EP0640761B2 - Controllable ignition system - Google Patents

Description

The invention relates to a method for controlling an ignition system for internal combustion engines according to the preamble of claim 1.

A generic ignition system is from the DE-OS 39 28 726 known, compared to conventional Ignition systems, for example so-called transistor ignitions with static high-voltage distribution, has the advantage that small and therefore cost-effective Ignition coils are used. Furthermore, according to the o. G. Document ensuring the optimal ignition thereby that they are independent for the entire burning time from the speed, remains on. Such Ignition system is referred to as AC ignition system, because it generates a bipolar spark current.

Another generic ignition system, the also generates a bipolar spark current, is known from US 4,998,526. This known Ignition system provides a spark current at the spark plug available, its height and length in are desirably adjustable. This is the bipolar Spark-burning current by means of a DC / AC inverter generates a transformer with a primary-side Center tap has. To generate a Spark becomes a previously charged capacitor unloaded about this center tap, while the case maintained spark current thereby maintained is that alternately over the primary Teilwindungen Energy is supplied. The settings of Burning time of the sparking current as well as the setting its value takes place by means of adjustable Voltage divider.

Furthermore, a fully electronic ignition system in DE 39 24 985 A1, in which a programmable Transistor ignition with a high voltage capacitor ignition device combined. Of the The reason for this is that the actual ignition energy with relatively limited time accuracy by the programmable transistor ignition provided is while the high voltage capacitor ignition system a high time accuracy with respect to aer high voltage application the individual ignition coils having. In this known ignition system, however does not produce a continuous spark spark current, but instead the burning time consists of a sequence of individual pulses, each impulse to a spark leads. In this case, the current amplitude of each pulse as well as the pulse repetition frequency in dependence be freely selected by machine parameters.

A likewise a bipolar ignition current generating Ignition system describes the DE-OS 24 44 242, after which after generation of a spark the spark plug with a relatively small Voltage of the sparking current for a certain period of time is maintained. This is done by means of a Multivibrators a transistor during each ignition period so clocked that thereby in the secondary winding the ignition transformer is a relatively constant Voltage of, for example, 3 kV is induced, the sufficient, at the spark plug a voltage of more as to generate 800 V, which is required to spark current uphold if this before was built. The spark burning time can be this way be chosen, as is the requirements of the internal combustion engine equivalent.

Finally, for the sake of completeness, that in US 4,230,078 a conventional ignition system is described with a closing time control whose Closing time depending on the speed and the pressure in the intake pipe is determined. To derive a Time for the closing time is entered in a ROM Speed map or a speed / pressure map saved.

In the previously known Zündungskonzepten the following demands were in the foreground: one ensure safe cold start and even with sooty Spark plugs the fuel / air mixture in the cylinder sure to ignite. To fulfill this requirement, a correspondingly large ignition energy was provided. This for the maximum need of the engine designed ignition energy is used for normal operation (warm engine) not needed. This leads to an unnecessary high electrode burn off the spark plugs, the in turn, reduces the life of the spark plugs and a frequent change of candles after draws.

The object of the present invention is therein, a method for controlling an ignition system specify according to the type mentioned, so that the spark plug replacement intervals at least 100,000 km.

This task is characterized by the characterizing Characteristics of claim 1 solved. hereafter is the value of the spark current and its Burning time depending on the motor parameters Motor load and speed controlled. For this purpose is from a means Ignition current map stored in a control unit a base value for the value of spark spark current and from one also in the controller stored burn duration map a base value for the burning time taken. Such ignition with controlled parameters causes a much lower Burning on the spark plugs as a common one Series ignition. This will change the spark plug replacement intervals significantly extended.

According to a preferred embodiment these basic values for the Zündstromwert and the Burning time according to the current operating state the internal combustion engine corrected. So a temperature compensation is performed if the engine temperature is a certain threshold has not reached yet. This will cause the cold start feature of the engine improved. Furthermore, the underlying asset for the Zündstromwert at a dynamic Change of state of the motor with a dynamic Factor applied proportional to the load value change is and decreases with time. After a certain Delay time has the dynamic factor Value zero is reached, with the corrected base value the Underlying for the new load state.

The process according to the invention can be advantageous for controlling AC or high voltage capacitor firings be used.

Figur 1

ein Blockschaltbild einer Wechselstrom-Zündanlage zur Durchführung des erfindungsgemäßen Verfahrens,

Figur 2

ein detailliertes Schaltbild einer Zündendstufe einer Wechselstrom-Zündanlage gemäß Figur 1,

Figur 3

Strom- und Spannungszeitdiagramme zur Erläuterung der Funktionsweise der Wechselstromzündung,

Figur 4

ein Brennstrom-Kennfeld gemäß des erfindungsgemäßen Verfahrens,

Figur 5

ein Zünddauer-Kennfeld gemäß des erfindungsgemäßen Verfahrens und

Figur 6

ein Diagramm zur Darstellung des Elektrodenabbrandes als Funktion der zurückgelegten Fahrstrecke.

In the following, the method according to the invention will be illustrated and explained by way of example with reference to an AC ignition system. Show it:

FIG. 1

a block diagram of an AC ignition system for carrying out the method according to the invention,

FIG. 2

1 is a detailed circuit diagram of an ignition output stage of an AC ignition system according to FIG. 1,

FIG. 3

Current and voltage time diagrams to explain the operation of the AC ignition,

FIG. 4

a fuel flow characteristic diagram according to the method according to the invention,

FIG. 5

an ignition duration map according to the inventive method and

FIG. 6

a diagram showing the electrode burn as a function of the distance traveled.

1 shows a block diagram of an AC ignition for carrying out the method according to the invention for a 4-cylinder engine. In this case, an ignition output stage Z1-Z4 is provided for each spark plug ZK1. These ignition output stages are connected via a circuit 9 for cylinder selection with a control unit 1, which generates an ignition signal 1 to 4 for each ignition output stage and simultaneously outputs a modulation voltage U _Mod for all ignition output stages, which is processed by a current control circuit 10. This modulation voltage sets a target value of the ignition current I _{is intended to} represent and is by means of a comparator with an on a shunt resistor R (see FIG. 2) of the primary circuit of the ignition actual value I generated _is compared. The result of the comparison is supplied to the cylinder selecting circuit 9. Furthermore, the control unit 1 with sensors 4, 5 and 6 for detecting the rotational speed n, the load L and the engine temperature T and with a device 7 for cylinder 1 detection and via lines 1a for controlling the electronic injection with an injection system 11, which contains the corresponding actuators connected. Finally, a switching power supply 3 generates the supply voltages (18 V / 180 V) for the ignition output stages Z1-Z4, which is supplied by an on-board battery 2.

An embodiment of an ignition output stage for driving a single ignition coil of Figure 1 is shown in Figure 2 and consists essentially of a transistor T, in the embodiment of an IGBT transistor (insulated gate bipolar transistor), an energy recovery diode D, a primary resonant circuit capacitor C. , One composed of a primary and secondary winding coil Tr with a coupling of about 50%, a spark plug ZK and a simple control circuit 10, which corresponds to the current control circuit 10 of Figure 1, but additionally includes a gate of the cylinder selection circuit 9. This control circuit 10 are therefore supplied to the prepared by the control unit 1 control signals, namely the ignition signal 1 and the modulation voltage U _Mod . The first-mentioned control signal sets the ignition time and the burning time t _B , while the second-mentioned control signal U _Mod defines the value of the primary current I _p and, as a result, the ignition voltage U _k , ie the value of the spark current i _B. The generation according to the invention of these two control signals ignition signal 1 and U _mod will be explained below.

The ignition output according to the figure 2 operates in current-controlled blocking and Durchflußwandlerbetrieb. For the duration of the turn-on of the transistor T, a collector current I _{k flows} , which corresponds to the primary coil current I _p according to FIG. This collector current I _k is limited by the control circuit 10 to a value determined by the modulation voltage U _mod I _soll . In order to obtain a short charging time, the ignition output stage is supplied with a already explained in connection with the figure 1 switching power supply with a voltage of 180 V. If the collector current I _{k has reached} the value predetermined by I _soll , the transistor T is switched off. The energy contained in the storage coil excites the output circuit (secondary inductance, spark plug capacitance) to oscillate. Part of the energy is transferred to the capacitor C and the other part to the spark plug capacitance. The voltages U _c on the capacitor C and the ignition voltage U _B on the spark plug ZK rise - as shown in Figure 3 - sinusoidally until no energy in the storage coil, so the primary coil is present.

In the subsequent period of time, the capacitively stored energy is again fed to the primary coil inductance until the voltage U _c at the capacitor C reaches zero (see FIG. 3). The primary-side voltage U _c can not be negative by the diode D. On the secondary side, the oscillation continues because of the only approx. 50% strong coupling between primary and secondary inductance. During this period, the transistor T is turned on again, because now there are the same voltage conditions as before the first turn on of the transistor. Power control always guarantees the same energy input into the primary coil. The portion of the injected energy that was not needed in the spark channel is completely fed back into the electrical system. The coupling of approx. 50% prevents total attenuation of the primary resonant circuit (primary coil, capacitor C) due to the strongly attenuated secondary resonant circuit in the event of a spark break.

As can be seen from FIG. 3, the duration of the complete cycle (charging of the primary coil, decay operation up to the zero crossing of the voltage U _c across the capacitor C) is about 80 μs. Thus, the charging time of the coil can be neglected. Therefore, in contrast to the transistor coil ignition, a closing angle control is not required. On the other hand, the burning time t _B per ignition process can be changed as desired by the variation of the number of switching cycles. The modulation of the spark-burning current i _B takes place via the change in the primary-side fed energy. However, due to the non-ideal current source character of the output stage, the secondary-side high-voltage supply U _k at the spark plug ZK also changes in certain areas in parallel to the spark-burning current. In the reduction of the spark current i _B thus also the decrease of the maximum high voltage must be considered in each case.

This technique of self-oscillating ignition output leaves a significant reduction in volume the ignition coil, because in contrast to the transistor coil ignition not all the energy for one Ignition must be stored in the coil, but replenished in several small units. For storing the smaller amount of energy is therefore only a reduced coil volume needed. Another advantage for the structure of the ignition coil is the needed coupling of only about 50%, since this with a simple rod core can be realized.

The control unit 1 represents a μ-controller system, for example, based on a Motorola device MC68HC811E2, which is an 8-bit controller with internal EEPROM program memory. The power supply of this control unit 1 takes place from the electrical system powered by the battery 2. To control the AC ignition system correctly, the control unit 1 requires a signal about the cylinder sequence (Cylinder 1 detection 7 according to Figure 1). For this purpose, for example, on the toothed wheel to attach a magnet to the camshaft, which is queried by a Hall sensor. This delivers all 360 ° of the camshaft or every 720 ° of the crankshaft a signal: the cylinder 1 mark.

With the method according to the invention, the AC ignition system according to FIG. 1 becomes an ignition system, which makes it possible to control the ignition energy with the aid of two parameters. The first parameter is the modulation voltage U _Mod , by means of which the primary current I _p (see FIG. 2) of the ignition coil is regulated. With this current I _p , the high voltage U _{k of} the secondary coil or the spark current i _B , with which the spark burns, influenced. This is a higher-frequency PWM signal, which is smoothed via an RC filter in the ignition output stage and which is output jointly for all 4 cylinders, as shown in FIG. For this purpose, the control unit 1 has a PWM output. According to Figure 1, the individual cylinders are ignited with the ignition signals 1 to 4. The burning time t _{B of} the ignition process represents the second parameter and is also determined by the control unit 1 and realized over the pulse width of the respective ignition signal.

The control program stored in the control unit 1 for the ignition output stages ensures, on the one hand, the correct ignition distribution and, on the other hand, the calculation of the optimum ignition parameters, namely in the form of the modulation voltage U _Mod and the burning time t _B and their output. Before the triggering of the ignition output stages can begin, the control unit 1 must be synchronized, ie, it waits for the first signal of the cylinder 1 detection of the device 7 (see FIG. This is followed by an infinite loop in which all calculations are performed and repeated at each ignition. In this loop, an analog-to-digital conversion is performed to detect the engine parameters generated by the sensors 5 and 6, such as load and temperature. The speed is determined by evaluating the time interval between successive pulses of the speed sensor.

With the help of the engine load L (which is determined either by the position of the throttle potentiometer or the detection of the amount of air in the intake manifold) and speed n, the new ignition parameters are calculated, for which purpose from two stored in the memory of the control unit 1 maps the corresponding base values U _base and t _{basis of} the modulation voltage U _Mod and the burning time t _{B are} taken. These two maps are shown in Figures 4 and 5, namely the fuel flow map and the ignition duration map. The interpretation of these maps depends on the ignition energy requirements. The characteristic diagram for the spark-burning current i _B according to FIG. 4 takes into account the offered current with a safety factor of 1.2. The highest current at idle speed is required regardless of the load. In full-load operation, the spark spark current required decreases gradually with speed, whereas in partial-load and no-load operation, the value decreases more quickly and reaches the minimum of 40 mA even at medium speeds. The minimum burn time was determined on a test bench in the combustion duration map. Over the entire partial and full load range, 120 μs ignition duration (equivalent to one ignition pulse) was found to be sufficient. In contrast, in the no-load range, especially at medium speeds, the burning time must be considerably extended. All operating points shown with the two maps according to Figures 4 and 5 correspond to a stationary running engine. The temperature and the dynamic behavior of the engine are, as shown below, additionally taken into account by the control unit 1.

The base values U _base and t _base for the modulation voltage U _Mod and the burn time t _B described above are corrected in the following manner in accordance with the current operating state of the motor: U Mod = U Base + U Temp + U dyn . where U _{base is} the _base value determined from the load-speed map, U _{Temp is} the temperature correction value, and U _{Dyn is} the dynamic correction value.

The temperature correction value is given by the following formula: U Temp = (T 70 ° C - T is ) · K T . where T _{70 ° C is} a certain threshold temperature, for example 70 ° C, T _is the current engine temperature and k _{T is} a proportional factor. Thus, the temperature correction is a proportional correction, that is, the motor temperature falls below a certain threshold, ie z. B. 70 ° C, a factor U _{Temp is} calculated by which the modulation voltage U _{Mod is} increased. This factor U _Temp is proportional to the difference between the motor temperature and the temperature threshold. When the engine is warm, this correction is not performed.

In the case of a dynamic change in the operating state of the engine, an increased high voltage is briefly offered, namely by the factor of the dynamic correction U _Dyn . This factor U _Dyn results according to the following formula: U dyn = (L is - L old ) · K B + U Dyn, old · K B-1 . where L _is or L _{old is} the current load value or the load value before the change of the operating state. k _B and k _B-1 are proportional factors determined by practical driving tests. After a load change, the modulation voltage U _Mod increases by this dynamic factor U _Dyn , which is proportional to the change in the load signal and decreases with time. After a delay time of, for example, 2 s, this factor U _Dyn has dropped to the value zero, with which the modulation voltage U _{Mod reaches} the new static base value for the new load state.

In the calculation of the burning time t _B is proceeded in a similar manner. Based on the base value t _base already described above, only a temperature correction is carried out according to the following formula: t B = t Base + t Temp . where t _{basis is} the combustion duration base value determined from the load-speed characteristic map and the temperature _correction value t _{Temp is} calculated with the following formula: t Temp = (T 70 ° C - T is ) · K tt . where T is _{70 ° C} a certain threshold, for example 70 ° C and T _is the current engine temperature, while k _Tt as in the corresponding temperature correction of the modulation voltage U _{Temp is} a proportionality factor. Also in the calculation of the burning time t _B , the temperature is taken into account only when the engine temperature T _is below the threshold temperature, that is, for example, of 70 ° C.

In a test run of the above-described AC ignition in a test vehicle after 15,000 km driving an electrode burn at the spark plugs of 0.03 mm versus 0.09 mm for spark plugs with a standard series ignition. Accordingly, the operating voltages of the Spark plugs in a pressure chamber only by 3.7 kV or 2.7 kV vs. 5.5 kV or 4.5 kV for spark plugs with a serial ignition. The more than triple Life of the spark plugs is to be expected.

Finally, an endurance test also showed that good results, which shows the figure 6, after which at the end of the endurance test the mileage the Value 120,000 km for those with the above AC ignition operated spark plugs (dashed Line shown) reached. About the same Period had the with a usual serial ignition operated spark plugs (with a solid line shown) are exchanged 4x, since they each have the wear limit, d. H. there were individual load changes Misfire detected reached. The Spark plugs with the AC ignition would be included continued trial can continue to be used.

The electrode burn of these spark plugs was over a factor of 3.9 smaller than the one with the the series ignition operated spark plugs.

By the inventive control of the ignition via a map is the AC ignition also increased demands on future ignition systems be fair, just. In particular an improvement through optimized combustion the exhaust emissions expected. The use is also conceivable of the method according to the invention in future Lean-burn engines over a prolonged burning time.

With the AC ignition according to the invention An ignition system is available that is optimal the different ignition energy requirements of the engine adapted, without sacrificing the reliability must become.

Claims (8)

1. A method of controlling an ignition system for internal-combustion engines, comprising of at least one ignition output stage (Z₁ ... Z₄) for actuating at least one ignition coil (Tr) which generates a spark-burning current (I_B), where the value of the spark-burning current (I_B) and its burning time (t_B) are adjustable, characterised in that as a function of the engine parameters engine load (L) and engine speed (N), a basic value (U_Basis) for the spark-burning current (I_B) is taken from an ignition current characteristic map stored in a control unit (1) and a basic value (t_Basis) for the burning time (t_B) is taken from a burning time characteristic map likewise stored in the control unit (1), whereby these characteristic maps are configured to reflect the energy required for sparking.
2. A method according to Claim 1, characterised in that the base values (U_Basis, t_Basis) are corrected in accordance with the instantaneous operating state of the internal-combustion engine.
3. A method according to Claim 2, characterised in that a temperature correction (U_Temp, t_Temp) is carried out as a function of the instantaneous engine temperature (T_ist).
4. A method according to Claim 2 or 3, characterised in that the base value (U_Basis) for the value of the spark burning current (i_B) is subjected to a dynamic correction in the event of a dynamic change in the operating state of the internal-combustion engine.
5. A method according to Claim 4, characterised in that following a change in load, the base value (U_Basis) increases by a dynamic factor (U_Dyn) which is proportional to the change in the load value (L_ist - L_alt) and reduces with time.
6. A method according to Claim 5, characterised in that after a specified delay time the dynamic factor (U_Dyn) reaches the value zero, where the corrected base value assumes the base value for the new load state.
7. A method according to one of the preceding claims for controlling an a.c. ignition system.
8. A method according to one of Claims 1 to 6 for controlling a high-voltage capacitor ignition system.

Images