EP0590181A1 - Method of determination of dwell of a primary circuit of an ignition system of a internal combustion engine - Google Patents

Abstract

Method for determining the dwell time of the primary circuit of an ignition coil in an ignition system of an internal combustion engine, the primary current of the ignition coil being compared with a threshold value. This threshold value is measured for each device before the ignition control system is first operated and stored in a non-volatile fashion. According to the time which is required for the primary current to reach this threshold value, the dwell time for the desired ignition current, which can be dependent on the engine speed and additionally on the operating state of the internal combustion engine, is calculated. <IMAGE>

Description

The invention relates to a method for determining the closing time of the primary circuit of an ignition coil in an ignition system of an internal combustion engine according to the preamble of claim 1 (DE-OS 30 34 440).

When operating an internal combustion engine with internal combustion, a control device with at least one ignition coil is used to generate the ignition sparks, the task of which is to switch on the primary current in the ignition coil in good time and to switch it off again at the time of ignition.

Taking the speed dynamics into account, the switch-on time of the primary current must be brought forward to ensure a sufficient ignition current value at the time of ignition so that so-called "acceleration misfires" are avoided. However, the primary current must not exceed a maximum value in order to prevent damage or destruction of the ignition system.

For example from DE-PS 29 03 978 it is known to control the closing time of the primary circuit depending on the operating voltage.

It is also known to limit the primary current to a predetermined value and to determine the closing time so that a predetermined duration of the current limitation is achieved (DE-OS 31 05 857).

From DE-OS 30 34 440 an ignition system is known in which the duration that the primary current takes to reach a definable threshold value, which is smaller than the primary current value at the time of ignition, is measured and from this, taking into account the measured acceleration, a value for the closing time is determined.

Although the circuits of these ignition control devices are designed in such a way that the threshold value or limit value of the primary current remain within their predetermined tolerance limits even in the case of component values at the limit of the permitted tolerances and, even in the worst case, enable a sufficient ignition current value, a current adjustment is usually carried out in order to to precisely determine the ignition current, for example by trimming (eg laser cutting) a resistor during the device test. Such adjustment work is time consuming and costly.

The object of the invention is therefore to develop a method, in the application of which the closing time of the primary circuit in the ignition control device can be determined with the required accuracy, without the need for expensive current balancing.

This object is achieved by the features mentioned in claim 1. Advantageous developments of the invention can be found in the subclaims.

Two embodiments of the invention are shown in the drawing and are explained in more detail below.

Figur 1

den prinzipiellen Aufbau einer Zündanlage und

Figur 2

ein Diagramm des Primärstroms über der Zeit und der Schließdauer über Drehzahl und Betriebszustand.

Show it:

Figure 1

the basic structure of an ignition system and

Figure 2

a diagram of the primary current over time and the closing time over speed and operating condition.

A _p-working with limitation of the primary current I ignition system of an internal combustion engine for a motor vehicle, there is according to Figure 1 from an unspecified executed ignition controller 1 and one contained in the latter controller 2, which to the positive terminal + U of the board voltage _b U _b through the primary winding 4 of an ignition coil 3 and a measuring resistor 7 to the negative pole -U _{b of} the on-board voltage flowing primary current I _p on and off via a switch 6 arranged between primary winding 4 and measuring resistor 7 and limited to a predetermined current limiting value I _BG , which is to be regarded as a threshold value for the onset of the current limiting .

The ignition control device 1 determines the ignition timing at which the primary current is interrupted and at one of the engine parameters P and the engine speed n and the operating state Z (start, training run, full load, etc.) of the internal combustion engine in a manner known per se Secondary winding 5 of the ignition coil 3 connected to the spark plug 8, an ignition spark arises, and starting from this the closing time for switching on the primary current I _p and transmits corresponding commands via a line la to the controller 2, which executes these commands by opening or closing the switch 6. The current limitation of the primary current I _p to the value I _{BG is carried} out by the controller itself by comparing the voltage drop across the measuring resistor 7 with a threshold value U _BG .

Due to the circuit design and the permitted tolerance values for the individual components of the ignition control unit, there is an initially unknown one without adjustment Value I _BG , at which the current limitation begins, which only has to meet the condition that it is above a minimum ignition current value I _min , which is certainly sufficient for an ignition of the fuel-air mixture.

In particular after the start and at low engine speeds and a low load, the internal combustion engine has a large acceleration capacity, so that the closing time in these areas must be increased as a precaution so that the required ignition current value I _{Z is} reached even at maximum acceleration. This acceleration capacity decreases with increasing engine speed n and becomes zero at maximum engine speed.

FIG. 2 shows a diagram which shows the relationship between primary current I _p (on the ordinate upwards) and the closing time (on the abscissa) and between this and the engine speed n (downwards on the ordinate).

When the primary circuit is switched on at the closing angle, the primary current I _p increases exponentially from the value zero to a saturation value (not shown), but is kept constant at this value when the current limit value I _{BG is} reached (curve A).

In the area of the lower two thirds of the entire primary current range, the temporal increase in the primary current can be regarded as sufficiently linear, cf. in Figure 2 the solid curve a with the dash-dotted line b. However, this also means that a certain ratio k of any ignition current value I _Z to this current limiting value I _BG lies on this curve a of the primary current I _p with sufficient accuracy.

des gewünschten Zündstromes I_Z zu diesem Strombegrenzungswert I_BG im Zündsteuergerät 1 nichtflüchtig abgespeichert. Für k < 1 ist I_Z < I_BG und für k ≧ 1 ist ${\text{I}}_{\text{Z}}{\text{= I}}_{\text{BG}}$

, wobei für k > 1 die Strombegrenzung wirksam wird.In the final test of each ignition control device, the device-specific value I _BG , at which the current limitation of the primary current begins, is measured and the ratio ${\text{k = I}}_{\text{Z.}}{\text{/ I}}_{\text{BG}}$

of the desired ignition current I _Z for this current limiting value I _{BG is} stored in a non-volatile manner in the ignition control device 1. For k <1 I _Z <I _BG and for k ≧ 1 ${\text{I.}}_{\text{Z.}}{\text{= I}}_{\text{BG}}$

, whereby the current limitation becomes effective for k> 1.

berechnet und der Schließwinkel so bestimmt, daß die Schließdauer im Zündwinkel, d.h., im Zündzeitpunkt endet.In operation of the ignition control device connected to the internal combustion engine, when certain operating states are reached, for example after completion of a starting process, when the on-board voltage has reached a static value, the threshold duration T _BG , which the primary current requires to rise from the value zero to the current limiting value I _BG , is exceeded a line 2a measured and stored. The required for reaching the predetermined Zündstromwertes I _Z T _Z closing duration is then according to the formula ${\text{T}}_{\text{Z.}}{\text{= k * T}}_{\text{BG}}$

calculated and the closing angle determined so that the closing period ends at the ignition angle, ie at the ignition point.

The dependency of the closing time T _Z and the threshold value time T _BG on the operating voltage U _b is thus also recorded and taken into account.

auch von unterschiedlichen Betriebszuständen Z der Brennkraftmaschine abhängig gemacht wird und die Tabelle zu einem Kennfeld k(n,Z) erweitert wird, denn es ist ohne weiteres einsichtig, daß im Startbetrieb andere Zündströme I_Z bzw. Schließdauern T_Z erforderlich sein können als im Leerlauf bzw. Schubbetrieb oder Teil- bzw. Vollast.A further advantageous and energy-saving improvement can be achieved in that the speed-dependent ratio ${\text{k (n) = I}}_{\text{Z.}}{\text{/ I}}_{\text{BG}}$

is also made dependent on different operating states Z of the internal combustion engine and the table is expanded to a map k (n, Z), because it is readily apparent that different starting currents I _Z or closing times T _Z may be required in starting operation than when idling or overrun or partial or full load.

können der Primärstrom I_p und das Verhältnis k auch - mit einem zum Zeitmaßstab proportionalen Maßstab - auf der Abzisse aufgetragen werden. Mit der auf der Ordinate nach unten aufgetragenen Drehzahl entsteht dann ein Diagramm für die Kurve k(n) bzw. mehrere Kurven k(n,Z), nach denen dann die aktuellen Schließdauern nach der Formel ${\text{T}}_{\text{Z}}{\text{= k(n) * T}}_{\text{BG}}$

oder ${\text{T}}_{\text{Z}}{\text{= k(n, Z) * T}}_{\text{BG}}$

berechnet werden können, welche über die betriebsspannungsabhängige Schwellwertdauer T_BG ebenfalls betriebsspannungsabhängig sind. So ist beispielsweise für den Betriebszustand Z₁ = Startvorgang eine Kennlinie k₁(Z₁) denkbar, die bis etwa 2000 U/min reicht und für den ganzen Bereich einen Wert k = 1,2 = konstant vorschreibt. Für den Betriebszustand Z₂ = Vollast kann die Kennlinie k₂(Z₂) den in Figur 2 gezeigten gestrichelten Verlauf haben, wobei das Verhältnis k von 1,2 bei etwa 1300 U/min kontinuierlich bis auf ${\text{k = I}}_{\text{min}}{\text{/I}}_{\text{BG}}$

bei der Maximaldrehzahl n_max abnimmt, entsprechend dem drehzahlabhängigen Beschleunigunsvermögen der Brennkraftmaschine. Eine dritte Kennlinie k₃(Z₃) könnte beispielsweise dem Betriebszustand Z₃ = Schubbetrieb zueordnet sein, wobei hier ${\text{k₃ = I}}_{\text{min}}{\text{/I}}_{\text{BG}}\text{= konstant}$

über den ganzen Drehzahlbereich ist. Weitere Kennlinien für andere Betriebszustände sind denkbar. Immer dann, wenn einer dieser Betriebszustände erreicht wird, oder wenn sich die Betriebsspannung U_b um einen bestimmten Betrag oder Anteil ändert, wird die Schwellwertdauer T_BG neu gemessen.According to the context ${\text{k = I}}_{\text{Z.}}{\text{/ I}}_{\text{BG}}{\text{= T}}_{\text{Z.}}{\text{/ T}}_{\text{BG}}$

the primary current I _p and the ratio k can also be plotted on the abscissa using a scale proportional to the time scale. With the speed plotted down on the ordinate, a diagram is then created for curve k (n) or several curves k (n, Z), according to which the current closing times are then based on the formula ${\text{T}}_{\text{Z.}}{\text{= k (n) * T}}_{\text{BG}}$

or ${\text{T}}_{\text{Z.}}{\text{= k (n, Z) * T}}_{\text{BG}}$

can be calculated, which are also dependent on the operating voltage depending on the operating voltage threshold duration T _BG . For example, a characteristic curve k 1 (Z 1) is conceivable for the operating state Z 1 = starting process, which extends to approximately 2000 rpm and prescribes a value k = 1.2 = constant for the entire range. For the operating state Z₂ = full load, the characteristic curve k₂ (Z₂) can have the dashed curve shown in FIG. 2, the ratio k of 1.2 at approximately 1300 rpm continuously up to ${\text{k = I}}_{\text{min}}{\text{/ I}}_{\text{BG}}$

decreases at the maximum speed n _max , corresponding to the speed-dependent acceleration capacity of the internal combustion engine. A third characteristic curve k₃ (Z₃) could, for example, be assigned to the operating state Z₃ = overrun, whereby here ${\text{k₃ = I}}_{\text{min}}{\text{/ I}}_{\text{BG}}\text{= constant}$

over the entire speed range. Further characteristic curves for other operating states are conceivable. Whenever one of these operating states is reached, or when the operating voltage U _{b changes} by a certain amount or proportion, the threshold duration T _{BG is} measured again.

A second exemplary embodiment of the method according to the invention relates to ignition systems without primary current limitation. In such ignition systems, a current limit value I _BG cannot be defined. Instead of controller 2 in FIG. 1, a comparator then takes place, in which the primary current is compared with a freely selected threshold value I _S. In FIG. 2, this is set, for example, to the smallest required ignition current I _min .

entsprechend ändern. Für ${\text{I}}_{\text{Z}}{\text{= I}}_{\text{min}}{\text{= I}}_{\text{S}}$

ergibt sich k = 1, für alle anderen I_Z > I_min ergibt sich k > 1.All further method steps are identical to those according to the first embodiment, only that the threshold value I _{S is} set in place of the current limit value I _BG and that the threshold value period T _S and the ratios now result instead of the current limit period T _BG ${\text{k = I}}_{\text{Z.}}{\text{/ I}}_{\text{S}}$

change accordingly. For ${\text{I.}}_{\text{Z.}}{\text{= I}}_{\text{min}}{\text{= I}}_{\text{S}}$

k = 1, for all other I _Z > I _{min there} is k> 1.

This method according to the second exemplary embodiment can also be applied to ignition systems which, although they have a primary current limitation, are only intended to prevent damage and do not operate during normal operation of the internal combustion engine.

The determination of the closing period T _Z can be recalculated for each ignition period or only if the ratio k or the threshold period T _BG or T _{S has} changed.

Claims (7)

Method for determining the closing time of the primary circuit of an ignition coil in an ignition system of an internal combustion engine, with an ignition control device, in which the primary current is compared with a threshold value (IS),
characterized, - That the device-specific threshold value (IS, IBG) is measured and the ratio ( $\text{k = IZ / IS}$

respectively. $\text{k = IZ / IBG}$

) at least one predetermined ignition current value (IZ) for this threshold value (IS, IBG) is stored in a non-volatile manner in the ignition control device, - That in operation of the internal combustion engine when certain operating states or at certain time intervals, the threshold value duration (TS, TBG), which the primary current needs to rise from zero to the threshold value (IS, IBG), is measured and stored, and - That the closing time (TZ) to reach the predetermined ignition current value (IZ) according to the formula $\text{TZ = k * TS}$

respectively. $\text{TZ = k * TBG}$

is calculated. Method according to claim 1, characterized in that the ratio (k (n)) is dependent on the speed (n) of the internal combustion engine. Method according to Claim 2, characterized in that the ratio (kz (n)) is additionally dependent on the operating state (Z) of the internal combustion engine. Method according to Claim 1, characterized in that the starting process, the end of a starting process, idling, coasting operation, partial or full load are specific operating states. Method according to Claim 1, characterized in that a change in the operating voltage (UB) by a predetermined amount or proportion is a specific operating state. Method according to claim 1, characterized in that the closing period (TZ) is calculated for each ignition period. Method according to Claim 1, characterized in that the closing time (TZ) is recalculated after each change in the ratio (k) or the threshold value time (TS, TBG).

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