speed (42) and temperature (40), and so devised as to apply to each injector (34) electrical control signals which, during normal engine operation, are periodic signals delivered in accordance with a normal synchronous law in synchronism with the engine rotation, and of which the duty ratio defined by the ratio of the injection time of the injector (34) to the signal repetition period is a function of said parameters and which, during a starting phase of the engine, beginning as soon as the engine is driven by the starter and ceasing when the speed of rotation (N) of the engine reaches a predetermined value (No), without being able to exceed a given time interval (to), are signals which are repeated a number of times per engine revolution, and of which the injection time depends on the temperature of the engine cooling liquid, so as to inject an increased quantity of fuel required for starting, characterised in that during the starting phase the signals are applied continuously and are only non-synchronous with a frequency very much greater than that that the normal synchronous control law would give, the repetition period and the said duty ratio of said non-synchronous signals and the said given time interval (to) of the starting phase being stored in a table, the repetition period being longer for the lowest values of the initial temperature of the engine cooling liquid and the said duty ratio and the said given time interval (to) of the starting phase each being limited to a value which decreases with increasing initial temperature of the engine cooling liquid.
2. A device according to claim 1, characterised in that the said predetermined speed of rotation value (No) is between 200 and 400 rpm and the said given time interval (to) assumes one of a number of values each of which remain constant over an initial temperature interval of the engine cooling liquid, the said values decreasing from one temperature interval to the next with increasing initial temperature of the engine cooling liquid.
3. A device according to claim 1 or 2, characterised in that the said repetition period of the non-synchronous signals is not more than 60 ms and assumes one of a number of values each of which remain constant over an initial temperature interval of the engine cooling liquid, the said values decreasing from one temperature interval to the next with increasing initial temperature of the engine cooling liquid.
4. A device according to any one of claims 1 to 3, characterised in that the said duty ratio is selected to be increasingly greater with increasingly reduced initial temperature of the engine cooling liquid.
5. A device according to any one of claims 1 to 4, characterised in that in order to avoid flooding the engine in the event of a start-up failure due to an excess of fuel, the electronic circuit (46) is adapted to replace the non-synchronous injection by a synchronous normal operation injection if a throttle member (10) of an air supply circuit of the device is brought to its fully open position detected by a sensor (12) connected to the circuit (46).
6. A device according to any one of claims 1 to 5, characterised in that the electronic circuit (46) is so devised that the starting phase (phase 1) is followed by a second phase (phase 2) of synchronous injection with an injection time equal to the injection time resulting from the calculation effected by the circuit (46) for permanent operation at the engine temperature, with a multiplicative or additive correction, for a predetermined number (M) of engine operating cycles.
7. A device according to claim 6, characterised in that the electronic circuit (46) is so devised that during the said second phase the multiplicative or additive correction is kept at a constant value.
8. A device according to claim 6 or 7, characterised in that the electronic circuit (46) is so devised that the second phase (phase 2) is followed by a third phase (phase 3) during which it reduces the multiplicative or additive correction in dependence on the number (M) of engine cycles.
9. A device according to claim 8, characterised in that the electronic circuit (46) is so devised as to control the reduction of the multiplicative or additive correction in accordance with a linear law or one which approaches a linear law, until the multiplicative correction becomes equal to 1 or the additive correction becomes equal to 0, this corresponding to the end of the third phase.
10. A device according to claim 9, characterised in that the electronic circuit (46) is so devised as to reduce the correction by a fraction of its original value on each engine cycle until the correction is cancelled out.

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