EP0547260B1 - Dwell time monitoring for an ignition end stage in an internal combustion engine - Google Patents

Description

The invention relates to an ignition device for internal combustion engines according to the preamble of claim (DE-A-39 24 129).

A monitoring device for the closing duration of the ignition coil primary circuit is known from the prior art mentioned, in which the limiting duration of the closing time is variably set as a function of the supply voltage.

The current intensity of the primary circuit, which is dependent on the closing time and reached at the time of ignition, determines the current intensity and voltage of the spark at the spark plug with other factors.

The switch-on time of the primary circuit, based on the crankshaft position of the internal combustion engine, is determined from the quantities of ignition timing and closing time calculated in a manner known per se.

If the closing times are too long, the ignition coils and switching transistors are extremely heavily loaded, which can lead to destruction by excessive temperatures.

Too long closing times can occur if the crankshaft position transmitter fails after the primary circuit is switched on, if software errors of the microprocessor forming the ignition device occur or if large negative engine speed gradients occur during the closing time.

Monitoring devices are used to avoid closing times that are too long. These facilities should respond as quickly as possible and end the closing time if this Respond as quickly as possible and end the closing time if it lasts too long.

In the known monitoring device, the monitoring or limitation period is set depending on the supply voltage. This leads to disproportionately long monitoring times, especially at high engine speeds, since the greatest closing time, that is to say when the engine is idling, must be taken into account in the case of a dependency on the supply voltage alone. In addition, a certain memory area in the microprocessor is required for the storage of the supply voltage-dependent table of the individual values of the monitoring duration.

It is an object of the invention to develop the known ignition device in such a way that in no case can unnecessarily long monitoring times occur and that memory space occupancies in the microprocessor can be largely saved.

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

The closing time SD of modern ignition devices is not only dependent on the supply voltage U _BATT , but also on the engine speed n, on the engine load L and on other influencing variables w: SD = f (U _BATT , n, L, w).

At high engine speeds, the closing time is additionally limited, since overlapping switch-on times are not possible with a single existing ignition coil and are not desirable with several ignition coils.

According to the invention, the monitoring period is therefore set as a function of the closing period and is always only slightly longer than this. For example, by multiplying the Closing time with a constant value K (for example 1.25), this operation can be carried out very easily. This requires an extremely small amount of memory (one or a few program lines).

The invention is explained in more detail with reference to the drawing.

In the drawing, the timing of the closing time SDx and the monitoring time ÜDx for the cylinder x is one Internal combustion engine schematically, but not to scale.

Line a shows the processed pulses KR of the position transmitter connected to the crankshaft of the internal combustion engine, the distances between which correspond to a specific crankshaft angle. These pulses are used to determine the crankshaft position and to calculate the speed and acceleration of the engine crankshaft. As a rule, the counting for each cycle (2 revolutions of the crankshaft corresponding to 720 ° KW) begins at the top dead center (not shown here) at the end of the compression stroke of a specific cylinder.

Line b shows the computing times Ax for the cylinder x in question and Ay for the following cylinder y. During the time Ax, the ignition time, closing duration and start of closing for the ignition of the cylinder x are determined or calculated in a manner known per se from various operating parameters of the internal combustion engine in the microprocessor (not shown) and corresponding data are output to so-called compare registers. A register R1, R3 is loaded with a certain number each for the start of ignition and the ignition timing during the calculation time Ax and is counted down to zero with the internal clock of the microprocessor from a predetermined crankshaft position (time B for the start of closure; time D for the ignition timing). The corresponding command (closing or opening of the primary circuit) is carried out at the moment when the counter reading reaches zero (time point C for the start of closing; time E for the ignition time).

The respective counter reading of registers R1 and R3 is shown in drawing c.

Line d shows the closing time SDx, which begins at time C when register R1 expires and ends at time E when register R 3 expires.

During the computing time Ax, a further compare register R2 is also loaded (line e), which is started when register R1 expires, ie at time C, at the start of the closing period SDx. This register is set in such a way that its running time, determined by the internal microprocessor clock, corresponds to the monitoring time UDx, for example 1.25 times the closing time SDx.

Due to one of the errors already mentioned (failure of the pulses of the crankshaft position transmitter after the start of register R1; software error of the microprocessor; large negative engine speed gradients in the CD area, etc.), it can happen that register R3 is not started in time or not at all .

If the primary circuit is still switched on at time F when register R2 expires (shown in dash-dotted lines in line d), then the circuit is opened and ignition is initiated at this point in time, indicated by a dash-dotted lightning symbol at time F (in contrast to the lightning symbol for the timely one Ignition point in time E).

Then the process is repeated for the next cylinder y, starting with the calculation time Ay and so on, for all cylinders of a cycle (720 ° KW) and for further cycles.

The monitoring period, as calculated above, implicitly takes into account all dependencies on the supply voltage, speed and load and any other parameters from which the closing period is determined.

Claims (2)

1. Ignition device for an internal combustion engine having a monitoring device for the dwell time (DT) of the primary circuit of at least one ignition coil which is actuated simultaneously with the start of closing (C) of the primary circuit and is opened again after a monitoring time (MT) of the primary circuit has expired, if the said primary circuit is still closed at this time, characterized in that the monitoring time (MT) is a function MT = f(DT) of the dwell time (DT) and is only slightly greater than it.
2. Ignition device according to Claim 1, characterized in that the monitoring time (MT) for each cylinder (x, y ...) is a function of the dwell time (DT) identified for this cylinder (x, y ...).

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