EP0547258B1 - Ignition device for internal combustion engine - Google Patents

Description

The invention relates to an ignition device for internal combustion engines according to the preamble of claim 1 (EP-A-0470277).

From DE-A-27 59 154 an ignition device for internal combustion engines is known in which the spark discharge duration is regulated to a predetermined value by comparing the time period within which the spark discharge current has dropped to a predetermined discharge current level with a predetermined target value and depending on the comparison result, the closing time of the primary circuit of the ignition coil is readjusted. This is intended to compensate for changes in the load on the spark plug if a shunt resistance is formed as a result of the spark plug electrodes being soiled or if the electrode spacing is increased by erosion.

From DE-A-21 45 285 it is known that the initial current intensity in the ignition spark is important for igniting the fuel-air mixture in a cylinder.

However, this peak value and the slope of the falling curve of the spark discharge current decrease with increasing contamination or enlargement of the electrode spacing, so that the available ignition energy can become ever smaller without readjusting the closing time for the object according to DE-A-27 59 154 to result.

In contrast, the object of the invention is to design the generic ignition device in such a way that such spark plug loads and, moreover, temperature effects of the ignition coil and manufacturer-specific differences in the ignition coils and spark plugs, ie the ignition circuit as a whole, can be recognized and compensated for.

This object is achieved by the features mentioned in the characterizing part of claim 1.

Particular embodiments of the invention are specified in dependent claims 2-7.

The peak value of the current flowing in the spark plug or secondary circuit at the time of ignition or shortly thereafter is compared with a target value by regulating the closing time. If the peak value is higher or lower than the specified target value, which in this exemplary embodiment depends on the engine speed and engine load, as a result of some cause - transmission ratio or quality of the ignition coil, plug or cable condition, contamination, contact wear, etc., the closing time of the primary circuit becomes shorter or longer to bring the actual value back to the setpoint.

This ensures a sufficient starting or peak value of the ignition current, which is required for reliable mixture ignition, regardless of the further course of the ignition current.

An embodiment of the invention is explained in more detail with reference to the drawing.

The only figure in the drawing shows a basic circuit diagram of the ignition device. The primary winding 1 of an ignition coil SP is controlled via a switching transistor 3. The first connection of the secondary winding 2 becomes one or more spark plugs ZK and the second connection is connected via a sensor 4 to the negative pole of a supply voltage source, not shown. A further secondary winding of possible further ignition coils, the second connections of which lead to the common point P, is indicated by dashed lines. From this point P, a measuring line 8 leads via a peak value rectifier 14 to a connection pin 12 of a microprocessor 16.

Up to this point, the circuit corresponds to the known ignition device from which the invention is based.

The microprocessor 16 has the function of a software Ignition control circuit on. The most important variables of an ignition control are the ignition timing ZZP and the closing time SD of the primary circuit. The start of closing, based on the crankshaft position of the internal combustion engine, can then be determined from both variables.

The ignition point is determined in a manner known per se from various operating parameters of the internal combustion engine and is of no further interest here.

The start and end of ignition determine the start and end of a control pulse ST which reaches the base of the switching transistor 3 and opens it, so that current can flow in the primary winding 1 of the ignition coil SP.

The peak value Ix of the secondary-side ignition current occurring when a specific cylinder x (index x = 1... Z, where z is the number of cylinders) is stored in the peak value rectifier 14. The value of the closing time consists of a pilot control value V, which is weighted with an adaptation value fakx.

In a first memory calculation 5, a plurality of pilot control values V are stored in a table or in a characteristic diagram as a function of at least one operating parameter, for example the engine speed N, the engine load LM, the engine temperature T or, as in this exemplary embodiment, the supply voltage UB.

In a second memory area 6, setpoints S for the peak value of the ignition current are stored in a map, depending on the engine speed N and engine load (measured via the air mass LM).

Actual value Ix and setpoint S are transmitted at a suitable time to a first arithmetic circuit 7 (these and other arithmetic circuits are included in the software of the microprocessor 16 in the computer program), which one of the difference between the two Adapted value fakx calculated values, which is then stored in a buffer 9. The assignment can be additive, multiplicative or other.

This buffer 9 has a memory location for each cylinder x of the internal combustion engine, in which the calculated adaptation value fakx is stored in a cylinder-selective manner until it is further processed for the next ignition process of this cylinder.

Before the intermediate storage, a further program step, shown in the drawing as a further arithmetic circuit 11, is also used to check whether the calculated value fakx is greater than a predetermined upper (fakmax) or less than a predetermined lower limit fakmin. If this is the case, fakx is set to this limit value before further processing and then buffered. In order to determine the next closing time SDx of this cylinder x, the currently valid pilot control value V and the adaptation value fakx are transferred from their memories 5 and 9 to a second arithmetic circuit 10, where they are combined with one another - for example, additively or multiplicatively - to the closing time SDx of the cylinder x.

In order not to reach the limit of the computing capacity of the microprocessor 16 at high engine speeds N - the latter has to perform a large number of calculations - it is provided in this exemplary embodiment that the cylinder-selective calculation of the adaptation value fakx is carried out only below a predetermined engine speed limit value NG and when or If this limit is exceeded, only calculate the adaptation value fakl of a certain first cylinder (x = 1) and use it for all other cylinders during a complete ignition cycle (2 revolutions of the crankshaft in a four-stroke engine).

For this purpose, a correction value korx is calculated in the speed range below the engine speed limit value NG for each additional cylinder (x = 2 ... z), which is the ratio fakx / fakl is assigned, and stored in a further memory area 13. These values remain saved even after the engine is switched off.

Above the engine speed limit NG, these correction values remain unchanged and are used to form the closing duration values SDx. The calculation of new correction values is only started after a predetermined number of engine revolutions after engine start.

Vor der Ausgabe der auf diese Weise ermittelten Schließdauerwerte SDx wird in diesem Ausführungsbeispiel noch geprüft, ob diese größer als ein vorgegebener oberer (SDmax) oder kleiner als ein vorgegebener unterer Grenzwert (SDmin) sind. Diese Grenzwerte können vorzugsweise selbst von wenigstens einem Betriebsparameter abhängig gespeichert sein.The closing times are thus calculated as follows:

Before the closing duration values SDx determined in this way are output, a check is also carried out in this exemplary embodiment to determine whether they are greater than a predetermined upper limit value (SDmax) or less than a predetermined lower limit value (SDmin). These limit values can preferably be stored as a function of at least one operating parameter.

If the closing duration value SD <SDmin is too small, reliable ignition is not guaranteed and if the closing duration value SD> SDmax is too high, there is a risk of the ignition coil becoming too hot.

Claims (7)

1. Ignition for internal combustion engines, having at least one ignition coil (SP) with a secondary winding (2) which is divided from the primary winding (1) which is part of the primary circuit, the first terminal of the secondary winding (2) leading directly to one spark plug (ZK) or via a distributor to a plurality of spark plugs (ZK), the second terminal of the secondary winding (2) of the one ignition coil or of all the ignition coils leading to a common point (P) and from the latter to the negative pole of a supply voltage source via a sensor (4), and with a measurement line (8) which leads from the common point (P) via a peak-value rectifier (14) to an ignition control circuit which is contained in a micro-processor (16), characterized in that the ignition control circuit

   - has a first memory area (5) in which pilot control values (V), which are assigned to at least one operating parameter, for the closing duration (SD) of the primary circuit of the ignition coil (SP) are stored,

   - has a second memory area (6) in which set values (S), dependent on at least one operating variable (N, LM) of the internal combustion engine, for the peak value of the ignition coil (I) are stored,

   - has a first computing circuit (7) to which the actual value (I), stored in the peak-value rectifier (14), of the peak value of the ignition current and the set value (S) are fed and which calculates therefrom an adaptation value (fak) which is assigned to the difference between the set value and actual value and is buffered in a third memory area (9), and

   - has a second computing circuit (10) which changes the pilot control value (V) as a function of the calculated adaptation value (fak), the changed pilot control value corresponding to the closing duration (SD).
2. Ignition device according to Claim 1, characterized in that an upper limit value (fakmax) and a lower limit value (fakmin) are prescribed for the adaptation value (fak).
3. Ignition device according to Claim 1, characterized in that a limit value (NG) for the engine rpm is prescribed, below which limit value (NG) the adaptation value (fakx) for each cylinder (x = 1 ... z) of the internal combustion engine is determined separately, i.e. selectively for each cylinder and above which it is only determined for a specific first cylinder (x = 1) but is assigned to all the other cylinders (x = 2 ... z), and in that a correction value (korx) is calculated for all the other cylinders (x = 2 ... z) below the limit value (NG) for the engine rpm and stored, which correction value (korx) is assigned to the ratio fakx/fak1 and which, above the limit value (NG) of the engine rpm, is logically connected additively or multiplicatively with the adaptation value (fak1) of the specific first cylinder (x = 1) to form an adaptation value ( $\text{fakx = fak1 * korx}$

   

   ).
4. Ignition device according to Claim 3, characterized in that the calculation of the correction value (korx) for the other cylinders (x = 2 ... z) is not started until after a prescribed number of revolutions of the engine after the engine has started.
5. Ignition device according to Claim 1, characterized in that an operating parameter for the pilot control value (V) is the supply voltage (UB).
6. Ignition device according to Claim 1, characterized in that an upper limit value (SDmax) and a lower limit value (SDmin) are prescribed for the value (SDx) of the closing duration.
7. Ignition device according to Claim 6, characterized in that at least one of the limit values (SDmax, SDmin) is dependent on at least one operating parameter.

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